The effect of acute simulated moderate altitude on power, performance and pacing strategies in well-trained cyclists

Independent, additive and interactive effects of acute normobaric hypoxia and cold on submaximal and maximal endurance exercise

PURPOSE

To evaluate the independent and combined effects of hypoxia (FiO2 = 13.5%) and cold (- 20 °C) on physiological and perceptual responses to endurance exercise.

METHODS

14 trained male subjects ( V . O2max: 64 ± 5 mL/kg/min) randomly performed a discontinuous maximal incremental test to exhaustion on a motorized treadmill under four environmental conditions: Normothermic-Normoxia (N), Normothermic-Hypoxia (H), Cold-Normoxia (C) and Cold-Hypoxia (CH). Performance and physiological and perceptual responses throughout exercise were evaluated.

RESULTS

Maximal WorkLoad (WL) and WL at lactate threshold (LT) were reduced in C (- 2.3% and - 3.5%) and H (- 18.0% and - 21.7%) compared to N, with no interactive (p = 0.25 and 0.81) but additive effect in CH (- 21.5% and - 24.6%). Similarly, HRmax and Vemax were reduced in C (- 3.2% and - 14.6%) and H (- 5.0% and - 7%), showing additive effects in CH (- 7.7% and - 16.6%). At LT, additive effect of C (- 2.8%) and H (- 3.8%) on HR reduction in CH (- 5.7%) was maintained, whereas an interactive effect (p = 0.007) of the two stressors combined was noted on Ve (C: - 3.1%, H: + 5.5%, CH: - 10.9%). [La] curve shifted on the left in CH, displaying an interaction effect between the 2 stressors on this parameter. Finally, RPE at LT was exclusively reduced by hypoxia (p < 0.001), whereas TSmax is synergistically reduced by cold and hypoxia (interaction p = 0.047).

CONCLUSION

If compared to single stress exposure, exercise performance and physiological and perceptual variables undergo additive or synergistic effects when cold and hypoxia are combined. These results provide new insight into human physiological responses to extreme environments.

Intermittent hypoxia in sport nutrition, performance, health status and body composition

Introduction

Intermittent hypoxia refers to the discontinuous use of low oxygen levels in normobaric environment. These conditions can be reproduced in hypoxic tents or chambers while the individual is training in different physical activity protocols. Intermittent hypoxia can affect several body systems, impacting nutrition, physical performance, health status and body composition. Therefore, it is necessary to assess protocols, regarding time and frequency of exposure, passive exposure or training in hypoxia, and the simulated altitude. At the molecular level, the hypoxia-inducible factor-1α is the primary factor mediating induction of target genes, including vascular endothelial growth factor and erythropoietin. The goal of these molecular changes is to preserve oxygen supply for cardiac and neuronal function. In addition, hypoxia produces a sympathetic adrenal activation that can increase the resting metabolic rate. Altogether, these changes are instrumental in protocols designed to improve physical performance as well as functional parameters for certain pathological disorders. In addition, nutrition must adapt to the increased energy expenditure. In this last context, performing physical activity in intermittent hypoxia improves insulin sensitivity by increasing the presence of the glucose transporter GLUT-4 in muscle membranes. These changes could also be relevant for obesity and type 2 diabetes treatment. Also, the anorectic effect of intermittent hypoxia modulates serotonin and circulating leptin levels, which may contribute to regulate food intake and favor body weight adaptation for optimal sport performance and health. All these actions suggest that intermittent hypoxia can be a very effective tool in sports training as well as in certain clinical protocols.

Changes in cycling economy and fractional utilization of V̇O2peak during a 40-min maximal effort exercise test with acute hypobaric hypoxia corresponding to 2800 m of altitude

INTRODUCTION

Peak oxygen uptake (V̇O2peak ) declines by ~7% per 1000 m of increasing altitude, whereas exercise performance seems reduced to a lesser extent. For example, 800-10 000 m track and field performances are decreased by 0.4%-2.4% above 1000 m as compared to below and some studies show similar drops in cycling performance. A greater decline in V̇O2peak than in endurance performance with altitude suggests a higher fractional utilization of V̇O2peak (%V̇O2peak ). Therefore, we hypothesized that the %V̇O2peak is higher with acute hypoxic exposure than near sea level.

METHODS

Sixteen lowlanders (8 women, age: 31 ± 7 years [mean ± SD], body mass: 68 ± 8 kg, V̇O2peak : 60 ± 8 mL min-1  kg-1 ) underwent cycling testing in a hypobaric hypoxic chamber on 6 test days, three conducted at 300 m and three at 2800 m of acute altitude. At both altitudes, V̇O2peak was determined, and during a 40-min all out maximal effort time trial (TT), mean power output (MPO) and mean V̇O2 (%V̇O2peak ) were assessed.

RESULTS

V̇O2peak decreased by 11.2 ± 3.0% (p < 0.001), while MPO during the TT declined by 10.7 ± 3.1% (p < 0.001) at 2800 m as compared to 300 m. During the TT, %V̇O2peak was higher at altitude, corresponding to 75.9 ± 4.5% at 300 m and 78.8 ± 4.2% at 2800 m (p = 0.011), and cycling economy (mL O2  kJ-1 ) was poorer (+3.4 ± 2.7%, p < 0.001).

CONCLUSION

The %V̇O2peak was higher during a cycling TT at 2800 m of altitude than near sea level, while cycling economy was poorer. This resulted in a similar reduction in performance and V̇O2peak . Future studies should address the physiological mechanisms underlying the elevated %V̇O2peak .

Arterial desaturation rate does not influence self-selected knee extension force but alters ventilatory response to progressive hypoxia: A pilot study

The absolute magnitude and rate of arterial desaturation each independently impair whole-body aerobic exercise. This study examined potential mechanisms underlying the rate-dependent relationship. Utilizing an exercise protocol involving unilateral, intermittent, isometric knee extensions (UIIKE), we provided sufficient reperfusion time between contractions to reduce the accumulation of intramuscular metabolic by-products that typically stimulate muscle afferents. The objective was to create a milieu conducive to accentuating any influence of arterial desaturation rate on muscular fatigue. Eight participants completed four UIIKE sessions, performing one 3 s contraction every 30s at a perceived intensity of 50% MVC for 25 min. Participants voluntarily adjusted their force generation to maintain perceptual effort at 50% MVC without feedback. Reductions in inspired oxygen fraction (FI O2 ) decreased arterial saturation from >98% to 70% with varying rates in three trials: FAST (5.3 ± 1.3 min), MED (11.8 ± 2.7 min), and SLOW (19.9 ± 3.7 min). FI O2 remained at 0.21 during the control trial. Force generation and muscle activation remained at baseline levels throughout UIIKE trials, unaffected by the magnitude or rate of desaturation. Minute ventilation increased with hypoxia (p < 0.05), and faster desaturation rates magnified this response. These findings demonstrate that arterial desaturation magnitude and rate independently affect ventilation, but do not influence fatigue development during UIIKE.

Travel related changes in performance and physiological markers: the effects of eastward travel on female basketball players

[Purpose] Purpose of this study is to measure the changes in various physiological markers and performance criteria for women basketball players over the course of a travel heavy season. [Participants and Methods] Fifty one Division-II female basketball players and a control group of 54 females joined this study. Measurements began at the beginning of the competitive season and concluded with final measurements at the end of the competitive season. [Results] The female basketball players showed noticeable increases in resting salivary cortisol, visceral trunk fat, resting heart rate, and resting blood pressure. These athletes also showed diminishment in isokinetic force of leg muscles, particularly in knee flexion strength. Vertical jump measurements also indicated a slight diminishment. In contrast, the control group experienced none of the same changes. [Conclusion] Over the course of a grueling flight schedule in combination with a full-length basketball season, the female athletes in this study showed significant declinations in many indicators of overall health. It is concluded that resulting prolonged intermittent stress of a travel-heavy season can lead to significant changes in certain physiological markers with notable decreases in isokinetic force of leg muscle.

Brain-muscle interplay during endurance self-paced exercise in normobaric and hypobaric hypoxia

Purpose: Hypoxia is one major environmental factor, supposed to mediate central motor command as well as afferent feedbacks at rest and during exercise. By using a comparison of normobaric (NH) and hypobaric (HH) hypoxia with the same ambient pressure in oxygen, we examined the potential differences on the cerebrovascular and muscular regulation interplay during a self-paced aerobic exercise.

Methods: Sixteen healthy subjects performed three cycling time-trials (250 kJ) in three conditions: HH, NH and normobaric normoxia (NN) after 24 h of exposure. Cerebral and muscular oxygenation were assessed by near-infrared spectroscopy, cerebral blood flow by Doppler ultrasound system. Gas exchanges, peripheral oxygen saturation, power output and associated pacing strategies were also continuously assessed.

Results: The cerebral oxygen delivery was lower in hypoxia than in NN but decreased similarly in both hypoxic conditions. Overall performance and pacing were significantly more down-regulated in HH versus NH, in conjunction with more impaired systemic (e.g. saturation and cerebral blood flow) and prefrontal cortex oxygenation during exercise.

