Leg- vs arm-cycling repeated sprints with blood flow restriction and systemic hypoxia

Muscle Oximetry in Sports Science: An Updated Systematic Review

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Impact of systemic hypoxia and blood flow restriction on mechanical, cardiorespiratory, and neuromuscular responses to a multiple-set repeated sprint exercise

Introduction: Repeated sprint cycling exercises (RSE) performed under systemic normobaric hypoxia (HYP) or with blood flow restriction (BFR) are of growing interest. To the best of our knowledge, there is no stringent consensus on the cardiorespiratory and neuromuscular responses between systemic HYP and BFR during RSE. Thus, this study assessed cardiorespiratory and neuromuscular responses to multiple sets of RSE under HYP or with BFR. Methods: According to a crossover design, fifteen men completed RSE (three sets of five 10-s sprints with 20 s of recovery) in normoxia (NOR), HYP, and with bilaterally-cuffed BFR at 45% of resting arterial occlusive pressure during sets in NOR. Power output, cardiorespiratory and neuromuscular responses were assessed. Results: Average peak and mean powers were lower in BFR (dz = 0.87 and dz = 1.23, respectively) and HYP (dz = 0.65 and dz = 1.21, respectively) compared to NOR (p < 0.001). The percentage decrement of power output was greater in BFR (dz = 0.94) and HYP (dz = 0.64) compared to NOR (p < 0.001), as well as in BFR compared to NOR (p = 0.037, dz = 0.30). The percentage decrease of maximal voluntary contraction of the knee extensors after the session was greater in BFR compared to NOR and HYP (p = 0.011, dz = 0.78 and p = 0.027, dz = 0.75, respectively). Accumulated ventilation during exercise was higher in HYP and lower in BFR (p = 0.002, dz = 0.51, and p < 0.001, dz = 0.71, respectively). Peak oxygen consumption was reduced in HYP (p < 0.001, dz = 1.47). Heart rate was lower in BFR during exercise and recovery (p < 0.001, dz = 0.82 and p = 0.012, dz = 0.43, respectively). Finally, aerobic contribution was reduced in HYP compared to NOR (p = 0.002, dz = 0.46) and BFR (p = 0.005, dz = 0.33). Discussion: Thus, this study indicates that power output during RSE is impaired in HYP and BFR and that BFR amplifies neuromuscular fatigue. In contrast, HYP did not impair neuromuscular function but enhanced the ventilatory response along with reduced oxygen consumption.

Manipulating Internal and External Loads During Repeated Cycling Sprints: A Comparison of Continuous and Intermittent Blood Flow Restriction

ABSTRACT

Mckee, JR, Girard, O, Peiffer, JJ, and Scott, BR. Manipulating internal and external loads during repeated cycling sprints: A comparison of continuous and intermittent blood flow restriction. J Strength Cond Res 38(1): 47-54, 2024-This study examined the impact of blood flow restriction (BFR) application method (continuous vs. intermittent) during repeated-sprint exercise (RSE) on performance, physiological, and perceptual responses. Twelve adult male semi-professional Australian football players completed 4 RSE sessions (3 × [5 × 5-second maximal sprints:25-second passive recovery], 3-minute rest between the sets) with BFR applied continuously (C-BFR; excluding interset rest periods), intermittently during only sprints (I-BFR WORK ), or intraset rest periods (I-BFR REST ) or not at all (Non-BFR). An alpha level of p < 0.05 was used to determine significance. Mean power output was greater for Non-BFR (  p < 0.001, dz = 1.58 ), I-BFR WORK (  p = 0.002, dz = 0.63 ), and I-BFR REST (  p = 0.003, dz = 0.69 ) than for C-BFR and for Non-BFR (  p = 0.043, dz = 0.55 ) compared with I-BFR REST . Blood lactate concentration (  p = 0.166) did not differ between the conditions. Mean oxygen consumption was higher during Non-BFR (  p < 0.001, dz = 1.29 and 2.31; respectively) and I-BFR WORK ( p < 0.001, dz = 0.74 and 1.63; respectively) than during I-BFR REST and C-BFR and for I-BFR REST (  p = 0.002, dz = 0.57) compared with C-BFR. Ratings of perceived exertion were greater for I-BFR REST (  p = 0.042, dz = 0.51) and C-BFR (  p = 0.011, dz = 0.90) than for Non-BFR and during C-BFR (  p = 0.023, dz = 0.54) compared with I-BFR WORK . Applying C-BFR or I-BFR REST reduced mechanical output and cardiorespiratory demands of RSE and were perceived as more difficult. Practitioners should be aware that BFR application method influences internal and external demands during RSE.

