The Oxidative-Glycolytic Balance Influenced by Sprint Duration Is Key during Repeated Sprint in Hypoxia

Muscle deoxygenation responses are similar between repeated sprints in hypoxia performed with uni- versus bi-lateral knee extensions but reduced compared to cycling

The aim of this study was to assess the effects of oxygen availability (normoxia vs. hypoxia), muscle mass and exercise type on pulse oxygen saturation, and quadriceps muscle oxygenation during repeated sprint exercises. Sixteen healthy participants completed 5× ${\times} $ 12 s sprints (21 s rest). This sprint-like exercise was performed under two environmental conditions (normoxia: FiO2 = 21%; systemic hypoxia: FiO2 = 13%) and for three exercise modalities: unilateral knee extensions (KE) involving the right leg extensors (UNI), bilateral KE involving both legs extensors (BIL), and bilateral leg cycling (CYC). Measurements included power output, pulse oxygen saturation (SpO2), and vastus lateralis oxygenation (delta in tissue saturation index; ΔTSI). In hypoxia, a similar minimal SpO2 was reported in UNI and BIL but SpO2 was lower in CYC (p = 0.047 and p = 0.021). ΔTSI during sprints and recoveries were similar in UNI and BIL but greater in CYC (p < 0.001) and in normoxia compared to hypoxia (main condition effect; p = 0.002). The power output was lower during KE exercises than during cycling, and no effect of hypoxia has been reported. The main results of this study indicate that unilateral and bilateral KE at high intensity induce comparable pulse and local muscular desaturation in hypoxia, and that these alterations are exacerbated during cycling.

Dose-response effects of caffeine during repeated cycling sprints in normobaric hypoxia to exhaustion

PURPOSE

With limited studies exploring the dose-response of caffeine consumption on repeated sprint ability in hypoxia, this study aimed to determine the optimal caffeine dose (low, moderate or high) during repeated sprints in hypoxia to exhaustion.

METHODS

On separate visits, twelve active males randomly performed four experimental trials in normobaric hypoxia (inspired oxygen fraction: 16.5 ± 0.2%). Participants ingested placebo (PLA) or caffeine capsules (3, 6 or 9 mg/kg or LOW, MOD and HIGH, respectively) 1 h before exercise and then underwent a repeated cycling sprint test (10 s sprint/20 s active recovery) to exhaustion. Total sprint number and work done, peak and mean power output, blood lactate concentration, cardiorespiratory and perceptual responses were recorded.

RESULTS

Total sprint number was greater in MOD and HIGH compared to PLA (20 ± 7 and 18 ± 8 vs. 13 ± 4; all P < 0.05), with MOD also higher than LOW (15 ± 6; P = 0.02). Total work done was greater in MOD (111 ± 40 kJ) and HIGH (100 ± 35 kJ) compared to LOW (83 ± 29 kJ) and PLA (76 ± 25 kJ) (all P < 0.05). However, there were no significant differences in total sprint number or total work done between MOD and HIGH (all P > 0.05). Blood lactate concentration was higher in both MOD and HIGH compared to PLA (all P < 0.05). However, peak and mean power outputs, fatigue index, and ratings of perceived exertion did not differ across different caffeine dosages (all P > 0.05).

CONCLUSION

A moderate dose of caffeine (6 mg/kg) is the optimal amount for enhancing repeated cycling sprint ability when compared to low and high doses in moderate normobaric hypoxia.

Effect of repeated sprint training in hypoxia on acute and chronic redox balance modulation