Conclusions: The difference in pacing was likely the consequence of a complex interplay between systemic alterations and cerebral oxygenation observed in HH compared to NH, aiming to maintain an equivalent cerebral oxygen delivery despite higher adaptive cost (lower absolute power output for the same relative exercise intensity) in HH compared to NH.

Altitude and Endurance Performance in Altitude Natives versus Lowlanders: Insights from Professional Cycling

INTRODUCTION

Acute altitude exposure influences exercise performance, although most research, especially regarding altitude natives, comes from laboratory data in nonathletes.

PURPOSE

We analyzed the influence of altitude on real-world cycling performance in top-level professional cyclists attending to whether they were altitude natives or not.

METHODS

Thirty-three male cyclists (29 ± 5 yr) were studied and were classified as lowlanders (n = 19) or altitude natives (n = 14) attending to the altitude of their place of birth (431 ± 380 and 2583 ± 334 meters above sea level (m a.s.l.), respectively). Both groups included top 3 finishers (including winners) in the general classification of Grand Tours and major races. Using data from both training and competitions during years 2013-2020 (8 ± 5 seasons per cyclist), we registered participants' mean maximal power (MMP) for efforts lasting 5 s, 30 s, 5 min, and 10 min, respectively, at altitudes ranging from 0-500 to >2000 m a.s.l.

RESULTS

A significant altitude-MMP interaction effect (two-factor repeated-measures ANOVA) was found in lowlanders (P < 0.001) but not in altitude natives (P = 0.150). In lowlanders, individual performance decreased in a dose-response manner with increasing altitudes compared with sea (or near-sea) level (0-500 m a.s.l.), whereas this trend was much less evident in natives. A significant altitude-MMP-group effect was found (P < 0.001), with nonsignificant (and overall trivial-to-small differences) between lowlanders and altitude natives for any effort duration at altitudes ≤1500 m a.s.l. but with significant differences at higher altitudes (≥1501 m a.s.l.).

CONCLUSIONS

Acute altitude exposure influences real-world performance differently in low landers and altitude natives, which might confer a competitive advantage to the latter, particularly in races including efforts at >1500 m a.s.l.

JA, Duque L, Chaves-Gomez S, Cristancho-Mejía E, Schmidt WFJ. Hemoglobin Mass, Blood Volume and VO2max of Trained and Untrained Children and Adolescents Living at Different Altitudes

Introduction: To a considerable extent, the magnitude of blood volume (BV) and hemoglobin mass (Hbmass) contribute to the maximum O2-uptake (VO2max), especially in endurance-trained athletes. However, the development of Hbmass and BV and their relationships with VO2max during childhood are unknown. The aim of the present cross-sectional study was to investigate Hbmass and BV and their relationships with VO2max in children and adolescents. In addition, the possible influence of endurance training and chronic hypoxia was evaluated.

Methods: A total of 475 differently trained children and adolescents (girls n = 217, boys n = 258; untrained n = 171, endurance trained n = 304) living at two different altitudes (∼1,000 m, n = 204, ∼2,600 m, n = 271) and 9–18 years old participated in the study. The stage of puberty was determined according to Tanner; Hbmass and BV were determined by CO rebreathing; and VO2max was determined by cycle ergometry and for runners on the treadmill.

Results: Before puberty, there was no association between training status and Hbmass or BV. During and after puberty, we found 7–10% higher values in the trained groups. Living at a moderate altitude had a uniformly positive effect of ∼7% on Hbmass in all groups and no effect on BV. The VO2max before, during and after puberty was strongly associated with training (pre/early puberty: boys +27%, girls +26%; mid puberty: +42% and +45%; late puberty: +43% and +47%) but not with altitude. The associated effects of training in the pre/early pubertal groups were independent of Hbmass and BV, while in the mid- and late pubertal groups, 25% of the training effect could be attributed to the elevated Hbmass.

Conclusions: The associated effects of training on Hbmass and BV, resulting in increased VO2max, can only be observed after the onset of puberty.

Effects of Short-Term Phosphate Loading on Aerobic Capacity under Acute Hypoxia in Cyclists: A Randomized, Placebo-Controlled, Crossover Study

The aim of this study was to evaluate the effects of sodium phosphate (SP) supplementation on aerobic capacity in hypoxia. Twenty-four trained male cyclists received SP (50 mg·kg-1 of FFM/day) or placebo for six days in a randomized, crossover study, with a three-week washout period between supplementation phases. Before and after each supplementation phase, the subjects performed an incremental exercise test to exhaustion in hypoxia (FiO2 = 16%). Additionally, the levels of 2,3-diphosphoglycerate (2,3-DPG), hypoxia-inducible factor 1 alpha (HIF-1α), inorganic phosphate (Pi), calcium (Ca), parathyroid hormone (PTH) and acid-base balance were determined. The results showed that phosphate loading significantly increased the Pi level by 9.0%, whereas 2,3-DPG levels, hemoglobin oxygen affinity, buffering capacity and myocardial efficiency remained unchanged. The aerobic capacity in hypoxia was not improved following SP. Additionally, our data revealed high inter-individual variability in response to SP. Therefore, the participants were grouped as Responders and Non-Responders. In the Responders, a significant increase in aerobic performance in the range of 3-5% was observed. In conclusion, SP supplementation is not an ergogenic aid for aerobic capacity in hypoxia. However, in certain individuals, some benefits can be expected, but mainly in athletes with less training-induced central and/or peripheral adaptation.

The Effects of Sodium Phosphate Supplementation on the Cardiorespiratory System and Gross Efficiency during Exercise under Hypoxia in Male Cyclists: A Randomized, Placebo-Controlled, Cross-Over Study

The main aim of this study was to evaluate the effects of six days of tri-sodium phosphate (SP) supplementation on the cardiorespiratory system and gross efficiency (GE) during exercise under hypoxia in cyclists. Twenty trained male cyclists received SP (50 mg·kg⁻¹ of fat-free mass/day) or placebo for six days in a randomized, cross-over study, with a three-week washout period between supplementation phases. Before and after each supplementation phase, the subjects performed an incremental exercise test to exhaustion under normobaric hypoxia (FiO₂ = 16%, ~2500 m). It was observed that short-term SP supplementation led to a decrease in heart rate, an increase in stroke volume, and an improvement in oxygen pulse (VO₂/HR) during low and moderate-intensity exercise under hypoxia. These changes were accompanied by an increase in the serum inorganic phosphate level by 8.7% (p < 0.05). No significant changes were observed in serum calcium levels. GE at a given workload did not change significantly after SP supplementation. These results indicated that SP promotes improvements in the efficiency of the cardiorespiratory system during exercise in a hypoxic environment. Thus, SP supplementation may be beneficial for endurance exercise in hypoxia.

Red Blood Cell 2,3-Diphosphoglycerate Decreases in Response to a 30 km Time Trial Under Hypoxia in Cyclists

Red blood cell 2,3-diphosphoglycerate (2,3-DPG) is one of the factors of rightward-shifted oxygen dissociation curves and decrease of Hb-O₂ affinity. The reduction of Hb-O₂ affinity is beneficial to O₂ unloading at the tissue level. In the current literature, there are no studies about the changes in 2,3-DPG level following acute exercise in moderate hypoxia in athletes. For this reason, the aim of this study was to analyze the effect of prolonged intense exercise under normoxic and hypoxic conditions on 2,3-DPG level in cyclists. Fourteen male trained cyclists performed a simulation of a 30 km time trial (TT) in normoxia and normobaric hypoxia (FiO₂ = 16.5%, ~2,000 m). During the TT, the following variables were measured: power, blood oxygen saturation (SpO₂), and heart rate (HR). Before and immediately after exercise, the blood level of 2,3-DPG and acid–base equilibrium were determined. The results showed that the mean SpO₂ during TT in hypoxia was 8% lower than in normoxia. The reduction of SpO₂ in hypoxia resulted in a decrease of average power by 9.6% (p < 0.001) and an increase in the 30 km TT completion time by 3.8% (p < 0.01) compared to normoxia. The exercise in hypoxia caused a significant (p < 0.001) decrease in 2,3-DPG level by 17.6%. After exercise in normoxia, a downward trend of 2,3-DPG level was also observed, but this effect was not statistically significant. The analysis also revealed that changes of acid–base balance were significantly larger (p < 0.05) after exercise in hypoxia than in normoxia. In conclusion, intense exercise in hypoxic conditions leads to a decrease in 2,3-DPG concentration, primarily due to exercise-induced acidosis.

