Muscle Oximetry in Sports Science: A Systematic Review

The impact of skinfold thickness and exercise intensity on the reliability of NIRS in the vastus lateralis

PURPOSE

The aims of this study were (1) to assess the test-retest reliability of the primary near infrared spectroscopy (NIRS) variables (i.e., StO2, T[Hb], [HbO2] and [HHb]) during cycling and (2) to investigate potential influences of exercise intensity and adipose tissue thickness (ATT) on this reliability.

METHODS

21 men and 20 women completed twelve constant work rate tests (6 min) at six different exercise intensities with each intensity performed twice. NIRS variables were measured at the vastus lateralis. The coefficient of variance (CV%), the intraclass correlation coefficient (ICC), mean bias and limits of agreement (LoA) were determined for reliability purposes.

RESULTS

The reliability of baseline values were acceptable to very good (CV% range: 5.83 - 21.96%). The reliability of end-values (CV% range: 0.02 - 25.02%, ICC range: 0.0 - 0.935) and amplitudes (CV% range: 0.46 - 5099%, ICC range: 0.0 - 0.887) were more variable. In general, the mean biases of end-values and amplitudes showed wide limits of agreement. A homogeneous influence of exercise intensity on reliability could not be established but reliability measures appeared to be lower in people with a lower skinfold thickness. Moreover, the NIRS signals decreased with increasing ATT but stabilized upon reaching a cut-off of 8 mm ATT. In addition, ATT did have a significant influence on [HHb] amplitude. In participants with ATT < 8 mm, higher amplitudes were observed with increasing intensity whereas in participants with ATT > 8 mm, there were no differences between the intensities.

CONCLUSION

The study reveals variable results with regards to reliability and there was no consistent influence of exercise intensity on reliability. Participants with a lower skinfold thickness showed stronger reliability. Moreover, NIRS signals decrease when ATT exceeds 8 mm. Careful consideration is necessary when interpreting NIRS signals in such cases.

Determination of Ventilatory Thresholds Using Near-Infrared Spectroscopy in Recreational Endurance and CrossFit Athletes

To define training zones, ventilatory thresholds (VTs) are commonly established by cardiopulmonary gas-exchange analysis during incremental exercise tests. Portable near-infrared spectroscopy (NIRS) devices have emerged as a potential tool for detecting these thresholds by monitoring muscle oxygenation. This study evaluated the accuracy of NIRS measurements to determine VTs or critical power (CP) based on muscle oxygen saturation and assesses the device's consistency across 2 constant-load tests. Data from 2 cross-sectional studies involving trained recreational endurance athletes (26 from study 1) and CrossFit athletes (59 from study 2) were examined. Incremental ramp tests on a cycle ergometer were performed and followed by either a constant-load test (study 1) or a CP test (study 2). When comparing power output or heart rate between NIRS-derived breakpoints and VTs, weak to moderate agreement was found. Mean differences in power output and heart rate ranged from 16.8 to 22.4 W and 3.8 to 6.0 beats·min-1 at the first threshold and 27.4 to 31.2 W and 7.1 to 7.8 beats·min-1 at the second threshold. Comparing with CP, mean differences ranged from -0.4 to 0.4 W and -0.6 to 0.9 beats·min-1. Test-retest reliability showed moderate agreement, with a mean bias of 1.2 percentage points between constant-load tests. Thus, NIRS may not be accurate for determining VTs or CP during exercise due to limited agreement in power output or hear rate, notable variability on individual level, and moderate reproducibility.

A Muscle Physiology-Based Framework for Quantifying Training Load in Resistance Exercises

BACKGROUND

Objective training load (TL) indexes used in resistance training lack physiological significance. This study was aimed to provide a muscle physiology-based approach for quantifying TL in resistance exercises (REs).

METHODS

Following individual torque-velocity profiling, fifteen participants (11 healthy males, stature: 178.36 ± 3.95 cm, and body mass (BM): 77.48 ± 7.74 kg; 4 healthy females, stature: 169.25 ± 5.03 cm, and body mass: 60.62 ± 3.91 kg) performed isokinetic leg extension exercise sessions at low, moderate, and high intensities (LI, MI, and HI, respectively). Systemic and local physiological responses were measured, and sessions were volume-equated according to the "volume-load" (VL) method.

RESULTS

Significant differences were found between sessions in terms of mechanical work (p<0.05 and p<0.001, for LI-MI and MI-HI, respectively), averaged normalised torque (p<0.001), mechanical impulse (p<0.001), and rate of force development (RFD, p<0.001 for LI-MI). RFD was mainly impacted by the accumulation of repetitions. Muscle function impairments mainly occurred at low intensities-long series, and high intensities, supported by greater RFD rate decay and changes in electromyographic activity. Therefore, accounting for muscle fatigue kinetics within objective TL indexes and using dimension reduction methods better described physiological responses to RE.

CONCLUSIONS

A generic equation of muscle fatigue rise could add value to TL quantification in RE. Considering other training-related information and TL indexes stands essential, applicable to field situations and supports the multidimensional facet of physiological responses to RE.

Impact of sprint interval training on post-fatigue mitochondrial rate in professional boxers

PURPOSE

Professional boxing is a sport that requires a high aerobic capacity to prevent fatigue and allow athletes to perform over 4-12 rounds. Typically, athletes will go into a heavy training period in a pre-bout camp lasting 6 to 9 weeks. This study investigates the impact of 3 weeks of repeated Wingate sprint interval training, performed on standard gym ergometer bikes, on skeletal muscle endurance and mitochondrial function.

METHODS

Ten male professional boxers (age: 26 ± 4 years, height: 175 ± 5 cm, weight: 70 ± 5 kg) participated in the study. Baseline testing involved a NIRS monitor attached to the rectus femoris muscle prior to an incremental time to exhaustion test on a treadmill. After the treadmill test participants underwent a series of arterial occlusions to determine mitochondrial function post-volitional exhaustion. Participants then continued their own training for 3 weeks and then repeated baseline testing. After the second testing session, participants undertook three weekly sprint sessions consisting of 3 × 30 s maximal sprints with 60 s recovery. Testing was repeated 3 weeks later.

RESULTS

The time to exhaustion increased by > 6% after 3 weeks of sprint interval training as compared to baseline and control (p < 0.05). Skeletal muscle oxygen saturation (SmO2) at exhaustion was increased by 5.5% after 3 weeks of sprint interval training as compared to baseline and control (p = 0.008). Skeletal muscle mitochondrial rate post exhaustion was increased by 160% after 3 weeks of sprint interval training as compared to baseline and control (p < 0.001).

CONCLUSION

The study demonstrated that SIT led to increased incremental time to exhaustion, higher SmO2 levels at volitional exhaustion and increased mitochondrial rates in professional boxers. These findings suggest that SIT should be an integral part of a boxe's conditioning regimen to improve performance and safety within the ring.

Profiles of muscle-specific oxygenation responses and thresholds during graded cycling incremental test

Compared to the determination of exercise thresholds based on systemic changes in blood lactate concentrations or gas exchange data, the determination of breakpoints based on muscle oxygen saturation offers a valid alternative to provide specific information on muscle-derived thresholds. Our study explored the profiles and timing of the second muscle oxygenation threshold (MOT2) in different muscles. Twenty-six cyclists and triathletes (15 male: age = 23 ± 7 years, height = 178 ± 5 cm, body mass = 70.2 ± 5.3 kg; 11 female: age = 22 ± 4 years, height = 164 ± 4 cm, body mass = 58.3 ± 8.1 kg) performed a graded exercise test (GXT), on a cycle ergometer. Power output, blood lactate concentration, heart rate, rating of perceived exertion, skinfolds and muscle oxygen saturation were registered in five muscles (vastus lateralis, biceps femoris, gastrocnemius medialis, tibialis anterior and triceps brachii) and percentage at which MOT2 occurred for each muscle was determinated using the Exponential Dmax. The results of Statistical Parametric Mapping and ANOVA showed that, although muscle oxygenation displayed different profiles in each muscle during a GXT, MOT2 occurred at a similar percentage of the GXT in each muscle (77% biceps femoris, 75% tibalis anterior, 76% gastrocnemius medialis and 72% vastus lateralis) and it was similar that systemic threshold (73% of the GXT). In conclusion, this study showed different profiles of muscle oxygen saturation in different muscles, but without notable differences in the timing for MOT2 and concordance with systemic threshold. Finally, we suggest the analysis of the whole signal and not to simplify it to a breakpoint.

Diagnosis, Pathophysiology and Management of Microvascular Dysfunction in Diabetes Mellitus

Microcirculation is an essential system that regulates oxygen and nutrients to cells and tissues in response to various environmental stimuli and pathophysiological conditions. Diabetes mellitus can cause microvascular complications including nephropathy, neuropathy, and retinopathy. The pathogenesis of microvascular dysfunction in diabetes is associated with hyperglycemia and the result of an interplay of various factors. Research studies have demonstrated that functional microvascular dysfunction appears much earlier than structural alterations in vasculature in diabetes. This finding of the progression from microvascular dysfunction to macrovascular disease establishes a foundation for the screening and early diagnosis of diabetes by assessing the microvascular function. This comprehensive review discusses technologies (laser Doppler, transcutaneous oximetry, infrared thermography and near-infrared spectroscopy) with computational methods (linear (time and frequency domains), nonlinear and machine learning approaches) for diagnosing microvascular dysfunction in diabetes. Pathophysiological changes of microvascular dysfunction leading to impaired vasomotion and blood flow oscillations in diabetes are reviewed. Recent findings in managing microvascular dysfunction using lifestyle modifications and force-based modulations are evaluated. A consensus endorsed by the American Diabetes Association has been reached that an effective exercise program would greatly slow down the progression of microvascular dysfunction and its impact on diabetic foot ulcers, muscle fatigue and weakness and peripheral neuropathy. However, it is imperative to determine the dose-response relationship of exercise and microvascular responses in patients with diabetes. Research studies have demonstrated that local vibration and whole-body vibration can improve microcirculation in various pathological conditions, including diabetes. Due to the complex nature of microvascular regulation, various computational methods have been developed to shed light on the influence of diabetes on microvascular dysfunction. This comprehensive review will contribute to the diagnosis and management of microvascular dysfunction in diabetes.

