THE BODY REACTS TO A CERTAIN LEVEL OF STRESS WHETHER IT BE SINGLE OR COMBINED STRESSORS

Girard, O., & Racinais, S. (2009). No cumulative effect of hot and hypoxic environment on thermal, cardiovascular, or metabolic strains during exercise. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

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This study determined whether performance limitation when exercising in both a hot and hypoxic environment is associated with different thermal, cardiovascular, and metabolic strains and perception of effort when compared to each individual environmental condition. Recreational athletes (N = 11) cycled to exhaustion at an intensity corresponding to 66% of their VO2max in four different conditions: a) Neutral/Sea level, b) Hot/Sea level, c) Neutral/Hypoxia, and d) Hot/Hypoxia. Neutral conditions were 22C and 30%RH and conditions were 35C and 40%RH. Hypoxia corresponded to a simulated altitude of 2,500 m. The following parameters were recorded at exhaustion: core temperature, skin temperature, heart rate, percent arterial oxygen saturation, rating of perceived exertion (Borg scale), and blood lactate concentration.

Time to exhaustion was reduced in Hot/Sea level and Neutral/Hypoxia conditions when compared to the control (Neutral/Sea level) condition. The Hot/Hypoxia condition further decreased performance, suggesting a parallel and cumulative effect of these two stressors on performance. Hot conditions significantly increased heart rate and skin temperature independently of the simulated altitude, while altitude exposure reduced percent arterial oxygen saturation independently of the environmental temperature. Lactate values were not differentiated between conditions. There was no significant interaction effect between temperature and altitude on heart rate, skin temperature, percent arterial oxygen saturation, or lactate. There was a significant interaction effect on time to exhaustion. This interaction was due to a slightly reduced effect of either a hot or an altitude exposure when the other stressor was present. That suggests that some limiting factors for performance are common to both a hot and hypoxic environments. In support of that interpretation, Ss stopped exercising at an equivalent core temperature and rating of perceived exertion in all conditions.

Implication. There is no cumulative effect of hot and hypoxic environments on cardiovascular, metabolic, or perceived strains despite exercise performance being reduced.

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