Effect of hypoxic exercise on glucose tolerance in healthy and prediabetic adults

This study aimed to investigate the mechanisms known to regulate glucose homeostasis in human skeletal muscle of healthy and prediabetic subjects exercising in normobaric hypoxia. Seventeen healthy (H; 28.8 ± 2.4 yr; maximal oxygen consumption (V̇O_2max): 45.1 ± 1.8 mL·kg^-1·min^-1) and 15 prediabetic (P; 44.6 ± 3.9 yr; V̇O_2max: 30.8 ± 2.5 mL·kg^-1·min^-1) men were randomly assigned to two groups performing an acute exercise bout (heart rate corresponding to 55% V̇O_2max) either in normoxic (NE) or in hypoxic (HE; fraction of inspired oxygen [Formula: see text] 14.0%) conditions. An oral glucose tolerance test (OGTT) was performed in a basal state and after an acute exercise bout. Muscle biopsies from m. vastus lateralis were taken before and after exercise. Venous blood samples were taken at regular intervals before, during, and after exercise. The two groups exercising in hypoxia had a larger area under the curve of blood glucose levels during the OGTT after exercise compared with baseline (H: +11%; P: +4%). Compared with pre-exercise, an increase in p-TBC1D1 Ser237 and in p-AMPK Thr172 was observed postexercise in P NE (+95%; +55%, respectively) and H HE (+91%; +43%, respectively). An increase in p-ACC Ser212 was measured after exercise in all groups (H NE: +228%; P NE: +252%; H HE: +252%; P HE: +208%). Our results show that an acute bout of exercise in hypoxia reduces glucose tolerance in healthy and prediabetic subjects. At a molecular level, some adaptations regulating glucose transport in muscle were found in all groups without associations with glucose tolerance after exercise. The results suggest that hypoxia negatively affects glucose tolerance postexercise through unidentified mechanisms.NEW & NOTEWORTHY The molecular mechanisms involved in glucose tolerance after acute exercise in hypoxia have not yet been elucidated in human. Due to the reversible character of their status, prediabetic individuals are of particular interest for preventing the development of type 2 diabetes. The present study is the first to investigate muscle molecular mechanisms during exercise and glucose metabolism after exercise in prediabetic and healthy subjects exercising in normoxia and normobaric hypoxia.

Inter- and intra-unit reliability of the COSMED K5: Implications for multicentric and longitudinal testing

Purpose

To evaluate the intra-unit (REL_INTRA) and inter-unit reliability (REL_INTER) of two structurally identical units of the metabolic analyser K5 (COSMED, Rome, Italy) that allows to utilize either breath-by-breath (BBB) or dynamic mixing chamber (DMC) technology.

Methods

Identical flow- and gas-signals were transmitted to both K5s that always operated simultaneously either in BBB- or DMC-mode. To assess REL_INTRA and REL_INTER, a metabolic simulator was applied to simulate four graded levels of respiration. REL_INTRA and REL_INTER were expressed as typical error (TE%) and Intraclass Correlation Coefficient (ICC). To assess also inter-unit differences via natural respiratory signals, 12 male athletes performed one incremental bike step test each in BBB- and DMC-mode. Inter-unit differences within biological testing were expressed as percentages.

Results

In BBB, TE% of REL_INTRA ranged 0.30–0.67 vs. REL_INTER 0.16–1.39 and ICC ranged 0.57–1.00 vs. 0.09–1.00. In DMC, TE% of REL_INTRA ranged 0.38–0.90 vs. REL_INTER 0.03–0.86 and ICC ranged 0.22–1.00 vs. 0.52–1.00. Mean inter-unit differences ranged -2.30–2.20% (Cohen’s ds (ds) 0.13–1.52) for BBB- and -0.55–0.61% (ds 0.00–0.65) for DMC-mode, respectively. Inter-unit differences for V˙O2 and RER were significant (p < 0.05) at each step.

Conclusion

Two structurally identical K5-units demonstrated accurate REL_INTRA with TE < 2.0% and similar REL_INTER during metabolic simulation. During biological testing, inter-unit differences for V˙O2 and RER in BBB-mode were higher than 2% with partially large ES in BBB. Hence, the K5 should be allocated personally wherever possible. Otherwise, e.g. in multicenter studies, a decrease in total reliability needs to be considered especially when the BBB-mode is applied.

Variations in exercise ventilation in hypoxia will affect oxygen uptake

Reports of VO2 response differences between normoxia and hypoxia during incremental exercise do not agree. In this study VO2 and VE were obtained from 15-s averages at identical work rates during continuous incremental cycle exercise in 8 subjects under ambient pressure (633 mmHg ≈1,600 m) and during duplicate tests in acute hypobaric hypoxia (455 mmHg ≈4,350 m), ranging from 49 to 100% of VO2 peak in hypoxia and 42-87% of VO2 peak in normoxia. The average VO2 was 96 mL/min (619 mL) lower at 455 mmHg (n.s. P = 0.15) during ramp exercises. Individual response points were better described by polynomial than linear equations (mL/min/W). The VE was greater in hypoxia, with marked individual variation in the differences which correlated significantly and directly with the VO2 difference between 455 mmHg and 633 mmHg (P = 0.002), likely related to work of breathing (Wb). The greater VE at 455 mmHg resulted from a greater breathing frequency. When a subject's hypoxic ventilatory response is high, the extra work of breathing reduces mechanical efficiency (E). Mean ∆E calculated from individual linear slopes was 27.7 and 30.3% at 633 and 455 mmHg, respectively (n.s.). Gross efficiency (GE) calculated from mean VO2 and work rate and correcting for Wb from a VE-VO2 relationship reported previously, gave corresponding values of 20.6 and 21.8 (P = 0.05). Individual variation in VE among individuals overshadows average trends, as also apparent from other reports comparing hypoxia and normoxia during progressive exercise and must be considered in such studies.

Effects of an Acute Pilates Program under Hypoxic Conditions on Vascular Endothelial Function in Pilates Participants: A Randomized Crossover Trial

This study aimed to compare the effects of an acute Pilates program under hypoxic vs. normoxic conditions on the metabolic, cardiac, and vascular functions of the participants. Ten healthy female Pilates experts completed a 50-min tubing Pilates program under normoxic conditions (N trial) and under 3000 m (inspired oxygen fraction = 14.5%) hypobaric hypoxia conditions (H trial) after a 30-min exposure in the respective environments on different days. Blood pressure, branchial ankle pulse wave velocity, and flow-mediated dilation (FMD) in the branchial artery were measured before and after the exercise. Metabolic parameters and cardiac function were assessed every minute during the exercise. Both trials showed a significant increase in FMD; however, the increase in FMD was significantly higher after the H trial than that after the N trial. Furthermore, FMD before exercise was significantly higher in the H trial than in the N trial. In terms of metabolic parameters, minute ventilation, carbon dioxide excretion, respiratory exchange ratio, and carbohydrate oxidation were significantly higher but fat oxidation was lower during the H trial than during the N trial. In terms of cardiac function, heart rate was significantly increased during the H trial than during the N trial. Our results suggested that, compared to that under normoxic conditions, Pilates exercise under hypoxic conditions led to greater metabolic and cardiac responses and also elicited an additive effect on vascular endothelial function.

Muscle Oxygenation During Hypoxic Exercise in Children and Adults

INTRODUCTION

While hypoxia is known to decrease peak oxygen uptake ( V . ⁢ o _{2 max}) and maximal power output in both adults and children its influence on submaximal exercise cardiorespiratory and, especially, muscle oxygenation responses remains unclear.

METHODS

Eight pre-pubertal boys (age = 8 ± 2 years.; body mass (BM) = 29 ± 7 kg) and seven adult males (age = 39 ± 4 years.; BM = 80 ± 8 kg) underwent graded exercise tests in both normoxic (P_iO₂ = 134 ± 0.4 mmHg) and hypoxic (P_iO₂ = 105 ± 0.6 mmHg) condition. Continuous breath-by-breath gas exchange and near infrared spectroscopy measurements, to assess the vastus lateralis oxygenation, were performed during both tests. The gas exchange threshold (GET) and muscle oxygenation thresholds were subsequently determined for both groups in both conditions.

RESULTS

In both groups, hypoxia did not significantly alter either GET or the corresponding V . ⁢ o ₂ at GET. In adults, higher V . _E levels were observed in hypoxia (45 ± 6 l/min) compared to normoxia (36 ± 6 l/min, p < 0.05) at intensities above GET. In contrast, in children both the hypoxic V . _E and V . ⁢ o ₂ responses were significantly greater than those observed in normoxia only at intensities below GET (p < 0.01 for V . _E and p < 0.05 for V . ⁢ o ₂). Higher exercise-related heart rate (HR) levels in hypoxia, compared to normoxia, were only noted in adults (p < 0.01). Interestingly, hypoxia per se did not influence the muscle oxygenation thresholds during exercise in neither group. However, and in contrast to adults, the children exhibited significantly higher total hemoglobin concentration during hypoxic as compared to normoxic exercise (tHb) at lower exercise intensities (30 and 60 W, p = 0.01).

CONCLUSION

These results suggest that in adults, hypoxia augments exercise ventilation at intensities above GET and might also maintain muscle blood oxygenation via increased HR. On the other hand, children exhibit a greater change of muscle blood perfusion, oxygen uptake as well as ventilation at exercise intensities below GET.

Cycling at Altitude: Lower Absolute Power Output as the Main Cause of Lower Gross Efficiency

BACKGROUND

Although cyclists often compete at altitude, the effect of altitude on gross efficiency (GE) remains inconclusive.

PURPOSE

To investigate the effect of altitude on GE at the same relative exercise intensity and at the same absolute power output (PO) and to determine the effect of altitude on the change in GE during high-intensity exercise.

