Comparison of NIRS exercise intensity thresholds with maximal lactate steady state, critical power and rowing performance

This study aimed to compare the intensity of deoxygenated haemoglobin concentration ([HHb]) and tissue saturation index (TSI) breakpoints ([HHb]-BP and TSI-BP) with maximal lactate steady state (MLSS) and critical power (CP), and to describe their association with 2000-m rowing ergometer performance. Fourteen male rowers performed on a rowing ergometer: I) a discontinuous incremental test with 3-min stages (INC3); II) a continuous incremental test with 1-min stages (INC1); III) constant workload tests to determine MLSS; and IV) performance tests of 500 m, 1000 m, 2000 m and 6000 m to determine CP.CP (257 ± 39 W; 3.79 ± 4.1 L · min-1) was higher than [HHb]-BP3 (205 ± 26 W; 3.48 ± 2.9 L · min-1), [HHb]-BP1 (207 ± 27 W; 3.27 ± 3.2 L · min-1), and TSI-BP3 (218 ± 31 W; 3.51 ± 3.0 L · min-1), but not higher than TSI-BP1 (222 ± 34 W; 3.43 ± 3.2 L · min-1). MLSS (187 ± 26 W; 3.33 ± 3.2 L · min-1) was lower than TSI-BP3 and TSI-BP1 for power output, but not different in any comparison for ⩒O2. The limits of agreement for power output and ⩒O2 suggest poor agreement among these thresholds. The low level of agreement compromises the use of [HHb]-BP and TSI-BP for estimating MLSS and CP; therefore, these thresholds should not be considered interchangeable.

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.

Effects of acute phosphodiesterase type 5 inhibition on skeletal muscle interstitial PO2 during contractions and recovery

The oxygen partial pressure within the interstitial space (PO2is; mmHg) provides the driving force for oxygen diffusion into the myocyte thereby supporting oxidative phosphorylation. We tested the hypothesis that potentiation of the nitric oxide pathway with sildenafil (phosphodiesterase type 5 inhibitor) would enhance PO2is during muscle metabolic transitions, thereby slowing PO2is on- and accelerating PO2is off-kinetics. The rat spinotrapezius muscle (n = 17) was exposed for PO2is measurements via phosphorescence quenching under control (CON), low-dose sildenafil (1 mg/kg i.a., SIL1) and high-dose sildenafil (7 mg/kg i.a., SIL7). Data were collected at rest and during submaximal twitch contractions (1 Hz, 4-6 V, 3 min) and recovery (3 min). Mean arterial blood pressure (MAP; mmHg) was reduced with both SIL1 (pre:132 ± 5; post:99 ± 5) and SIL7 (pre:111 ± 6; post:99 ± 4) (p < 0.05). SIL7 elevated resting PO2is (18.4 ± 1.1) relative to both CON (15.7 ± 0.7) and SIL1 (15.2 ± 0.7) (p < 0.05). In addition, SIL7 increased end-recovery PO2is (17.7 ± 1.6) compared to CON (12.8 ± 0.9) and SIL1 (13.4 ± 0.8) (p < 0.05). The overall PO2is response during recovery (i.e., area under the PO2is curve) was greater in SIL7 (4107 ± 444) compared to CON (3493 ± 222) and SIL1 (3114 ± 205 mmHg s) (p < 0.05). Contrary to our hypothesis, there was no impact of acute SIL (1 or 7 mg/kg) on the speed of the PO2is response during contractions or recovery (p > 0.05). However, sildenafil lowered MAP and improved skeletal muscle interstitial oxygenation in healthy rats. Specifically, SIL7 enhanced PO2is at rest and during recovery from submaximal muscle contractions. Potentiation of the nitric oxide pathway with sildenafil enhances microvascular blood-myocyte O2 transport and is expected to improve repeated bouts of contractile activity.

Influence of cuff stiffness on hemodynamics and perceived cuff pressure in the upper extremities in males and females: implications for practical blood flow restriction training

BACKGROUND

Practical blood flow restriction (pBFR) during exercise is a cost-saving alternative to traditional blood flow restriction using pneumatic cuffs, particularly when exercising in a group setting. Depending on the pBFR technique, several factors (e.g., cuff width, limb circumference) have already been shown to be of importance when applying the pBFR pressure. Given that elastic cuffs are often used for pBFR, the cuff stiffness might be an additional influencing factor. Therefore, the present study compared the acute effects of three elastic cuffs with identical width but different stiffness (high stiffness (HS), medium stiffness (MS), and low stiffness (LS)) on hemodynamic measures and perceived cuff pressure at rest.

METHODS

In a randomized, counter-balanced cross-over study, 36 young and normotensive participants completed three experimental trials. After a 10-min rest period in supine position, the cuff was loosely and proximally applied to the right upper arm. Following baseline data recording, the cuff was successively tightened in 10%-increments with respect to the limb circumference (%overlap) until arterial blood flow was occluded. At baseline and during each %overlap, systolic peak blood flow velocity of the brachial artery, rating of perceived cuff pressure, as well as muscle oxygen saturation and total hemoglobin concentration of the biceps brachii muscle were recorded.

RESULTS

The %overlap required to occlude arterial blood flow was different between the three cuffs (HS: 30.9 ± 3.8%, MS: 43.9 ± 6.1%, LS: 54.5 ± 8.3%). Furthermore, at 30% overlap, systolic peak blood flow velocity was lower when applying the HS (9.0 ± 10.9 cm∙s- 1) compared to MS (48.9 ± 21.9 cm∙s- 1) and LS cuff (62.9 ± 19.1 cm∙s- 1). Rating of perceived cuff pressure at 30% overlap was higher when using the HS (6.5 ± 1.5 arbitrary unit (a.u.)) compared to MS (5.1 ± 1.4 a.u.) and LS cuff (4.9 ± 1.5 a.u.) with no difference between the MS and LS cuff. However, muscle oxygen saturation and total hemoglobin concentration were not different between the three cuffs.

CONCLUSIONS

The present study revealed that the cuff stiffness influenced blood flow velocity and arterial occlusion pressure. Therefore, cuff stiffness seems an important factor for the application of pBFR.

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.

Carbohydrate intake before and during high intensity exercise with reduced muscle glycogen availability affects the speed of muscle reoxygenation and performance

Muscle glycogen state and carbohydrate (CHO) supplementation before and during exercise may impact responses to high-intensity interval training (HIIT). This study determined cardiorespiratory, substrate metabolism, muscle oxygenation, and performance when completing HIIT with or without CHO supplementation in a muscle glycogen depleted state. On two occasions, in a cross-over design, eight male cyclists performed a glycogen depletion protocol prior to HIIT during which either a 6% CHO drink (60 g.hr^-1) or placebo (%CHO, PLA) was consumed. HIIT consisted of 5 × 2 min at 80% peak power output (PPO), 3 × 10-min bouts of steady-state (SS) cycling (50, 55, 60% PPO), and a time-to-exhaustion (TTE) test. There was no difference in SS [Formula: see text], HR, substrate oxidation and gross efficiency (GE %) between CHO and PLA conditions. A faster rate of muscle reoxygenation (%. s^-1) existed in PLA after the 1st (Δ - 0.23 ± 0.22, d = 0.58, P < 0.05) and 3rd HIIT intervals (Δ - 0.34 ± 0.25, d = 1.02, P < 0.05). TTE was greater in CHO (7.1 ± 5.4 min) than PLA (2.5 ± 2.3 min, d = 0.98, P < 0.05). CHO consumption before and during exercise under reduced muscle glycogen conditions did not suppress fat oxidation, suggesting a strong regulatory role of muscle glycogen on substrate metabolism. However, CHO ingestion provided a performance benefit under intense exercise conditions commenced with reduced muscle glycogen. More research is needed to understand the significance of altered muscle oxygenation patterns during exercise.

Adaptations to 4 weeks of high-intensity interval training in healthy adults with different training backgrounds

PURPOSE

This study investigated the physical fitness and oxygen uptake kinetics ([Formula: see text]) along with the exercise-onset O₂ delivery (heart rate kinetics, τHR; changes in normalized deoxyhemoglobin/[Formula: see text] ratio, Δ[HHb]/[Formula: see text]) adaptations of individuals with different physical activity (PA) backgrounds responding to 4 weeks of high-intensity interval training (HIIT), and the possible effects of skeletal muscle mass (SMM) on training-induced adaptations.

METHODS

Twenty subjects (10 high-PA level, HIIT-H; 10 moderate-PA level, HIIT-M) engaged in 4 weeks of treadmill HIIT. Ramp-incremental (RI) test and step-transitions to moderate-intensity exercise were performed. Cardiorespiratory fitness, body composition, muscle oxygenation status, VO₂ and HR kinetics were assessed at baseline and post-training.

RESULTS

HIIT improved fitness status for HIIT-H ([Formula: see text], + 0.26 ± 0.07 L/min; SMM, + 0.66 ± 0.70 kg; body fat, - 1.52 ± 1.93 kg; [Formula: see text], - 7.11 ± 1.05 s, p < 0.05) and HIIT-M ([Formula: see text], 0.24 ± 0.07 L/min, SMM, + 0.58 ± 0.61 kg; body fat, - 1.64 ± 1.37 kg; [Formula: see text], - 5.48 ± 1.05 s, p < 0.05) except for visceral fat area (p = 0.293) without between-group differences (p > 0.05). Oxygenated and deoxygenated hemoglobin amplitude during the RI test increased for both groups (p < 0.05) except for total hemoglobin (p = 0.179). The Δ[HHb]/[Formula: see text] overshoot was attenuated for both groups (p < 0.05) but only eliminated in HIIT-H (1.05 ± 0.14 to 0.92 ± 0.11), and no change was observed in τHR (p = 0.144). Linear mixed-effect models presented positive effects of SMM on absolute [Formula: see text] (p < 0.001) and ΔHHb (p = 0.034).

CONCLUSION

Four weeks of HIIT promoted positive adaptations in physical fitness and [Formula: see text] kinetics, with the peripheral adaptations attributing to the observed improvements. The training effects are similar between groups suggesting that HIIT is effective for reaching higher physical fitness levels.

Adding heat stress to repeated-sprint training in hypoxia does not enhance performance improvements in canoe/kayak athletes

PURPOSE

The present study investigated the effects of adding heat stress to repeated-sprint training in hypoxia on performance and physiological adaptations in well-trained athletes.