Study of Physiological Adaptations in Vertical Kilometer Runners: Focus on Cardiorespiratory and Local Muscle Demands

Background: Research into key performance factors in trail running, particularly in vertical kilometer (VK) races, is crucial for effective training and periodization. However, recent studies on metabolic and cardiorespiratory responses during VK races, especially using field tests, are limited. Objectives: Therefore, the aim of this study is to evaluate the metabolic and cardiorespiratory responses during a VK field test, identifying differences based on sex and performance level, as well as key performance factors and their deterioration due to fatigue. Fifteen trained trail runners (ten males and five females, 19 to 38 years old) perform a VK race. Methods: The global physiological response is evaluated using the portable gas analyzer Cosmed K5 and the local response using near-infrared spectroscopy technology. Results: In gender comparisons, the ANCOVA test shows significant differences (p < 0.05) in the ventilation, tidal volume, expiratory time-to-inspiratory time ratio, inspiratory flow rate, end-tidal CO2 partial pressure, heart rate, oxygen pulse, and total hemoglobin. Additionally, the performance comparison reveals significant differences in the variables' velocity, oxygen consumption, carbon dioxide production, ventilation, dead space-to-tidal volume ratio, total time of the breathing cycle, expiratory time-to-inspiratory time ratio, inspiratory duty cycle, expiratory fractions of CO2, quadriceps saturation index, and VE/VCO2 ratio. Finally, the correlation analysis shows oxygen consumption (r = -0.80 mean; r = -0.72 peak), carbon dioxide production (r = -0.91 mean; r = -0.75 peak), expiratory time-to-inspiratory time ratio (r = 0.68 peak), ventilation (r = -0.58 mean), and quadriceps saturation index (r = 0.54 mean; r = -0.76 coefficient of variation) as the key performance factors in the VK race. Conclusions: Overall, the physiological analysis indicates the importance of local muscular adaptations and respiratory system capacity in this type of short-duration race.

Characterization of muscle oxygenation response in well-trained handcyclists

PURPOSE

 Peripheral responses might be important in handcycling, given the involvement of small muscles compared to other exercise modalities. Therefore, the goal of this study was to compare changes in muscle oxygen saturation (∆SmO2) and deoxyhemoglobin level (∆[HHb]) between different efforts and muscles.

METHODS

 Handcyclists participated in a Wingate, a maximal incremental test and a 20-min time-trial (TT). Oxygen uptake (VO2) as well as ∆SmO2, ∆[HHb], deoxygenation and reoxygenation rates in the triceps brachii (TB), biceps brachii (BB), anterior deltoid (AD) and extensor carpi radialis brevis (ER) were measured.

RESULTS

 ER ∆[HHb]max was 37% greater in the incremental test than in the Wingate (ES = 0.392, P = 0.031). TT mean power (W/kg) was associated with BB ∆SmO2min measured in the incremental test (r = -0.998 [-1.190, -0.806], P = 0.002) and in the Wingate (r = -0.994 [-1.327, -0.661], P = 0.006). MAP (W/kg) was associated with Wingate BB ∆SmO2min (r = -0.983 [-0.999, -0.839], P = 0.003), and Wingate peak (r = 0.649 [0.379, 0.895], P = 0.008) and mean power (W/kg) (r = 0.925 [0.752, 0.972], P = 0.003) was associated with right handgrip force. The strongest physiological predictor for TT performance was BB ∆SmO2min in the incremental test (P = 0.002, r2 = 0.993, SEE 0.016 W/kg), Wingate BB ∆SmO2min for MAP (P = 0.003, r2 = 0.956, SEE 0.058 W/kg) and right handgrip force for Wingate peak power (P = 0.005, r2 = 0.856, SEE 0.551 W/kg).

CONCLUSION

 Peripheral aerobic responses (muscle oxygenation) were predictive of handcycling performance.

Reliability of near-infrared spectroscopy in measuring muscle oxygenation during squat exercise

Monitoring of changes in skeletal muscle oxygenation during exercise has increased in recent years. Tissue oxygenation, which is related to fatigue and muscle hypertrophy, is often measured using near-infrared spectroscopy (NIRS).

OBJECTIVES

This study aimed to determine the test-retest reliability of a non-portable NIRS (NIRO200Nx) during the full-squat exercise and recovery in young healthy men.

DESIGN

Twenty-five male participants (21.8 ± 2.6 years) were recruited for this original research. Each participant completed an 8-repetition test with a load that elicited a velocity of 1 m·s-1. The test was conducted twice, with a 48-hour washout period between sessions.

METHODS

The NIRS measured the changes of oxygenated-Hemoglobin (O2Hb), deoxygenated-Hemoglobin (HHb) and Tissue Oxygenation Index (TOI) in both Vastus Lateralis and Vastus Medialis during rest, exercise, and recovery. Coefficient of Variation (CV), Standard Error Measurement (SEM) and Intraclass Correlation Coefficient (ICC) were used to evaluate the reliability of the data. Significance was set at p < 0.05.

RESULTS

The results indicated that TOI had good to acceptable absolute reliability (CVTOI = 2.7-10.2 %). A good relative relativity for the overall test was found for Vastus Medialis O2Hb (ICC = 0.851), HHb (ICC = 0.852), and TOI (ICC = 0.864), and Vastus Lateralis O2Hb (ICC = 0.898), HHb (ICC = 0.899), and TOI (ICC = 0.897).

CONCLUSIONS

We conclude that NIRO200Nx is a reliable instrument for measuring muscle oxygen saturation through the TOI parameter in not-to-failure dynamic resistance exercises (1 set of 8 reps against ∼40 % 1 repetition maximum). Tissue oxygenation assessment could be a new way of individualizing exercise through dynamic resistance exercises.

The effects of endurance training on muscle oxygen desaturation during incremental exercise tests: a systematic review and meta-analysis

Objective

Minimum muscle oxygen saturation (SmO2min) measured via near-infrared spectroscopy (NIRS) is a common measure during incremental exercise testing (IET). Our objective was to determine the effects of pre-to-post endurance training on SmO2min (ΔSmO2min) during an IET, using a meta-analysis.

Data sources

MEDLINE, EMBASE, and SPORTDiscus.

Study selection

Studies including healthy individuals had to meet the following criteria: (1) endurance training intervention; (2) peripheral muscle NIRS; (3) incremental exercise test pre/post training; (4) SmO2 or analogous saturation parameter measured.

Analysis

A PEDro scale was used for risk of bias analysis. A random effect meta-analysis model was used to synthesize the effect of training on ΔSmO2min in individual studies. Statistical heterogeneity was quantified using I2 statistic. A meta-regression was used to estimate the effect of training on the relationship between peak cycling power output (Wpeak), peak pulmonary oxygen uptake (V˙O2peak), and ΔSmO2min. A mixed-effect model was used to estimate categorical variables.

Results

Five studies met the inclusion criteria. No difference in SmO2min was detected following training pre- and post-intervention IETs. A trend for an effect of training on the relationship between Wpeak and ΔSmO2min was observed (p = 0.06).

Conclusion

This meta-analysis showed no effects of endurance training on SmO2min during an IET. Our results showed a trend for an effect of training on the relationship between Wpeak and ΔSmO2min, with no effect for V˙O2peak and ΔSmO2min. It is possible that SmO2min is not affected by endurance training, and may be used as a physiological marker for improvements in submaximal performance rather than at peak.

Acute Effect of Fixed vs. Self-Selected Rest Interval Between Sets on Physiological and Performance-Related Responses

Background: Although the comparison between self-managed rest and fixed rest periods in subjects experienced in lower-limb strength training has been investigated, the results remain unclear due to controversies among some studies. Therefore, the present study aimed to analyze the role of self-managed rest versus fixed rest in athletic performance, mean propulsive velocity, velocity loss, muscle oxygen saturation, and rest time in trained subjects; Methods: Thirteen subjects with a minimum of one year of training experience (age (years): 26.31 ± 3.84; height (cm): 175.46 ± 5.61; weight (kg): 79.24 ± 6.83) were randomly assigned to two groups (self-selected rest group [SR] = 7 and fixed rest group [FR] = 6). The subjects underwent a session for evaluation (one maximum repetition (1RM) estimation, familiarization, and data collection) and another day for a traditional strength training session for the back squat, consisting of five sets of four repetitions at 80% of 1RM. One group took a fixed 2 min break, while the other group managed their breaks autonomously (resuming when they felt ready to perform the next set at maximum velocity). Mean propulsive velocity (MPV) was monitored using a linear position transducer, and muscle oxygen saturation (SmO2) was measured with a near-infrared spectroscopy device; Results: Significant differences between the groups were found for the rest time between the first and second sets (SR 97.29 ± 23.70 seg vs. FR 120 ± 0.00 seg). However, no differences were found for MPV, velocity loss, or SmO2; Conclusions: Given the similarities in performance and physiological outcomes between fixed and self-selected rest conditions, both can be used equally depending on the preferences and training goals of coaches and athletes.

Best practices for simultaneous measurement of NIRS-based cerebral and muscle oximetry during exercise

•NIRS-based oximetry is a valuable tool for exercise physiology. •NIRS-based oximetry measurements are influenced by the device used. •NIRS-based oximetry measurements must be interpreted carefully.

Muscle Oxygen Saturation Dynamics During Upper-Body Resistance Exercise

Research examining the changes in muscle oxygen saturation across multiple sets of resistance exercise is limited. The purpose of this study was to describe the physiological response of muscle oxygenation parameters during upper-body resistance exercise and examine the differential effects of relevant participant characteristics on resistance training performance and muscle oxygen saturation dynamics. Sixty-one recreationally trained men (n = 44; 21.8 ± 2.6 years) and women (n = 17; 20.2 ± 1.8 years) completed five-repetition maximum sets of barbell bench presses at a load equal to 75% 1-RM with a 2 min rest interval. Muscle oxygen saturation (SmO2) dynamics within the anterior deltoid were monitored using a portable near-infrared spectroscopy sensor. The percent change in SmO2 (∆%SmO2), the muscle oxygen re-saturation rate (SmO2RecSlope), and the highest measured SmO2 value during recovery periods (SmO2Peak) were measured. Two-way (sex [men, women] x time [sets 1-5]) repeated measures analyses of variance (ANOVA) were performed on muscle saturation variables. To examine the effect of relevant controlling variables, separate analyses of covariance (ANCOVA) with repeated measures were also performed. No differences were seen with ∆%SmO2 across sets. The main effects for sets occurred for SmO2RecSlope, whereby a decline was noted on sets 4 and 5 (p = 0.001) compared to set 1. Additionally, SmO2Peak was the lowest on set 5 (p < 0.001) compared to all other sets. Moreover, body mass (p = 0.013), diastolic blood pressure (p = 0.044), and mean arterial pressure (p = 0.033) for ∆%SmO2 were the only significant covariates noted amongst the muscle oxygenation variables. In conclusion, no sex differences and only a few set differences in muscle oxygen saturation dynamics were seen without employing any covariates. Body mass, diastolic blood pressure, and mean arterial pressure were identified as factors that could influence observed responses.