METHODS

Twenty-one trained men performed 3 maximal incremental tests and 5 GE tests at sea level, 1500 m, and 2500 m of acute simulated altitude. The GE tests at altitude were performed once at the same relative exercise intensity and once at the same absolute PO as at sea level.

RESULTS

Altitude resulted in an unclear effect at 1500 m (-3.8%; ±3.3% [90% confidence limit]) and most likely negative effect at 2500 m (-6.3%; ±1.7%) on pre-GE, when determined at the same relative exercise intensity. When pre-GE was determined at the same absolute PO, unclear differences in GE were found (-1.5%; ±2.6% at 1500 m; -1.7%; ±2.4% at 2500 m). The effect of altitude on the decrease in GE during high-intensity exercise was unclear when determined at the same relative exercise intensity (-0.4%; ±2.8% at 1500 m; -0.7%; ±1.9% at 2500 m). When GE was determined at the same absolute PO, altitude resulted in a substantially smaller decrease in GE (2.8%; ±2.4% at 1500 m; 5.5%; ±2.9% at 2500 m).

CONCLUSION

The lower GE found at altitude when exercise is performed at the same relative exercise intensity is mainly caused by the lower PO at which cyclists exercise.

The Potential to Change Pacing and Performance During 4000-m Cycling Time Trials Using Hyperoxia and Inspired Gas-Content Deception

PURPOSE

Determine if a series of trials with fraction of inspired oxygen (FiO2) content deception could improve 4000-m cycling time-trial (TT) performance.

METHODS

Fifteen trained male cyclists (mean ± SD: body mass 74.2 ± 8.0 kg; peak oxygen uptake 62 ± 6 mL.kg-1.min-1) completed six, 4000-m cycling TTs in a semi-randomised order. After a familiarisation TT, cyclists were informed in two initial trials they were inspiring normoxic air (NORM, FiO2: 0.21), however in one trial (deception condition) they inspired hyperoxic air (NORM-DEC, FiO2: 0.36). During two subsequent TTs, cyclists were informed they were inspiring hyperoxic air (HYPER, FiO2: 0.36), but in one trial normoxic air was inspired (HYPER-DEC). In the final TT (NORM-INFORM) the deception was revealed, and cyclists were asked to reproduce their best TT performance while inspiring normoxic air.

RESULTS

Greater power output and faster performances occurred when cyclists inspired hyperoxic air in both truthful (HYPER) and deceptive (NORM-DEC) trials compared to NORM (P < 0.001). However, performance only improved in NORM-INFORM (377 W [95% CI 325, 429]) vs NORM (352 W [299, 404]), P < 0.001) when participants (n = 4) completed the trials in the following order: NORM-DEC, NORM, HYPER-DEC, HYPER.

CONCLUSIONS

Cycling performance improved with acute exposure to hyperoxia. Mechanisms for the improvement were likely physiological, however improvement in a deception trial suggests an additional placebo effect may be present. Finally, a particular sequence of oxygen deception trials may have built psycho-physiological belief in cyclists such that performance improved in a subsequent normoxic trial.

Delayed parasympathetic reactivation and sympathetic withdrawal following maximal cardiopulmonary exercise testing (CPET) in hypoxia

PURPOSE

This study investigated the effects of acute hypoxic exposure on post-exercise cardiac autonomic modulation following maximal cardiopulmonary exercise testing (CPET).

METHODS

Thirteen healthy men performed CPET and recovery in normoxia (N) and normobaric hypoxia (H) (FiO₂ = 13.4%, ≈ 3500 m). Post-exercise cardiac autonomic modulation was assessed during recovery (300 s) through the analysis of fast-phase and slow-phase heart rate recovery (HRR) and heart rate variability (HRV) indices.

RESULTS

Both short-term, T30 (mean difference (MD) 60.0 s, 95% CI 18.2-101.8, p = 0.009, ES 1.01), and long-term, HRRt (MD 21.7 s, 95% CI 4.1-39.3, p = 0.020, ES 0.64), time constants of HRR were higher in H. Fast-phase (30 and 60 s) and slow-phase (300 s) HRR indices were reduced in H either when expressed in bpm or in percentage of HR_peak (p < 0.05). Chronotropic reserve recovery was lower in H than in N at 30 s (MD - 3.77%, 95% CI - 7.06 to - 0.49, p = 0.028, ES - 0.80) and at 60 s (MD - 7.23%, 95% CI - 11.45 to - 3.01, p = 0.003, ES - 0.81), but not at 300 s (p = 0.436). Concurrently, Ln-RMSSD was reduced in H at 60 and 90 s (p < 0.01) but not at other time points during recovery (p > 0.05).

CONCLUSIONS

Affected fast-phase, slow-phase HRR and HRV indices suggested delayed parasympathetic reactivation and sympathetic withdrawal after maximal exercise in hypoxia. However, a similar cardiac autonomic recovery was re-established within 5 min after exercise cessation. These findings have several implications in cardiac autonomic recovery interpretation and in HR assessment in response to high-intensity hypoxic exercise.

Limitation of Maximal Heart Rate in Hypoxia: Mechanisms and Clinical Importance

The use of exercise intervention in hypoxia has grown in popularity amongst patients, with encouraging results compared to similar intervention in normoxia. The prescription of exercise for patients largely rely on heart rate recordings (percentage of maximal heart rate (HR_max) or heart rate reserve). It is known that HR_max decreases with high altitude and the duration of the stay (acclimatization). At an altitude typically chosen for training (2,000-3,500 m) conflicting results have been found. Whether or not this decrease exists or not is of importance since the results of previous studies assessing hypoxic training based on HR may be biased due to improper intensity. By pooling the results of 86 studies, this literature review emphasizes that HR_max decreases progressively with increasing hypoxia. The dose–response is roughly linear and starts at a low altitude, but with large inter-study variabilities. Sex or age does not seem to be a major contributor in the HR_max decline with altitude. Rather, it seems that the greater the reduction in arterial oxygen saturation, the greater the reduction in HRmax, due to an over activity of the parasympathetic nervous system. Only a few studies reported HR_max at sea/low level and altitude with patients. Altogether, due to very different experimental design, it is difficult to draw firm conclusions in these different clinical categories of people. Hence, forthcoming studies in specific groups of patients are required to properly evaluate (1) the HR_max change during acute hypoxia and the contributing factors, and (2) the physiological and clinical effects of exercise training in hypoxia with adequate prescription of exercise training intensity if based on heart rate.

Sodium bicarbonate supplementation improves severe-intensity intermittent exercise under moderate acute hypoxic conditions

Acute moderate hypoxic exposure can substantially impair exercise performance, which occurs with a concurrent exacerbated rise in hydrogen cation (H⁺) production. The purpose of this study was therefore, to alleviate this acidic stress through sodium bicarbonate (NaHCO₃) supplementation and determine the corresponding effects on severe-intensity intermittent exercise performance. Eleven recreationally active individuals participated in this randomised, double-blind, crossover study performed under acute normobaric hypoxic conditions (FiO₂% = 14.5%). Pre-experimental trials involved the determination of time to attain peak bicarbonate anion concentrations ([HCO₃⁻]) following NaHCO₃ ingestion. The intermittent exercise tests involved repeated 60-s work in their severe-intensity domain and 30-s recovery at 20 W to exhaustion. Participants ingested either 0.3 g kg bm⁻¹ of NaHCO₃ or a matched placebo of 0.21 g kg bm⁻¹ of sodium chloride prior to exercise. Exercise tolerance (+ 110.9 ± 100.6 s; 95% CI 43.3–178 s; g = 1.0) and work performed in the severe-intensity domain (+ 5.8 ± 6.6 kJ; 95% CI 1.3–9.9 kJ; g = 0.8) were enhanced with NaHCO₃ supplementation. Furthermore, a larger post-exercise blood lactate concentration was reported in the experimental group (+ 4 ± 2.4 mmol l⁻¹; 95% CI 2.2–5.9; g = 1.8), while blood [HCO₃⁻] and pH remained elevated in the NaHCO₃ condition throughout experimentation. In conclusion, this study reported a positive effect of NaHCO₃ under acute moderate hypoxic conditions during intermittent exercise and therefore, may offer an ergogenic strategy to mitigate hypoxic induced declines in exercise performance.

Cerebrocortical activity during self-paced exercise in temperate, hot and hypoxic conditions

AIM

Heat stress and hypoxia independently influence cerebrocortical activity and impair prolonged exercise performance. This study examined the relationship between electroencephalography (EEG) activity and self-paced exercise performance in control (CON, 18 °C, 40% RH), hot (HOT, 35 °C, 60% RH) and hypoxic (HYP, 18 °C, 40% RH FiO₂ : 0.145) conditions.

METHODS

Eleven well-trained cyclists completed a 750 kJ cycling time trial in each condition on separate days in a counterbalanced order. EEG activity was recorded with α- and β-activity evaluated in the frontal (F3 and F4) and central (C3 and C4) areas. Standardized low-resolution brain electromagnetic tomography (sLORETA) was also utilized to localize changes in cerebrocortical activity.

