Separate and combined influences of heat and hypobaric hypoxia on self-paced aerobic exercise performance

Bradbury, Karleigh E.; Coffman, Kirsten E.; Mitchell, Katherine; Luippold, Adam J.; Fulco, Charles S.; Kenefick, Robert W.

doi:10.1152/japplphysiol.00023.2019

Cited by 19 publications

(15 citation statements)

References 32 publications

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“…However, in H+H, muscle and skin temperatures reached 38.1 ± 0.1 • C and 36.2 ± 0.2 • C, respectively, by the end of exercise. These levels are comparable with those observed in previous studies, reporting skin temperatures of approximately 35 • C during exercise under 35 • C (Bradbury et al, 2019). We also evaluated muscle oxygenation because previous studies reported that lower muscle oxygenation (increased muscle deoxygenation) may aggravate the accumulation of exercise-induced metabolites (Grassi et al, 1999).…”

Section: Discussionsupporting

confidence: 81%

Endocrine and Metabolic Responses to Endurance Exercise Under Hot and Hypoxic Conditions

et al. 2020

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Purpose: We explored the effect of heat stress during an acute endurance exercise session in hypoxia on endocrine and metabolic responses. Methods: A total of 12 healthy males cycled at a constant workload (60% of the power output associated with their maximal oxygen uptake under each respective condition) for 60 min in three different environments: exercise under hot and hypoxia (H+H; fraction of inspiratory oxygen or FiO 2 : 14.5%, 32 • C), exercise under hypoxia (HYP; FiO 2 : 14.5%, 23 • C), and exercise under normoxia (NOR; FiO 2 : 20.9%, 23 • C). After completing the exercise, participants remained in the chamber for 3 h to evaluate metabolic and endocrine responses under each environment. Changes in muscle oxygenation (only during exercise), blood variables, arterial oxygen saturation, and muscle temperature were determined up to 3 h after exercise. Results: Serum erythropoietin (EPO) level was increased to similar levels in both H+H and HYP at 3 h after exercise compared with before exercise (P < 0.05), whereas no significant increase was found under NOR. No significant difference between H+H and HYP was observed in the serum EPO level, blood lactate level, or muscle oxygenation at any time (P > 0.05). Exercise-induced serum growth hormone (GH) elevation was significantly greater in H+H compared with HYP (P < 0.05) and HYP showed significantly lower value than NOR (P < 0.05). Arterial oxygen saturation during exercise was significantly lower in H+H and HYP compared with NOR (P < 0.05). Furthermore, H+H showed higher value compared with HYP (P < 0.05). Conclusion: The serum EPO level increased significantly with endurance exercise in hypoxia. However, the addition of heat stress during endurance exercise in hypoxia did not augment the EPO response up to 3 h after completion of exercise. Exercise-induced GH elevation was significantly augmented when the hot exposure was combined during endurance exercise in hypoxia. Muscle oxygenation levels during endurance

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Section: Discussionsupporting

confidence: 81%

Endocrine and Metabolic Responses to Endurance Exercise Under Hot and Hypoxic Conditions

et al. 2020

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“…Variables including heart rate and ventilation have been shown to be related to RPE during exercise (1). Our recent work in simulated altitude (7) suggests that individuals titrate their work rate during self-paced TT exercise based on physiological feedback such as HR and RPE to maintain an optimal exercise intensity. The lack of difference in HR and RPE between treatments may suggest that AZ did not increase the difficulty of the exercise bout and individuals were able to maintain an optimal intensity in both trials.…”

Section: Discussionmentioning

confidence: 99%

Acetazolamide does not alter endurance exercise performance at 3,500-m altitude

Bradbury

Yurkevicius

Mitchell

et al. 2020

Journal of Applied Physiology

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Acetazolamide (AZ) is a medication commonly used to prevent acute mountain sickness (AMS) during rapid ascent to high altitude. However, it is unclear whether AZ use impairs exercise performance; previous literature regarding this topic is equivocal. The purpose of this study was to evaluate the impact of AZ on time-trial (TT) performance during a 30-h exposure to hypobaric hypoxia equivalent to 3,500-m altitude. Ten men [sea-level peak oxygen consumption (VO2peak): 50.8 ± 6.5 mL·kg−1·min−1; body fat %: 20.6 ± 5.2%] completed 2 30-h exposures at 3,500 m. In a crossover study design, subjects were given 500 mg/day of either AZ or a placebo. Exercise testing was completed 2 h and 24 h after ascent and consisted of 15-min steady-state treadmill walking at 40%–45% sea-level VO2peak, followed by a 2-mile self-paced treadmill TT. AMS was assessed after ~12 h and 22 h at 3,500 m. The incidence of AMS decreased from 40% with placebo to 0% with AZ. Oxygen saturation was higher ( P < 0.05) in AZ versus placebo trials at the end of the TT after 2 h (85 ± 3% vs. 79 ± 3%) and 24 h (86 ± 3% vs. 81 ± 4%). There was no difference in time to complete 2 miles between AZ and PL after 2 h (20.7 ± 3.2 vs. 22.7 ± 5.0 min, P > 0.05) or 24 h (21.5 ± 3.4 vs. 21.1 ± 2.9 min, P > 0.05) of exposure to altitude. Our results suggest that AZ (500 mg/day) does not negatively impact endurance exercise performance at 3,500 m. NEW & NOTEWORTHY To our knowledge, this is the first study to examine the impact of acetazolamide (500 mg/day) versus placebo on self-paced, peak-effort exercise performance using a short-duration exercise test in a hypobaric hypoxic environment with a repeated-measures design. In the present study, acetazolamide did not impact exercise performance after 2-h or 24-h exposure to 3,500-m simulated altitude.

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“…This range widens under heat stress when exercise becomes protracted however, as a disassociation develops between %VO2peak, heart rate and perceived exertion. The %V̇O2peak sustained during self-paced cycling is related to the duration or distance of the event, with time trials of 45-60 min conducted at ~85% VO2peak and shorter efforts performed at a greater fraction of maximal aerobic power (132,574,644,732,733,972). Perceived exertion during such trials in the heat is similar and often higher than in cooler conditions (727,731,962,993).…”

Section: Self-paced Exercise In the Heatmentioning

confidence: 99%

Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies

Périard

Eijsvogels²,

Daanen

2021

Physiological Reviews

212

166

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A rise in body core temperature and loss of body water via sweating are natural consequences of prolonged exercise in the heat. This review provides a comprehensive and integrative overview of how the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions. The fundamental concepts and physiological processes associated with thermoregulation and fluid balance are initially described, followed by a summary of methods to determine thermal strain and hydration status. An outline is provided on how exercise-heat stress disrupts these homeostatic processes, leading to hyperthermia, hypohydration, sodium disturbances and in some cases exertional heat illness. The impact of heat stress on human performance is also examined, including the underlying physiological mechanisms that mediate the impairment of exercise performance. Similarly, the influence of hydration status on performance in the heat and how systemic and peripheral hemodynamic adjustments contribute to fatigue development is elucidated. This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat, by examining the benefits of heat acclimation, cooling strategies and hyperhydration. Finally, contemporary controversies are summarized and future research directions provided.

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Separate and combined influences of heat and hypobaric hypoxia on self-paced aerobic exercise performance

Cited by 19 publications

References 32 publications

Endocrine and Metabolic Responses to Endurance Exercise Under Hot and Hypoxic Conditions

Endocrine and Metabolic Responses to Endurance Exercise Under Hot and Hypoxic Conditions

Acetazolamide does not alter endurance exercise performance at 3,500-m altitude

Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies

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