Acute psycho-physiological responses to submaximal constant-load cycling under intermittent hypoxia-hyperoxia vs. hypoxia-normoxia in young males

Background

Hypoxia and hyperoxia can affect the acute psycho-physiological response to exercise. Recording various perceptual responses to exercise is of particular importance for investigating behavioral changes to physical activity, given that the perception of exercise-induced pain, discomfort or unpleasure, and a low level of exercise enjoyment are commonly associated with a low adherence to physical activity. Therefore, this study aimed to compare the acute perceptual and physiological responses to aerobic exercise under intermittent hypoxia-hyperoxia (IHHT), hypoxia-normoxia (IHT), and sustained normoxia (NOR) in young, recreational active, healthy males.

Methods

Using a randomized, single-blinded, crossover design, 15 males (age: 24.5 ± 4.2 yrs) performed 40 min of submaximal constant-load cycling (at 60% peak oxygen uptake, 80 rpm) under IHHT (5 × 4 min hypoxia and hyperoxia), IHT (5 × 4 min hypoxia and normoxia), and NOR. Inspiratory fraction of oxygen during hypoxia and hyperoxia was set to 14% and 30%, respectively. Heart rate (HR), total hemoglobin (tHb) and muscle oxygen saturation (SmO2) of the right vastus lateralis muscle were continuously recorded during cycling. Participants' peripheral oxygen saturation (SpO2) and perceptual responses (i.e., perceived motor fatigue, effort perception, perceived physical strain, affective valence, arousal, motivation to exercise, and conflict to continue exercise) were surveyed prior, during (every 4 min), and after cycling. Prior to and after exercise, peripheral blood lactate concentration (BLC) was determined. Exercise enjoyment was ascertained after cycling. For statistical analysis, repeated measures analyses of variance were conducted.

Results

No differences in the acute perceptual responses were found between conditions (p ≥ 0.059, ηp 2 ≤ 0.18), while the physiological responses differed. Accordingly, SpO2 was higher during the hyperoxic periods during the IHHT compared to the normoxic periods during the IHT (p < 0.001, ηp 2 = 0.91). Moreover, HR (p = 0.005, ηp 2 = 0.33) and BLC (p = 0.033, ηp 2 = 0.28) were higher during IHT compared to NOR. No differences between conditions were found for changes in tHb (p = 0.684, ηp 2 = 0.03) and SmO2 (p = 0.093, ηp 2 = 0.16).

Conclusion

IHT was associated with a higher physiological response and metabolic stress, while IHHT did not lead to an increase in HR and BLC compared to NOR. In addition, compared to IHT, IHHT seems to improve reoxygenation indicated by a higher SpO2 during the hyperoxic periods. However, there were no differences in perceptual responses and ratings of exercise enjoyment between conditions. These results suggest that replacing normoxic by hyperoxic reoxygenation-periods during submaximal constant-load cycling under intermittent hypoxia reduced the exercise-related physiological stress but had no effect on perceptual responses and perceived exercise enjoyment in young recreational active healthy males.

Microvascular Reactivity Is Greater Following Blood Flow Restriction Resistance Exercise Compared with Traditional Resistance Exercise

ABSTRACT

Perlet, MR, Hosick, PA, Licameli, N, and Matthews, EL. Microvascular reactivity is greater following blood flow restriction resistance exercise compared with traditional resistance exercise. J Strength Cond Res 38(10): e553-e562, 2024-Chronic blood flow restriction (BFR) resistance exercise can improve muscular strength, hypertrophy, and microvasculature function, but the acute microvascular effects are unknown. We aimed to test the effects of acute BFR resistance exercise on postexercise microvascular reactivity in an exercising muscle and nonexercising muscle compared with traditional resistance exercise (TRE). Twenty-five adults (men = 14, women = 11, age: 22 ± 3 years, body mass: 71.69 ± 14.49 kg, height: 170 ± 10 cm) completed barbell back squat 1-repetition maximum (1RM) testing followed by 2 randomized and counterbalanced resistance exercise visits separated by ≥48 hours. The 2 visits involved either BFR (4 sets of 30-15-15-15 repetitions at 30% 1RM, with 60-second rest intervals) or TRE (4 sets of 10 repetitions at 70% 1RM, 60-second rest intervals). During each exercise visit, a pre- and postbarbell back squat vascular occlusion test was performed using near-infrared spectroscopy to measure skeletal muscle oxygen (SmO 2 ) in the vastus lateralis (VL) and flexor carpi radialis (FCR). Two-way repeated-measures ANOVA found an interaction effect ( p = 0.020) for SmO 2 reactivity in the VL. Post hoc analysis found greater reactive hyperemia postexercise in the VL for the BFR condition ( p < 0.001) but not the TRE condition ( p ≥ 0.05). There were no time, condition, or interaction effects (all p > 0.05) for the same analysis in the FCR. This analysis suggests that BFR, but not TRE, lead to acutely improved microvasculature function. Moreover, it suggests that the effects of BFR resistance exercise are local to the exercised or occluded limb and not systemic.

Side differences and reproducibility of the Moxy muscle oximeter during cycling in trained men

PURPOSE

Portable near-infrared spectroscopy devices allow measurements of muscle oxygen saturation (SmO2) in real time and non-invasively. To use NIRS for typical applications including intensity control and load monitoring, the day-to-day variability needs to be known to interpret changes confidently. This study investigates the absolute and relative test-retest reliability of the Moxy Monitor and investigates side differences of SmO2 at the vastus lateralis muscle of both legs in cyclists.

METHODS

Twelve trained cyclists and triathletes completed 3 incremental step tests with 5 min step duration starting at 1.0 W/kg with an increase of 0.5 W/kg separated by 2-7 days. SmO2 was averaged over the last minute of each stage. For all power outputs, the intra-class coefficient (ICC), the standard error of measurement (SEM) and the minimal detectable change (MDC) were calculated. Dominant and non-dominant leg SmO2 were compared using a three-factor ANOVA and limits of agreement (LoA).

RESULTS

ANOVA showed no significant systematic differences between trials and side. For both legs and all intensities, the ICC ranged from 0.79 to 0.92, the SEM from 5 to 9% SmO2 and the MDC from 14 to 18% SmO2. The bias and LoA between both legs were -2.0% ± 19.9% SmO2.

CONCLUSION

Relative reliability of SmO2 was numerically good to excellent according to current standards. However, it depends on the specific analytical goal whether the test-retest reliability is deemed sufficient. Wide LoA indicate side differences in muscle oxygenation during exercise unexplained by leg dominance.

Acute Effects of Combined and Distinctive Stretching, Foam Rolling, and Eccentric Exercise in Young Men with Hamstring Tightness

This study investigated the changes in fascicle length (FL), musculotendinous unit (MTU) stiffness, muscle oxygen saturation (SmO2), and muscular performance following a single bout of a combination of static stretching (SS) or dynamic stretching (DS) with foam rolling (FR), SS only, and eccentric exercise (ECC) only in young men with hamstring tightness. Twenty-five men (20.5 ± 1.5 years) participated in a crossover randomized study of the four conditions (DS+FR, SS+FR, SS, and ECC); each session was spaced seven days apart. FL, MTU stiffness during the straight leg raise (SLR), hamstring SmO2, and isometric and eccentric torque were measured before, immediately and 30 min after exercise. Immediately after exercise, the SLR increased significantly by means of 7.4% (d = 1.07), 6% (d = 1.27), 6% (d = 1.10), and 8% (d = 1.04, all p < 0.001) for DS+FR, SS+FR, ECC, and SS, respectively. FL was longer after exercise under all four conditions (p < 0.05). MTU stiffness decreased after ECC (p = 0.038, d = 0.40). SmO2 tended to decrease for ECC (p > 0.05), but it was increased immediately after those three exercises. Hamstring isometric torque was significantly reduced by an average of 6-9%, but eccentric torque changes varied among conditions. In conclusion, substantial and similar immediate increases in hamstring flexibility, coupled with reduced isometric torque following various exercises, were accompanied by condition-specific alterations in fascicle length, MTU stiffness, or SmO2. These findings provide practical insights for acutely enhancing range of motion in individuals with tight hamstrings.

Effects of occlusion pressure on hemodynamic responses recorded by near-infrared spectroscopy across two visits

Ischemic Preconditioning (IPC) has emerged as a promising approach to mitigate the impact of hypoxia on physiological functions. However, the heterogeneity of occlusion pressures for inducing arterial occlusion has led to inconsistent hemodynamic outcomes across studies. This study aims to evaluate the peripheral hemodynamic responses to partial and total blood-flow occlusions on the left arm at rest, using absolute or individualized pressures, on two occasions. Thirty-five young males volunteered to participate in this study. IPC procedure (3 × 7-min) was performed on the left upper arm with cuff pressures at 50 mmHg (G1), 50 mmHg over the systolic blood pressure (SBP + 50 mmHg) (G2) or 250 mmHg (G3). NIRS-derived parameters were assessed for each occlusion and reperfusion phase in the brachioradialis. Results showed a significantly lower magnitude of deoxygenation (TSIAUC) for G1 compared to G2 (-1959.2 ± 1417.4 vs. -10908.1 ± 1607.5, P < 0.001) and G3 -1959.2 ± 1417.4 vs. -11079.3 ± 1828.1, P < 0.001), without differences between G2 and G3. However, G3 showed a significantly faster reoxygenation only for tissue saturation index (TSIslope) compared to G2 (1.3 ± 0.1 vs. 1.0 ± 0.2, P = 0.010), but without differences in the speed of recovery of deoxyhemoglobin [(HHb) slope], or in the magnitude of post-occlusive hyperemia (PORH). Besides TSI reoxygenation speed, G2 and G3 elicit comparable resting hemodynamic responses measured by NIRS. Thus, this study highlights the practicality and effectiveness of using relative occlusion pressures based on systolic blood pressure (SBP) rather than relying on excessively high absolute pressures.

Estimation of Lactate Thresholds, Aerobic Capacity and Recovery Rate from Muscle Oxygen Saturation in Highly Trained Speed Skaters and Healthy Untrained Individuals

Objective: The main objective of this study was to compare lactate thresholds and aerobic capacity from a graded-intensity exercise test (GXT) for near-infrared spectroscopy measurements in healthy, untrained individuals and highly trained athletes. Methods: This study included 29 untrained students (13 females) and 27 highly trained speed skaters (13 females). A maximal effort GXT was performed on a cycloergometer. The lactate-based aerobic and anaerobic thresholds, and the corresponding thresholds for muscle oxygen saturation (SmO2), were determined. Results: The power values determined for all thresholds were significantly higher in female and male speed skaters compared to male and female college students. SmO2 at anaerobic thresholds was significantly lower in female speed skaters than in female students. Both female and male skaters showed greater changes in SmO2 after the GXT compared to students. The recovery did not significantly differ between groups within gender. There was a significant positive correlation in females between the rate of muscle reoxygenation and VO2max power (r = 0.610). In speed skaters, the rate of muscle reoxygenation was not significantly higher than students and correlated positively with VO2max (r = 0.449). Conclusions: The SmO2 at the exercise thresholds, during and after maximal exercise, depends on the training status of the individual. The participants with a higher physical fitness level showed greater decreases in ΔSmO2 at the AT level, as well as after maximal exercise. SmO2 corresponding to the well-established exercise thresholds may be applied to guide training prescription. The rate of muscle reoxygenation after a GXT was also dependent on the aerobic capacity of the participants.