METHODS

Sixteen canoe/kayak sprinters conducted 2 weeks of repeated-sprint training consisting of three sets of 5 × 10 s sprints with 20 s active recovery periods under conditions of either normobaric hypoxia (RSH, FiO₂: 14.5%, ambient temperature: 18 ℃, n = 8) or combined heat and normobaric hypoxia (RSHH, FiO₂: 14.5%, ambient temperature: 38 ℃, n = 8). Before and after training, the 10 × 10 s repeated-sprint ability (RSA) test and 500 m time trial were performed on a canoe/kayak ergometer.

RESULTS

Peak and average power outputs during the RSA test were significantly improved after training in both RSH (peak power: + 21.5 ± 4.6%, P < 0.001; average power: + 12.5 ± 1.9%, P < 0.001) and RSHH groups (peak power: + 18.8 ± 6.6%, P = 0.005; average power: + 10.9 ± 6.8%, P = 0.030). Indirect variables of skeletal muscle oxygen extraction (deoxygenated hemoglobin) and blood perfusion (total hemoglobin) during the RSA test were significantly increased after training in the RSH group (P = 0.041 and P = 0.034, respectively) but not in the RSHH group. In addition, finish time during the 500 m time trial was significantly shortened after the training only in the RSH group (RSH: - 3.9 ± 0.8%, P = 0.005; RSHH: - 3.1 ± 1.4%, P = 0.078).

CONCLUSION

Adding heat stress to RSH does not enhance performance improvement and may partially mask muscle tissue adaptation.

Agreement between multiparametric MRI (PIVOT), Doppler ultrasound, and near-infrared spectroscopy-based assessments of skeletal muscle oxygenation and perfusion

Skeletal muscle perfusion and oxygenation are commonly evaluated using Doppler ultrasound and near-infrared spectroscopy (NIRS) techniques. However, a recently developed magnetic resonance imaging (MRI) sequence, termed PIVOT, permits the simultaneous collection of skeletal muscle perfusion and T2* (an index of skeletal muscle oxygenation).

PURPOSE

To determine the level of agreement between PIVOT, Doppler ultrasound, and NIRS-based assessments of skeletal muscle perfusion and oxygenation.

METHODS

Twelve healthy volunteers (8 females, 25 ± 3 years, 170 ± 11 cm, 71.5 ± 8.0 kg) performed six total reactive hyperemia protocols. During three of these reactive hyperemia protocols, Tissue Saturation Index (TSI) and oxygenated hemoglobin (O2Hb) were recorded from the medial gastrocnemius (MG) and tibialis anterior (TA), and blood flow velocity was recorded from the popliteal artery (BFvpop) via Doppler Ultrasound. The other three trials were performed inside the bore of a 3 T MRI scanner, and the PIVOT sequence was used to assess perfusion (PIVOTperf) and oxygenation (T2*) of the medial gastrocnemius and tibialis anterior muscles. Positive incremental areas under the curve (iAUC) and times to peak (TTP) were calculated for each variable, and the level of agreement between collection methods was evaluated via Bland-Altman analyses and Spearman's Rho correlation analyses.

RESULTS

The only significant bivariate relationships observed were between the T2* vs. TSI iAUC and PIVOTperf vs. BFvpop values recorded from the MG. Significant mean differences were observed for all comparisons (all P ≤ 0.038), and significant proportional biases were observed for the PIVOTperf vs. tHb TTP (R2 = 0.848, P < 0.001) and T2* vs. TSI TTP comparisons in the TA (R2 = 0.488, P = 0.011), and the PIVOTperf vs. BFvpop iAUC (R2 = 0.477, P = 0.013) and time to peak (R2 = 0.851, P < 0.001) comparisons in the MG.

CONCLUSIONS

Our findings suggest that the PIVOT technique has, at best, a moderate level of agreement with Doppler ultrasound and NIRS assessment methods and is subject to significant proportional bias. These findings do not challenge the accuracy of either measurement technique but instead reflect differences in the vascular compartments, sampling volumes, and parameters being evaluated.

The impact of leg position on muscle blood flow and oxygenation during low-intensity rhythmic plantarflexion exercise

PURPOSE

Resistance training (RT) is an effective countermeasure to combat physical deconditioning whereby localized hypoxia within the limb increases metabolic stress eliciting muscle adaptation. The current study sought to examine the influence of gravity on muscle oxygenation (SmO₂) alongside vascular hemodynamic responses.

METHODS

In twelve young healthy adults, an ischemic occlusion test and seven minutes of low-intensity rhythmic plantarflexion exercise were used alongside superficial femoral blood flow and calf near-infrared spectroscopy to assess the microvascular vasodilator response, conduit artery flow-mediated dilation, exercise-induced hyperemia, and SmO₂ with the leg positioned above or below the heart in a randomized order.

RESULTS

The microvascular vasodilator response, assessed by peak blood flow (798 ± 231 mL/min vs. 1348 ± 290 mL/min; p < 0.001) and reperfusion slope 10 s of SmO₂ after cuff deflation (0.75 ± 0.45%.s-1 vs.2.40 ± 0.94%.s-1; p < 0.001), was attenuated with the leg above the heart. This caused a blunted dilatation of the superficial femoral artery (3.0 ± 2.4% vs. 5.2 ± 2.1%; p = 0.008). Meanwhile, blood flow area under the curve was comparable (above the heart: 445 ± 147 mL vs. below the heart: 474 ± 118 mL; p = 0.55) in both leg positions. During rhythmic exercise, the increase in femoral blood flow was lower in the leg up position (above the heart: 201 ± 94% vs. below the heart: 292 ± 114%; p = 0.001) and contributed to a lower SmO₂ (above the heart: 41 ± 18% vs. below the heart 67 ± 5%; p < 0.001).

CONCLUSION

Positioning the leg above the heart results in attenuated peak vascular dilator response and exercise-induced hyperemia that coincided with a lower SmO₂ during low-intensity plantarflexion exercise.

Relationship Between Muscle Deoxygenation and Cardiac Output in Subjects Without Attenuation of Deoxygenation Hemoglobin Concentration Near the End of Ramp Cycling Exercise: A Longitudinal Study

The aim of this study was to investigate the longitudinal relationship between the slopes of systemic and quadriceps muscle O2 dynamics in subjects without attenuation point in deoxygenated hemoglobin concentration at vastus lateralis (APdeoxy-Hb@VL) during high-intensity cycling. Seven young men without APdeoxy-Hb@VL performed ramp cycling exercise until exhaustion before and after 8 weeks, while continuing recreational physical activities throughout that period. Muscle O2 saturation (SmO2) and deoxy-Hb were monitored at the vastus lateralis (VL) and rectus femoris (RF) by near infrared spectroscopy oximetry during exercise. Cardiac output (CO) was also continuously assessed. During high-intensity exercise, at VL, a significantly steeper slope of deoxy-Hb was found after 8 weeks compared with before, while the slopes of deoxy-Hb at RF were not significantly changed. Though a decrease in the slope of CO after 8 weeks did not reach significance (p = 0.12), the change in the slope of CO was significantly related to the change in the slopes of deoxy-Hb at VL (rs = -0.89, p < 0.01) and RF (rs = -0.86, p < 0.05). Our data reinforces the idea that, in subjects without APdeoxy-Hb@VL, the slope of muscle deoxygenation at VL during high-intensity cycling exercise may partly be explained by systemic O2 supply, rather than O2 balance in other thigh muscles.

No Difference in Muscle Basal Oxygenation in a Bedridden Population Pre and Post Rehabilitation

Long periods of bed rest for elderly population, due to a femur fracture event, can cause a deterioration in the muscular capacity. Therefore, monitoring of the muscle oxidative capacity in this fragile population is necessary to define the muscular oxidative metabolism state before and after a rehabilitation period. The time-domain near-infrared spectroscopy (TD-NIRS) technique enables the absolute values to be calculated for hemodynamic parameters such as oxy- (O2Hb), deoxy- (HHb), total- (tHb) haemoglobin, and tissue oxygen saturation (SO2) of the muscular tissue. In this work, we have characterized vastus lateralis muscle hemodynamics during a baseline period at two different time points: after the surgery (PRE) and after 15 days of rehabilitation (POST). The mean values for the absolute values of the hemodynamic parameters were: O2Hb_PRE = 49.1 ± 14.1 μM; O2Hb_POST = 47.1 ± 13.4 μM; HHb_PRE = 28.3 ± 10.3 μM; HHb_POST = 26.7 ± 9.9 μM; tHb_PRE = 77.3 ± 23.6 μM; tHb_POST = 73.8 ± 21.4 μM; SO2_PRE = 63.9 ± 4.0% and SO2_POST = 64.9 ± 5.6%. The hemodynamic parameters did not show significant differences at both group and single subject level. These results suggest that for this kind of population, the baseline of the hemodynamic parameters is not the best one to consider to assess the rehabilitation progresses in terms of muscular oxidative metabolism.

Assessing functional sympatholysis during rhythmic handgrip using Doppler ultrasound and near-infrared spectroscopy: sex differences and test-retest reliability

The effects of sympathetic activity on vasoconstriction are dampened in active skeletal muscle during exercise, a phenomenon termed functional sympatholysis. Limited work has examined the influence of sex on the magnitude of sympatholysis or the test-retest reliability of measurements. In 16 women and 15 men, forearm blood flow (FBF; Doppler ultrasound), muscle oxygenation (near-infrared spectroscopy; NIRS) and beat-to-beat mean arterial pressure (MAP; photoplethysmography) were measured during lower-body negative pressure (LBNP; -20mmHg) at rest and simultaneously during rhythmic handgrip exercise (30% maximum contraction). Measures were taken twice within the same visit (separated by 15-min) and repeated on a second visit. Forearm vascular conductance (FVC) was calculated as FBF/MAP. The magnitude of sympatholysis was calculated as the difference of LBNP-induced changes between handgrip and rest. LBNP decreased FBF (∆-45±15%), FVC (∆-45±16%), and muscle oxygenation (∆-14±11%); however, these responses were attenuated when LBNP was applied during rhythmic handgrip exercise (∆-7±9%, ∆-9±10%, and ∆-6±9%, respectively). The magnitude of sympatholysis was not different between men and women (FBF: 40±16% vs. 35±9%, P=0.37; FVC: 38±16% vs. 35±11%, P=0.53; muscle oxygenation: 5±9% vs. 11±11%, P=0.11). Furthermore, sympatholysis measurements demonstrated good to excellent intra-day (intraclass-correlation coefficients; ICC≥0.85) and inter-day (ICC≥0.72) test-retest reliability (all P£0.01) in both sexes. The coefficients of variation were larger with NIRS (68-91%) than Doppler ultrasound (16-22%) assessments of functional sympatholysis. Collectively, these findings demonstrate that assessments of functional sympatholysis are not impacted by biological sex and that Doppler ultrasound-derived measures of sympatholysis have better within-subject reliability than NIRS-derived measures in young healthy adults.

