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Many sport competitions, typically involving the completion of single- (e.g. track-and-field or track cycling events) and multiple-sprint exercises (e.g. team and racquet sports, cycling races), are staged at terrestrial altitudes ranging from 1000 to 2500 m. Our aim was to comprehensively review the current knowledge on the responses to either acute or chronic altitude exposure relevant to single and multiple sprints. Performance of a single sprint is generally not negatively affected by acute exposure to simulated altitude (i.e. normobaric hypoxia) because an enhanced anaerobic energy release compensates for the reduced aerobic adenosine triphosphate production. Conversely, the reduction in air density in terrestrial altitude (i.e. hypobaric hypoxia) leads to an improved sprinting performance when aerodynamic drag is a limiting factor. With the repetition of maximal efforts, however, repeated-sprint ability is more altered (i.e. with earlier and larger performance decrements) at high altitudes (>3000–3600 m or inspired fraction of oxygen <14.4–13.3%) compared with either normoxia or low-to-moderate altitudes (<3000 m or inspired fraction of oxygen >14.4%). Traditionally, altitude training camps involve chronic exposure to low-to-moderate terrestrial altitudes (<3000 m or inspired fraction of oxygen >14.4%) for inducing haematological adaptations. However, beneficial effects on sprint performance after such altitude interventions are still debated. Recently, innovative ‘live low-train high’ methods, in isolation or in combination with hypoxic residence, have emerged with the belief that up-regulated non-haematological peripheral adaptations may further improve performance of multiple sprints compared with similar normoxic interventions.

Background Repeated-sprint training in hypoxia (RSH) is a recent intervention regarding which numerous studies have reported effects on sea-level physical performance outcomes that are debated. No previous study has performed a meta-analysis of the effects of RSH. Objective We systematically reviewed the literature and meta-analyzed the effects of RSH versus repeated-sprint training in normoxia (RSN) on key components of sea-level physical performance, i.e., best and mean (all sprint) performance during repeated-sprint exercise and aerobic capacity (i.e., maximal oxygen uptake [ V ˙ O 2 max ]). Methods The PubMed/MEDLINE, SportDiscus ® , ProQuest, and Web of Science online databases were searched for original articles—published up to July 2016—assessing changes in physical performance following RSH and RSN. The meta-analysis was conducted to determine the standardized mean difference (SMD) between the effects of RSH and RSN on sea-level performance outcomes. Results After systematic review, nine controlled studies were selected, including a total of 202 individuals (mean age 22.6 ± 6.1 years; 180 males). After data pooling, mean performance during repeated sprints (SMD = 0.46, 95% confidence interval [CI] −0.02 to 0.93; P  = 0.05) was further enhanced with RSH when compared with RSN. Although non-significant, additional benefits were also observed for best repeated-sprint performance (SMD = 0.31, 95% CI −0.03 to 0.89; P  = 0.30) and V ˙ O 2 max (SMD = 0.18, 95% CI −0.25 to 0.61; P  = 0.41). Conclusion Based on current scientific literature, RSH induces greater improvement for mean repeated-sprint performance during sea-level repeated sprinting than RSN. The additional benefit observed for best repeated-sprint performance and V ˙ O 2 max for RSH versus RSN was not significantly different.

Acute breath‐holding (apnoea) induces a spleen contraction leading to a transient increase in haemoglobin concentration. Additionally, the apnoea‐induced hypoxia has been shown to lead to an increase in erythropoietin concentration up to 5 h after acute breath‐holding, suggesting long‐term haemoglobin enhancement. Given its potential to improve haemoglobin content, an important determinant for oxygen transport, apnoea has been suggested as a novel training method to improve aerobic performance. This review aims to provide an update on the current state of the literature on this topic. Although the apnoea‐induced spleen contraction appears to be effective in improving oxygen uptake kinetics, this does not seem to transfer into immediately improved aerobic performance when apnoea is integrated into a warm‐up. Furthermore, only long and intense apnoea protocols in individuals who are experienced in breath‐holding show increased erythropoietin and reticulocytes. So far, studies on inexperienced individuals have failed to induce acute changes in erythropoietin concentration following apnoea. As such, apnoea training protocols fail to demonstrate longitudinal changes in haemoglobin mass and aerobic performance. The low hypoxic dose, as evidenced by minor oxygen desaturation, is likely insufficient to elicit a strong erythropoietic response. Apnoea therefore does not seem to be useful for improving aerobic performance. However, variations in apnoea, such as hypoventilation training at low lung volume and repeated‐sprint training in hypoxia through short end‐expiratory breath‐holds, have been shown to induce metabolic adaptations and improve several physical qualities. This shows promise for application of dynamic apnoea in order to improve exercise performance. What is the topic of this review? Apnoea is considered as an innovative method to improve performance. This review discusses the effectiveness of apnoea (training) on performance. What advances does it highlight? Although the apnoea‐induced spleen contraction and the increase in EPO observed in freedivers seem promising to improve haematological variables both acutely and on the long term, they do not improve exercise performance in an athletic population. However, performing repeated sprints on end‐expiratory breath‐holds seems promising to improve repeated‐sprint capacity.