Application of blood flow restriction in hypoxic environment augments muscle deoxygenation without compromising repeated sprint exercise performance

NEW FINDINGS

What is the central question of this study? Does applying blood flow restriction during the rest periods of repeated sprint exercise in a hypoxic environment lead to greater local hypoxia within exercising muscles without compromising training workload? What is the main finding and its importance? Repeated sprint exercise with blood flow restriction administered during rest periods under systemic hypoxia led to severe local hypoxia within the exercised muscles without a reduction in power output. The maintained power output might be due to elevated neuromuscular activation. Accordingly, the proposed repeated sprint exercise in the current study may be an effective training modality.

ABSTRACT

Repeated sprint exercise (RSE) is a popular training modality for a wide variety of athletic activities. The purpose of this study was to assess the combined effects of systemic hypoxia and blood flow restriction (BFR) on muscle deoxygenation and RSE performance. Twelve healthy young men performed a standard RSE training modality (five sets of 10 s maximal sprint with a 60 s rest) under four different conditions: (1) normoxic control (NC), normoxia (N, 20.9%) + control BFR (C, 0 mmHg); (2) normoxic BFR (NB), normoxia (N, 20.9%) + BFR (B, 140 mmHg); (3) hypoxic control (HC), hypoxia (H, 13.7%) + control BFR (C, 0 mmHg); and (4) hypoxic BFR (HB): hypoxia (H, 13.7%) + BFR (B, 140 mmHg). BFR was only administered during the rest period of the respective RSE trials. In the local exercising muscles, muscle oxygen saturation (Sm O 2 $\textit{Sm}{O}_{2}$ ) and neuromuscular activity were measured using near-infrared spectroscopy and surface electromyography, respectively. SmO2 was lower in systemic hypoxia conditions relative to normoxia conditions (P < 0.05). A rther decrease in SmO2 was observed in HB relative to HC (Set 1: HC 70.0 ± 17.5 vs. HB 57.4 ± 11.3%, P = 0.001; Set 4: HC 67.5 ± 14.6 vs. HB 57.0 ± 12.0%, P = 0.013; Set 5: HC 61.0 ± 15.3 vs. HB 47.7 ± 11.9%, P < 0.001). No differences in RSE performance were observed between any of the conditions (P > 0.05). Interestingly, an elevated neuromuscular activity was seen in response to the BFR, particularly during conditions of systemic hypoxia (P < 0.05). Thus, RSE with BFR administered during rest periods under systemic hypoxia led to severe local hypoxia without compromising training workload.

Acute performance, physiological, and perceptual changes in response to repeated cycling sprint exercise combined with systemic and local hypoxia in young males

This study investigated the acute performance, physiological, and perceptual changes during repeated sprint exercise (RSE) under normobaric hypoxia and with blood flow restriction (BFR). Fourteen active males completed standardized RSE (6 × 10s cycling sprints with 30s passive rest) in three randomized conditions: under normobaric hypoxia (F_iO₂∼14.4%, HYP), normoxia (F_iO₂∼20.9%, SHAM), and with BFR (40% arterial occlusion pressure). The percentage decrement score of power output (S_dec) was used to quantify motor performance fatigue. During RSE, muscle oxygenation and activity of the right quadriceps were measured. Perceived motor fatigue, physical strain, affective valence, and arousal were queried after each sprint. Blood lactate concentration (BLC) and peripheral oxygenation (S_pO₂) were measured before and after RSE. S_dec was greater in HYP and BFR compared to SHAM (p≤0.008). BFR decreased mean power output (p<0.001) and muscle activity (p=0.027) compared to SHAM. Muscle oxygenation was lower in BFR during each rest (p≤0.005) and in HYP during rest 4 (p=0.006) compared to SHAM. HYP increased BLC and decreased S_pO₂ compared to BFR (p<0.001) and SHAM (p=0.002). There were no differences between conditions for any rating scale (p≥0.060). HYP and BFR increased motor performance fatigue but with different physiological responses, whereas perceptual responses were unaffected during RSE.

