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IMPLICATIONS OF DISCONTINUOUS EXERCISE ON THE MAINTENANCE OF THERMOREGULATION IN THE HEAT

Abstract

IMPLICATIONS OF DISCONTINUOUS EXERCISE ON THE MAINTENANCE OF THERMOREGULATION IN THE HEAT

T.J. Hampton, F. von Sydow, J.S. Cuddy, B.C. Ruby, FACSM, and C.L. Dumke, FACSM.

University of Montana, Missoula, MT

Increases in physiological strain index (PSI) can be a barrier to endurance performance. The efficacy of discontinuous work on the attenuation of rises in PSI during exercise in the heat remains unclear. PURPOSE: To evaluate discontinuous exercise on the maintenance of thermoregulation in the heat. METHODS: Eight recreationally active men (age 28.5±5.5 yr., body mass 75.3±11.5 kg, VO2max 56.3 ±6.3 ml/kg/min)performed 2 trials of 60 minutes each (discontinuous (DCON) run/walk and continuous (CONT) running) matched for overall work. Five of these subjects performed the trials outdoors (OUT) on a 400m gravel track at 30.9 ±3.1 °C and humidity of 25.5±5.5% RH. The speeds for the trials were 187.8 and 203.8 m/min for CONT and DCON, respectively. During the DCON trial, participants ran for 8.5 minutes then walked at 1 minute (80.5 m/min). Subsequently, three men acclimated to a climate chamber (IN) for 15 minutes and then performed DCON and CONT incremental trials on a treadmill at 34°C and 40% humidity. The trials were similar to the OUT conditions, where work was matched over the course of 1 hr., but with 3 different intensities increasing every 20 minutes. This was followed by a time trial (TT) which included an incremental increase in treadmill grade at 187.8 m/min until failure. RESULTS: The OUT group exhibited a significant effect of trial in DCON and CON for HR (152±14 vs 132±30 bpm; P=0.04), Tsk (36.75±1.3 vs 34.2±0.6 ˚C; P=0.002) and a trend towards significance in PSI (6.1±2.1 vs 5.2±3.1, P=0.101). The IN group showed a trend in reduced HR (141±21 vs 150±30 bpm for DCON and CON, respectively; P=0.05) and PSI (5.0±3.3 vs 5.6±3.9 for DCON and CON respectively; P=0.09). There was no significant difference in TT performance (P>0.05) between trials. CONCLUSION: These findings imply that when total work is held constant DCON has a significant impact on HR and Tsk but not on Tc or PSI during exercise in the heat.

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