Breast cancer survivors with preserved or rescued cardiorespiratory fitness have similar cardiac, pulmonary and muscle function compared to controls

Breast cancer survivors (BCS) have a high prevalence of cardiovascular disease and low cardiorespiratory fitness (CRF). CRF is an important predictor of survival in BCS. However, the physiological factors that contribute to low CRF in BCS have not been completely elucidated. To assess differences in physiological factors (cardiac, pulmonary, muscle function) related to CRF between BCS and controls. Twenty-three BCS and 23 age-body mass index (BMI) matched controls underwent a peak cycling exercise test to determine CRF, with physiological factors measured at resting and at peak exercise. Cardiac hemodynamics (stroke volume [SV], SVindex, heart rate [HR], cardiac output [Formula: see text], and [Formula: see text]index) were evaluated using ultrasonography. Pulmonary function was evaluated using the oxygen uptake efficiency slope (OUES), ventilation to carbon dioxide production slope [Formula: see text] and breathing reserve at peak exercise (BR). Muscle oxygenation variables (oxygenated [HbO₂] deoxygenated [HHb] and total hemoglobin [Hb], and tissue oxygenation index [TSI]) were measured with near-infrared spectroscopy (NIRS). Both groups had similar CRF and similarly increased all hemodynamic variables (HR, SV, SVindex, [Formula: see text] and [Formula: see text]index) at peak exercise compared to resting (p < 0.001). BCS had higher overall HR and lower SVindex (group effect, p < 0.05). BCS had similar OUES, [Formula: see text] and BR compared to the controls. Both groups decreased TSI, and increased Hb and HHb similarly at peak exercise compared to resting (p < 0.001). Our data suggest BCS do not exhibit differences in cardiac, pulmonary, or muscle function at peak exercise compared to controls, when both groups have similar CRF and physical activity.

Muscle Oxygenation of the Paretic and Nonparetic Legs During and After Arterial Occlusion in Chronic Stroke

Oxygen delivery and demand are reduced in the paretic leg post-stroke, reflecting decreased vascular function and reduced muscle quantity and quality. However, it is unknown how muscle oxygenation, the balance between muscle oxygen delivery and utilization, is altered in chronic stroke during and after occlusion-induced ischemia.

OBJECTIVES

The objective was to determine muscle oxygen consumption rate, microvascular responsiveness and reactive hyperemia in the paretic and nonparetic legs during and after arterial occlusion post-stroke.

MATERIALS AND METHODS

Muscle oxygen saturation was measured with near-infrared spectroscopy on the vastus lateralis of each leg during 3-minute arterial occlusion and recovery (3 min). Muscle oxygen consumption was derived from the desaturation slope during ischemia, microvascular responsiveness was derived from the resaturation slope after ischemia and reactive hyperemia was derived from the area under the curve above baseline after ischemia.

RESULTS

Eleven subjects (91% male; 32.2±6.1 months post-stroke; age 62.9±13.6 years) with a hemiparetic gait pattern participated. There was no significant between-leg muscle oxygenation difference at rest (paretic: 64.9±16.6%; nonparetic: 70.6±15.6%, p = 0.13). Muscle oxygen consumption in the paretic leg (-0.53±0.24%/s) was significantly reduced compared to the nonparetic leg (-0.70±0.36%/s; p = 0.03). Microvascular responsiveness was significantly reduced in the paretic leg compared to the nonparetic leg (paretic: 4.6±1.8%/s; nonparetic: 5.7±1.6%/s, p = 0.04). Reactive hyperemia was not significantly different between legs (paretic:4384±2341%·s; nonparetic: 3040±2216%·s, p = 0.07).

CONCLUSION

Muscle oxygen consumption and microvascular responsiveness are impaired in the paretic compared to the nonparetic leg, suggesting both reduced skeletal muscle aerobic function and reduced ability to maximally perfuse muscle tissue.

Effects of the exercise training on skeletal muscle oxygen consumption in heart failure patients with reduced ejection fraction

AIMS

Skeletal muscle dysfunction is a systemic consequence of heart failure (HF) that correlates with functional capacity. However, the impairment within the skeletal muscle is not well established. We investigated the effect of exercise training on peripheral muscular performance and oxygenation in HF patients.

METHODS AND RESULTS

HF patients with ejection fraction ≤40% were randomized 2:1 to exercise training or control for 12 weeks. Muscle tissue oxygen was measured noninvasively by near-infrared spectroscopy (NIRS) during rest and a symptom-limited cardiopulmonary exercise test (CPET) before and after intervention. Measurements included skeletal muscle oxygenated hemoglobin concentration, deoxygenated hemoglobin concentration, total hemoglobin concentration, VO₂ peak, VE/VCO₂ slope, and heart rate. Muscle sympathetic nerve activity by microneurography, and muscle blood flow by plethysmography were also assessed at rest pre and post 12 weeks. Twenty-four participants (47.5 ± 7.4 years, 58% men, 75% no ischemic) were allocated to exercise training (ET, n = 16) or control (CG, n = 8). At baseline, no differences between groups were found. Exercise improved VO₂ peak, slope VE/VCO₂, and heart rate. After the intervention, significant improvements at rest were seen in the ET group in muscle sympathetic nerve activity and muscle blood flow. Concomitantly, a significant decreased in Oxy-Hb (from 29.4 ± 20.4 to 15.7 ± 9.0 μmol, p = 0.01), Deoxi-Hb (from 16.3 ± 8.2 to 12.2 ± 6.0 μmol, p = 0.003) and HbT (from 45.7 ± 27.6 to 27.7 ± 13.4 μmol, p = 0.008) was detected at peak exercise after training. No changes were observed in the control group.

CONCLUSION

Exercise training improves skeletal muscle function and functional capacity in HF patients with reduced ejection fraction. This improvement was associated with increased oxygenation of the peripheral muscles, increased muscle blood flow, and decreased sympathetic nerve activity.

Running exercise with end-expiratory breath holding up to the breaking point induces large and early fall in muscle oxygenation

PURPOSE

The goal of this study was to assess the effects of repeated running bouts with end-expiratory breath holding (EEBH) up to the breaking point on muscle oxygenation.

METHODS

Eight male runners participated in three randomised sessions each including two exercises on a motorised treadmill. The first exercise consisted in performing 10-12 running bouts with EEBH of maximum duration either (separate sessions) at 60% (active recovery), 80% (passive recovery) or 100% (passive recovery) of the maximal aerobic velocity (MAV). Each repetition started at the onset of EEBH and ended at its release. In the second exercise of the session, subjects replicated the same procedure but with normal breathing (NB). Arterial oxygen saturation (SpO₂), heart rate (HR) and the change in vastus lateralis muscle deoxy-haemoglobin/myoglobin (Δ[HHb/Mb]) and total haemoglobin/myoglobin (Δ[THb/Mb]) were continuously monitored throughout exercises.

RESULTS

On average, the EEBHs were maintained for 10.1 ± 1.1 s, 13.2 ± 1.8 s and 12.2 ± 1.7 s during exercise at 60%, 80% and 100% of MAV, respectively. In the three exercise intensities, SpO₂ (mean nadir values: 76.3 ± 2.5 vs 94.5 ± 2.5%) and HR were lower with EEBH than with NB at the end of the repetitions; whereas, the mean Δ[HHb/Mb] (12.6 ± 5.2 vs 7.7 ± 4.4 µm) and Δ[THb/Mb] (- 0.6 ± 2.3 vs 3.8 ± 2.6 µm) were, respectively, higher and lower with EEBH (p < 0.05).

CONCLUSION

This study showed that performing repeated bouts of running exercises with EEBH up to the breaking point induced a large and early drop in muscle oxygenation compared with the same exercise with NB. This phenomenon was probably the consequence of the strong arterial oxygen desaturation induced by the maximal EEBHs.

Changes in muscle activation, oxygenation, and morphology following a fatiguing repetitive forward reaching task in young adult males and females

We sought to evaluate sex-specific 1) muscle activation patterns, hemodynamics, and swelling responses to short-cycle repetitive fatigue; 2) relationships between muscular responses and perceived fatigability. Asymptomatic participants (N = 26, 13 females) completed a repetitive pointing task until 8/10 on the Borg CR10 scale. Upper trapezius (UT), supraspinatus (SUPRA), and biceps brachii (BIC) muscle activation, activation variability (CV), median power frequency (MdPF) and thickness, and UT oxygenation were recorded. Males had higher BIC CV, UT and SUPRA MdPF, and UT and BIC thickness. Longer time to fatigue-terminal was correlated to greater SUPRA activation increase (ρ = 0.624) and BIC MdPF decrease (ρ = -0.674) in males, while in females it was correlated to greater (ρ = -0.657) and lower (ρ = 0.683) decrease of SUPRA and BIC CV, respectively. Male's greater increase in SUPRA thickness correlated to greater increase in UT thickness and tissue oxygenation index, and to lower increase of UT deoxyhemoglobin. Females' greater decrease of SUPRA MdPF correlated to greater decrease of UT MdPF, while greater UT activation increase was related to lower UT thickness increase. Results suggest that despite comparable time to fatigue-terminal, males have greater force-generating capacity and neuromuscular reliance on recruitment and excitation rates, while females have greater reliance on activation variability. Further, there are relationships between hemodynamic and swelling patterns in males, while there are relationships between activation and swelling patterns in females. Although there were no differences in experimental task-induced changes, there are sex-specific relationships between muscular patterns and perceived fatigability, which may help explain sex-specific mechanisms of musculoskeletal disorders.