Acute physiological responses to steady-state arm cycling ergometry with and without blood flow restriction

PURPOSE

To compare heart rate (HR), oxygen consumption (VO₂), blood lactate (BL), and ratings of perceived exertion (RPE) during arm cycling with and without a blood flow restriction (BFR).

METHODS

Twelve healthy males (age: 23.9 ± 3.75 years) completed four, randomized, 15-min arm cycling conditions: high-workload (HW: 60% maximal power output), low-workload (LW: 30% maximal power output), low-workload with BFR (LW-BFR), and BFR with no exercise (BFR-only). In the BFR conditions, cuff pressure to the proximal biceps brachii was set to 70% of occlusion pressure. HR, VO₂, and RPE were recorded throughout the exercise, and BL was measured before, immediately after, and five minutes post-exercise. Within-subject repeated-measures ANOVA was used to evaluate condition-by-time interactions.

RESULTS

HW elicited the greatest responses in HR (91% of peak; 163.3 ± 15.8 bpm), VO₂ (71% of peak; 24.0 ± 3.7 ml kg^-1 min^-1), BL (7.7 ± 2.5 mmol L^-1), and RPE (14 ± 1.7) and was significantly different from the other conditions (p < 0.01). The LW and LW-BFR conditions did not differ from each other in HR, VO₂, BL, and RPE mean of conditions: ~ 68%, 41%, 3.5 ± 1.6 mmol L^-1, 10.4 ± 1.6, respectively; p > 0.05). During the BFR-only condition, HR increased from baseline by ~ 15% (on average) (p < 0.01) without any changes in VO₂, BL, and RPE (p > 0.05).

CONCLUSIONS

HW arm cycling elicited the largest and most persistent physiological responses compared to LW arm cycling with and without a BFR. As such, practitioners who prescribe arm cycling for their clients should be advised to augment the demands of exercise via increases in exercise intensity (i.e., power output), rather than by adding BFR.

Acute and Chronic Effects of Blood Flow Restricted High-Intensity Interval Training: A Systematic Review

Background

The implementation of blood flow restriction (BFR) during exercise is becoming an increasingly useful adjunct method in both athletic and rehabilitative settings. Advantages in pairing BFR with training can be observed in two scenarios: (1) training at lower absolute intensities (e.g. walking) elicits adaptations akin to high-intensity sessions (e.g. running intervals); (2) when performing exercise at moderate to high intensities, higher physiological stimulus may be attained, leading to larger improvements in aerobic, anaerobic, and muscular parameters. The former has been well documented in recent systematic reviews, but consensus on BFR (concomitant or post-exercise) combined with high-intensity interval training (HIIT) protocols is not well established. Therefore, this systematic review evaluates the acute and chronic effects of BFR + HIIT.

Methods

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used to identify relevant studies. A systematic search on 1 February 2022, was conducted on four key databases: ScienceDirect, PubMed, Scopus and SPORTDiscus. Quality of each individual study was assessed using the Physiotherapy Evidence Database (PEDro) scale. Extraction of data from included studies was conducted using an adapted version of the 'Population, Intervention, Comparison, Outcome' (PICO) framework.

Results

A total of 208 articles were identified, 18 of which met inclusion criteria. Of the 18 BFR + HIIT studies (244 subjects), 1 reported both acute and chronic effects, 5 examined acute responses and 12 investigated chronic effects. Acutely, BFR challenges the metabolic processes (vascular and oxygenation responses) during high-intensity repeated sprint exercise—which accelerates central and peripheral neuromuscular fatigue mechanisms resulting in performance impairments. Analysis of the literature exploring the chronic effects of BFR + HIIT suggests that BFR does provide an additive physiological training stimulus to HIIT protocols, especially for measured aerobic, muscular, and, to some extent, anaerobic parameters.

Conclusion

Presently, it appears that the addition of BFR into HIIT enhances physiological improvements in aerobic, muscular, and, to some extent, anaerobic performance. However due to large variability in permutations of BFR + HIIT methodologies, it is necessary for future research to explore and recommend standardised BFR guidelines for each HIIT exercise type.

Differences in the limb blood flow between two types of blood flow restriction cuffs: A pilot study

Introduction: The determination of the optimal occlusion level is a key parameter in blood flow restriction (BFR). This study aimed to compare the effects of elastic (BStrong) vs. nylon (Hokanson) BFR cuffs on blood flow in the lower and upper limbs.