Reproducibility and sex differences in muscle oxygenation during brachial artery occlusion in healthy participants

SIGNIFICANCE

Near-infrared spectroscopy (NIRS) measurement is a widely used technique to measure muscle oxygenation. A knowledge of the reproducibility of NIRS measurements is essential for the correct interpretation of data.

AIM

Our aim was to test the reproducibility and sex differences of NIRS measurements during brachial artery occlusion in healthy participants.

APPROACH

An NIRS device was used to measure muscle oxygenation and microvascular function during a 5 min brachial occlusion. Muscle oxygen consumption (mVO2) and tissue saturation index (TSI%) were used. The occlusion test was performed three times on separate days for males (n = 13, 28 ± 8 years) and females (n = 13, 29 ± 7 years).

RESULTS

During the occlusion phase, the reproducibility of mVO2 was excellent (intraclass correlation; ICC = 0.90). During the reperfusion phase, the maximal change in TSI% revealed the best reproducibility (ICC = 0.77). There were no sex differences in reproducibility. Male participants had higher muscle oxygenation during occlusion (mVO2, 0.054 ± 0.010 vs. 0.038 ± 0.012 mLO2/min/100 g, p = 0.001, male and female, respectively). There were no sex differences during the reperfusion phase.

CONCLUSION

The reproducibility of NIRS to measure muscle oxygenation and microvascular function during circulation occlusion and reperfusion is good to excellent. Muscle oxygen capacity measured during occlusion is higher in males compared to females, and there are no sex differences in microvascular function during the reperfusion phase.

Characteristics of central cortex and upper-limb flexors synchrony oxygenation during grasping in people with stroke: a controlled trial study protocol

Background

Upper limb motor impairment is a common consequence of stroke, and the effectiveness and underlying mechanisms of rehabilitation therapy for improving upper limb function remain uncertain. Functional near-infrared spectroscopy, a reliable wearable neuroimaging technique, holds promise for investigating brain activity during functional tasks. This study aims to explore the synchronous oxygenation characteristics of the central cortex and upper-limb flexors during a grasping task and investigate the rehabilitation mechanisms of upper limb motor function in individuals with stroke.

Methods

Participants with stroke who demonstrate the ability to grasp and lift cubic wood blocks of different sizes (2.5cm3, 5cm3, and 10cm3) using their affected hand will be divided into three groups: A, B, and C. Each group will consist of twenty stroke patients, resulting in a total of sixty participants with stroke. Additionally, twenty matched healthy subjects will be enrolled as a control group. Comprehensive assessments will be conducted before and after the intervention, including blood oxygen parameter monitoring of the cerebral cortex and upper limb flexors using fNIRS during the grasping task. Other assessments will include MyotonPRO, the Modified Ashworth Scale, the upper extremity section of the Fugl-Meyer Assessment, the Action Research Arm Test, and the Modified Barthel Index. The study will be undertaken between January 2024 and September 2025.

Conclusions

The results of this trial will provide an in-depth understanding of the Characteristics of central cortex and upper-limb flexors synchronous oxygenation during grasping task and how it may relate to the rehabilitation mechanism of upper limb motor function in people with stroke.

Clinical trial registration

https://www.chictr.org.cn, identifier ChiCTR2400080619.

Cerebral and muscle tissue oxygenation during exercise in healthy adults: A systematic review

BACKGROUND

Near-infrared spectroscopy (NIRS) technology has allowed for the measurement of cerebral and skeletal muscle oxygenation simultaneously during exercise. Since this technology has been growing and is now successfully used in laboratory and sports settings, this systematic review aimed to synthesize the evidence and enhance an integrative understanding of blood flow adjustments and oxygen (O2) changes (i.e., the balance between O2 delivery and O2 consumption) within the cerebral and muscle systems during exercise.

METHODS

A systematic review was conducted using PubMed, Embase, Scopus, and Web of Science databases to search for relevant studies that simultaneously investigated cerebral and muscle hemodynamic changes using the near-infrared spectroscopy system during exercise. This review considered manuscripts written in English and available before February 9, 2023. Each step of screening involved evaluation by 2 independent authors, with disagreements resolved by a third author. The Joanna Briggs Institute Critical Appraisal Checklist was used to assess the methodological quality of the studies.

RESULTS

Twenty studies were included, of which 80% had good methodological quality, and involved 290 young or middle-aged adults. Different types of exercises were used to assess cerebral and muscle hemodynamic changes, such as cycling (n = 11), treadmill (n = 1), knee extension (n = 5), isometric contraction of biceps brachii (n = 3), and duet swim routines (n = 1). The cerebral hemodynamics analysis was focused on the frontal cortex (n = 20), while in the muscle, the analysis involved vastus lateralis (n = 18), gastrocnemius (n = 3), biceps brachii (n = 5), deltoid (n = 1), and intercostal muscle (n = 1). Overall, muscle deoxygenation increases during exercise, reaching a plateau in voluntary exhaustion, while in the brain, oxyhemoglobin concentration increases with exercise intensity, reaching a plateau or declining at the exhaustion point.

CONCLUSION

Muscle and cerebral oxygenation respond differently to exercise, with muscle increasing O2 utilization and cerebral tissue increasing O2 delivery during exercise. However, at the exhaustion point, both muscle and cerebral oxygenation become compromised. This is characterized by a reduction in blood flow and a decrease in O2 extraction in the muscle, while in the brain, oxygenation reaches a plateau or decline, potentially resulting in motor failure during exercise.

A Surface Electromyography (sEMG) System Applied for Grip Force Monitoring

Muscles play an indispensable role in human life. Surface electromyography (sEMG), as a non-invasive method, is crucial for monitoring muscle status. It is characterized by its real-time, portable nature and is extensively utilized in sports and rehabilitation sciences. This study proposed a wireless acquisition system based on multi-channel sEMG for objective monitoring of grip force. The system consists of an sEMG acquisition module containing four-channel discrete terminals and a host computer receiver module, using Bluetooth wireless transmission. The system is portable, wearable, low-cost, and easy to operate. Leveraging the system, an experiment for grip force prediction was designed, employing the bald eagle search (BES) algorithm to enhance the Random Forest (RF) algorithm. This approach established a grip force prediction model based on dual-channel sEMG signals. As tested, the performance of acquisition terminal proceeded as follows: the gain was up to 1125 times, and the common mode rejection ratio (CMRR) remained high in the sEMG signal band range (96.94 dB (100 Hz), 84.12 dB (500 Hz)), while the performance of the grip force prediction algorithm had an R2 of 0.9215, an MAE of 1.0637, and an MSE of 1.7479. The proposed system demonstrates excellent performance in real-time signal acquisition and grip force prediction, proving to be an effective muscle status monitoring tool for rehabilitation, training, disease condition surveillance and scientific fitness applications.

Calculating Load and Intensity Using Muscle Oxygen Saturation Data

The study aimed to calculate training intensity and load using muscle oxygen saturation (SmO2) during two differentiated physical tasks. 29 university athletes participated in a 40-m Maximal Shuttle Run Test (MST, 10 × 40-m with 30 s recovery between sprints) and a 3000-m time trial run. Distance and time were used to calculate external load (EL). Internal load indicators were calculated based on percentage of maximum heart rate (%HRMAX) and SmO2 variables: muscle oxygen extraction (∇%SmO2) and the cardio-muscle oxygen index (CMOI) was also provided by relating ∇%SmO2 ÷ %HRMAX, and the training load were calculated as the product of speed (m/min × IL) and the efficiency index [Effindex (m/min ÷ IL)]. A student t test was applied based on Bayesian factor analysis. As expected, EL differed in the 40-m MST (331 ± 22.8) vs. 3000-m trials (222 ± 56.8) [BF10 = 6.25e+6; p = <0.001]. Likewise, IL showed higher values in 40-m MST (39.20 ± 15.44) vs. 3000-m (30.51 ± 8.67) in CMOI: [BF10 = 1.70; p = 0.039]. Training load was greater in 40-m MST (85.77 ± 27.40) vs. 3000-m (15.55 ± 6.77) [(m/min × ∇%SmO2): BF10 = 12.5; p = 0.003] and 40-m MST (129.27 ± 49.44) vs. 3000-m (70.63 ± 32.98) [(m/min × CMOI): BF10 = 169.6; p = <0.001]. Also, the Effindex was higher in 40-m MST (10.19 ± 4.17) vs. 3000-m (6.06 ± 2.21) [(m/min × ∇%SmO2): BF10 = 137.03; p = <0.001] and 40-m MST (9.69 ± 4.11) vs. 3000-m (7.55 ± 1.87) [(m/min × CMOI): BF10 = 1.86; p = 0.035]. This study demonstrates calculations of training intensity and load based on SmO2 as an internal load indicator along with speed as an external load indicator during two differentiated exercises.

Effects of Hypoxia Severity on Muscle Oxygenation Kinetics Using Statistical Parametric Mapping During Repeated Treadmill Sprints

PURPOSE

We examined the effects of increasing hypoxia severity on oxygenation kinetics in the vastus lateralis muscle during repeated treadmill sprints, using statistical parametric mapping (SPM).

METHODS

Ten physically active males completed 8 sprints of 5 seconds each (recovery = 25 s) on a motorized sprint treadmill in normoxia (sea level; inspired oxygen fraction = 0.21), moderate hypoxia (inspired oxygen fraction = 0.17), and severe hypoxia (SH; inspired oxygen fraction = 0.13). Continuous assessment of tissue saturation index (TSI) in the vastus lateralis muscle was conducted using near-infrared spectroscopy. Subsequently, TSI data were averaged for the sprint-recovery cycle of all sprints and compared between conditions.

RESULTS

The SPM analysis revealed no discernible difference in TSI signal amplitude between conditions during the actual 5-second sprint phase. However, during the latter portion of the 25-second recovery phase, TSI values were lower in SH compared with both sea level (from 22 to 30 s; P = .003) and moderate hypoxia (from 16 to 30 s; P = .001). The mean distance covered at sea level (22.9 [1.0] m) was greater than for both moderate hypoxia (22.5 [1.2] m; P = .045) and SH (22.3 [1.4] m; P = .043).