RESULTS

Both α- and β-activity decreased in the frontal and central areas during exercise in HOT relative to CON (P < 0.05). α-activity was also lower in HYP compared with CON (P < 0.05), whereas β-activity remained similar. β-activity was higher in HYP than in HOT (P < 0.05). sLORETA revealed that α- and β-activity increased at the onset of exercise in the primary somatosensory and motor cortices in CON and HYP, while only β-activity increased in HOT. A decrease in α- and β-activity occurred thereafter in all conditions, with α-activity being lower in the somatosensory and somatosensory association cortices in HOT relative to CON.

CONCLUSION

High-intensity prolonged self-paced exercise induces cerebrocortical activity alterations in areas of the brain associated with the ability to inhibit conflicting attentional processing under hot and hypoxic conditions, along with the capacity to sustain mental readiness and arousal under heat stress.

Quantifying the effects of acute hypoxic exposure on exercise performance and capacity: A systematic review and meta-regression

OBJECTIVE

To quantify the effects of acute hypoxic exposure on exercise capacity and performance, which includes continuous and intermittent forms of exercise.

DESIGN

A systematic review was conducted with a three-level mixed effects meta-regression. The ratio of means method was used to evaluate main effects and moderators providing practical interpretations with percentage change.

DATA SOURCES

A systemic search was performed using three databases (Google scholar, PubMed and SPORTDiscus). Eligibility criteria for selecting studies: Inclusion was restricted to investigations that assessed exercise performance (time trials (TTs), sprint and intermittent exercise tests) and capacity (time to exhaustion test, TTE) with acute hypoxic (<24 h) exposure and a normoxic comparator.

RESULTS

Eighty-two outcomes from 53 studies (N = 798) were included in this review. The results show an overall reduction in exercise performance/capacity -17.8 ± 3.9% (95% CI -22.8% to -11.0%), which was significantly moderated by -6.5 ± 0.9% per 1000 m altitude elevation (95% CI -8.2% to -4.8%) and oxygen saturation (-2.0 ± 0.4%; 95% CI -2.9% to -1.2%). TT (-16.2 ± 4.3%; 95% CI -22.9% to -9%) and TTE (-44.5 ± 6.9%; 95% CI -51.3% to -36.7%) elicited a negative effect, whilst indicating a quadratic relationship between hypoxic magnitude and both TTE and TT performance. Furthermore, exercise less than 2 min exhibited no ergolytic effect from acute hypoxia. Summary/Conclusion: This review highlights the ergolytic effect of acute hypoxic exposure, which is curvilinear for TTE and TT performance with increasing hypoxic levels, but short duration intermittent and sprint exercise seem to be unaffected.

Acute Normobaric Hypoxia Increases Post-exercise Lipid Oxidation in Healthy Males

The primary objective of the current study was to determine the effect of moderate normobaric hypoxia exposure during constant load cycling on post-exercise energy metabolism recorded in normoxia. Indirect calorimetry was used to examine whole body substrate oxidation before, during, 40–60 min post, and 22 h after performing 60 min of cycling exercise at two different fractions of inspired oxygen (F_IO₂): (i) F_IO₂ = 0.2091 (normoxia) and (ii) F_IO₂ = 0.15 (hypoxia). Seven active healthy male participants (26 ± 4 years of age) completed both experimental trials in randomized order with a 7-day washout period to avoid carryover effects between conditions. Resting energy expenditure was initially elevated following cycling exercise in normoxia and hypoxia (Δ 0.14 ± 0.05, kcal min⁻¹, p = 0.037; Δ 0.19 ± 0.03 kcal min⁻¹, p < 0.001, respectively), but returned to baseline levels the next morning in both conditions. Although, the same absolute workload was used in both environmental conditions (157 ± 10 W), a shift in resting substrate oxidation occurred after exercise performed in hypoxia while post-exercise measurements were similar to baseline after cycling exercise in normoxia. The additional metabolic stress of hypoxia exposure was sufficient to increase the rate of lipid oxidation (Δ 42 ± 11 mg min⁻¹, p = 0.019) and tended to suppress carbohydrate oxidation (Δ −55 ± 26 mg min⁻¹, p = 0.076) 40–60 min post-exercise. This shift in substrate oxidation persisted the next morning, where lipid oxidation remained elevated (Δ 9 ± 3 mg min⁻¹, p = 0.0357) and carbohydrate oxidation was suppressed (Δ −22 ± 6 mg min⁻¹, p = 0.019). In conclusion, prior exercise performed under moderate normobaric hypoxia alters post-exercise energy metabolism. This is an important consideration when evaluating the metabolic consequences of hypoxia exposure during prolonged exercise, and future studies should evaluate its role in the beneficial effects of intermittent hypoxia training observed in persons with obesity and insulin resistance.

Prediction of Critical Power and W' in Hypoxia: Application to Work-Balance Modelling

Purpose: Develop a prediction equation for critical power (CP) and work above CP (W′) in hypoxia for use in the work-balance (WBAL′) model.

Methods: Nine trained male cyclists completed cycling time trials (TT; 12, 7, and 3 min) to determine CP and W′ at five altitudes (250, 1,250, 2,250, 3,250, and 4,250 m). Least squares regression was used to predict CP and W′ at altitude. A high-intensity intermittent test (HIIT) was performed at 250 and 2,250 m. Actual and predicted CP and W′ were used to compute W′ during HIIT using differential (WBALdiff′) and integral (WBALint′) forms of the WBAL′ model.

Results: CP decreased at altitude (P < 0.001) as described by 3rd order polynomial function (R² = 0.99). W′ decreased at 4,250 m only (P < 0.001). A double-linear function characterized the effect of altitude on W′ (R² = 0.99). There was no significant effect of parameter input (actual vs. predicted CP and W′) on modelled WBAL′ at 2,250 m (P = 0.24). WBALdiff′ returned higher values than WBALint′ throughout HIIT (P < 0.001). During HIIT, WBALdiff′ was not different to 0 kJ at completion, at 250 m (0.7 ± 2.0 kJ; P = 0.33) and 2,250 m (−1.3 ± 3.5 kJ; P = 0.30). However, WBALint′ was lower than 0 kJ at 250 m (−0.9 ± 1.3 kJ; P = 0.058) and 2,250 m (−2.8 ± 2.8 kJ; P = 0.02).

Conclusion: The altitude prediction equations for CP and W′ developed in this study are suitable for use with the WBAL′ model in acute hypoxia. This enables the application of WBAL′ modelling to training prescription and competition analysis at altitude.

Determinants of curvature constant (W') of the power duration relationship under normoxia and hypoxia: the effect of pre-exercise alkalosis

Purpose

This study investigated the effect of induced alkalosis on the curvature constant (W’) of the power-duration relationship under normoxic and hypoxic conditions.

Methods

Eleven trained cyclists (mean ± SD) Age: 32 ± 7.2 years; body mass (bm): 77.0 ± 9.2 kg; VO_2peak: 59.2 ± 6.8 ml·kg⁻¹·min⁻¹ completed seven laboratory visits which involved the determination of individual time to peak alkalosis following sodium bicarbonate (NaHCO₃) ingestion, an environment specific ramp test (e.g. normoxia and hypoxia) and four x 3 min critical power (CP) tests under different experimental conditions. Participants completed four trials: alkalosis normoxia (ALN); placebo normoxia (PLN); alkalosis hypoxia (ALH); and placebo hypoxia (PLH). Pre-exercise administration of 0.3 g.kg⁻¹ BM of NaHCO₃ was used to induce alkalosis. Environmental conditions were set at either normobaric hypoxia (FiO₂: 14.5%) or normoxia (FiO₂: 20.93%).

Results

An increase in W’ was observed with pre-exercise alkalosis under both normoxic (PLN: 15.1 ± 6.2 kJ vs. ALN: 17.4 ± 5.1 kJ; P = 0.006) and hypoxic conditions (ALN: 15.2 ± 4.9 kJ vs. ALN: 17.9 ± 5.2 kJ; P < 0.001). Pre-exercise alkalosis resulted in a larger reduction in bicarbonate ion (HCO₃⁻) concentrations during exercise in both environmental conditions (p < 0.001) and a greater blood lactate accumulation under hypoxia (P = 0.012).

Conclusion

Pre-exercise alkalosis substantially increased W’ and, therefore, may determine tolerance to exercise above CP under normoxic and hypoxic conditions. This may be due to NaHCO₃ increasing HCO₃⁻ buffering capacity to delay exercise-induced acidosis, which may, therefore, enhance anaerobic energy contribution.