Methods: Eleven healthy participants undertook several BFR sessions with 2 different cuffs of similar width on their lower and upper limbs at different pressures [200, 250, 300, 350, and 400 mmHg for BStrong and 0, 40, and 60% of the arterial occlusion pressure (AOP) for Hokanson]. Doppler ultrasound recorded blood flows through the brachial and femoral artery at rest.

Results: With BStrong, only 350 and 400 mmHg pressures were significantly different from resting values (0% AOP). With Hokanson, both 40% and 60% of the AOP were significantly different from resting values (p < 0.05).

Discussion: While both cuffs elicited BFR, they failed to accurately modulate blood flow. Hokanson is appropriate for research settings while BStrong appears to be a convenient tool for practitioners due to its safety (i.e., the impossibility of completely occluding arteries) and the possibility of exercising freely detached from the pump.

Complex Network Model Reveals the Impact of Inspiratory Muscle Pre-Activation on Interactions among Physiological Responses and Muscle Oxygenation during Running and Passive Recovery

Simple Summary

Different warm-ups can be used to improve physical and sports performance. Among these strategies, we can include the pre-activation of the inspiratory muscles. Our study aimed to investigate this pre-activation model in high-intensity running performance and recovery using an integrative computational analysis called a complex network. The participants in this study underwent four sessions. The first and second sessions were performed to explain the procedures, characterize them and determine the individualized pre-activation intensity (40% of the maximum inspiratory pressure). Subsequently, on different days, the subjects were submitted to high-intensity tethered runs on a non-motorized treadmill with monitoring of the physiological responses during and after this effort. To understand the impacts of the pre-activation of inspiratory muscles on the organism, we studied the centrality metrics obtained by complex networks, which help in the interpretation of data in a more integrated way. Our results revealed that the graphs generated by this analysis were altered when inspiratory muscle pre-activation was applied, emphasizing muscle oxygenation responses in the leg and arm. Blood lactate also played an important role, especially after our inspiratory muscle strategy. Our findings confirm that the pre-activation of inspiratory muscles promotes modulations in the organism, better integrating physiological responses, which could increase performance and improve recovery.

Abstract

Although several studies have focused on the adaptations provided by inspiratory muscle (IM) training on physical demands, the warm-up or pre-activation (PA) of these muscles alone appears to generate positive effects on physiological responses and performance. This study aimed to understand the effects of inspiratory muscle pre-activation (IM_PA) on high-intensity running and passive recovery, as applied to active subjects. In an original and innovative investigation of the impacts of IM_PA on high-intensity running, we proposed the identification of the interactions among physical characteristics, physiological responses and muscle oxygenation in more and less active muscle to a running exercise using a complex network model. For this, fifteen male subjects were submitted to all-out 30 s tethered running efforts preceded or not preceded by IM_PA, composed of 2 × 15 repetitions (1 min interval between them) at 40% of the maximum individual inspiratory pressure using a respiratory exercise device. During running and recovery, we monitored the physiological responses (heart rate, blood lactate, oxygen saturation) and muscle oxygenation (in vastus lateralis and biceps brachii) by wearable near-infrared spectroscopy (NIRS). Thus, we investigated four scenarios: two in the tethered running exercise (with or without IM_PA) and two built into the recovery process (after the all-out 30 s), under the same conditions. Undirected weighted graphs were constructed, and four centrality metrics were analyzed (Degree, Betweenness, Eigenvector, and Pagerank). The IM_PA (40% of the maximum inspiratory pressure) was effective in increasing the peak and mean relative running power, and the analysis of the complex networks advanced the interpretation of the effects of physiological adjustments related to the IM_PA on exercise and recovery. Centrality metrics highlighted the nodes related to muscle oxygenation responses (in more and less active muscles) as significant to all scenarios, and systemic physiological responses mediated this impact, especially after IM_PA application. Our results suggest that this respiratory strategy enhances exercise, recovery and the multidimensional approach to understanding the effects of physiological adjustments on these conditions.