Relative variability in muscle activation amplitude, muscle oxygenation, and muscle thickness: Changes with dynamic low-load elbow flexion fatigue and relationships in young and older females

In repetitive upper limb activities, variability of muscle activity (a feature of motor variability) is linked to upper limb fatigability. Prior studies suggest that the variability response may change with age and could be related to the oxygen saturation of hemoglobin within the muscle. We determined, in female adults, how age affects adjustments in movement-to-movement variability of electromyograph (EMG) amplitude (RMS), oxygenation, and thickness with fatigue, and explored how these responses were related. Fifteen young (23.3 ± 3.1 years) and ten older (62.8 ± 6.9 years) females completed repeated trials of low-load, isokinetic, concentric/eccentric elbow flexion until maximal torque ≤ 70% of baseline. Movement-to-movement variability of EMG RMS in concentric phases of movement was quantified by the coefficient of variation (EMG CV), and muscle oxygenation and thickness (MTH) were quantified using near-infrared spectroscopy, and B-mode ultrasonography. Age*Time and Spearman ρ analyses were conducted. Age did not affect fatigability or Time-related changes in muscular measures (p > 0.05). Biceps brachii and brachialis EMG CV decreased, biceps brachii HbO₂ decreased and did not fully recover, and biceps brachii and brachialis MTH increased. Higher initial brachialis EMG CV was related to less blunted oxygenation in young females (p = 0.021). Oxygenation responses were related to altered anterior deltoid EMG CV in young females but altered biceps brachii and brachialis EMG CV in older females. Age was not associated with changes in EMG CV, oxygenation, or thickness at similar performance fatigability in the concentric/eccentric elbow flexion task studied. Adjustments in biceps brachii oxygenation were linked to changes in EMG CV more local to the site of fatigue with older age.

Multiple-day high-dose beetroot juice supplementation does not improve pulmonary or muscle deoxygenation kinetics of well-trained cyclists in normoxia and hypoxia

Dietary nitrate (NO₃^-) supplementation via beetroot juice (BR) has been reported to lower oxygen cost (i.e., increased exercise efficiency) and speed up oxygen uptake (VO₂) kinetics in untrained and moderately trained individuals, particularly during conditions of low oxygen availability (i.e., hypoxia). However, the effects of multiple-day, high dose (12.4 mmol NO_3- per day) BR supplementation on exercise efficiency and VO₂ kinetics during normoxia and hypoxia in well-trained individuals are not resolved. In a double-blinded, randomized crossover study, 12 well-trained cyclists (66.4 ± 5.3 ml min^-1∙kg^-1) completed three transitions from rest to moderate-intensity (~70% of gas exchange threshold) cycling in hypoxia and normoxia with supplementation of BR or nitrate-depleted BR as placebo. Continuous measures of VO₂ and muscle (vastus lateralis) deoxygenation (ΔHHb, using near-infrared spectroscopy) were acquired during all transitions. Kinetics of VO₂ and deoxygenation (ΔHHb) were modeled using mono-exponential functions. Our results showed that BR supplementation did not alter the primary time constant for VO₂ or ΔHHb during the transition from rest to moderate-intensity cycling. While BR supplementation lowered the amplitude of the VO₂ response (2.1%, p = 0.038), BR did not alter steady state VO₂ derived from the fit (p = 0.258), raw VO₂ data (p = 0.231), moderate intensity exercise efficiency (p = 0.333) nor steady state ΔHHb (p = 0.224). Altogether, these results demonstrate that multiple-day, high-dose BR supplementation does not alter exercise efficiency or oxygen uptake kinetics during normoxia and hypoxia in well-trained athletes.

The Use of Near Infrared Spectroscopy to Evaluate the Effect of Exercise on Peripheral Muscle Oxygenation in Patients with Lower Extremity Artery Disease: A Systematic Review

OBJECTIVE

Near infrared spectroscopy (NIRS) has been suggested as a new diagnostic tool in patients with lower extremity artery disease (LEAD). The aim of this systematic review was to summarise the impact of exercise therapy on lower limb muscle oxygenation, evaluated by NIRS, in patients with LEAD, and to give an overview on NIRS instruments and methodology.

DATA SOURCES

MEDLINE and Embase.

REVIEW METHODS

A systematic search was conducted in MEDLINE and Embase, from the earliest date available until 16 March 2020, to identify peer reviewed studies involving the use of NIRS in the evaluation of exercise training on muscle oxygenation in patients with LEAD. Primary outcomes were NIRS derived variables during treadmill exercise. Effect sizes were calculated as standardised mean differences. Assessment of methodological quality was done using a combined checklist from the Cochrane bias and the quality assessment tool for before and after studies without a control group.

RESULTS

Eleven original trials were included involving 16 exercise groups and four control groups. Tissue saturation index (TSI) at rest remained unchanged following the exercise interventions. Exercise training increased time to minimum TSI during exercise (range effect sizes: +0.172 to +0.927). In addition, exercise training led to a faster recovery to half and full TSI rest values in most intervention groups (range effect sizes -0.046 to -0.558 and -0.269 to -0.665, respectively). Finally, NIRS data reproducibility and analytic methods were under reported in the included studies.

CONCLUSION

The available data suggest that exercise training improves de-oxygenation and re-oxygenation patterns, as measured with NIRS, in patients with LEAD. Whereas NIRS is a promising tool in the evaluation of LEAD, the low number of randomised controlled trials, as well as large heterogeneity in NIRS assessment methods, outcome measures, and instrumentation, warrants more research to better understand the role of muscle oxygenation associated with exercise induced improvements in walking capacity.

Critical oxygenation: Can muscle oxygenation inform us about critical power?

The power-duration relationship is well documented for athletic performance and is formulated out mathematically in the critical power (CP) model. The CP model, when applied properly, has great predictive power, e.g. pedaling at a specific power output on an ergometer the model precisely calculates the time over which an athlete can sustain this power. However, CP presents physiological inconsistencies and process-oriented problems. The rapid development of near-infrared spectroscopy (NIRS) to measure muscle oxygenation (SmO₂) dynamics provides a physiological exploration of the CP model on a conceptual and empirical level. Conceptually, the CP model provides two components: first CP is defined as the highest metabolic rate that can be achieved through oxidative means. And second, work capacity above CP named W'. SmO₂ presents a steady-state in oxygen supply and demand and thereby represents CP specifically at a local level of analysis. Empirically, exploratory data quickly illustrates the relationship between performance and SmO₂, as shown during 3-min all-out cycling tests to assess CP. During these tests, performance and SmO₂ essentially mirror each other, and both CP and W' generate solid correlation with what would be deemed their SmO₂ counterparts: first, the steady-state of SmO₂ correlates with CP. And second, the tissue oxygen reserve represented in SmO₂, when calculated as an integral corresponds to W'. While the empirical data presented is preliminary, the proposition of a concurring physiological model to the current CP model is a plausible inference. Here we propose that SmO₂ steady-state representing CP as critical oxygenation or CO. And the tissue oxygen reserve above CO would then be identified as O'. This new CO model could fill in the physiological gap between the highly predictive CP model and at times its inability to track human physiology consistently. For simplicity's sake, this would include acute changes in physiology as a result of changing climate or elevation with travel, which can affect performance. These types of acute fluctuations, but not limited to, would be manageable when applying a CO model in conjunction with the CP model. Further, modeling is needed to investigate the true potential of NIRS to model CP, with a focus on repeatability, recovery, and systemic vs local workloads.

Reduced Scattering Coefficient During Incremental Exercise Is Constant Without Being Affected by Changes in Muscle Oxygenation or Hemodynamics

Previous studies have reported that the reduced scattering coefficient (μ_s') in the vastus lateralis changes during ramp-incremental exercise due to blood volume changes or accumulation of metabolic by-products. We aimed to clarify the influences of deoxygenation and blood volume changes during exercise on μ_s' dynamics in subjects with various aerobic capacities. Twenty-three healthy young men participated in this study. All subjects performed a ramp-incremental cycling exercise until exhaustion and were divided into two groups: lower (Low: n = 12; peak pulmonary oxygen uptake per kg of fat-free mass (VO_2peak), 54.2 ± 5.3 mL/kg/min) and higher aerobic capacity group (High: n = 11; VO_2peak, 69.7 ± 5.2 mL/kg/min) by median of VO_2peak. Deoxygenated hemoglobin and myoglobin concentrations (deoxy[Hb + Mb]) and total [Hb + Mb] (total[Hb + Mb]) in the vastus lateralis were monitored during the exercise by three-wavelength (760, 800, and 830 nm) time-resolved NIRS. Similarly, μ_s' at each wavelength was continuously monitored. With increasing exercise intensity, deoxy[Hb + Mb] and total[Hb + Mb] significantly increased in both groups, and the average values of the peak amplitudes of deoxy[Hb + Mb] and total[Hb + Mb] during exercise showed a 106.4% increase and a 17.9% increase from the start of the exercise, respectively. Furthermore, the peak amplitude of total[Hb + Mb] was significantly greater in High. Conversely, there were no changes in μ_s' at any wavelength during exercise and no differences between two groups, suggesting that the great deoxygenation and blood volume changes during incremental exercise have little effect on μ_s' dynamics.

Acute effects of functional dry needling on skeletal muscle function

INTRODUCTION

Functional dry needling (FDN) is commonly used to treat soft tissue pain-related conditions. Previous research has demonstrated benefits to chronic resistance training; however, objective physiological measures sensitive to acute exercise have not been found. The purpose of this study was to evaluate the acute effects of FDN on muscle strength and endurance.

METHODS

Ten subjects (height 168 ± 9 cm, mass 68.2 ± 11.3 kg) were tested bilaterally (pre and post) for vastus lateralis (VL) isometric strength, isokinetic fatigue index, muscle electrical activity, and muscle oxygenation. FDN was administered to one leg, while the other served as a control.

RESULTS

Limited acute effects of functional dry needling were observed (p < 0.05).

DISCUSSION

FDN does not appear to acutely improve muscle function in healthy young adults. Although there were no improvements in muscle function, there were no adverse effects either, contributing to the safety of FDN healthy populations.

CONCLUSION

Acute FDN does not appear to enhance muscle performance in a healthy, non-clinical population. Thus, clinicians should consider the population and desired outcome when applying FDN.

Application of carbon dioxide to the skin and muscle oxygenation of human lower-limb muscle sites during cold water immersion

Background

Cold therapy has the disadvantage of inducing vasoconstriction in arterial and venous capillaries. The effects of carbon dioxide (CO₂) hot water depend mainly on not only cutaneous vasodilation but also muscle vasodilation. We examined the effects of artificial CO₂ cold water immersion (CCWI) on skin oxygenation and muscle oxygenation and the immersed skin temperature.