Rate dependent influence of arterial desaturation on self-selected exercise intensity during cycling

The purpose of this study was to clarify if Ratings of Perceived Exertion (RPE) and self-selected exercise intensity are sensitive not only to alterations in the absolute level of arterial saturation (SPO2) but also the rate of change in SPO2. Twelve healthy participants (31.6 ± 3.9 y, 175.5 ± 7.7 cm, 73.3 ± 10.3 kg, 51 ± 7 mL·kg-1·min-1 [Formula: see text]) exercised four times on a cycle ergometer, freely adjusting power output (PO) to maintain RPE at 5 on Borg's 10-point scale with no external feedback to indicate their exercise intensity. The fraction of inspired oxygen (FIO2) was reduced during three of those trials such that SPO2 decreased during exercise from starting values (>98%) to 70%. These trials were differentiated by the time over which the desaturation occurred: 3.9 ± 1.4 min, -8.7 ± 4.2%•min-1 (FAST), 11.0 ± 3.7 min, -2.8 ± 1.3%•min-1 (MED), and 19.5 ± 5.8 min, -1.5 ± 0.8%•min-1 (SLOW) (P < 0.001). Compared to stable PO throughout the control condition (no SPO2 manipulation), PO significantly decreased across the experimental conditions (FAST = 2.8 ± 2.1 W•% SPO2-1; MED = 2.5 ± 1.8 W•% SPO2-1; SLOW = 1.8 ± 1.6 W•% SPO2-1; P < 0.001). The rates of decline in PO during FAST and MED were similar, with both greater than SLOW. Our results confirm that decreases in absolute SPO2 impair exercise performance and that a faster rate of oxygen desaturation magnifies that impairment.

The Manipulation of Pace within Endurance Sport

In any athletic event, the ability to appropriately distribute energy is essential to prevent premature fatigue prior to the completion of the event. In sport science literature this is termed "pacing." Within the past decade, research aiming to better understand the underlying mechanisms influencing the selection of an athlete's pacing during exercise has dramatically increased. It is suggested that pacing is a combination of anticipation, knowledge of the end-point, prior experience and sensory feedback. In order to better understand the role each of these factors have in the regulation of pace, studies have often manipulated various conditions known to influence performance such as the feedback provided to participants, the starting strategy or environmental conditions. As with all research there are several factors that should be considered in the interpretation of results from these studies. Thus, this review aims at discussing the pacing literature examining the manipulation of: (i) energy expenditure and pacing strategies, (ii) kinematics or biomechanics, (iii) exercise environment, and (iv) fatigue development.

Variations in Hypoxia Impairs Muscle Oxygenation and Performance during Simulated Team-Sport Running

Purpose: To quantify the effect of acute hypoxia on muscle oxygenation and power during simulated team-sport running. Methods: Seven individuals performed repeated and single sprint efforts, embedded in a simulated team-sport running protocol, on a non-motorized treadmill in normoxia (sea-level), and acute normobaric hypoxia (simulated altitudes of 2,000 and 3,000 m). Mean and peak power was quantified during all sprints and repeated sprints. Mean total work, heart rate, blood oxygen saturation, and quadriceps muscle deoxyhaemoglobin concentration (assessed via near-infrared spectroscopy) were measured over the entire protocol. A linear mixed model was used to estimate performance and physiological effects across each half of the protocol. Changes were expressed in standardized units for assessment of magnitude. Uncertainty in the changes was expressed as a 90% confidence interval and interpreted via non-clinical magnitude-based inference. Results: Mean total work was reduced at 2,000 m (-10%, 90% confidence limits ±6%) and 3,000 m (-15%, ±5%) compared with sea-level. Mean heart rate was reduced at 3,000 m compared with 2,000 m (-3, ±3 min^-1) and sea-level (-3, ±3 min^-1). Blood oxygen saturation was lower at 2,000 m (-8, ±3%) and 3,000 m (-15, ±2%) compared with sea-level. Sprint mean power across the entire protocol was reduced at 3,000 m compared with 2,000 m (-12%, ±3%) and sea-level (-14%, ±4%). In the second half of the protocol, sprint mean power was reduced at 3,000 m compared to 2,000 m (-6%, ±4%). Sprint mean peak power across the entire protocol was lowered at 2,000 m (-10%, ±6%) and 3,000 m (-16%, ±6%) compared with sea-level. During repeated sprints, mean peak power was lower at 2,000 m (-8%, ±7%) and 3,000 m (-8%, ±7%) compared with sea-level. In the second half of the protocol, repeated sprint mean power was reduced at 3,000 m compared to 2,000 m (-7%, ±5%) and sea-level (-9%, ±5%). Quadriceps muscle deoxyhaemoglobin concentration was lowered at 3,000 m compared to 2,000 m (-10, ±12%) and sea-level (-11, ±12%). Conclusions: Simulated team-sport running is impaired at 3,000 m compared to 2,000 m and sea-level, likely due to a higher muscle deoxygenation.

Cycling Time Trial Is More Altered in Hypobaric than Normobaric Hypoxia

PURPOSE

Slight physiological differences between acute exposure in normobaric hypoxia (NH) and hypobaric hypoxia (HH) have been reported. Taken together, these differences suggest different physiological responses to hypoxic exposure to a simulated altitude (NH) versus a terrestrial altitude (HH). For this purpose, in the present study, we aimed to directly compare the time-trial performance after acute hypoxia exposure (26 h, 3450 min) by the same subjects under three different conditions: NH, HH, and normobaric normoxia (NN). Based on all of the preceding studies examining the differences among these hypoxic conditions, we hypothesized greater performance impairment in HH than in NH.

METHODS

The experimental design consisted of three sessions: NN (Sion: FiO2, 20.93), NH (Sion, hypoxic room: FiO2, 13.6%; barometric pressure, 716 mm Hg), and HH (Jungfraujoch: FiO2, 20.93; barometric pressure, 481 mm Hg). The performance was evaluated at the end of each session with a cycle time trial of 250 kJ.

RESULTS

The mean time trial duration in NN was significantly shorter than under the two hypoxic conditions (P < 0.001). In addition, the mean duration in NH was significantly shorter than that in HH (P < 0.01). The mean pulse oxygen saturation during the time trial was significantly lower for HH than for NH (P < 0.05), and it was significantly higher in NN than for the two other sessions (P < 0.001).

CONCLUSION

As previously suggested, HH seems to be a more stressful stimulus, and NH and HH should not be used interchangeability when endurance performance is the main objective. The principal factor in this performance difference between hypoxic conditions seemed to be the lower peripheral oxygen saturation in HH at rest, as well as during exercise.

Effect of Environmental and Feedback Interventions on Pacing Profiles in Cycling: A Meta-Analysis

In search of their optimal performance athletes will alter their pacing strategy according to intrinsic and extrinsic physiological, psychological and environmental factors. However, the effect of some of these variables on pacing and exercise performance remains somewhat unclear. Therefore, the aim of this meta-analysis was to provide an overview as to how manipulation of different extrinsic factors affects pacing strategy and exercise performance. Only self-paced exercise studies that provided control and intervention group(s), reported trial variance for power output, disclosed the type of feedback received or withheld, and where time-trial power output data could be segmented into start, middle and end sections; were included in the meta-analysis. Studies with similar themes were grouped together to determine the mean difference (MD) with 95% confidence intervals (CIs) between control and intervention trials for: hypoxia, hyperoxia, heat-stress, pre-cooling, and various forms of feedback. A total of 26 studies with cycling as the exercise modality were included in the meta-analysis. Of these, four studies manipulated oxygen availability, eleven manipulated heat-stress, four implemented pre-cooling interventions and seven studies manipulated various forms of feedback. Mean power output (MPO) was significantly reduced in the middle and end sections (p < 0.05), but not the start section of hypoxia and heat-stress trials compared to the control trials. In contrast, there was no significant change in trial or section MPO for hyperoxic or pre-cooling conditions compared to the control condition (p > 0.05). Negative feedback improved overall trial MPO and MPO in the middle section of trials (p < 0.05), while informed feedback improved overall trial MPO (p < 0.05). However, positive, neutral and no feedback had no significant effect on overall trial or section MPO (p > 0.05). The available data suggests exercise regulation in hypoxia and heat-stress is delayed in the start section of trials, before significant reductions in MPO occur in the middle and end of the trial. Additionally, negative feedback involving performance deception may afford an upward shift in MPO in the middle section of the trial improving overall performance. Finally, performance improvements can be retained when participants are informed of the deception.

Predicting physiological capacity of human load carriage - a review

This review article aims to evaluate a proposed maximum acceptable work duration model for load carriage tasks. It is contended that this concept has particular relevance to physically demanding occupations such as military and firefighting. Personnel in these occupations are often required to perform very physically demanding tasks, over varying time periods, often involving load carriage. Previous research has investigated concepts related to physiological workload limits in occupational settings (e.g. industrial). Evidence suggests however, that existing (unloaded) workload guidelines are not appropriate for load carriage tasks. The utility of this model warrants further work to enable prediction of load carriage durations across a range of functional workloads for physically demanding occupations. If the maximum duration for which personnel can physiologically sustain a load carriage task could be accurately predicted, commanders and supervisors could better plan for and manage tasks to ensure operational imperatives were met whilst minimising health risks for their workers.

Impact of Altitude on Power Output during Cycling Stage Racing

PURPOSE

The purpose of this study was to quantify the effects of moderate-high altitude on power output, cadence, speed and heart rate during a multi-day cycling tour.

METHODS

Power output, heart rate, speed and cadence were collected from elite male road cyclists during maximal efforts of 5, 15, 30, 60, 240 and 600 s. The efforts were completed in a laboratory power-profile assessment, and spontaneously during a cycling race simulation near sea-level and an international cycling race at moderate-high altitude. Matched data from the laboratory power-profile and the highest maximal mean power output (MMP) and corresponding speed and heart rate recorded during the cycling race simulation and cycling race at moderate-high altitude were compared using paired t-tests. Additionally, all MMP and corresponding speeds and heart rates were binned per 1000 m (<1000 m, 1000-2000, 2000-3000 and >3000 m) according to the average altitude of each ride. Mixed linear modelling was used to compare cycling performance data from each altitude bin.