Little is known regarding the effects high-intensity training performed in hypoxia on the oxidative stress and antioxidant systems. The aim of this study was to assess the potential effect of 4 weeks of repeated sprint training in hypoxia (RSH) on the redox balance. Forty male well-trained cyclists were matched into two different interventions (RSH, n = 20) or in normoxia, RSN, n = 20) and tested twice (before (Pre-) and after (Post-) a 4-week of training) for performance (repeated sprint ability (RSA) test), oxidative stress, and antioxidant status. Antioxidant enzyme activity (Superoxide Dismutase, Glutathione Peroxidase, and catalase), NO metabolites (NOx: nitrites and nitrates), ferric reducing antioxidant power, Malondialdehyde (MDA), nitrotyrosine, and carbonyls were measured in plasma. At Post-, MDA, and carbonyls increased (p < 0.05) in the RSN group both at rest (+90.6%) and also acutely in response to RSA (+22.9%); but not in RSH. At Post-, in the RSH group, catalase increased (p < 0.05) both at rest (+44.7%) and in response to the RSA test (+66.3%). At Post-, SOD, and nitrotyrosine decreased after RSA and at rest, regardless of the group (p = 0.0012 and p = 0.0413, respectively). At Post-, NOx decreased after the RSA test, regardless of the group (p < 0.05). In conclusion, several weeks of RSH training limits the increase in oxidative stress markers both at rest and in response to RSA test. Moreover, such training downregulated SOD activity, possibly due to an overproduction of reactive oxygen species. These findings could constitute a paradigm shift with a better enzymatic adaptation after RSH concomitant with a distinct reactive oxygen species (ROS) production between RSH and RSN.

Cardiorespiratory and muscle oxygenation responses to voluntary hypoventilation at low lung volume in upper body repeated sprints

PURPOSE

To investigate the impact of voluntary hypoventilation at low lung volumes (VHL) during upper body repeated sprints (RS) on performance, metabolic markers and muscle oxygenation in Brazilian Jiu-Jitsu (BJJ) athletes.

METHODS

Eighteen male well-trained athletes performed two randomized RS sessions, one with normal breathing (RSN) and another with VHL (RS-VHL), on an arm cycle ergometer, consisting of two sets of eight all-out 6-s sprints performed every 30 s. Peak (PPO), mean power output (MPO), and RS percentage decrement score were calculated. Arterial oxygen saturation (SpO2), heart rate (HR), gas exchange, and muscle oxygenation of the long head of the triceps brachii were continuously recorded. Blood lactate concentration ([La]) was measured at the end of each set. Bench press throw peak power (BPPP) was recorded before and after the RS protocol.

RESULTS

Although SpO2 was not different between conditions, PPO and MPO were significantly lower in RS-VHL. V ˙ E, HR, [La], and RER were lower in RS-VHL, and VO2 was higher in RS-VLH than in RSN. Muscle oxygenation was not different between conditions nor was its pattern of change across the RS protocol influenced by condition. [La] was lower in RS-VHL than in RSN after both sets.

CONCLUSION

Performance was significantly lower in RS-VHL, even though SPO2 was not consistent with hypoxemia. However, the fatigue index was not significantly affected by VHL, nor was the neuromuscular upper body power after the RS-VHL protocol. Additionally, [La] was lower, and oxygen consumption was higher in RS-VHL, suggesting a higher aerobic contribution in this condition.

Repeated-sprint training in hypoxia: A review with 10 years of perspective

Over the past decade, numerous studies have investigated an innovative "live low-train high" approach based on the repetition of short (<30 s) "all-out" sprints with incomplete recoveries in hypoxia; the so-called Repeated-Sprint training in Hypoxia (RSH). The aims of the present review are therefore threefold. First, this study summarizes the available evidence on putative additional performance enhancement after RSH comparing to the same training in normoxia (RSN). Second, a critical analysis of underpinning mechanisms discusses how advantages can be obtained through RSH for sea-level performance enhancement. An enhanced microcirculatory vasodilation leading to improved muscle perfusion and/or oxygenation and an increase in muscular phosphocreatine content may help explain the superiority of RSH vs. RSN. Third, the present review aims to provide guidelines for coaches, athletes and scientists to apply RSH interventions with regard to the interval duration, exercise-to-rest ratio and training volume. In conclusion, this review supports repeated-sprint training in hypoxia as an efficient (but not magic) training intervention with 77% of the controlled studies reporting an additional benefit with added hypoxia, mainly for team-, combat- and racket-sports athletes but also for all other sports (e.g. endurance) that require repeated accelerations with lesser fatigue.

