Effects on Heat Tolerance of Physical Training in Water and on Land,
ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA
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A 4-week training program was undertaken by 15 untrained, unacclimated males who were divided into 3 groups matched on maximal aerobic capacity VO2 max and trained either in water or on land to determine how physical training PT in these different media affects heat tolerance. Subjects trained on a bicycle ergometer for 1 hday, 5 daysweek at 75 VO2 max, with the exercise intensity progressively increased to maintain a constant training stimulus. Group I exercised on land, while II and III exercised while immersed to the neck in water of either 32 C II or 20 C III. Daily exercise increased core temperature Tc in I and II, but not in III. Training elicited similar increases approx. 15 in VO2 max in the 3 groups. Before and after PT, all subjects exercised at approx. 30 VO2 max for 3 h at 49 C, 20 rh. Compared to before training, I and II showed a decrease in final Tc and heart rate HR in the post-training heat exposure. Seat rate SR increased 25 in II, but remained the same in I. Group III demonstrated a decrease in final HR but final Tc was higher than before training. SR did not increase in III and was lower than the other groups. It was concluded that PT can improve the cardiovascular response to dry heat without affecting thermoregulatory capacity. PT appears to enhance heat tolerance only if Tc is permitted to rise during exercise, thus stimulating the temperature-regulating center for heat dissapation.
- Stress Physiology