RESULTS

Power output was similar between the laboratory power-profile and the race simulation, however MMPs for 5-600 s and 15, 60, 240 and 600 s were lower (p ≤ 0.005) during the race at altitude compared with the laboratory power-profile and race simulation, respectively. Furthermore, peak power output and all MMPs were lower (≥ 11.7%, p ≤ 0.001) while racing >3000 m compared with rides completed near sea-level. However, speed associated with MMP 60 and 240 s was greater (p < 0.001) during racing at moderate-high altitude compared with the race simulation near sea-level.

CONCLUSION

A reduction in oxygen availability as altitude increases leads to attenuation of cycling power output during competition. Decrement in cycling power output at altitude does not seem to affect speed which tended to be greater at higher altitudes.

Moderate Altitude Affects High Intensity Running Performance in a Collegiate Women's Soccer Game

The effect of altitude on soccer game activity profiles was retrospectively examined in six NCAA Division I female soccer players. Comparisons were made between two matches played at sea level (SL) and one match played at a moderate altitude (1839 m). A 10-Hz global positioning system device was used to measure distance and velocity. The rate of total distance capacity (TDC) and high intensity running (HIR) as well as percent of time at HIR were evaluated. Significant differences were seen in the distance rate (120.55 ± 8.26 m·min−1 versus 105.77 ± 10.19 m·min−1) and the HIR rate (27.65 ± 9.25 m·min−1 versus 25.07 ± 7.66 m·min−1) between SL and altitude, respectively. The percent of time at HIR was not significantly different (p = 0.064), yet tended to be greater at SL (10.4 ± 3.3%) than at altitude (9.1 ± 2.2%). Results indicate that teams residing at SL and competing at a moderate altitude may have a reduced ability in distance covered and a high intensity run rate.

Improvement of 10-km Time-Trial Cycling With Motivational Self-Talk Compared With Neutral Self-Talk

Purpose:

Unpleasant physical sensations during maximal exercise may manifest themselves as negative cognitions that impair performance, alter pacing, and are linked to increased rating of perceived exertion (RPE). This study examined whether motivational self-talk (M-ST) could reduce RPE and change pacing strategy, thereby enhancing 10-km time-trial (TT) cycling performance in contrast to neutral self-talk (N-ST).

Methods:

Fourteen men undertook 4 TTs, TT1–TT4. After TT2, participants were matched into groups based on TT2 completion time and underwent M-ST (n = 7) or N-ST (n = 7) after TT3. Performance, power output, RPE, and oxygen uptake (VO2) were compared across 1-km segments using ANOVA. Confidence intervals (95%CI) were calculated for performance data.

Results:

After TT3 (ie, before intervention), completion times were not different between groups (M-ST, 1120 ± 113 s; N-ST, 1150 ± 110 s). After M-ST, TT4 completion time was faster (1078 ± 96 s); the N-ST remained similar (1165 ± 111 s). The M-ST group achieved this through a higher power output and VO2 in TT4 (6th–10th km). RPE was unchanged. CI data indicated the likely true performance effect lay between 13- and 71-s improvement (TT4 vs TT3).

Conclusion:

M-ST improved endurance performance and enabled a higher power output, whereas N-ST induced no change. The VO2 response matched the increase in power output, yet RPE was unchanged, thereby inferring a perceptual benefit through M-ST. The valence and content of self-talk are important determinants of the efficacy of this intervention. These findings are primarily discussed in the context of the psychobiological model of pacing.

Stage racing at altitude induces hemodilution despite an increase in hemoglobin mass

Plasma volume (PV) can be modulated by altitude exposure (decrease) and periods of intense exercise (increase). Cycle racing at altitude combines both stimuli, although presently no data exist to document which is dominant. Hemoglobin mass (Hbmass), hemoglobin concentration ([Hb]), and percent reticulocytes (%Retics) of altitude (ALT; n = 9) and sea-level (SL; n = 9) residents were measured during a 14-day cycling race, held at 1,146–4120 m, as well as during a simulated tour near sea level (SIM; n = 12). Hbmass was assessed before and on days 9 and 14 of racing. Venous blood was collected on days 0, 3, 6, 10, and 14. PV was calculated from Hbmass and [Hb]. A repeated-measures ANOVA was used to assess the impact of racing at altitude over time, within and between groups. [Hb] decreased significantly in all groups over time ( P < 0.0001) with decreases evident on the third day of racing. %Retics increased significantly in SL only ( P < 0.0001), with SL values elevated at day 6 compared with prerace ( P = 0.02), but were suppressed by the end of the race ( P = 0.0002). Hbmass significantly increased in SL after 9 ( P = 0.0001) and 14 ( P = 0.008) days of racing and was lower at the end of the race than midrace ( P = 0.018). PV increased in all groups ( P < 0.0001). Multiday cycle racing at altitude induces hemodilution of a similar magnitude to that observed during SL racing and occurs in nonacclimatized SL residents, despite an altitude-induced increase in Hbmass. Osmotic regulatory mechanisms associated with intense exercise appear to supersede acute enhancement of oxygen delivery at altitude.

Methods of the international study on soccer at altitude 3600 m (ISA3600)

Background

We describe here the 3-year process underpinning a multinational collaboration to investigate soccer played at high altitude—La Paz, Bolivia (3600 m). There were two main aims: first, to quantify the extent to which running performance would be altered at 3600 m compared with near sea level; and second, to characterise the time course of acclimatisation of running performance and underlying physiology to training and playing at 3600 m. In addition, this project was able to measure the physiological changes and the effect on running performance of altitude-adapted soccer players from 3600 m playing at low altitude.

Methods

A U20 Bolivian team (‘The Strongest’ from La Paz, n=19) played a series of five games against a U17 team from sea level in Australia (The Joeys, n=20). 2 games were played near sea level (Santa Cruz 430 m) over 5 days and then three games were played in La Paz over the next 12 days. Measures were (1) game and training running performance—including global positioning system (GPS) data on distance travelled and velocity of movement; (2) blood—including haemoglobin mass, blood volume, blood gases and acid–base status; (3) acclimatisation—including resting heart rate variability, perceived altitude sickness, as well as heart rate and perceived exertion responses to a submaximal running test; and (4) sleep patterns.

Conclusions

Pivotal to the success of the project were the strong professional networks of the collaborators, with most exceeding 10 years, the links of several of the researchers to soccer federations, as well as the interest and support of the two head coaches.

Wellness, fatigue and physical performance acclimatisation to a 2-week soccer camp at 3600 m (ISA3600)

Objectives

To examine the time course of wellness, fatigue and performance during an altitude training camp (La Paz, 3600 m) in two groups of either sea-level (Australian) or altitude (Bolivian) native young soccer players.

Methods

Wellness and fatigue were assessed using questionnaires and resting heart rate (HR) and HR variability. Physical performance was assessed using HR responses to a submaximal run, a Yo-Yo Intermittent recovery test level 1 (Yo-YoIR1) and a 20 m sprint. Most measures were performed daily, with the exception of Yo-YoIR1 and 20 m sprints, which were performed near sea level and on days 3 and 10 at altitude.

Results

Compared with near sea level, Australians had moderate-to-large impairments in wellness and Yo-YoIR1 relative to the Bolivians on arrival at altitude. The acclimatisation of most measures to altitude was substantially slower in Australians than Bolivians, with only Bolivians reaching near sea-level baseline high-intensity running by the end of the camp. Both teams had moderately impaired 20 m sprinting at the end of the camp. Exercise HR had large associations (r>0.5–0.7) with changes in Yo-YoIR1 in both groups.

Conclusions

Despite partial physiological and perceptual acclimatisation, 2 weeks is insufficient for restoration of physical performance in young sea-level native soccer players. Because of the possible decrement in 20 m sprint time, a greater emphasis on speed training may be required during and after altitude training. The specific time course of restoration for each variable suggests that they measure different aspects of acclimatisation to 3600 m; they should therefore be used in combination to assess adaptation to altitude.

Position statement--altitude training for improving team-sport players' performance: current knowledge and unresolved issues

Despite the limited research on the effects of altitude (or hypoxic) training interventions on team-sport performance, players from all around the world engaged in these sports are now using altitude training more than ever before. In March 2013, an Altitude Training and Team Sports conference was held in Doha, Qatar, to establish a forum of research and practical insights into this rapidly growing field. A round-table meeting in which the panellists engaged in focused discussions concluded this conference. This has resulted in the present position statement, designed to highlight some key issues raised during the debates and to integrate the ideas into a shared conceptual framework. The present signposting document has been developed for use by support teams (coaches, performance scientists, physicians, strength and conditioning staff) and other professionals who have an interest in the practical application of altitude training for team sports. After more than four decades of research, there is still no consensus on the optimal strategies to elicit the best results from altitude training in a team-sport population. However, there are some recommended strategies discussed in this position statement to adopt for improving the acclimatisation process when training/competing at altitude and for potentially enhancing sea-level performance. It is our hope that this information will be intriguing, balanced and, more importantly, stimulating to the point that it promotes constructive discussion and serves as a guide for future research aimed at advancing the bourgeoning body of knowledge in the area of altitude training for team sports.