CONCLUSIONS

The application of SPM demonstrated that only SH reduced muscle oxygenation levels during the late portion of the passive (recovery) phase and not the active (sprint) phase during repeated treadmill sprints. These findings underscore the usefulness of SPM for assessing muscle oxygenation differences due to hypoxic exposure and the importance of the duration of the between-sprints recovery period.

Muscle Oximetry in Sports Science: An Updated Systematic Review

BACKGROUND

In the last 5 years since our last systematic review, a significant number of articles have been published on the technical aspects of muscle near-infrared spectroscopy (NIRS), the interpretation of the signals and the benefits of using the NIRS technique to measure the physiological status of muscles and to determine the workload of working muscles.

OBJECTIVES

Considering the consistent number of studies on the application of muscle oximetry in sports science published over the last 5 years, the objectives of this updated systematic review were to highlight the applications of muscle oximetry in the assessment of skeletal muscle oxidative performance in sports activities and to emphasize how this technology has been applied to exercise and training over the last 5 years. In addition, some recent instrumental developments will be briefly summarized.

METHODS

Preferred Reporting Items for Systematic Reviews guidelines were followed in a systematic fashion to search, appraise and synthesize existing literature on this topic. Electronic databases such as Scopus, MEDLINE/PubMed and SPORTDiscus were searched from March 2017 up to March 2023. Potential inclusions were screened against eligibility criteria relating to recreationally trained to elite athletes, with or without training programmes, who must have assessed physiological variables monitored by commercial oximeters or NIRS instrumentation.

RESULTS

Of the identified records, 191 studies regrouping 3435 participants, met the eligibility criteria. This systematic review highlighted a number of key findings in 37 domains of sport activities. Overall, NIRS information can be used as a meaningful marker of skeletal muscle oxidative capacity and can become one of the primary monitoring tools in practice in conjunction with, or in comparison with, heart rate or mechanical power indices in diverse exercise contexts and across different types of training and interventions.

CONCLUSIONS

Although the feasibility and success of the use of muscle oximetry in sports science is well documented, there is still a need for further instrumental development to overcome current instrumental limitations. Longitudinal studies are urgently needed to strengthen the benefits of using muscle oximetry in sports science.

Paraspinal muscle oxygenation and mechanical efficiency are reduced in individuals with chronic low back pain

This study aimed to compare the systemic and local metabolic responses during a 5-min trunk extension exercise in individuals with chronic low back pain (CLBP) and in healthy individuals. Thirteen active participants with CLBP paired with 13 healthy participants performed a standardised 5-min trunk extension exercise on an isokinetic dynamometer set in continuous passive motion mode. During exercise, we used near-infrared spectroscopy to measure tissue oxygenation (TOI) and total haemoglobin-myoglobin (THb). We used a gas exchange analyser to measure breath-by-breath oxygen consumption (V̇O2) and carbon dioxide produced (V̇CO2). We also calculated mechanical efficiency. We assessed the intensity of low back pain sensation before and after exercise by using a visual analogue scale. In participants with CLBP, low back pain increased following exercise (+ 1.5 units; p < 0.001) and THb decreased during exercise (- 4.0 units; p = 0.043). Paraspinal muscle oxygenation (65.0 and 71.0%, respectively; p = 0.009) and mechanical efficiency (4.7 and 5.3%, respectively; p = 0.034) were both lower in participants with CLBP compared with healthy participants. The increase in pain sensation was related to the decrease in tissue oxygenation (R2 = - 0.420; p = 0.036). Decreases in total haemoglobin-myoglobin and mechanical efficiency could involve fatigability in exercise-soliciting paraspinal muscles and, therefore, exacerbate inabilities in daily life. Given the positive correlation between tissue oxygenation and exercise-induced pain exacerbation, muscle oxygenation may be related to persisting and crippling low back pain.

Use of NIRS to explore skeletal muscle oxygenation during different training sessions in professional boxing

PURPOSE

The physiological examination of boxing has been limited to systemic response in amateur athletes. The demands of professional boxing have been overlooked, despite the different competition format. We sought to determine the physiological demands placed on skeletal muscle in professional boxing.

METHODS

Ten male professional boxers (age 26 ± 5 years, height 177 ± 4 cm, weight 71 ± 6 kg) were recruited for this observational study. On different days, the athletes completed 6 × 3 min rounds of pad, bag or spar-based training with 1 min recovery between each round. Prior to each session, participants put on a heart rate monitor and near-infrared spectroscopy attached to the belly of the rectus femoris muscle to record heart rate and muscle oxygenation.

RESULTS

There were significantly less punches thrown in sparring compared to other training modalities (p < 0.001). Skeletal muscle oxygenation across training modalities consisted of a delay, fast desaturation and steady state. Across rounds there was a significant increase in time delay for desaturation (p = 0.016), rate of fast desaturation (p < 0.001) and duration of fast desaturation (p = 0.019). There was a significant difference in sparring for the heart rate where skeletal muscle oxygenation changes occurred compared to pads or bag sessions (p < 0.001).

CONCLUSION

The findings highlight differences in the skeletal muscle response to the different training modalities. Practitioners need to be aware of the muscular demands of each session to allow optimal adaptation across a training camp. Training needs to allow the skeletal muscle to achieve a new oxygenation steady state rapidly to promote efficient performance across rounds.

Sex Differences in Test-Retest Reliability of Near-Infrared Spectroscopy During Postocclusive Reactive Hyperemia of the Vastus Lateralis

ABSTRACT

Shoemaker, ME, Smith, CM, Gillen, ZM, and Cramer, JT. Sex differences in test-retest reliability of near-infrared spectroscopy during postocclusive reactive hyperemia of the vastus lateralis. J Strength Cond Res 38(2): e40-e48, 2024-The purpose of this study was to determine test-retest reliability for vascular reactivity measures and ranges for normalization of near-infrared spectroscopy (NIRS) variables from the vastus lateralis using postocclusive reactive hyperemia (PORH) procedure in male subjects, female subjects, and combined. Concentrations of oxygenated hemoglobin (Hb) + myoglobin (Mb) (O 2 Hb) and deoxygenated Hb + Mb (HHb) to derive total Hb + Mb (THb), difference in Hb + Mb signal (Hbdiff), and muscle tissue oxygen saturation (StO 2 ) from the vastus lateralis were measured during the PORH in 12 male subjects (age: 23.17 ± 1.77 years; stature: 180.88 ± 4.59 cm; and mass: 81.47 ± 9.68 kg) and 10 female subjects (age: 23.80 ± 2.07 years; stature: 165.95 ± 4.92 cm; and mass: 70.93 ± 10.55 kg) on 2 separate days. Adipose tissue thickness at the NIRS site was measured with ultrasonography. There were no significant differences between the mean values from visit 1 to visit 2 ( p > 0.076-0.985). In the composite sample, intraclass correlation coefficient (ICC) and coefficient of variation (CV) ranged from 0.35 to 0.91 and 4.74 to 39.18%, respectively. In male subjects, ICC and CV values ranged from 0.57 to 0.89 and 2.44 to 28.55%, respectively. In female subjects, ICC and CV values ranged from -0.05 to 0.75 and 7.83 to 61.19%, respectively. Although NIRS variables were overall reliable during PORH, when separated by sex, reliability in male subjects generally increased, whereas female subjects were not reliable, suggesting adipose tissue thickness may be a contributing factor. Understanding sex differences in reliability is important when using this technique for normalization or examining vascular reactivity during athletic performance. With greater utilization of NIRS monitoring in athletes to examine training adaptations, it is important for practitioners to understand the capabilities and potential limitations of the tool.

A Comparison of Leg Muscle Oxygenation, Cardiorespiratory Responses, and Blood Lactate between Walking and Running at the Same Speed

It is not known whether different gait modes, or movement patterns, at the same speed elicit differences in muscle oxygen oxygenation, expressed as muscle oxygen saturation (SmO2). Thus, the aim of this study was to compare the oxygenation of two leg muscles (vastus lateralis and gastrocnemius medialis), as well as the heart rate, respiratory gases, and blood lactate between two gait modes (walking and running) of the same speed and duration. Ten men walked and ran for 30 min each at 7 km/h in a random, counterbalanced order. SmO2, heart rate, and respiratory gases were monitored continuously. Blood lactate was measured at rest, at the end of each exercise, and after 15 min of recovery. Data were analyzed by two-way (gait mode × time) or three-way (gait mode × muscle × time) ANOVA, as applicable. Heart rate and oxygen consumption were higher when running compared to walking. SmO2 was lower during exercise compared to rest and recovery, in gastrocnemius medialis compared to vastus lateralis, and in running compared to walking. Blood lactate increased during exercise but did not differ between gait modes. In conclusion, running caused higher deoxygenation in leg muscles (accompanied by higher whole-body oxygen uptake and heart rate) than walking at the same speed (one that was comfortable for both gait modes), thus pointing to a higher internal load despite equal external load. Thus, preferring running over walking at the same speed causes higher local muscle deoxygenation, which may be beneficial in inducing favorable training adaptations.

Agreement between Ventilatory Thresholds and Bilaterally Measured Vastus Lateralis Muscle Oxygen Saturation Breakpoints in Trained Cyclists: Effects of Age and Performance

This study focused on comparing metabolic thresholds derived from local muscle oxygen saturation (SmO2) signals, obtained using near-infrared spectroscopy (NIRS), with global pulmonary ventilation rates measured at the mouth. It was conducted among various Age Groups within a well-trained cyclist population. Additionally, the study examined how cycling performance characteristics impact the discrepancies between ventilatory thresholds (VTs) and SmO2 breakpoints (BPs).

METHODS

Junior (n = 18) and Senior (n = 15) cyclists underwent incremental cycling tests to assess their aerobic performance and to determine aerobic (AeT) and anaerobic (AnT) threshold characteristics through pulmonary gas exchange and changes in linearity of the vastus lateralis (VL) muscle SmO2 signals. We compared the relative power (Pkg) at ventilatory thresholds (VTs) and breakpoints (BPs) for the nondominant (ND), dominant (DO), and bilaterally averaged (Avr) SmO2 during the agreement analysis. Additionally, a 30 s sprint test was performed to estimate anaerobic performance capabilities and to assess the cyclists' phenotype, defined as the ratio of P@VT2 to the highest 5 s sprint power.

RESULTS

The Pkg@BP for Avr SmO2 had higher agreement with VT values than ND and DO. Avr SmO2 Pkg@BP1 was lower (p < 0.05) than Pkg@VT1 (mean bias: 0.12 ± 0.29 W/kg; Limits of Agreement (LOA): -0.45 to 0.68 W/kg; R2 = 0.72) and mainly among Seniors (0.21 ± 0.22 W/kg; LOA: -0.22 to 0.63 W/kg); there was no difference (p > 0.05) between Avr Pkg@BP2 and Pkg@VT2 (0.03 ± 0.22 W/kg; LOA: -0.40 to 0.45 W/kg; R2 = 0.86). The bias between two methods correlated significantly with the phenotype (r = -0.385 and r = -0.515 for AeT and AnT, respectively).

