Molloy, J. M., Smith J., & Pascoe, D. D. (2004). Effect of a 14-day high intensity exercise protocol on heat acclimation responses. Medicine and Science in Sports and Exercise, 36(5), Supplement abstract 569.

"Heat acclimation (HA) reduces physiological strain, optimizes performance, and lessens thermal injury risk during occupational or athletic activities. Few HA protocols have focused on relative exercise intensities >60% VO2max. Little is known about time course or magnitude of high intensity-based adaptive responses beyond 9 days of heat exposure. This is pertinent, for higher intensity exercise HA protocols are more applicable than low intensity protocols to many work, exercise, or athletic settings. It is unknown how individuals of different ages will respond differentially to a high intensity protocol. This has practical implications for many older adults who regularly exercise, work, or compete in athletic events in the heat" (p. S83).

Young (N = 9; ~20 yr) and older (N = 8; ~45 yr) aerobically fit males for 14 days ran daily for 30 minutes at 75% VO2max in a hot, humid (35C; 35% relative humidity) environment. Measures of heat reaction, perceived exertion, physiological strain, and blood parameters were taken.

VO2max did not differ between groups or change across the study. Core temperature, heart rate, physiological strain, perceived exertion, and thermal sensation decreased over the time of the study. Heart rate and physiological strain were significantly less for the older Ss than the younger Ss. However, heart rate decreased similarly for both groups despite the HR differences. Both groups experienced similar increases in resting plasma volume and decreases in sweat sodium concentration. Sweat volume did not change for either group. Most changes were evidenced by Day 8 in the 14-day period.

Implication. Fit older and younger males adapt to heat acclimation similarly. Adaptation occurred within eight days.

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