Year of Award


Document Type


Degree Type

Master of Science (MS)

Degree Name

Health and Human Performance (Exercise Science Option)

Department or School/College

Department of Health and Human Performance

Committee Chair

Charles Dumke

Commitee Members

Brent Ruby, James Laskin


thermoregulation, PSI, discontinuous exercise, physiological strain index, walk/run


University of Montana


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, VO2peak 56.3 ±6.3 ml*kg-1*min-1) 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 Tsk (36.75±1.3 vs 34.2±0.6 ˚C; P=0.002) and a trend towards significance in HR (152±14 vs 132±30 bpm; P=0.095) and PSI (6.1±2.1 vs 5.2±3.1, P=0.062). The IN group showed an effect of time for HR (141±21 vs 150±30 bpm for DCON and CON, respectively; P=0.016). There was no significant difference in TT performance (P=0.15) 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 and that the Dcon trial did not result in elevated PSI despite working at a higher workload than the control trial.



© Copyright 2014 Timothy J. Hampton