Augmented muscle deoxygenation during repeated sprint exercise with post-exercise blood flow restriction

Blood flow restriction (BFR) during low-intensity exercise has been known to be a potent procedure to alter metabolic and oxygen environments in working muscles. Moreover, the use of BFR during inter-set rest periods of repeated sprint exercise has been recently suggested to be a potent procedure for improving training adaptations. The present study was designed to determine the effect of repeated sprint exercise with post-exercise BFR (BFR during rest periods between sprints) on muscle oxygenation in working muscles. Eleven healthy males performed two different conditions on different days: either repeated sprint exercise with BFR during rest periods between sets (BFR condition) or without BFR (CON condition). A repeated sprint exercise consisted of three sets of 3 × 6-s maximal sprints (pedaling) with 24s rest periods between sprints and 5 min rest periods between sets. In BFR condition, two min of BFR (100-120 mmHg) for both legs was conducted between sets. During the exercise, power output and arterial oxygen saturation (SpO₂ ) were evaluated. Muscle oxygenation for the vastus lateralis muscle, exercise-induced changes in muscle blood flow, and muscle oxygen consumption were measured. During BFR between sets, BFR condition presented significantly higher deoxygenated hemoglobin + myoglobin (p < 0.01) and lower tissue saturation index (p < 0.01) than those in CON condition. However, exercise-induced blood lactate elevation and reduction of blood pH did not differ significantly between the conditions. Furthermore, power output throughout nine sprints did not differ significantly between the two conditions. In conclusion, repeated sprint exercise with post-exercise BFR augmented muscle deoxygenation and local hypoxia, without interfering power output.

Muscle Oxygenation during Repeated Cycling Sprints in a Combined Hot and Hypoxic Condition

The aim of the present study was to examine the effects of a combined hot and hypoxic environment on muscle oxygenation and performance during repeated cycling sprints. In a single-blind, counterbalanced, cross-over research design, 10 male athletes performed three sets of 3 × 10-s maximal pedaling interspersed with 40-s recovery between sprints under four different environments. Each condition consisted of a control (CON; 20°C, 20.9% FiO₂), normobaric hypoxia (HYP; 20°C, 14.5% FiO₂), hot (HOT; 35°C, 20.9% FiO₂), and combined hot and normobaric hypoxia (HH; 35°C, 14.5% FiO₂). Power output and vastus lateralis muscle oxygenation were measured. Peak power output was significantly higher in HOT (892±27 W) and HH (887±24 W) than in CON (866±25 W) and HYP (859±25 W) during the first set (p<0.05). The increase in total hemoglobin during recovery periods was larger in HH than in HYP (p<0.05), while change in tissue saturation index was smaller in HYP than in CON and HOT (p<0.05). The findings suggest that the combination of hot and hypoxia during repeated cycling sprints presented different characteristics for muscle metabolism and power output compared to temperature or altitude stressor alone.

Neuromuscular responses at acute moderate and severe hypoxic exposure during fatiguing exercise of the biceps brachii

Purpose

The present study examined acute normobaric hypoxic exposure on the number of repetitions to failure, electromyographic (EMG) repetition duration (Time), EMG root mean square (RMS) and EMG mean power frequency (MPF) during biceps brachii (BB) dynamic constant external resistance (DCER) exercise.

Methods

Thirteen subjects performed two sets of fatiguing DCER arm curl repetitions to failure at 70% of their one repetition maximum under normoxic (NH), moderate hypoxia FiO₂ = 15% (MH) and severe hypoxia FiO₂ = 13% (SH). Electromyography of the BB was analyzed for EMG Time, EMG RMS, and EMG MPF. Repetitions were selected as 25%, 50%, 75%, and 100% of total repetitions (%Fail) completed. Pulse oximetry (SpO₂) was measured pre-and post-fatigue.

Results

There was no significant three-way (Condition x Set x %Fail) or two-way (Condition x Set) interaction for any variable. The number of repetitions to failure significantly decreased from (mean ± SEM) 18.2 ± 1.4 to 9.5 ± 1.0 with each Set. In addition, EMG Time increased (25% < 50%<75% < 100%), EMG RMS decreased (50% > 75%>100%), and EMG MPF decreased (75% > 100%) as a result of fatiguing exercise. SpO₂ was lower during MH (Δ5.3%) and SH (Δ9.2%) compared to NH and as a result of fatiguing exercise increased only in MH (Δ2.1%) and SH (Δ5.7%).

Conclusion

The changes in BB EMG variables indicated exercise caused myoelectric manifestations of fatigue, however, acute moderate or severe hypoxia had no additional influence on the rate of fatigue development or neuromuscular parameters.