Purpose This study aimed to determine the neuro-mechanical and metabolic adjustments in the lower limbs induced by the running anaerobic sprint test (the so-called RAST). Methods Eight professional football players performed 6 × 35 m sprints interspersed with 10 s of active recovery on artificial turf with their football shoes. Sprinting mechanics (plantar pressure insoles), root mean square activity of the vastus lateralis (VL), rectus femoris (RF), and biceps femoris (BF) muscles (surface electromyography, EMG) and VL muscle oxygenation (near-infrared spectroscopy) were monitored continuously. Results Sprint time, contact time and total stride duration increased from the first to the last repetition (+17.4, +20.0 and +16.6 %; all P  < 0.05), while flight time and stride length remained constant. Stride frequency (−13.9 %; P  < 0.001) and vertical stiffness decreased (−27.2 %; P  < 0.001) across trials. Root mean square EMG activities of RF and BF (−18.7 and −18.1 %; P  < 0.01 and 0.001, respectively), but not VL (−1.2 %; P  > 0.05), decreased over sprint repetitions and were correlated with the increase in running time ( r  = −0.82 and −0.90; both P  < 0.05). Together with a better maintenance of RF and BF muscles activation levels over sprint repetitions, players with a better repeated-sprint performance (lower cumulated times) also displayed faster muscle de- (during sprints) and re-oxygenation (during recovery) rates ( r  = −0.74 and −0.84; P  < 0.05 and 0.01, respectively). Conclusion The repeated anaerobic sprint test leads to substantial alterations in stride mechanics and leg-spring behaviour. Our results also strengthen the link between repeated-sprint ability and the change in neuromuscular activation as well as in muscle de- and re-oxygenation rates.

Near‐infrared spectroscopy (NIRS) has emerged as a potential alternative method for determination of breakpoints equivalent to lactate thresholds. However, the optimal NIRS location remains unclear, particularly in Nordic skiing, which requires both upper‐ and lower‐limb contributions. This study aimed to evaluate the feasibility and accuracy of NIRS‐derived breakpoints determination (i.e., BP1 and BP2) compared to first (LT1) and second (LT2) lactate thresholds and to compare different muscle sites in male and female world‐class Nordic skiers. Fifty‐two world‐class Nordic skiers (29 males, 23 females) performed an incremental treadmill test on roller skis. NIRS sensors were located simultaneously on four muscles: vastus lateralis (VL), biceps femoris (BF), biceps brachii (BB), and triceps brachii (TB). Oxygen saturation (SmO2 ${S_{{\\mathrm{m}}{{\\mathrm{O}}_2}}}$ ) was collected and analysed to detect BP1 and BP2 vs. LT1 and LT2. First, BP1 was too often undetectable or inaccurately detected, suggesting an unsuitable practical use. Second, BP2 was detected in VL (88.5%), BF (96.2%) and BB (86.5%) but not in TB (24.1%). Third, there was a very good accuracy (i.e., bias [95% CI] in heart rate between BP2 and LT2 in VL (−0.6 bpm [−8.9, 7.8]), BF (+1.3 bpm [−2.8, 4.2]) and BB (+1.0 bpm [−7.5, 9.5]). Finally, no significant differences were found between male and female athletes. NIRS appears as an effective non‐invasive method for detecting breakpoint equivalent to LT2 in both male and female world‐class Nordic skiers, especially if positioned on both BB and BF. What is the central question of this study? Can near‐infrared spectroscopy (NIRS) muscle oxygen saturation breakpoints (BP1, BP2) validly replace lactate thresholds (LT1, LT2) in world‐class Nordic skiers? Which muscles provide the best signal (vastus lateralis, biceps femoris, biceps brachii, triceps brachii)? Are there are sex‐related differences? What is the main finding and its importance? BP1 was unreliable, but BP2 closely matched LT2 when measured on biceps femoris and biceps brachii (small heart rate bias, high agreement), while triceps brachii performed poorly. No meaningful sex differences were found, likely due to low adipose tissue thickness in elite athletes. Practically, NIRS offers a non‐invasive field alternative to estimate LT2 in Nordic skiing, with recommended sensor placement on biceps femoris and biceps brachii.

Background Aging is a degenerative process that is associated with an increased risk of diseases. Intermittent hypoxia has been investigated in reference to performance and health-related functions enhancement. This systematic review aimed to summarize the effect of either passive or active intermittent normobaric hypoxic interventions compared with normoxia on health-related outcomes in healthy older adults. Methods Relevant studies were searched from PubMed and Web of Science databases in accordance with PRISMA guidelines (since their inceptions up until August 9, 2022) using the following inclusion criteria: (1) randomized controlled trials, clinical trials and pilot studies; (2) Studies involving humans aged > 50 years old and without any chronic diseases diagnosed; (3) interventions based on in vivo intermittent systemic normobaric hypoxia exposure; (4) articles focusing on the analysis of health-related outcomes (body composition, metabolic, bone, cardiovascular, functional fitness or quality of life). Cochrane Collaboration recommendations were used to assess the risk of bias. Results From 509 articles initially found, 17 studies were included. All interventions were performed in moderate normobaric hypoxia, with three studies using passive exposure, and the others combining intermittent hypoxia with training protocols ( i.e., using resistance-, whole body vibration- or aerobic-based exercise). Conclusions Computed results indicate a limited effect of passive/active intermittent hypoxia (ranging 4–24 weeks, 2–4 days/week, 16–120 min/session, 13–16% of fraction of inspired oxygen or 75–85% of peripheral oxygen saturation) compared to similar intervention in normoxia on body composition, functional fitness, cardiovascular and bone health in healthy older (50–75 years old) adults. Only in specific settings ( i.e., intermediate- or long-term interventions with high intensity/volume training sessions repeated at least 3 days per week), may intermittent hypoxia elicit beneficial effects. Further research is needed to determine the dose–response of passive/active intermittent hypoxia in the elderly. Trial registration . Systematic review registration: PROSPERO 2022 CRD42022338648.