Subjects and Methods

Fifteen healthy young males participated. CO₂-rich water containing CO₂ >1,150 ppm was prepared using a micro-bubble device. Each subject’s single leg was immersed up to the knee in the CO₂-rich water (20 °C) for 15 min, followed by a 20-min recovery period. As a control study, a leg of the subject was immersed in cold tap-water at 20 °C (CWI). The skin temperature at the lower leg under water immersion (T_sk-WI) and the subject’s thermal sensation at the immersed and non-immersed lower legs were measured throughout the experiment. We simultaneously measured the relative changes of local muscle oxygenation/deoxygenation compared to the basal values (Δoxy[Hb+Mb], Δdeoxy[Hb+Mb], and Δtotal[Hb+Mb]) at rest, which reflected the blood flow in the muscle, and we measured the tissue O₂ saturation (S_tO₂) by near-infrared spectroscopy on two regions of the tibialis anterior (TA) and gastrocnemius (GAS) muscles.

Results

Compared to the CWI results, the Δoxy[Hb+Mb] and Δtotal[Hb+Mb] in the TA muscle at CCWI were increased and continued at a steady state during the recovery period. In GAS muscle, the Δtotal[Hb+Mb] and Δdeoxy[Hb+Mb] were increased during CCWI compared to CWI. Notably, S_tO₂values in both TA and GAS muscles were significantly increased during CCWI compared to CWI. In addition, compared to the CWI, a significant decrease in T_sk at the immersed leg after the CCWI was maintained until the end of the 20-min recovery, and the significant reduction continued.

Discussion

The combination of CO₂ and cold water can induce both more increased blood inflow into muscles and volume-related (total heme concentration) changes in deoxy[Hb+Mb] during the recovery period. The T_sk-WI stayed lower with the CCWI compared to the CWI, as it is associated with vasodilation by CO₂.

Rolling massage acutely improves skeletal muscle oxygenation and parameters associated with microvascular reactivity: The first evidence-based study

Although it has been claimed that rolling massage (RM), may lead to improvements in skeletal muscle oxygenation, metabolism, blood flow, and vascular function, scientific evidence has not yet been provided. Thus, the current study investigated the effects of 30 s and 2 min of RM on forearm muscle oxygenation, parameters associated with oxidative metabolism, and microvascular reactivity as well as brachial artery endothelial function. Forearm skeletal muscle parameters were assessed in 12 healthy young men (26 ± 6 yrs) using near-infrared spectroscopy (NIRS) combined with a 5-min vascular occlusion test. Additionally, brachial artery endothelial function was simultaneously assessed by measuring the relative change in brachial artery diameter normalized to the hyperemic blood flow (Normalized %FMD). These measurements were performed before and after the RM interventions performed on the anterior forearm muscles. Forearm muscle oxygenation increased after 30 s of RM (62 ± 7 to 71 ± 11%; p = 0.02) while there was no change from baseline to post-intervention after 2 min of RM. No change was observed for oxidative metabolism, however, the significant main effect (p = 0.02) for NIRS-derived reperfusion slope (%·s^-1) indicated that microvascular function improved after both 30 s (2.30 ± 0.5 to 2.61 ± 0.70%·s^-1) and 2 min of RM (2.33 ± 0.4 to 2.60 ± 0.85%·s^-1). The lack of significant effects of RM on Normalized %FMD suggest that the RM did not acutely improve brachial artery endothelial function. These findings provide, for the first time, evidence that RM improves skeletal muscle oxygenation and parameters associated with microvascular reactivity. Additionally, RM increased brachial artery blood flow, but not upstream brachial artery endothelial function.

Sessional work-rate does not affect the magnitude to which simulated hypoxia can augment acute physiological responses during resistance exercise

PURPOSE

To investigate whether performing resistance exercise in hypoxia augments physiological and perceptual responses, and if altering work-rate by performing repetitions to failure compared to sub-maximally increases the magnitude of these responses.

METHODS

Twenty male university students (minimum of 2 year resistance training experience) completed four sessions, two in hypoxia (fraction of inspired oxygen [F_iO₂] = 0.13), and two in normoxia (F_iO₂ = 0.21). For each condition, session one comprised three sets to failure of shoulder press and bench press (high work-rate session), while session two involved the same volume load, distributed over six sets (low work-rate session). Muscle oxygenation (triceps brachii), surface electromyographic activity (anterior deltoid, pectoralis major, and triceps brachii), heart rate (HR), and arterial blood oxygen saturation were recorded. Blood lactate concentration ([Bla^-]) was recorded pre-exercise and 2 min after each exercise. Muscle thickness was measured pre- and post-exercise via ultrasound.

RESULTS

Muscle oxygenation values during sets and inter-set rest periods were lower in hypoxia vs normoxia (p = 0.001). Hypoxia caused greater [Bla^-] during the shoulder press of failure sessions (p = 0.003) and both shoulder press (p = 0.048) and bench press (p = 0.005) of non-failure sessions. Hypoxia increased HR during non-failure sessions (p < 0.001). There was no effect of hypoxia on muscular swelling, surface electromyographic activity, perceived exertion, or number of repetitions performed.

CONCLUSIONS

Hypoxia augmented metabolite accumulation, but had no impact on any other physiological or perceptual response compared to the equivalent exercise in normoxia. Furthermore, the magnitude to which hypoxia increased the measured physiological responses was not influenced by sessional work-rate.

Dietary nitrate improves skeletal muscle microvascular oxygenation in HIV-infected patients receiving highly active antiretroviral therapy: a randomised, double-blind, cross-over, placebo-controlled study

HIV-1 proteins and highly active antiretroviral therapy (HAART) have been associated with microvascular endothelial dysfunction. Although nitrate-rich beetroot juice (NR-BJ) consumption has been shown to improve endothelial function in clinical population, its effects in HIV-infected patients has not been addressed. We investigated the effect of a single dose of NR-BJ on muscle oxygen saturation parameters in response to a handgrip exercise in HIV-infected patients. Fifteen HIV-infected patients received NR-BJ or nitrate-depleted beetroot juice (ND-BJ) in a double-blind cross-over design. Near-IR spectroscopy was utilised to assess muscle oxygen saturation parameters during rhythmic handgrip exercise after NR-BJ or ND-BJ supplementation. A significant faster muscle oxygen desaturation rate during exercise (-7·97 (sd 5·00) v. -5·45 (3·94) %/s, P = 0·005) and muscle oxygen resaturation rate during exercise recovery (0·43 (0·24) v. 0·28 (0·24) %/s, P = 0·030) after NR-BJ ingestion was found. However, no significant difference in exercise time until fatigue was observed. Salivary nitrite and urinary nitrate concentration were analysed after NR-BJ or ND-BJ. A significant increase in salivary nitrite and urinary nitrate in NR-BJ was observed compared with ND-BJ (P < 0·05). Our findings suggest that NR-BJ consumption may acutely improve muscle oxygen saturation during exercise and exercise recovery in HIV-infected patients undergoing HAART and who are expected to present microvascular damage. Thus, future studies investigating the chronic effects of NR-BJ are warranted to delineate a better nutritional strategy based on nitrate-rich foods.

Effects of 21 days of bed rest and whey protein supplementation on plantar flexor muscle fatigue resistance during repeated shortening contractions

PURPOSE

Space flight and bed rest (BR) lead to a rapid decline in exercise capacity. Whey protein plus potassium bicarbonate diet-supplementation (NUTR) could attenuate this effect by improving oxidative metabolism. We evaluated the impact of 21-day BR and NUTR on fatigue resistance of plantar flexor muscles (PF) during repeated shortening contractions, and whether any change was related to altered energy metabolism and muscle oxygenation.

METHODS

Ten healthy men received a standardized isocaloric diet with (n = 5) or without (n = 5) NUTR. Eight bouts of 24 concentric plantar flexions (30 s each bout) with 20 s rest between bouts were employed. PF muscle size was assessed by means of peripheral quantitative computed tomography. PF muscle volume was assessed with magnetic resonance imaging. PF muscle force, contraction velocity, power and surface electromyogram signals were recorded during each contraction, as well as energy metabolism (31P nuclear magnetic resonance spectroscopy) and oxygenation (near-infrared spectroscopy). Cardiopulmonary parameters were measured during an incremental cycle exercise test.

RESULTS

BR caused 10-15% loss of PF volume that was partly recovered 3 days after re-ambulation, as a consequence of fluid redistribution. Unexpectedly, PF fatigue resistance was not affected by BR or NUTR. BR induced a shift in muscle metabolism toward glycolysis and some signs of impaired muscle oxygen extraction. NUTR did not attenuate the BR-induced-shift in energy metabolism.

CONCLUSIONS

Twenty-one days' BR did not impair PF fatigue resistance, but the shift to glycolytic metabolism and indications of impaired oxygen extraction may be early signs of developing reduced muscle fatigue resistance.

Muscle Oxygen Demands of the Vastus Lateralis in Back and Front Squats

In resistance training squats are often used to strengthen the muscles of the lower extremities and core muscles. There are two common forms of squats that use a barbell for loading, the back squat and the front squat. The technique and loading of each squat differ markedly. However, the energetic demands on the muscle between the two forms are not well understood. The purpose of this study was to investigate the difference in energy demands between front and back squats by measuring the change in skeletal muscle oxygen saturation (SmO2) through the use of near infrared spectroscopy (NIRS).

METHODS

Eleven resistance trained individuals, (5 female, 6 male) with an average age of 23.7 ± 1.4, completed 3 sets of 15 repetitions at 70% of their 1-RM weight for both back and front squats. Skeletal muscle oxygen saturation (SmO2) of the vastus lateralis was measured using a wireless NIRS device.

RESULTS

The ΔSmO2 was not significantly different between back and front squats but was different between sets 1-3 (44.76 ± 3.24% vs. 55.19 ± 2.75% vs. 56.30 ± 2.63%), main effect p ≤ 0.0001. The recovery of SmO2 was significantly different between back (42.5 ± 3.4 sec) and front squats (30.9 ± 2.8 sec), main effect p ≤ 0.05.

CONCLUSIONS

The findings of this study suggest that the energetic demands placed on the vastus lateralis during both front and back squats are similar with a slower recovery of energetics in the back squat.

A model for evaluation of the electric activity and oxygenation in the erector spinae muscle during isometric loading adapted for spine patients

BACKGROUND

Simultaneous measurement of electromyography (EMG) and local muscle oxygenation is proposed in an isometric loading model adjusted for patients that have undergone spinal surgery.