Sprint training in hypoxia and with blood flow restriction: Controversies and perspectives

This narrative review assesses the effects of repeated sprint training (RST) in hypoxia (RSH) and blood flow restriction (BFR) methods on skeletal muscle adaptations and performance. Current literature suggests that RSH promotes metabolic modifications in muscle cells, especially driven by reactive oxygen species production, HIF-1α stabilization, and changes in metabolism. Training with BFR promotes metabolite accumulation in working muscles due to limited blood flow, however, cellular mechanisms affected by BFR during RST are less explored. Data highlight that RSH improves repeated sprint ability (RSA) in several sport disciplines (e.g. rugby, tennis, soccer, cross-country skiing). However, recent studies showed that addition of hypoxia or BFR during RST did not promote supplementary benefits on aerobic performance, force-velocity power profile, and V ˙ O 2 max . Nonetheless, gains in V ˙ O 2 max were observed during sprint interval training protocols when BFR was applied during recovery between sets. Finally, recent studies highlighted that RSH can improve RSA in a short period. Thus, RSH and sprint training with BFR may be useful for sports disciplines requiring high glycolytic demand and can promote gains in RSA in a short window. Further studies must be encouraged to better understand the biological consequences of adding such stimuli to exercise, especially BFR, on long-term adaptation.

Exercise responses to repeated cycle sprints with continuous and intermittent hypoxic exposure

We examine the impact of the acute manipulation of oxygen availability during discrete phases (active and passive) of a repeated-sprint cycling protocol on performance, physiological, and perceptual responses. On separate days, twelve trained males completed four sets of five 5-s 'all out' cycle sprints (25-s inter-sprint recovery and 5-min interset rest) in four randomized conditions: normobaric hypoxia (inspired oxygen fraction of 12.9%) applied continuously (C-HYP), intermittently during only the sets of sprints (I-HYPSPRINT) or between-sets recovery periods (I-HYPRECOVERY), or not at all (C-NOR). Peak and mean power output, peripheral oxygen saturation, heart rate, blood lactate concentration, exercise-related sensations, and vastus lateralis muscle oxygenation using near-infrared spectroscopy were assessed. Peak and mean power output was ∼4%-5% lower for C-HYP compared to C-NOR (P ≤ 0.050) and I-HYPRECOVERY (P ≤ 0.027). Peripheral oxygen saturation was lower during C-HYP and I-HYPSPRINT compared with C-NOR and I-HYPRECOVERY during sets of sprints (∼83-85 vs. ∼95%-97%; P < 0.001), while lower values were obtained for C-HYP and I-HYPRECOVERY than C-NOR and I-HYPSPRINT during between-sets rest period (∼84-85 vs. ∼96%; P < 0.001). Difficulty in breathing was ∼21% higher for C-HYP than C-NOR (P = 0.050). Ratings of perceived exertion (P = 0.435), limb discomfort (P = 0.416), heart rate (P = 0.605), blood lactate concentration (P = 0.976), and muscle oxygenation-derived variables (P = 0.056 to 0.605) did not differ between conditions. In conclusion, the method of hypoxic exposure application (continuous vs. intermittent) affects mechanical performance, while internal demands remained essentially comparable during repeated cycle sprints.

Repeated sprint training in hypoxia induces specific skeletal muscle adaptations through S100A protein signaling

Athletes increasingly engage in repeated sprint training consisting in repeated short all-out efforts interspersed by short recoveries. When performed in hypoxia (RSH), it may lead to greater training effects than in normoxia (RSN); however, the underlying molecular mechanisms remain unclear. This study aimed at elucidating the effects of RSH on skeletal muscle metabolic adaptations as compared to RSN. Sixteen healthy young men performed nine repeated sprint training sessions in either normoxia (FIO2 = 0.209, RSN, n = 7) or normobaric hypoxia (FIO2 = 0.136, RSH, n = 9). Before and after the training period, exercise performance was assessed by using repeated sprint ability (RSA) and Wingate tests. Vastus lateralis muscle biopsies were performed to investigate muscle metabolic adaptations using proteomics combined with western blot analysis. Similar improvements were observed in RSA and Wingate tests in both RSN and RSH groups. At the muscle level, RSN and RSH reduced oxidative phosphorylation protein content but triggered an increase in mitochondrial biogenesis proteins. Proteomics showed an increase in several S100A family proteins in the RSH group, among which S100A13 most strongly. We confirmed a significant increase in S100A13 protein by western blot in RSH, which was associated with increased Akt phosphorylation and its downstream targets regulating protein synthesis. Altogether our data indicate that RSH may activate an S100A/Akt pathway to trigger specific adaptations as compared to RSN.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Recommendations for Women in Mountain Sports and Hypoxia Training/Conditioning