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Acute MH (FiO₂ 15%) and SH (FiO₂ 14%) did not alter the muscle contractile process.

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Arm curl repetitions to failure decreased MU recruitment and conduction velocity.

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EMG fatigue analysis, hypoxia and arm curls to failure, EMG RMS, EMG MPF and Time.

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SpO₂ was lower at MH and SH which increased following fatiguing exercise.

Effects of Blood Flow Restriction on O2 Muscle Extraction and O2 Pulmonary Uptake Kinetics During Heavy Exercise

This study aimed to determine the effects of three levels of blood flow restriction (BFR) on V˙O2 and O₂ extraction kinetics during heavy cycling exercise transitions. Twelve healthy trained males completed two bouts of 10 min heavy intensity exercise without BFR (CON), with 40% or 50% BFR (BFR40 and BFR50, respectively). V˙O2 and tissue saturation index (TSI) were continuously measured and modelled using multiexponential functions. The time constant of the V˙O2 primary phase was significantly slowed in BFR40 (26.4 ± 2.0s; p < 0.001) and BFR50 (27.1 ± 2.1s; p = 0.001) compared to CON (19.0 ± 1.1s). The amplitude of the V˙O2 slow component was significantly increased (p < 0.001) with BFR in a pressure-dependent manner 3.6 ± 0.7, 6.7 ± 0.9 and 9.7 ± 1.0 ml·min⁻¹·kg⁻¹ for CON, BFR40, and BFR50, respectively. While no acceleration of the primary component of the TSI kinetics was observed, there was an increase (p < 0.001) of the phase 3 amplitude with BFR (CON −0.8 ± 0.3% VS BFR40 −2.9 ± 0.9%, CON VS BFR50 −2.8 ± 0.8%). It may be speculated that BFR applied during cycling exercise in the heavy intensity domain shifted the working muscles to an O₂ dependent situation. The acceleration of the extraction kinetics could have reached a plateau, hence not permitting compensation for the slowdown of the blood flow kinetics, and slowing V˙O2 kinetics.

Acute Effect of Repeated Sprint Exercise With Blood Flow Restriction During Rest Periods on Muscle Oxygenation

Purpose

This study aimed to examine the effect of applying BFR during rest periods of repeated cycling sprints on muscle oxygenation.

Methods

Seven active males performed 5 × 10-s maximal pedaling efforts with 40-s passive rest, with or without BFR application during rest period. BFR was applied for 30 s between sprints (between 5 and 35 s into rest) through a pneumatic pressure cuff inflated at 140 mmHg. Vastus lateralis muscle oxygenation was monitored using near-infrared spectroscopy. In addition, blood lactate concentration and heart rate were also evaluated.

Results

The BFR trial showed significantly lower oxyhemoglobin (oxy-Hb) and tissue saturation (StO₂) levels than the CON trial (P < 0.05). However, power output and blood lactate concentration did not significantly differ between the two trials (P > 0.05).

Conclusion

Applying BFR during rest periods of repeated cycling sprints decreased muscle oxygenation of active musculature, without interfering with power output during sprints.

Effects of combined hot and hypoxic conditions on muscle blood flow and muscle oxygenation during repeated cycling sprints

PURPOSE

The purpose of the present study was to determine muscle blood flow and muscle oxygenation during repeated-sprint exercise under combined hot and hypoxic conditions.

METHODS

In a single-blind, cross-over research design, 11 active males performed three sets of 5 × 6-s maximal sprints with 30-s active recovery on a cycling ergometer under control (CON; 23 °C, 50% rH, 20.9% FiO₂), normobaric hypoxic (HYP; 23 °C, 50% rH, 14.5% FiO₂), or hot + normobaric hypoxic (HH; 35 °C, 50% rH, 14.5% FiO₂) conditions. The vastus lateralis muscle blood flow after each set and muscle oxygenation during each sprint were evaluated using near-infrared spectroscopy methods.

RESULTS

Despite similar repeated-sprint performance among the three conditions (peak and mean power outputs, percent decrement score), HH was associated with significantly higher muscle blood flow compared with CON after the first set (CON: 0.61 ± 0.10 mL/min/100 g; HYP: 0.81 ± 0.13 mL/min/100 g; HH: 0.99 ± 0.16 mL/min/100 g; P < 0.05). The tissue saturation index was significantly lower in HYP than in CON during the latter phase of the exercise (P < 0.05), but it did not differ between HH and CON.