METHODS

Twelve patients with degenerative lumbar spinal stenosis (DLSS) were included. They were subjected to a test protocol before and after surgery. The protocol consisted of two parts, a dynamic and an isometric Ito loading with a time frame of 60 s and accompanying rest of 120 s. The Ito test was repeated three times. EMG was measured bilaterally at the L4 level and L2 and was recorded using surface electrodes and collected (Biopac Systems Inc.). EMG signal was expressed as RMS and median frequency (MF). Muscle tissue oxygen saturation (MrSO₂) was monitored using a near-infrared spectroscopy (NIRS) device (INVOS® 5100C Oxymeter). Two NIRS sensors were positioned bilaterally at the L4 level. The intensity of the leg and back pain and perceived exertion before, during, and after the test was evaluated with a visual analogue scale (VAS) and Borg RPE-scale, respectively.

RESULTS

All patients were able to perform and complete the test protocol pre- and postoperatively. A consistency of lower median and range values was noted in the sensors of EMG1 (15.3 μV, range 4.5-30.7 μV) and EMG2 (13.6 μV, range 4.0-46.5 μV) that were positioned lateral to NIRS sensors at L4 compared with EMG3 (18.9 μV, range 6.5-50.0 μV) and EMG4 (20.4 μV, range 7.5-49.0 μV) at L2. Right and left side of the erector spinae exhibited a similar electrical activity behaviour over time during Ito test (60 s). Regional MrSO₂ decreased over time during loading and returned to the baseline level during recovery on both left and right side. Both low back and leg pain was significantly reduced postoperatively.

CONCLUSION

Simultaneous measurement of surface EMG and NIRS seems to be a promising tool for objective assessment of paraspinal muscle function in terms of muscular activity and local muscle oxygenation changes in response to isometric trunk extension in patients that have undergone laminectomy for spinal stenosis.

A single oral dose of beetroot-based gel does not improve muscle oxygenation parameters, but speeds up handgrip isometric strength recovery in recreational combat sports athletes

Although the effect of beetroot supplementation on exercise performance has been widely demonstrated to improve the performance of cyclists, runners, and swimmers, its effect on combat sports remains inconclusive. The present study assessed the effect of beetroot-based gel (BG) supplementation on maximal voluntary contraction (MVC), exercise time until fatigue (ETF), muscle O₂ saturation (SmO₂), and blood volume (tHb) in response to handgrip isotonic exercise (HIE) in recreational combat sport athletes. In a randomized, crossover, double-blind study, 14 combat sports athletes performed three sets of HIE (at 40% MVC) until fatigue after BG or nitrate-depleted gel (PLA) supplementation, in which forearm SmO₂ and tHb were continuously monitored using near-infrared spectroscopy. MVC was evaluated at baseline and 20 min after HIE. MVC values were analysed as the change from baseline values (ΔMVC). There was a significant increase accompanied by a large effect size in ΔMVC (p = 0.036, d = 0.94) after HIE in the BG condition compared to PLA. However, there were no changes in SmO₂ parameters (p> 0.05), tHb (p> 0.05) or ETF (p = 0.161) throughout the three sets of HIE. Additionally, a trivial to small effect size was observed in near-infrared spectroscopy (NIRS) parameters and ETF (d = ≤ 0.2 to 0.5). Therefore, a single dose of beetroot gel supplementation may be considered as a good nutritional strategy to improve strength recovery in combat sports athletes.

Differences in cerebral and muscle oxygenation patterns during exercise in children with univentricular heart after Fontan operation compared to healthy peers

BACKGROUND

We assess whether the lower exercise tolerance in children with univentricular heart (UVH) after Fontan operation is associated with altered peripheral muscular and cerebral tissue oxygenation.

METHODS

18 children with UVH and 20 healthy subjects performed an incremental ramp exercise test. Changes in the cerebral and muscular pattern of oxygenated (O₂Hb) and deoxygenated hemoglobin (HHb) and local tissue oxygenation (TOI) were analyzed by means of Near Infrared Spectroscopy (NIRS). Correlations between arterial saturation during exercise and tissue oxygenation were evaluated.

RESULTS

In UVH, maximal oxygen consumption (VO₂peak/kg, 28.9 ± 7.9 vs. 46.3 ± 11.9 ml/min/kg, P < 0.001), heart rate (HRpeak, 168 ± 13 vs. 193 ± 12 bpm, P < 0.001) and load (Ppeak, 73 ± 19 vs. 133 ± 68 W, P < 0.001) were lower, VE/VCO₂ slope was higher (34.5 ± 5.9 vs. 27.1 ± 3.9, P < 0.001). A faster and steeper course up to the same level of HHb and absent increase in O₂Hb was seen at cerebral level in UVH; tissue oxygenation index (TOI) demonstrated a steady decrease from the start of exercise. At the muscular level, HHb curve has a similar pattern compared to controls, with an early cessation. O₂Hb has a similar pattern, but with early discontinuation at a higher O₂Hb-level. Muscular TOI has the same course throughout exercise, starting from a lower level. Lower arterial saturation and higher age correlated with lower VO₂peak; higher amplitude of muscular TOI and lower amplitude cerebral TOI correlated with higher VO₂peak.

CONCLUSION

Children after Fontan procedure have different oxygenation mechanisms at muscular and cerebral level. This reflects a different balance between O₂ supply to O₂ demand which might contribute to the reduced exercise tolerance in this patient population.

Separate and combined effects of local and systemic hypoxia in resistance exercise

PURPOSES

This study quantified performance, physiological, and perceptual responses during resistance exercise to task failure with blood flow restriction (BFR), in systemic hypoxia, and with these stimuli combined.

METHODS

Fourteen young men were tested for 1-repetition maximum (1RM) in the barbell biceps curl and lying triceps extension exercises. On separate visits, subjects performed exercise trials (4 sets to failure at 70% 1RM with 90 s between sets) in six separate randomized conditions, i.e., in normoxia or hypoxia (fraction of inspired oxygen = 20.9% and 12.9%, respectively) combined with three different levels of BFR (0%, 45%, or 60% of resting arterial occlusion pressure). Muscle activation and oxygenation were monitored via surface electromyography and near-infrared spectroscopy, respectively. Arterial oxygen saturation, heart rate, and perceptual responses were assessed following each set.

RESULTS

Compared to set 1, the number of repetitions before failure decreased in sets 2, 3, and 4 for both exercises (all P < 0.001), independently of the condition (P > 0.065). Arterial oxygen saturation was lower with systemic hypoxia (P < 0.001), but not BFR, while heart rate did not differ between conditions (P > 0.341). Muscle oxygenation and activation during exercise trials remained unaffected by the different conditions (all P ≥ 0.206). A significant main effect of time, but not condition, was observed for overall perceived discomfort, difficulty breathing, and limb discomfort (all P < 0.001).

CONCLUSION

Local and systemic hypoxic stimuli, or a combination of both, did not modify the fatigue-induced change in performance, trends of muscle activation or oxygenation, nor exercise-related sensations during a multi-set resistance exercise to task failure.

Reliability of NIRS portable device for measuring intercostal muscles oxygenation during exercise

This study assessed the intra-individual reliability of oxygen saturation in intercostal muscles (SmO₂-m.intercostales) during an incremental maximal treadmill exercise by using portable NIRS devices in a test-retest study. Fifteen marathon runners (age, 24.9 ± 2.0 years; body mass index, 21.6 ± 2.3 kg·m^-2; V̇O₂-peak, 63.7 ± 5.9 mL·kg^-1·min^-1) were tested on two separate days, with a 7-day interval between the two measurements. Oxygen consumption (V̇O₂) was assessed using the breath-by-breath method during the V̇O₂-test, while SmO₂ was determined using a portable commercial device, based in the near-infrared spectroscopy (NIRS) principle. The minute ventilation (VE), respiratory rate (RR), and tidal volume (Vt) were also monitored during the cardiopulmonary exercise test. For the SmO₂-m.intercostales, the intraclass correlation coefficient (ICC) at rest, first (VT1) and second ventilatory (VT2) thresholds, and maximal stages were 0.90, 0.84, 0.92, and 0.93, respectively; the confidence intervals ranged from -10.8% - +9.5% to -15.3% - +12.5%. The reliability was good at low intensity (rest and VT1) and excellent at high intensity (VT2 and max). The Spearman correlation test revealed (p ≤ 0.001) an inverse association of SmO₂-m.intercostales with V̇O₂ (ρ = -0.64), VE (ρ = -0.73), RR (ρ = -0.70), and Vt (ρ = -0.63). The relationship with the ventilatory variables showed that increased breathing effort during exercise could be registered adequately using a NIRS portable device.

The Effect of Prolonged Walking With Intermittent Standing on Erector Spinae and Soleus Muscle Oxygenation and Discomfort

Prolonged periods of walking have been associated with musculoskeletal discomfort and injuries. Previous research has shown that muscle fatigue is related to decreases in muscle oxygenation during short term walking. The objective of the proposed research is to determine the impact of prolonged walking with intermittent standing on musculoskeletal discomfort and muscle oxygenation measures in young adults. Nine young adults walked for a period of 2 hours. Ratings of perceived discomfort were recorded using a questionnaire. Muscle oxygenation and hemoglobin levels were collected from the lower back erector spinae and soleus muscles using near infrared spectroscopy (NIRS). Subjective discomfort significantly increased throughout the 2 hours. Prolonged walking generally induced increased oxygenation of the erector spinae and soleus across walking periods, within walking periods and across standing periods. These increases were more pronounced at the beginning of the walking session and continued through the second or third periods. Erector spinae and soleus total hemoglobin increased within walking period one and two. Only the soleus total hemoglobin significantly increased after the first walking and standing periods and during all the transitions from walking to standing. Increased oxygenation and total hemoglobin during prolonged walking with intermittent standing are likely a result of the repeated dynamic contractions and exercise-induced blood volume expansion. Increased discomfort was found; however, this was not explained by detrimental changes in oxygenation or total hemoglobin.

Acute Effects of L-Arginine Supplementation on Oxygen Consumption Kinetics and Muscle Oxyhemoglobin and Deoxyhemoglobin during Treadmill Running in Male Adults

L-arginine is used as a nitric oxide related supplement intended to improve sports performance, and to enhance muscular recovery during exercise. However, the literature is inconclusive. The aim of this study was to determine the effects of acute oral L-arginine supplementation on O2 consumption kinetics and local muscle blood volume and oxygenation during treadmill running at two different intensities. Using a double-blind, crossover and placebo-controlled design, 11 young healthy male adults were randomly assigned to 6 g of L-arginine (ARG) or placebo (PLA) supplementation that was ingested 60 min before the exercise test. Tests consisted of treadmill run at two different intensities (5 min each; moderate, 90% of ventilatory threshold, VT; and heavy, 50% of the difference between VT and VO2peak) interspersed by 1-min walking. Respiratory gas exchange variables were measured continuously with an automated metabolic cart. Near infrared spectroscopy (NIRS) was used to continuously monitor muscle oxyhemoglobin and deoxyhemoglobin and total hemoglobin. Blood samples were collected before supplementation and 6 min after exercise. Two-way repeated measures ANOVA did not show differences in plasma nitrite concentrations between ARG or PLA conditions during the running tests. No significant differences were observed between ARG and PLA conditions for O2 kinetics as well as for NIRS variables. ARG supplementation does not improve physiological responses associated with oxygen cost and NIRS variables during running treadmill tests. Hence, our results do not support the use of L-arginine as an ergogenic aid for running performance in young healthy males.