The (patho-)physiological responses to hypoxia are highly heterogeneous between individuals. In this review, we focused on the roles of sex differences, which emerge as important factors in the regulation of the body's reaction to hypoxia. Several aspects should be considered for future research on hypoxia-related sex differences, particularly altitude training and clinical applications of hypoxia, as these will affect the selection of the optimal dose regarding safety and efficiency. There are several implications, but there are no practical recommendations if/how women should behave differently from men to optimise the benefits or minimise the risks of these hypoxia-related practices. Here, we evaluate the scarce scientific evidence of distinct (patho)physiological responses and adaptations to high altitude/hypoxia, biomechanical/anatomical differences in uphill/downhill locomotion, which is highly relevant for exercising in mountainous environments, and potentially differential effects of altitude training in women. Based on these factors, we derive sex-specific recommendations for mountain sports and intermittent hypoxia conditioning: (1) Although higher vulnerabilities of women to acute mountain sickness have not been unambiguously shown, sex-dependent physiological reactions to hypoxia may contribute to an increased acute mountain sickness vulnerability in some women. Adequate acclimatisation, slow ascent speed and/or preventive medication (e.g. acetazolamide) are solutions. (2) Targeted training of the respiratory musculature could be a valuable preparation for altitude training in women. (3) Sex hormones influence hypoxia responses and hormonal-cycle and/or menstrual-cycle phases therefore may be factors in acclimatisation to altitude and efficiency of altitude training. As many of the recommendations or observations of the present work remain partly speculative, we join previous calls for further quality research on female athletes in sports to be extended to the field of altitude and 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.

Inter-effort recovery hypoxia: a new paradigm in sport science?

High-intensity interval training (HIIT) is a popular method for optimising sports performance and, more recently, improving health-related parameters. The inclusion of hypoxia during HIIT can promote additional gains compared with normoxia. However, reductions in the effort intensities compared with the same training performed in normoxia have been reported. Studies have reported that adding hypoxia during periods of inter-effort recovery (IEH) enables maintenance of the intensity of efforts. It also promotes additional gains from exposure to hypoxia. Our call is for researchers to consider IEH in experiments involving different models of HIIT. Additionally, we consider the need to answer the following questions: What is the clinically relevant minimum dose of exposure to hypoxia during the recovery periods between efforts so that favourable adaptations of parameters are associated with health and sports performance? How does the intensity of exertion influence the responses to hypoxia exposure during recovery periods? What are the chronic effects of different models of HIIT and hypoxia recovery on sports performance?

Effects of 2 Different Protocols of Repeated-Sprint Training in Hypoxia in Elite Female Rugby Sevens Players During an Altitude Training Camp

OBJECTIVES

Repeated-sprint training in hypoxia (RSH) is an effective way of improving physical performance compared with similar training in normoxia. RSH efficiency relies on hypoxia severity, but also on the oxidative-glycolytic balance determined by both sprint duration and exercise-to-rest ratio. This study investigated the effect of 2 types of RSH sessions during a classic altitude camp in world-class female rugby sevens players.

METHODS

Sixteen players performed 5 RSH sessions on a cycle ergometer (simulated altitude: 3000 m above sea level [asl]) during a 3-week natural altitude camp (1850 m asl). Players were assigned to 2 different protocols with either a high (RSH1:3, sprint duration: 8-10 s; exercise-to-rest ratios: 1:2-1:3; n = 7) or a low exercise-to-rest ratio (RSH1:5, sprint duration: 5-15 s; exercise-to-rest ratios: 1:2-1:5; n = 9). Repeated-sprint performances (maximal and mean power outputs [PPOmax, and PPOmean]) were measured before and after the intervention, along with physiological responses.

RESULTS

PPOmax (962 [100] to 1020 [143] W, P = .008, Cohen d = 0.47) and PPOmean (733 [71] to 773 [91] W, P = .008, d = 0.50) increased from before to after. A significant interaction effect (P = .048, d = 0.50) was observed for PPOmean, with a larger increase observed in RSH1:3 (P = .003). No interaction effects were observed (P > .05) for the other variables.

CONCLUSION

A classic altitude camp with 5 RSH sessions superimposed on rugby-sevens-specific training led to an improved repeated-sprint performance, suggesting that RSH effects are not blunted by prolonged hypoxic exposure. Interestingly, using a higher exercise-to-rest ratio during RSH appears to be more effective than when applying a lower exercise-to-rest ratio.