CONCLUSIONS

Two breakpoints can be defined in the NIRS-captured SmO2 signal of VL, but the agreement between the two methods at the individual level was too low for interchangeable usage of those methods in the practical training process. Older cyclists generally exhibited earlier thresholds in muscle oxygenation signals compared to systemic responses, unlike younger cyclists who showed greater variability and no significant differences in this regard in bias values between the two threshold evaluation methods with no significant difference between methods. More sprinter-type cyclists tended to have systemic VT thresholds earlier than local NIRS-derived thresholds than athletes with relatively higher aerobic abilities.

A systematic review of the relationship between muscle oxygen dynamics and energy rich phosphates. Can NIRS help?

BACKGROUND

Phosphocreatine dynamics provide the gold standard evaluation of in-vivo mitochondrial function and is tightly coupled with oxygen availability. Low mitochondrial oxidative capacity has been associated with health issues and low exercise performance.

METHODS

To evaluate the relationship between near-infrared spectroscopy-based muscle oxygen dynamics and magnetic resonance spectroscopy-based energy-rich phosphates, a systematic review of the literature related to muscle oxygen dynamics and energy-rich phosphates was conducted. PRISMA guidelines were followed to perform a comprehensive and systematic search of four databases on 02-11-2021 (PubMed, MEDLINE, Scopus and Web of Science). Beforehand pre-registration with the Open Science Framework was performed. Studies had to include healthy humans aged 18-55, measures related to NIRS-based muscle oxygen measures in combination with energy-rich phosphates. Exclusion criteria were clinical populations, laboratory animals, acutely injured subjects, data that only assessed oxygen dynamics or energy-rich phosphates, or grey literature. The Effective Public Health Practice Project Quality Assessment Tool was used to assess methodological quality, and data extraction was presented in a table.

RESULTS

Out of 1483 records, 28 were eligible. All included studies were rated moderate. The studies suggest muscle oxygen dynamics could indicate energy-rich phosphates under appropriate protocol settings.

CONCLUSION

Arterial occlusion and exercise intensity might be important factors to control if NIRS application should be used to examine energetics. However, more research needs to be conducted without arterial occlusion and with high-intensity exercises to support the applicability of NIRS and provide an agreement level in the concurrent course of muscle oxygen kinetics and muscle energetics.

TRIAL REGISTRATION

https://osf.io/py32n/ .

KEY POINTS

1. NIRS derived measures of muscle oxygenation agree with gold-standard measures of high energy phosphates when assessed in an appropriate protocol setting. 2. At rest when applying the AO protocol, in the absence of muscle activity, an initial disjunction between the NIRS signal and high energy phosphates can been seen, suggesting a cascading relationship. 3. During exercise and recovery a disruption of oxygen delivery is required to provide the appropriate setting for evaluation through either an AO protocol or high intensity contractions.

Exploring the physiological benefits of carrying a suspended backpack versus a traditional backpack

This study investigates the differences in metabolic energy cost and physiological adaptations between carrying a suspended backpack and a traditional backpack during exercise. For that, 30 males completed the Bruce test while carrying a loaded backpack. Researchers used a metabolic system to obtain variables, analysed muscle oxygen saturation, and used a 2-way RM ANOVA. As results, a significant fatigue interaction was found, but the interaction between fatigue and backpack was non-significant. Using a suspended backpack resulted in energetic advantages in oxygen consumption, muscle oxygen saturation, and performance compared to a traditional backpack. In conclusion, this study offers insights into the physiological implications of using a suspended backpack, suggesting it may reduce the risk of musculoskeletal issues and improve performance for those carrying heavy loads.Practitioner summary: The suspended-load backpacks have been proposed as an alternative to traditional backpacks. This study highlighted that the use of a suspended backpack provided some energetical advantages adaptation compared to the traditional backpack in terms of oxygen consumption, muscle oxygen saturation and performance during a multistage treadmill test walking-running test.

Do freedivers and spearfishermen differ in local muscle oxygen saturation and anaerobic power?

BACKGROUND

Freediving is defined as an activity where athletes repetitively dive and are exposed to long efforts with limited oxygen consumption. Therefore, anaerobic features are expected to be an important facet of diving performance. This study aimed to investigate differences in anaerobic capacity and local muscle oxygenation in spearfisherman and freedivers.

METHODS

The sample of participants included 17 male athletes (nine freedivers, and eight spearfishermen), with an average age of 37.0±8.8 years, training experience of 10.6±9.5 years, body mass of 82.5±9.5 kg and height of 184.2±5.7 cm. Anthropometric characteristics included: body mass, body height, seated height, and body fat percentage. Wingate anaerobic test was conducted, during which local muscle oxygenation was measured with a NIRS device (Moxy monitor). Wingate power outputs were measured (peak power [W/kg] and average power [W/kg]), together with muscle oxygenation variables (baseline oxygen saturation [%], desaturation slope [%/s], minimum oxygen saturation [%], half time recovery [s], and maximum oxygen saturation [%]).

RESULTS

The differences were not obtained between freedivers and spearfisherman in power outputs (peak power (9.24±2.08 spearfisherman; 10.68±1.04 freedivers; P=0.14); average power (6.85±0.95 spearfisherman; 7.44±0.60 freedivers; P=0.15) and muscle oxygenation parameters. However, analysis of effect size showed a moderate effect in training experience (0.71), PP (0.89), AP (0.75), Desat slope mVLR (0.66), half time recovery mVLR (0.90).

CONCLUSIONS

The non-existence of differences between freedivers and spearfishermen indicates similar training adaptations to the anaerobic demands. However, the results show relatively low anaerobic capacities of our divers that could serve as an incentive for the further development of these mechanisms.

Effects of Different Gum Hardness on Masseter Muscle Activity During Gum Chewing: An NIRS Oximetry Study

Gum chewing is used in orofacial therapy to improve oral functions, such as a patient's chewing ability, bite force, tongue pressure, and lip closure strength. However, its effects on masseter muscle oxygen dynamics and muscle activity may vary with the hardness and features of the gum base. Therefore, when considering gum chewing for therapeutic purposes, it is essential to select gum of an appropriate hardness. This study aimed to elucidate the impact of gum hardness differences on masseter muscle tissue oxygen dynamics and muscle activity. We conducted a 120-s gum chewing study using three types of gum with different hardness levels on 11 healthy adult males. Each patient's masseter muscle tissue oxygen dynamics, muscle activity, and heart rate were measured, and the extent of masseter fatigue was assessed using a visual analogue scale (VAS). Per our findings, as gum hardness increased, significant reductions in oxygen saturation (StO2) and significant increases in deoxyhaemoglobin (Deoxy-Hb) concentrations were observed in masseter muscle tissue oxygen dynamics. Likewise, muscle activity, heart rate, and muscle fatigue (according to VAS) also increased significantly as gum hardness increased. The findings of this study reveal that increasing gum base hardness not only affects masseter muscle tissue oxygen dynamics but also increases muscle activity, masseter fatigue, and heart rate. When selecting gum for orofacial therapy involving gum chewing exercises, it is crucial to choose the appropriate gum.

Near-Infrared Spectroscopy Analysis of Triceps Brachii Muscle Oxygenation During Sprinting in Wheelchair Basketball Players: A Pilot Study

The purpose of this study was to clarify the characteristics of muscle fatigue by measuring the oxygenation of muscles during wheelchair sprinting in wheelchair basketball players, using near-infrared spectroscopy (NIRS). We believe that this information will be helpful in planning rehabilitation and training programmes.Five male wheelchair basketball players (mean age 30.0 ± 12.0 years, mean height 166.0 ± 12.1 cm, and mean weight 61.0 ± 15.8 kg) participated in this study.These participants performed six 20 m sprint tests after warming up. NIRS measurements were obtained at rest before the start of exercise, during sprinting movements, and during the recovery time after sprinting. Measurements were taken using a wireless NIRS device (PortaMon, Artinis, The Netherlands; sampling rate, 10 Hz) with a single-channel system for tissue oxygenation measurements. The NIRS sensor was applied to the triceps muscle on the participant's dominant arm and fixed with an upper arm supporter. The measurement data were imported into a dedicated computer and the tissue saturation index (TSI) was calculated. Statistical analysis was performed using the Friedman test to compare the TSI before sprinting and at each sprint, and a post hoc Bonferroni test was conducted.Compared to the pre-sprint measurements, TSI significantly decreased during sprints second, fourth, and fifth.In the present study, changes in the oxygen status of the triceps muscle during wheelchair driving varied greatly among individuals, and a tendency was observed towards the oxygen saturation being lowest by the fourth sprint, with the decrease being suppressed from this point on.

A comparative analysis of mathematical methods for detecting lactate thresholds using muscle oxygenation data during a graded cycling test

Objective. Threshold determination for improving training and sports performance is important for researchers and trainers, who currently use different methods for determining lactate, ventilatory or muscle oxygenation (SmO2) thresholds. Our study aimed to compare the identification of the intensity at the first and second thresholds using lactate and SmO2data by different mathematical methods in different muscles during a graded cycling test.Approach. Twenty-six cyclists (15 males and 11 females; 23 ±6 years, 1.71 ± 0.09 m, 64.3 ± 8.8 Kg and 12 ± 3 training hours per week) performed a graded test on the cycle ergometer. Power output and saturation of muscle oxygen in four muscles (vastus lateralis, biceps femoris, gastrocnemius and tibialis anterior) were measured, along with systemic lactate concentration.Main Results. Our results showed that any method was reliable for determining the first muscle oxygenation threshold (MOT1) when comparing the lactate threshold in any muscle. However, the best method for determining the second muscle oxygenation threshold (MOT2) was the Exp-Dmax (p< 0.01; ICC = 0.79-0.91) in all muscles. In particular, the vastus lateralis muscle showed the highest intraclass correlation coefficient (ICC = 0.91, CI95% [0.81, 0.96]). However, results varied per sex across all muscles analyzed.Significance. Although the first muscle oxygenation threshold could not be determined using mathematical methods in all the muscles analyzed, the Exp-Dmax method presented excellent results in detecting the second systemic threshold in the vastus lateralis.