Walking performances and muscle oxygen desaturation are increased after supervised exercise training in Takayasu arteritis: a case report and a review of the literature

Background

Takayasu arteritis (TAK) is a rare chronic inflammatory vasculitis predominantly affecting the aorta and its main branches. Takayasu arteritis has been shown to increase cardiovascular risk. Supervised exercise training (SET) is a well-recognized and effective therapeutic tool improving walking performances in patients with chronic atherosclerotic disease; however, the effects of SET, and the underlying mechanisms, remain poorly documented in TAK patients.

Case summary

We reviewed the literature and investigated the effects of a 12-week SET programme on walking performances, physical function, and calf muscle oxygen saturation (StO₂; assessed by near-infrared spectroscopy) during exercise in a 28-year-old man with TAK and symptoms of arterial lower limb claudication. The literature review evidences only two recent publications suggesting that exercise training is effective and well-tolerated in patients with arteritis. The treadmill pain-free (+22%) and maximal (+273%) walking distance, 6-min walking distance (+66%), and physical function of lower extremities (+20%) following SET were significantly improved in our patient. Moreover, we observed a greater muscle oxygen desaturation (increased oxygen extraction) during exercise.

Discussion

Following SET, the increased oxygen extraction may be related to improved microvascular milieu leading to a better match between muscle oxygen supply and demand during exercise. These new results may contribute to mechanistic insights in peripheral adaptations following exercise training in TAK patients and may help to explain, at least partly, the increased walking performances. Although more studies are needed to better explore the impact of exercise training, these results suggest that exercise should be recommended in TAK patients.

Physiological responses to hypoxic constant-load and high-intensity interval exercise sessions in healthy subjects

PURPOSE

The aim of this study was to assess the acute cardiorespiratory as well as muscle and cerebral tissue oxygenation responses to submaximal constant-load (CL) and high-intensity interval (HII) cycling exercise performed in normoxia and in hypoxia at similar intensity, reproducing whole-body endurance exercise training sessions as performed in sedentary and clinical populations.

METHODS

Healthy subjects performed two CL (30 min, 75% of maximal heart rate, n = 12) and two HII (15 times 1-min high-intensity exercise-1-min passive recovery, n = 12) cycling exercise sessions in normoxia and in hypoxia [mean arterial oxygen saturation 76 ± 1% (clamped) during CL and 77 ± 5% (inspiratory oxygen fraction 0.135) during HII]. Cardiorespiratory and near-infrared spectroscopy parameters as well as the rate of perceived exertion were continuously recorded.

RESULTS

Power output was 21 ± 11% and 15% (according to protocol design) lower in hypoxia compared to normoxia during CL and HII exercise sessions, respectively. Heart rate did not differ between normoxic and hypoxic exercise sessions, while minute ventilation was higher in hypoxia during HII exercise only (+ 13 ± 29%, p < 0.05). Quadriceps tissue saturation index did not differ significantly between normoxia and hypoxia (CL 60 ± 8% versus 59 ± 5%; HII 59 ± 10% versus 56 ± 9%; p > 0.05), while prefrontal cortex deoxygenation was significantly greater in hypoxia during both CL (66 ± 4% versus 56 ± 6%) and HII (58 ± 5% versus 55 ± 5%; p < 0.05) sessions. The rate of perceived exertion did not differ between normoxic and hypoxic CL (2.4 ± 1.7 versus 2.9 ± 1.8) and HII (6.9 ± 1.4 versus 7.5 ± 0.8) sessions (p > 0.05).

CONCLUSION

This study indicates that at identical heart rate, reducing arterial oxygen saturation near 75% does not accentuate muscle deoxygenation during both CL and HII exercise sessions compared to normoxia. Hence, within these conditions, larger muscle hypoxic stress should not be expected.

Impact of ischaemia-reperfusion cycles during ischaemic preconditioning on 2000-m rowing ergometer performance

PURPOSE

Although ischaemic preconditioning (IPC), induced by cycles of transient limb ischaemia and reperfusion, seems to improve exercise performance, the optimal duration of ischaemia-reperfusion cycles is not established. The present study investigated the effect of ischaemia-reperfusion duration within each IPC cycle on performance in a 2000-m rowing ergometer test.

METHODS

After incremental and familiarization tests, 16 trained rowers (mean ± SD: age, 24 ± 11 years; weight, 74.1 ± 5.9 kg; [Formula: see text] peak, 67.2 ± 7.4 mL·kg^-1·min^-1) were randomly submitted to a 2000-m rowing test preceded by intermittent bilateral cuff inflation of the lower limbs with three cycles of ischaemia-reperfusion, lasting 5 min (IPC-5) or 10 min (IPC-10) at 220 or 20 mmHg (control). Power output, [Formula: see text], heart rate, blood lactate concentration, pH, ratings of perceived exertion (RPE), and near-infrared spectroscopy-derived measurements of the vastus lateralis muscle were continuously recorded.

RESULTS

No differences among treatments were found in the 2000-m test (control: 424 ± 17; IPC-5: 425 ± 16; IPC-10: 424 ± 17 s; P = 0.772). IPC-10 reduced the tissue saturation index and oxy-haemoglobin concentration during exercise compared with control. The power output during the last 100-m segment was significantly lower with IPC-10. The IPC treatments increased the heart rate over the first 500 m and decreased the pH after exercise. No alterations were observed in [Formula: see text], blood lactate, or RPE among the trials.

CONCLUSION

In conclusion, IPC does not improve the 2000-m rowing ergometer performance of trained athletes regardless of the length of ischaemia-reperfusion cycles.

Physiological and psychological determinants of whole-body endurance exercise following short-term sustained operations with partial sleep deprivation

Purpose

The study examined the effects of short-term field-based military training with partial sleep deprivation on whole-body endurance performance in well-trained individuals.

Methods

Before and after a 2-day sustained operations (SUSOPS), 14 cadets performed a 15-min constant-load cycling at 65% of peak power output (PPO; CLT₆₅), followed by an exhaustive constant-load trial at 85% of PPO (CLT₈₅). Physiological [oxygen uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot {V}$$\end{document}V˙O₂), heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), and regional oxygenation (TOI) in the frontal cerebral cortex and vastus lateralis muscle] and psychological [effort perception (RPE), affective valence (FS), and perceived activation (FAS)] variables were monitored during exercise.

Results

SUSOPS reduced time to exhaustion in CLT₈₅ by 29.1% (p = 0.01). During the CLT₆₅ trial, SUSOPS potentiated the exercise-induced elevations in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot {V}$$\end{document}V˙O₂ and HR (p < 0.05), and blunted MAP (p = 0.001). CO did not differ between trials. Yet, towards the end of both CLT₈₅ trials, CO tended to decline (p ≤ 0.08); a response that occurred at an earlier stage in the SUSOPS trial. During CLT₆₅, SUSOPS altered neither cerebral nor muscle TOI. The SUSOPS CLT₈₅ trial, however, was terminated at similar leg-muscle deoxygenation (p > 0.05) and lower prefrontal cortex deoxygenation (p < 0.01). SUSOPS increased RPE at submaximal intensities (p = 0.05), and suppressed FAS and FS throughout (p < 0.01).

Conclusions

The present findings indicate, therefore, that a brief period of military sustained operations with partial sleep deprivation augment cardiorespiratory and psychological strain, limiting high-intensity endurance capacity.

Underwater near-infrared spectroscopy can measure training adaptations in adolescent swimmers

The development of an underwater near-infrared spectroscopy (uNIRS) device has enabled previously unattainable measurements of peripheral muscle hemodynamics and oxygenation to be taken within the natural aquatic environment. The purposes of this study were (i) to trial the use of uNIRS, in a real world training study, and (ii) to monitor the effects of a swim training program upon muscle oxygenation status in short distance swimming. A total of 14 junior club level swimmers completed a repeated swim sprint test before and after an eight week endurance training program. A waterproof, portable Near-Infrared Spectroscopy device was attached to the vastus lateralis. uNIRS successfully measured changes in muscle oxygenation and blood volume in all individuals; rapid sub-second time resolution of the device was able to demonstrate muscle oxygenation changes during the characteristic swim movements. Post training heart rate recovery and swim performance time were significantly improved. uNIRS data also showed significant changes. A larger rise in deoxyhemoglobin during individual sprints suggested training induced an increase in muscle oxygen extraction; a faster recovery time for muscle oxygenation suggested positive training induced changes and significant changes in muscle blood flow also occur. As a strong correlation was seen between an increased reoxygenation rate and an improved swim performance time, these findings support the use of uNIRS as a new performance analysis tool in swimming.

Exercise training in older adults, what effects on muscle oxygenation? A systematic review

AIM

To determine the effects of different modality of exercise training programs on muscle oxygenation in older adults.

METHODS

Relevant articles were searched in PubMed, Web of Science, Science Direct and Scopus, using the keywords: "Aged" AND "Muscle oxygenation" AND (Exercise OR "Exercise therapy" OR "Exercise Movement Techniques" OR Hydrotherapy), without limitation concerning the publication date. To be included in the full analysis, the study had to be a randomized controlled trial in which older adults participants (mean age: 65 years at least) were submitted to an exercise-training program and muscle oxygenation assessment.

RESULTS

The searches resulted in 1238 articles from which 7 met all the inclusion criteria. The trials involved 370 older adults (68.7±1.7years), healthy and with peripheral arterial disease. Studies included resistance and endurance exercises as well as walking sessions. Training sessions were 2-6 time per week, lasted 3-24 months and with different training intensity throughout studies. After a long-term resistance training, healthy older adults showed enhanced muscle oxygen extraction capacity, regulation of vessels and vascular endothelium function; endurance training is reported to improve microvascular blood flow and matching of oxygen delivery to oxygen utilization, muscle oxidative capacity and muscle saturation, and walking sessions results in better muscle oxygen availability and muscle oxygen extraction capacity in older adults with peripheral arterial disease.