CONCLUSION

These findings suggest that a combination of normobaric hypoxia and heat stress partially facilitated the exercise-induced increase in local blood flow, but it did not enhance tissue desaturation.

Data Processing in Functional Near-Infrared Spectroscopy (fNIRS) Motor Control Research

FNIRS pre-processing and processing methodologies are very important-how a researcher chooses to process their data can change the outcome of an experiment. The purpose of this review is to provide a guide on fNIRS pre-processing and processing techniques pertinent to the field of human motor control research. One hundred and twenty-three articles were selected from the motor control field and were examined on the basis of their fNIRS pre-processing and processing methodologies. Information was gathered about the most frequently used techniques in the field, which included frequency cutoff filters, wavelet filters, smoothing filters, and the general linear model (GLM). We discuss the methodologies of and considerations for these frequently used techniques, as well as those for some alternative techniques. Additionally, general considerations for processing are discussed.

Effects of high intensity interval exercise on cerebrovascular function: A systematic review

High intensity interval exercise (HIIE) improves aerobic fitness with decreased exercise time compared to moderate continuous exercise. A gap in knowledge exists regarding the effects of HIIE on cerebrovascular function such as cerebral blood velocity and autoregulation. The objective of this systematic review was to ascertain the effect of HIIE on cerebrovascular function in healthy individuals. We searched PubMed and the Cumulative Index to Nursing and Allied Health Literature databases with apriori key words. We followed the Preferred Reporting Items for Systematic Reviews. Twenty articles were screened and thirteen articles were excluded due to not meeting the apriori inclusion criteria. Seven articles were reviewed via the modified Sackett’s quality evaluation. Outcomes included middle cerebral artery blood velocity (MCAv) (n = 4), dynamic cerebral autoregulation (dCA) (n = 2), cerebral de/oxygenated hemoglobin (n = 2), cerebrovascular reactivity to carbon dioxide (CO₂) (n = 2) and cerebrovascular conductance/resistance index (n = 1). Quality review was moderate with 3/7 to 5/7 quality criteria met. HIIE acutely lowered exercise MCAv compared to moderate intensity. HIIE decreased dCA phase following acute and chronic exercise compared to rest. HIIE acutely increased de/oxygenated hemoglobin compared to rest. HIIE acutely decreased cerebrovascular reactivity to higher CO₂ compared to rest and moderate intensity. The acute and chronic effects of HIIE on cerebrovascular function vary depending on the outcomes measured. Therefore, future research is needed to confirm the effects of HIIE on cerebrovascular function in healthy individuals and better understand the effects in individuals with chronic conditions. In order to conduct rigorous systematic reviews in the future, we recommend assessing MCAv, dCA and CO₂ reactivity during and post HIIE.

Mitochondrial oxygen affinity increases after sprint interval training and is related to the improvement in peak oxygen uptake

AIMS

The body responds to exercise training by profound adaptations throughout the cardiorespiratory and muscular systems, which may result in improvements in maximal oxygen consumption (VO₂ peak) and mitochondrial capacity. By convenience, mitochondrial respiration is often measured at supra-physiological oxygen levels, an approach that ignores any potential regulatory role of mitochondrial affinity for oxygen (p50_mito ) at physiological oxygen levels.

METHODS

In this study, we examined the p50_mito of mitochondria isolated from the Vastus lateralis and Triceps brachii in 12 healthy volunteers before and after a training intervention with seven sessions of sprint interval training using both leg cycling and arm cranking. The changes in p50_mito were compared to changes in whole-body VO₂ peak.

RESULTS

We here show that p50_mito is similar in isolated mitochondria from the Vastus (40 ± 3.8 Pa) compared to Triceps (39 ± 3.3) but decreases (mitochondrial oxygen affinity increases) after seven sessions of sprint interval training (to 26 ± 2.2 Pa in Vastus and 22 ± 2.7 Pa in Triceps, both P < .01). The change in VO₂ peak modelled from changes in p50_mito was correlated to actual measured changes in VO₂ peak (R²  = .41, P = .002).

CONCLUSION

Together with mitochondrial respiratory capacity, p50_mito is a critical factor when measuring mitochondrial function, it can decrease with sprint interval training and should be considered in the integrative analysis of the oxygen cascade from lung to mitochondria.