In vivocharacterization of the optical and hemodynamic properties of the human sternocleidomastoid muscle through ultrasound-guided hybrid near-infrared spectroscopies

Objective.In this paper, we present a detailedin vivocharacterization of the optical and hemodynamic properties of the human sternocleidomastoid muscle (SCM), obtained through ultrasound-guided near-infrared time-domain and diffuse correlation spectroscopies.Approach.A total of sixty-five subjects (forty-nine females, sixteen males) among healthy volunteers and thyroid nodule patients have been recruited for the study. Their SCM hemodynamic (oxy-, deoxy- and total hemoglobin concentrations, blood flow, blood oxygen saturation and metabolic rate of oxygen extraction) and optical properties (wavelength dependent absorption and reduced scattering coefficients) have been measured by the use of a novel hybrid device combining in a single unit time-domain near-infrared spectroscopy, diffuse correlation spectroscopy and simultaneous ultrasound imaging.Main results.We provide detailed tables of the results related to SCM baseline (i.e. muscle at rest) properties, and reveal significant differences on the measured parameters due to variables such as side of the neck, sex, age, body mass index, depth and thickness of the muscle, allowing future clinical studies to take into account such dependencies.Significance.The non-invasive monitoring of the hemodynamics and metabolism of the sternocleidomastoid muscle during respiration became a topic of increased interest partially due to the increased use of mechanical ventilation during the COVID-19 pandemic. Near-infrared diffuse optical spectroscopies were proposed as potential practical monitors of increased recruitment of SCM during respiratory distress. They can provide clinically relevant information on the degree of the patient's respiratory effort that is needed to maintain an optimal minute ventilation, with potential clinical application ranging from evaluating chronic pulmonary diseases to more acute settings, such as acute respiratory failure, or to determine the readiness to wean from invasive mechanical ventilation.

Monitoring Changes in Oxygen Muscle during Exercise with High-Flow Nasal Cannula Using Wearable NIRS Biosensors

Exercise increases the cost of breathing (COB) due to increased lung ventilation (V˙E), inducing respiratory muscles deoxygenation (∇SmO2), while the increase in workload implies ∇SmO2 in locomotor muscles. This phenomenon has been proposed as a leading cause of exercise intolerance, especially in clinical contexts. The use of high-flow nasal cannula (HFNC) during exercise routines in rehabilitation programs has gained significant interest because it is proposed as a therapeutic intervention for reducing symptoms associated with exercise intolerance, such as fatigue and dyspnea, assuming that HFNC could reduce exercise-induced ∇SmO2. SmO2 can be detected using optical wearable devices provided by near-infrared spectroscopy (NIRS) technology, which measures the changes in the amount of oxygen bound to chromophores (e.g., hemoglobin, myoglobin, cytochrome oxidase) at the target tissue level. We tested in a study with a cross-over design whether the muscular desaturation of m.vastus lateralis and m.intercostales during a high-intensity constant-load exercise can be reduced when it was supported with HFNC in non-physically active adults. Eighteen participants (nine women; age: 22 ± 2 years, weight: 65.1 ± 11.2 kg, height: 173.0 ± 5.8 cm, BMI: 21.6 ± 2.8 kg·m-2) were evaluated in a cycle ergometer (15 min, 70% maximum watts achieved in ergospirometry (V˙O2-peak)) breathing spontaneously (control, CTRL) or with HFNC support (HFNC; 50 L·min-1, fiO2: 21%, 30 °C), separated by seven days in randomized order. Two-way ANOVA tests analyzed the ∇SmO2 (m.intercostales and m.vastus lateralis), and changes in V˙E and ∇SmO2·V˙E-1. Dyspnea, leg fatigue, and effort level (RPE) were compared between trials by the Wilcoxon matched-paired signed rank test. We found that the interaction of factors (trial × exercise-time) was significant in ∇SmO2-m.intercostales, V˙E, and (∇SmO2-m.intercostales)/V˙E (p < 0.05, all) but not in ∇SmO2-m.vastus lateralis. ∇SmO2-m.intercostales was more pronounced in CTRL during exercise since 5' (p < 0.05). Hyperventilation was higher in CTRL since 10' (p < 0.05). The ∇SmO2·V˙E-1 decreased during exercise, being lowest in CTRL since 5'. Lower dyspnea was reported in HFNC, with no differences in leg fatigue and RPE. We concluded that wearable optical biosensors documented the beneficial effect of HFNC in COB due to lower respiratory ∇SmO2 induced by exercise. We suggest incorporating NIRS devices in rehabilitation programs to monitor physiological changes that can support the clinical impact of the therapeutic intervention implemented.

Sex-related differences in profiles of muscle oxygen saturation of different muscles in trained cyclists during graded cycling exercise

Although in recent years near-infrared spectroscopy has been used in many sports to monitor muscle oxygen saturation (SmO2), there is a lack of knowledge about the sex differences in SmO2 during exercise in different muscles. Our study aimed to examine SmO2 differences in muscles between female and male cyclists, during a graded cycling test and at the first and second lactate thresholds. Twenty-five trained cyclists and triathletes (15 males: 23 ± 7 yr, 1.78 ± 0.05 m, 70.2 ± 5.3 kg, and 10 females: 22 ± 5 yr, 1.64 ± 0.06 m, 58 ± 8 kg) performed a graded cycling test on the cycle ergometer. Power output and SmO2 in five muscles (dominant vastus lateralis, tibialis anterior, gastrocnemius medial, biceps femoris, and triceps brachii) were measured. Our mixed regression models showed that the interaction between power output and sex was significant for all the muscles analyzed (P < 0.001), indicating a greater decrease in SmO2 for males as power output increased. Moreover, the statistical parametric mapping analyses showed for females higher SmO2 in the middle of the test in biceps femoris (P = 0.03), gastrocnemius medial (P = 0.02), and tibialis anterior (P = 0.04). Finally, the males presented a lower SmO2 in all muscles where the second lactate threshold occurred, with greater evidence than in the first lactate threshold. In conclusion, females have higher SmO2 in all muscles, and these differences are more noticeable during the graded cycling test, such that males seem to have a greater reliance on oxygen extraction than females for a given relative intensity of exercise.NEW & NOTEWORTHY This study investigated the profiles of muscle oxygen saturation (SmO2) during incremental exercise in females and males. Females presented higher overall SmO2 than males during moderate and heavy intensity domain exercise in all muscles including muscles that are not mainly involved in pedaling (triceps brachii), from those that are stabilizers (medial gastrocnemius, tibialis anterior, and biceps femoris), to those that are related to power output production (vastus lateralis).

Assessment of Intercostal Muscle Near-Infrared Spectroscopy for Estimating Respiratory Compensation Point in Trained Endurance Athletes

This study aimed to assess the reliability and validity of estimating the respiratory compensation point (RCP) in trained endurance athletes by analyzing intercostal muscles' NIRS-derived tissue oxygenation dynamics. Seventeen experienced trail runners underwent an incremental treadmill protocol on two separate occasions, with a 7-day gap between assessments. Gas exchange and muscle oxygenation data were collected, and the oxygen saturation breakpoint (SmO2BP) measured in the intercostal muscles was compared to the RCP, which was identified by the increase in the VE/V.CO2 slope and the point at which the PetCO2 started to decrease. No statistically significant differences were observed between the two methods for any of the variables analyzed. Bland-Altman analysis showed significant agreement between the NIRS and gas analyzer methods for speed (r = 0.96, p < 0.05), HR (r = 0.98, p < 0.05), V.O2 relative to body mass (r = 0.99, p < 0.05), and %SmO2 (r = 0.98, p < 0.05). The interclass correlation coefficient values showed moderate to good reliability (0.60 to 0.86), and test-retest analysis revealed mean differences within the confidence intervals for all variables. These findings suggest that the SmO2BP measured using a portable NIRS device in the intercostal muscles is a reliable and valid tool for estimating the RCP for experienced trail runners and might be useful for coaches and athletes to monitor endurance training.

Association between Fractional Oxygen Extraction from Resting Quadriceps Muscle and Body Composition in Healthy Men

This study aimed to associate body composition with fractional oxygen extraction at rest in healthy adult men. Fourteen healthy adults (26.93 ± 2.49 years) from Chile participated. Body composition was assessed with octopole bioimpedance, and resting muscle oxygenation was evaluated in the vastus lateralis quadriceps with near-infrared spectroscopy (NIRS) during a vascular occlusion test, analyzing the muscleVO2, resaturation velocity during reactive hyperemia via the muscle saturation index (%TSI), and the area above the curve of HHb (AACrep). It was observed that the total and segmented fat mass are associated with lower reoxygenation velocities during hyperemia (p = 0.008; β = 0.678: p = 0.002; β = 0.751), and that the total and segmented skeletal muscle mass are associated with higher reoxygenation velocities during hyperemia (p = 0.020; β = -0.614: p = 0.027; β = -0.587). It was also observed that the total and segmented fat mass were associated with a higher area above the curve of HHb (AACrep) during hyperemia (p = 0.007; β = 0.692: p = 0.037; β = 0.564), and that total and segmented skeletal muscle mass was associated with a lower area above the curve of HHb (AACrep) during hyperemia (p = 0.007; β = -0.703: p = 0.017; β = -0.632). We concluded that fat mass is associated with lower resaturation rates and lower resting fractional O2 extraction levels. In contrast, skeletal muscle mass is associated with higher resaturation rates and fractional O2 extraction during reactive hyperemia. The AACrep may be relevant in the evaluation of vascular adaptations to exercise and metabolic health.

Muscle oxygen saturation rates coincide with lactate-based exercise thresholds

INTRODUCTION

Monitoring muscle metabolic activity via blood lactate is a useful tool for understanding the physiological response to a given exercise intensity. Recent indications suggest that skeletal muscle oxygen saturation (SmO2), an index of the balance between local O2 supply and demand, may describe and predict endurance performance outcomes.

PURPOSE

We tested the hypothesis that SmO2 rate is tightly related to blood lactate concentration across exercise intensities, and that deflections in SmO2 rate would coincide with established blood lactate thresholds (i.e., lactate thresholds 1 and 2).

METHODS

Ten elite male soccer players completed an incremental running protocol to exhaustion using 3-min work to 30 s rest intervals. Blood lactate samples were collected during rest and SmO2 was collected continuously via near-infrared spectroscopy from the right and left vastus lateralis, left biceps femoris and the left gastrocnemius.

RESULTS

Muscle O2 saturation rate (%/min) was quantified after the initial 60 s of each 3-min segment. The SmO2 rate was significantly correlated with blood lactate concentrations for all muscle sites; RVL, r = - 0.974; LVL, r = - 0.969; LG, r = - 0.942; LHAM, r = - 0.907. Breakpoints in SmO2 rate were not significantly different from LT1 or LT2 at any muscle sites (P > 0.05). Bland-Altman analysis showed speed threshold estimates via SmO2 rate and lactate are similar at LT2, but slightly greater for SmO2 rate at LT1.

