Thermoregulatory responses to heat and vibration in men.

To determine if exposure to vibration influences thermoregulation, six healthy Caucasian men, 22-33 years old, were heat-acclimated and then simultaneously exposed to heat and whole-body vibration (WBV). The WBV exposures were divided into two intensity levels, and included tests at frequencies of 5, 10, 16, 30, and 80 Hz. Rectal temperature, local sweat rate, heart rate, and local blood flow were measured. There were no statistically significant differences (p less than 0.05) in rectal temperatures or heart rate as a function of frequency. The mean rectal temperatures for the WBV intensity-level exposures became elevated more quickly than in the control period. WBV produced an initial increase (p less than 0.05) in heart rate over the control level only during the initial 20 min of exposure. There were both intensity- and frequency-dependent WBV relationships in localized blood flows and sweat rates. Vibration appears to reduce the efficiency of the cooling mechanisms during a heat exposure at rest, which results in significant increases in rectal temperatures compared with those from heat exposures alone.