CONCLUSIONS

This review supports the fact that depending on the clinical status of the participants and the modality, exercise training improves different aspects of the muscle oxygenation in older adults.

Phenylephrine increases near-infrared spectroscopy determined muscle oxygenation in men

Phenylephrine increases mean arterial pressure (MAP) by enhanced total peripheral resistance (TPR) but near-infrared spectroscopy (NIRS) determined muscle oxygenation (S_mO₂) increases. We addressed that apparent paradox during supine rest and head-up tilt (HUT). Variables were determined ± phenylephrine in males during supine rest (n = 17) and 40° HUT (n = 7). MAP, stroke volume (SV), heart rate (HR), and TPR were derived by Modelflow^® and NIRS determined biceps S_mO₂ and (tibial) bone oxygenation (S_tibialO₂). For ten subjects, cardiac filling and the diameter of the inferior caval vein (ICV collapsibility index: ((ICV_expiration - ICV_inspiration)/ICV_expiration) × 100) were assessed by ultrasound. Pancreatic polypeptide (PP) and atrial natriuretic peptide (proANP) in plasma were determined by immunoassay. Brachial artery blood flow was assessed by ultrasound and skin oxygenation (S_skinO₂) monitored by white light spectroscopy. Phenylephrine increased MAP by 34% and TPR (62%; P < 0.001) during supine rest. The ICV collapsibility index decreased (24%; P < 0.001) indicating augmented cardiac preload although volume of the left atrium and ventricle did not change. SV increased (18%; P < 0.001) as HR decreased (24%; P < 0.001). ProANP increased by 9% (P = 0.002) with unaffected PP. Brachial artery blood flow tended to decrease while S_skinO₂ together with S_tibialO₂ decreased by 11% (P = 0.026) and 20% (P < 0.001), respectively. Conversely, phenylephrine increased S_mO₂ (9%) and restored the HUT elicited decrease in S_mO₂ (by 19%) along with SV (P = 0.02). Phenylephrine reduces skin and bone oxygenation and tends to reduce arm blood flow, suggesting that the increase in S_mO₂ reflects veno-constriction with consequent centralization of the blood volume.

Effects of friction massage of the popliteal fossa on dynamic changes in muscle oxygenation and ankle flexibility

[Purpose] This study aimed to examine whether or not friction massage of the popliteal fossa would be effective for achieving dynamic changes in muscle oxygenation and ankle flexibility. [Subjects and Methods] Twelve healthy male university students participated. Before and after friction massage, dynamic changes in muscle oxygenation and ankle flexibility were measured by near-infrared spectroscopy to evaluate its efficacy. [Results] Oxygenated hemoglobin was significantly higher after as compared to before massage. The range of ankle dorsiflexion tended to increase after massage. [Conclusion] These results suggest that friction massage of the popliteal fossa stimulates venous return in the lower leg.

Effect of heavy-intensity 'priming' exercise on oxygen uptake and muscle deoxygenation kinetics during moderate-intensity step-transitions initiated from an elevated work rate

We examined the effect of heavy-intensity 'priming' exercise on the rate of adjustment of pulmonary O₂ uptake (τV˙O_2p) initiated from elevated intensities. Fourteen men (separated into two groups: τV˙O_2p≤25s [Fast] or τV˙O_2p>25s [Slow]) completed step-transitions from 20W to 45% lactate threshold (LT; lower-step, LS) and 45% to 90%LT (upper-step, US) performed (i) without; and (ii) with US preceded by heavy-intensity exercise (HUS). Breath-by-breath V˙O_2p and near-infrared spectroscopy-derived muscle deoxygenation ([HHb+Mb]) were measured. Compared to LS, τV˙O_2p was greater (p<0.05) in US in both Fast (LS, 19±4s; US, 30±4s) and Slow (LS, 25±5s; US, 40±11s) with τV˙O_2p in US being lower (p<0.05) in Fast. In HUS, τV˙O_2p in Slow was reduced (28±8s, p<0.05) and was not different (p>0.05) from LS or Fast group US. In Slow, τ[HHb+Mb] increased (p<0.05) in US relative to HUS; this finding coupled with a reduced τV˙O_2p indicates a priming-induced improvement in matching of muscle O₂ delivery-to-O₂ utilization during transitions from elevated intensities in those with Slow but not Fast V˙O_2p kinetics.

Local Muscle Metabolic Demand Induced by Neuromuscular Electrical Stimulation and Voluntary Contractions at Different Force Levels: A NIRS Study

Functional Muscle metabolic demand during contractions evoked by neuromuscular electrical stimulation (NMES) has been consistently documented to be greater than voluntary contractions (VOL) at the same force level (10-50% maximal voluntary contraction-MVC). However, we have shown using a near-infrared spectroscopy (NIRS) technique that local muscle metabolic demand is similar between NMES and VOL performed at MVC levels, thus controversy exists. This study therefore compared biceps brachii muscle metabolic demand (tissue oxygenation index-TOI and total hemoglobin volume-tHb) during a 10s isometric contraction of the elbow flexors between NMES (stimulation frequency of 30Hz and current level to evoke 30% MVC) and VOL at 30% MVC (VOL-30%MVC) and MVC (VOL-MVC) level in 8 healthy men (23-33-y). Greater changes in TOI and tHb induced by NMES than VOL-30%MVC confirm previous studies of a greater local metabolic demand for NMES than VOL at the same force level. The same TOI and tHb changes for NMES and VOL-MVC suggest that local muscle metabolic demand and intramuscular pressure were similar between conditions. In conclusion, these findings indicate that NMES induce a similar local muscle metabolic demand as that of maximal VOL.

Underwater Near-Infrared Spectroscopy: Muscle Oxygen Changes in the Upper and Lower Extremities in Club Level Swimmers and Triathletes

To date, measurements of oxygen status during swim exercise have focused upon systemic aerobic capacity. The development of a portable, waterproof NIRS device makes possible a local measurement of muscle hemodynamics and oxygenation that could provide a novel insight into the physiological changes that occur during swim exercise. The purpose of this study was to observe changes in muscle oxygenation in the vastus lateralis (VL) and latissimus dorsi (LD) of club level swimmers and triathletes. Ten subjects, five club level swimmers and five club level triathletes (three men and seven women) were used for assessment. Swim group; mean±SD=age 21.2±1.6 years; height 170.6±7.5 cm; weight 62.8±6.9 kg; vastus lateralis skin fold 13.8±5.6 mm; latissimus dorsi skin fold 12.6±3.7. Triathlete group; mean±SD=age 44.0±10.5 years; height 171.6±7.0 cm; weight 68.6±12.7 kg; vastus lateralis skin fold 11.8±3.5 mm; latissimus dorsi skin fold 11.2±3.1. All subjects completed a maximal 200 m freestyle swim, with the PortaMon, a portable NIR device, attached to the subject's dominant side musculature. ΔTSI% between the vastus lateralis and latissimus dorsi were analysed using either paired (2-tailed) t-tests or Wilcoxon signed rank test. The level of significance for analysis was set at p<0.05. No significant difference (p=0.686) was found in ΔTSI (%) between the VL and LD in club level swimmers. A significant difference (p=0.043) was found in ΔTSI (%) between the VL and LD in club level triathletes. Club level swimmers completed the 200 m freestyle swim significantly faster (p=0.04) than club level triathletes. Club level swimmers use both the upper and lower muscles to a similar extent during a maximal 200 m swim. Club level triathletes predominately use the upper body for propulsion during the same exercise. The data produced by NIRS in this study are the first of their kind and provide insight into muscle oxygenation changes during swim exercise which can indicate the contribution of one muscle compared to another. This also enables a greater understanding of the differences in swimming techniques seen between different cohorts of swimmers and potentially within individual swimmers.

Relationship of post-exercise muscle oxygenation and duration of cycling exercise

BACKGROUND

Aerobic adaptations following interval training are supposed to be mediated by increased local blood supply. However, knowledge is scarce on the detailed relationship between exercise duration and local post-exercise blood supply and oxygen availability. This study aimed to examine the effect of five different exercise durations, ranging from 30 to 240 s, on post-exercise muscle oxygenation and relative changes in hemoglobin concentration.

METHODS

Healthy male subjects (N = 18) performed an experimental protocol of five exercise bouts (30, 60, 90, 120, and 240 s) at 80 % of peak oxygen uptake [Formula: see text] in a randomized order, separated by 5-min recovery periods. To examine the influence of aerobic fitness, we compared subjects with gas exchange thresholds (GET) above 60 % [Formula: see text] (GET60+) with subjects reaching GET below 60 % [Formula: see text] (GET60-). [Formula: see text] and relative changes in concentrations of oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin were continuously measured with near-infrared spectroscopy of the vastus lateralis muscle.

RESULTS

Post-exercise oxygen availability and local blood supply increased significantly until the 90-s exercise duration and reached a plateau thereafter. Considering aerobic fitness, the GET60+ group reached maximum post-exercise oxygen availability earlier (60 s) than the GET60- group (90 s).

CONCLUSIONS

Our results suggest that (1) 90 s has evolved as the minimum interval duration to enhance local oxygen availability and blood supply following cycling exercise at 80 % [Formula: see text]; whereas (2) 60 s is sufficient to trigger the same effects in subjects with GET60 + .

Does voluntary hypoventilation during exercise impact EMG activity?

It has been reported that exercise under hypoxic conditions induces reduced muscle oxygenation, which could be related to enhanced activity on electromyography (EMG). Although it has been demonstrated that exercise under conditions of voluntary hypoventilation (VH) evokes muscle deoxygenation, it is unclear whether VH during exercise impacts EMG. Seven men performed bicycle exercise for 5 min at 65 % of peak oxygen uptake with normal breathing (NB) and VH. Muscle oxygenation; concentration changes in oxyhemoglobin (Oxy-Hb), deoxyhemoglobin (Deoxy-Hb) and total hemoglobin (Total-Hb); and surface EMG in the vastus lateralis muscle were simultaneously measured. In the VH condition, Oxy-Hb was significantly lower and Deoxy-Hb was significantly higher compared to those in the NB condition (P < 0.05 for both), whereas there was no significant difference in Total-Hb between the two conditions. We observed significantly higher values (P < 0.05) on integrated EMG during exercise under VH conditions compared to those under NB conditions. This study suggests that VH during exercise augments EMG activity.