Soccer activity profile of altitude versus sea-level natives during acclimatisation to 3600 m (ISA3600)

OBJECTIVES

We investigated the effect of high altitude on the match activity profile of elite youth high altitude and sea level residents.

METHODS

Twenty Sea Level (Australian) and 19 Altitude-resident (Bolivian) soccer players played five games, two near sea level (430 m) and three in La Paz (3600 m). Match activity profile was quantified via global positioning system with the peak 5 min period for distance ((D₅(peak)) and high velocity running (>4.17 m/s, HIVR₅(peak)); as well as the 5 min period immediately subsequent to the peak for both distance (D₅(sub)) and high-velocity running (HIVR₅(sub)) identified using a rolling 5 min epoch. The games at 3600 m were compared with the average of the two near sea-level games.

RESULTS

The total distance per minute was reduced by a small magnitude in the first match at altitude in both teams, without any change in low-velocity running. There were variable changes in HiVR, D₅(peak) and HiVR₅(peak) from match to match for each team. There were within-team reductions in D₅(peak) in each game at altitude compared with those at near sea level, and this reduction was greater by a small magnitude in Australians than Bolivians in game 4. The effect of altitude on HiVR₅(peak) was moderately lower in Australians compared with Bolivians in game 3. There was no clear difference in the effect of altitude on maximal accelerations between teams.

CONCLUSIONS

High altitude reduces the distance covered by elite youth soccer players during matches. Neither 13 days of acclimatisation nor lifelong residence at high altitude protects against detrimental effects of altitude on match activity profile.

Effect of altitude on football performance: analysis of the 2010 FIFA World Cup Data

Laboratory studies show that altitude ascent impairs endurance performance. Limited data exist on football, and information from official matches is very scarce even for other team sports. The aim of this study was to examine the effect of altitude on football performance during the 2010 World Cup in South Africa. It was hypothesized that (a) total distance covered, an index of endurance, would be reduced above the altitude of 580 m, and (b) technical skills would be affected because altitude alters ball flight characteristics. Physical performance, goals scored, and goalkeepers' errors that resulted in goals conceded were recorded from the official game statistics of Fédération Internationale de Football Association during the South Africa 2010 World Cup. Matches were played at sea level (altitude: 0 m), 660, 1200-1400, and 1401-1753 m. After testing for data normality, mean differences were checked with a one-way analysis of variance. Results show a 3.1% lower total distance that was covered by the teams during the matches played at 1200-1400 and 1401-1753 m (p < 0.05) compared with sea level. Indices of technical skills, including number of goals scored per game and errors made by the goalkeepers that resulted in goals conceded, did not differ with altitude. It is concluded that playing football above 1200 m had negative effects on endurance but not on technical skills during World Cup 2010 matches. It seems that teams should follow several days of acclimatization before playing at altitude as low as 1200 m, to ameliorate the negative effects of altitude on physical performance.

Effects of isolated locomotor muscle fatigue on pacing and time trial performance

PURPOSE

Locomotor muscle fatigue impairs exercise performance during time to exhaustion tests. However, its effect on self-regulation of power output (pacing) is unknown. The primary aim of this study was to investigate the effects of locomotor muscle fatigue on pacing and time trial performance.

METHODS

Ten healthy recreationally active men completed a 15-min time trial on a cycle ergometer 30 min after undergoing an eccentric fatiguing protocol designed to induce a substantial strength loss in the knee extensor muscles without inducing significant metabolic stress. This fatigue condition was compared with a control condition, using a randomly counterbalanced AB/BA crossover design.

RESULTS

Total work completed during the 15-min cycling time trial was significantly reduced by 4.8 % in the fatigue condition compared with the control condition. This was caused by a significant reduction in power output. Rating of perceived exertion was significantly higher in the fatigue condition compared with the control condition only during the first 3 min of the time trial. Heart rate and vastus lateralis integrated electromyogram were not significantly different between the two conditions.

CONCLUSION

The results show that participants with fatigued locomotor muscles reduce their pace but do not change their pacing strategy. As a result, there was a significant reduction in time trial performance. As predicted by the psychobiological model of exercise performance, a slower pace may be a behavioral response to compensate for the significant increase in perception of effort induced by locomotor muscle fatigue.

Lower running performance and exacerbated fatigue in soccer played at 1600 m

PURPOSE

This study investigated the decrement in running performance of elite soccer players competing at low altitude and time course for abatement of these decrements.

METHODS

Twenty elite youth soccer players had their activity profile, in a sea-level (SL) and 2 altitude (Alt, 1600 m, d 4, and d 6) matches, measured with a global positioning system. Measures expressed in meters per minute of match time were total distance, low- and high-velocity running (LoVR, 0.01-4.16 m/s; HiVR, 4.17-10.0 m/s), and frequency of maximal accelerations (>2.78 m/s2). The peak and subsequent stanza for each measure were identified and a transient fatigue index calculated. Mean heart rate (HR) during the final minute of a submaximal running task (5 min, 11 km/h) was recorded at SL and for 10 d at Alt. Differences were determined between SL and Alt using percentage change and effect-size (ES) statistic with 90% confidence intervals.

RESULTS

Mean HR almost certainly increased on d 1 (5.4%, ES 1.01 ± 0.35) and remained probably elevated on both d 2 (ES 0.42 ± 0.31) and d3 (ES 0.30 ± 0.25), returning to baseline at d 5. Total distance was almost certainly lower than SL (ES -0.76 ± 0.37) at d 4 and remained probably reduced on d 6 (ES -0.42 ± 0.36). HiVR probably decreased at d 4 vs SL (-0.47 ± 0.59), with no clear effect of altitude at d 6 (-0.08 ± 0.41). Transient fatigue in matches was evident at SL and Alt, with a possibly greater decrement at Alt.

CONCLUSION

Despite some physiological adaptation, match running performance of youth soccer players is compromised for at least 6 d at low altitude.

Enhancing team-sport athlete performance: is altitude training relevant?

Field-based team sport matches are composed of short, high-intensity efforts, interspersed with intervals of rest or submaximal exercise, repeated over a period of 60-120 minutes. Matches may also be played at moderate altitude where the lower oxygen partial pressure exerts a detrimental effect on performance. To enhance run-based performance, team-sport athletes use varied training strategies focusing on different aspects of team-sport physiology, including aerobic, sprint, repeated-sprint and resistance training. Interestingly, 'altitude' training (i.e. living and/or training in O(2)-reduced environments) has only been empirically employed by athletes and coaches to improve the basic characteristics of speed and endurance necessary to excel in team sports. Hypoxia, as an additional stimulus to training, is typically used by endurance athletes to enhance performance at sea level and to prepare for competition at altitude. Several approaches have evolved in the last few decades, which are known to enhance aerobic power and, thus, endurance performance. Altitude training can also promote an increased anaerobic fitness, and may enhance sprint capacity. Therefore, altitude training may confer potentially-beneficial adaptations to team-sport athletes, which have been overlooked in contemporary sport physiology research. Here, we review the current knowledge on the established benefits of altitude training on physiological systems relevant to team-sport performance, and conclude that current evidence supports implementation of altitude training modalities to enhance match physical performances at both sea level and altitude. We hope that this will guide the practice of many athletes and stimulate future research to better refine training programmes.

Effect of airline travel on performance: a review of the literature

The need for athletes to travel long distances has spurred investigation into the effect of air travel across multiple time zones on athletic performance. Rapid eastward or westward travel may negatively affect the body in many ways; therefore, strategies should be employed to minimise these effects which may hamper athletic performance. In this review, the fundamentals of circadian rhythm disruption are examined along with additional effects of airline travel including jet lag, sleep deprivation, travel at altitude and nutritional considerations that negatively affect performance. Evidence-based recommendations are provided at the end of the manuscript to minimise the effects of airline travel on performance.

Is gross efficiency lower at acute simulated altitude than at sea level?

PURPOSE

The purpose of this study was to test the assumption that gross efficiency (GE) at sea level (SL) is representative of GE at altitude (AL). It was hypothesized that an increased cost of ventilation and heart rate, combined with a higher respiratory-exchange ratio, at AL might result in a decrease in GE.

METHODS

Trained men (N = 16) completed 2 maximal incremental tests and 2 GE tests, 1 at SL and 1 at an acute simulated AL of 1500 m (hypobaric chamber). GE was determined during submaximal exercise at 45%, 55%, and 65% of the altitude-specific power output attained at VO2max.

RESULTS

GE determined at the highest submaximal exercise intensity with a mean RER ≤1.0, matched for both conditions, was significantly lower at AL (AL 20.7% ± 1.1% and SL 21.4% ± 0.8%, t15 = 2.9, P < .05).

CONCLUSION

These results demonstrate that moderate AL resulted in a significantly lower GE during cycling exercise than SL. However, it might be that the lower GE at AL is caused by the lower absolute exercise intensity.