Insights for Blood Flow Restriction and Hypoxia in Leg Versus Arm Submaximal Exercise

PURPOSE

To assess tissue oxygenation, along with metabolic and physiological responses during blood flow restriction (BFR, bilateral vascular occlusion) and systemic hypoxia conditions during submaximal leg- versus arm-cycling exercise.

METHODS

In both legs and arms, 4 randomized sessions were performed (normoxia 400 m, fraction of inspired oxygen [FIO2] 20.9% and normobaric hypoxia 3800 m, FIO2 13.1% [0.1%]; combined with BFR at 0% and 45% of resting pulse elimination pressure). During each session, a single 6-minute steady-state submaximal exercise was performed to measure physiological changes and oxygenation (near-infrared spectroscopy) of the muscle tissue in both the vastus lateralis (legs) and biceps brachii (arms).

RESULTS

Total hemoglobin concentration ([tHb]) was 65% higher (P < .001) in arms versus legs, suggesting that arms had a greater blood perfusion capacity than legs. Furthermore, there were greater changes in tissue blood volume [tHb] during BFR compared with control conditions (P = .017, F = 5.45). The arms elicited 7% lower tissue saturation (P < .001) and were thus more sensitive to the hypoxia-induced reduction in oxygen supply than legs, no matter the condition. This indicates that legs and arms may elicit different regulatory hemodynamic mechanisms (ie, greater blood flow in arms) for limiting the decreased oxygen delivery during exercise with altered arterial oxygen content.

CONCLUSIONS

The combination of BFR and/or hypoxia led to increased [tHb] in both limbs likely due to greater vascular resistance; further, arms were more responsive than legs. This possibly influences the maintenance of oxygen delivery and enhances perfusion pressure, suggesting greater vascular reactivity in arms than in legs.

New Insights into Mechanical, Metabolic and Muscle Oxygenation Signals During and After High-Intensity Tethered Running

High-intensity exercises including tethered efforts are commonly used in training programs for athletes, active and even sedentary individuals. Despite this, the knowledge about the external and internal load during and after this effort is scarce. Our study aimed to characterize the kinetics of mechanical and physiological responses in all-out 30 seconds (AO30) tethered running and up to 18 minutes of passive recovery. Additionally, in an innovative way, we investigated the muscle oxygenation in more or less active muscles (vastus lateralis and biceps brachii, respectively) during and after high-intensity tethered running by near-infrared spectroscopy – NIRS. Twelve physically active young men were submitted to AO30 on a non-motorized treadmill to determine the running force, velocity and power. We used wearable technologies to monitor the muscle oxygenation and heart rate responses during rest, exercise and passive recovery. Blood lactate concentration and arterial oxygen saturation were also measured. In a synchronized analysis by high capture frequency of mechanical and physiological signals, we advance the understanding of AO30 tethered running. Muscle oxygenation responses showed rapid adjustments (both, during and after AO30) in a tissue-dependence manner, with very low tissue saturation index observed in biceps brachii during exercise when compared to vastus lateralis. Significant correlations between peak and mean blood lactate with biceps brachii oxygenation indicate an important participation of less active muscle during and after high-intensity AO30 tethered running.

An Updated Panorama of "Living Low-Training High" Altitude/Hypoxic Methods

With minimal costs and travel constraints for athletes, the “living low-training high” (LLTH) approach is becoming an important intervention for modern sport. The popularity of the LLTH model of altitude training is also associated with the fact that it only causes a slight disturbance to athletes' usual daily routine, allowing them to maintain their regular lifestyle in their home environment. In this perspective article, we discuss the evolving boundaries of the LLTH paradigm and its practical applications for athletes. Passive modalities include intermittent hypoxic exposure at rest (IHE) and Ischemic preconditioning (IPC). Active modalities use either local [blood flow restricted (BFR) exercise] and/or systemic hypoxia [continuous low-intensity training in hypoxia (CHT), interval hypoxic training (IHT), repeated-sprint training in hypoxia (RSH), sprint interval training in hypoxia (SIH) and resistance training in hypoxia (RTH)]. A combination of hypoxic methods targeting different attributes also represents an attractive solution. In conclusion, a growing number of LLTH altitude training methods exists that include the application of systemic and local hypoxia stimuli, or a combination of both, for performance enhancement in many disciplines.