CONCLUSIONS

Muscle O2 saturation rate appears to provide actionable information about maximal metabolic steady state and is consistent with bioenergetic reliance on oxygen and its involvement in the attainment of metabolic steady state.

Local microvascular tissue oxygenation of the intrinsic foot muscles in patients with diabetes: A cross-sectional case-comparison study

BACKGROUND

Foot-related complications including impaired peripheral circulation and lower limb ulceration are severe consequences for those with diabetes mellitus. This study aimed to assess differences in tissue oxygenation and oxygen utilization of the plantar surface intrinsic foot muscles between diabetic participants and healthy comparisons following short foot exercise and a standard walking protocol.

METHODS

Eighteen participants, 9 with diabetes and 9 healthy age- and sex-matched comparisons, completed two interventions in a randomized order. For the short foot exercise intervention, participants completed 5 sets of 15 intrinsic foot muscle contractions. For the walking intervention, participants completed a modified six-minute walk test. Tissue oxygenation variables including oxygenated hemoglobin, deoxygenated hemoglobin, and tissue saturation index were measured using near-infrared spectroscopy in quiet stance and during intrinsic foot muscle contraction cycles following each intervention. Means, standard deviations, 95 % confidence intervals, mean differences, and Cohen's d effect sizes were calculated for each tissue oxygenation variable.

RESULTS

The results of this study indicated no significant group differences in quiet standing tissue oxygenation measures at baseline and following each intervention. Participants in the diabetic group had significantly less change in tissue saturation index during intrinsic foot muscle contractions compared to healthy participants after the short foot exercise intervention (ES= 4.00, P = .0002) and walking intervention (ES= 1.33, P = .015).

CONCLUSIONS

By utilizing wireless NIRS and novel research methodology, this study was able to explore changes in plantar surface tissue oxygenation of the intrinsic foot muscles following a targeted short foot exercise intervention as well as a standard walking protocol in patients diagnosed with diabetes compared to age- and sex- matched individuals without diabetes. We identified that diabetic participants presented with less oxygen utilization during intrinsic foot muscle contractions performed following both exercise interventions compared to their healthy age- and sex- matched comparisons.

Reliability of threshold determination using portable muscle oxygenation monitors during exercise testing: a systematic review and meta-analysis

Over the last few years, portable Near-Infrared Spectroscopy (NIRS) technology has been suggested for determining metabolic/ventilator thresholds. This systematic review and meta-analysis aimed to assess the reliability of a portable muscle oxygenation monitor for determining thresholds during exercise testing. The proposed PICO question was: Is the exercise intensity of muscle oxygenation thresholds, using portable NIRS, reliable compared with lactate and ventilatory thresholds for exercise intensity determined in athletes? A search of Pubmed, Scopus and Web of Science was undertaken and the review was conducted following PRISMA guidelines. Fifteen articles were included. The domains which presented the highest biases were confounders (93% with moderate or high risk) and participant selection (100% with moderate or high risk). The intra-class correlation coefficient between exercise intensity of the first ventilatory or lactate threshold and the first muscle oxygenation threshold was 0.53 (obtained with data from only 3 studies), whereas the second threshold was 0.80. The present work shows that although a portable muscle oxygenation monitor has moderate to good reliability for determining the second ventilatory and lactate thresholds, further research is necessary to investigate the mathematical methods of detection, the capacity to detect the first threshold, the detection in multiple regions, and the effect of sex, performance level and adipose tissue in determining thresholds.

Comparing the reliability of muscle oxygen saturation with common performance and physiological markers across cycling exercise intensity

Introduction

Wearable near-infrared spectroscopy (NIRS) measurements of muscle oxygen saturation (SmO2) demonstrated good test-retest reliability at rest. We hypothesized SmO2 measured with the Moxy monitor at the vastus lateralis (VL) would demonstrate good reliability across intensities. For relative reliability, SmO2 will be lower than volume of oxygen consumption (V̇O2) and heart rate (HR), higher than concentration of blood lactate accumulation ([BLa]) and rating of perceived exertion (RPE). We aimed to estimate the reliability of SmO2 and common physiological measures across exercise intensities, as well as to quantify within-participant agreement between sessions.

Methods

Twenty-one trained cyclists completed two trials of an incremental multi-stage cycling test with 5 min constant workload steps starting at 1.0 watt per kg bodyweight (W·kg-1) and increasing by 0.5 W kg-1 per step, separated by 1 min passive recovery intervals until maximal task tolerance. SmO2, HR, V̇O2, [BLa], and RPE were recorded for each stage. Continuous measures were averaged over the final 60 s of each stage. Relative reliability at the lowest, median, and highest work stages was quantified as intraclass correlation coefficient (ICC). Absolute reliability and within-subject agreement were quantified as standard error of the measurement (SEM) and minimum detectable change (MDC).

Results

Comparisons between trials showed no significant differences within each exercise intensity for all outcome variables. ICC for SmO2 was 0.81-0.90 across exercise intensity. ICC for HR, V̇O2, [BLa], and RPE were 0.87-0.92, 0.73-0.97, 0.44-0.74, 0.29-0.70, respectively. SEM (95% CI) for SmO2 was 5 (3-7), 6 (4-9), and 7 (5-10)%, and MDC was 12%, 16%, and 18%.

Discussion

Our results demonstrate good-to-excellent test-retest reliability for SmO2 across intensity during an incremental multi-stage cycling test. V̇O2 and HR had excellent reliability, higher than SmO2. [BLa] and RPE had lower reliability than SmO2. Muscle oxygen saturation measured by wearable NIRS was found to have similar reliability to V̇O2 and HR, and higher than [BLa] and RPE across exercise intensity, suggesting that it is appropriate for everyday use as a non-invasive method of monitoring internal load alongside other metrics.

Aerobic capacity and V ˙ O 2 kinetics adaptive responses to short-term high-intensity interval training and detraining in untrained females

PURPOSE

This study investigated the physical fitness and oxygen uptake kinetics (τV ˙ O 2 p ) along with the O2 delivery and utilization (heart rate kinetics, τHR; deoxyhemoglobin/V ˙ O 2 ratio, ∆[HHb]/V ˙ O 2 ) adaptations of untrained female participants responding to 4 weeks of high-intensity interval training (HIIT) and 2 weeks of detraining.

METHODS

Participants were randomly assigned to HIIT (n = 11, 4 × 4 protocol) or nonexercising control (n = 9) groups. Exercising group engaged 4 weeks of treadmill HIIT followed by 2 weeks of detraining while maintaining daily activity level. Ramp-incremental (RI) tests and step-transitions to moderate-intensity exercise were performed. Aerobic capacity and performance (maximal oxygen uptake,V ˙ O 2 max ; gas-exchange threshold, GET; power output, PO), body composition (skeletal muscle mass, SMM; body fat percentage, BF%), muscle oxygenation status (∆[HHb]),V ˙ O 2 , and HR kinetics were assessed.

RESULTS

HIIT elicited improvements in aerobic capacity (V ˙ O 2 max , + 0.17 ± 0.04 L/min; GET, + 0.18 ± 0.05 L/min, P < 0.01; PO-V ˙ O 2 max , ± 23.36 ± 8.37 W; PO-GET, + 17.18 ± 3.07 W, P < 0.05), body composition (SMM, + 0.92 ± 0.17 kg; BF%, - 3.08% ± 0.58%, P < 0.001), and speed up the τV ˙ O 2 p (- 8.04 ± 1.57 s, P < 0.001) significantly, extending to better ∆[HHb]/V ˙ O 2 ratio (1.18 ± 0.08 to 1.05 ± 0.14). After a period of detraining, the adaptation in body composition and aerobic capacity, as well as the accelerated τV ˙ O 2 p were maintained in the HIIT group, but the PO-V ˙ O 2 max and PO-GET declined below the post-training level (P < 0.05), whereas no changes were reported in controls (P > 0.05). Four weeks of HIIT induced widespread physiological adaptations in females, and the majority of improvements were preserved after 2 weeks of detraining except for power output corresponding toV ˙ O 2 max and GET.

Review of recent advances in frequency-domain near-infrared spectroscopy technologies [Invited]

Over the past several decades, near-infrared spectroscopy (NIRS) has become a popular research and clinical tool for non-invasively measuring the oxygenation of biological tissues, with particular emphasis on applications to the human brain. In most cases, NIRS studies are performed using continuous-wave NIRS (CW-NIRS), which can only provide information on relative changes in chromophore concentrations, such as oxygenated and deoxygenated hemoglobin, as well as estimates of tissue oxygen saturation. Another type of NIRS known as frequency-domain NIRS (FD-NIRS) has significant advantages: it can directly measure optical pathlength and thus quantify the scattering and absorption coefficients of sampled tissues and provide direct measurements of absolute chromophore concentrations. This review describes the current status of FD-NIRS technologies, their performance, their advantages, and their limitations as compared to other NIRS methods. Significant landmarks of technological progress include the development of both benchtop and portable/wearable FD-NIRS technologies, sensitive front-end photonic components, and high-frequency phase measurements. Clinical applications of FD-NIRS technologies are discussed to provide context on current applications and needed areas of improvement. The review concludes by providing a roadmap toward the next generation of fully wearable, low-cost FD-NIRS systems.

Reactive hyperemia half-time response is associated with skeletal muscle oxygen saturation changes during cycling exercise

We investigated the relationship between muscle microvascular responses during reactive hyperemia as assessed using near-infrared spectroscopy (NIRS) with changes in skeletal muscle oxygen saturation during exercise. Thirty young untrained adults (M/W: 20/10; 23 ± 5 years) completed a maximal cycling exercise test to determine exercise intensities performed on a subsequent visit separated by seven days. At the second visit, post-occlusive reactive hyperemia was measured as changes in NIRS-derived tissue saturation index (TSI) at the left vastus lateralis muscle. Variables of interest included desaturation magnitude, resaturation rate, resaturation half-time, and hyperemic area under the curve. Afterwards, two 4-minute bouts of moderate intensity cycling followed by one bout of severe intensity cycling to fatigue took place while TSI was measured at the vastus lateralis muscle. TSI was averaged across the last 60-s of each moderate intensity bout then averaged together for analysis, and at 60-s into severe exercise. The change in TSI (∆TSI) during exercise is expressed relative to a 20 W cycling baseline. On average, the ΔTSI was -3.4 ± 2.4 % and -7.2 ± 2.8 % during moderate and severe intensity cycling, respectively. Resaturation half-time was correlated with the ΔTSI during moderate (r = -0.42, P = 0.01) and severe (r = -0.53, P = 0.002) intensity exercise. No other reactive hyperemia variable was found to correlate with ΔTSI. These results indicate that resaturation half-time during reactive hyperemia represents a resting muscle microvascular measure that associates with the degree of skeletal muscle desaturation during exercise in young adults.