Effects of daily and intermittent exposures on heat acclimation of women.

A B S T R A C T . Twelve women, who d i f f e r ed in phys i ca l cond i t ion and body s ize , w e r e hea t a c c l i m a t e d u t i l i z ing e i t h e r a da i ly or i n t e r m i t t e n t ( e v e r y 3 rd day) ex p o s u r e p a t t e r n in an e n v i r o n m e n t a l c h a m b e r . The w o m e n walked for 100 rain at 5 .2 km~h up a 2 .5% g r a d e on a m o t o r d r i v e n t r e a d m i l l C l i m a t i c c h a m b e r c o n d i t ions w e r e 4 6 . 5 ° C Ta, 2 4 . 5 ° C Twb +_ 0 . 5 ° C . Al though individual a c c l i m a t i o n va r i ed , s ign i f i can t r e d u c t i o n in hea t s t r a i n was o b s e r v e d in al l sub j ec t s , e . g . , t he ab i l i ty to c o m p l e t e the a s s i g n e d t a s k wi th i n c r e a s i n g ease , a d e c r e a s e in work ing h e a r t r a t e , a d e c r e a s e in r e c t a l t e m p e r a t u r e r i s e , a d e c r e a s e in m e a n skin t e m p e r a t u r e , an i n c r e a s e in swea t r a t e , an i n c r e a s e in e v a p o r a t i v e r a t e , and a d e c r e a s e in hea t s t o r a g e . The p a t t e r n of hea t e x p o s u r e s , da i ly or e v e r y t h i r d day, had no d i s c e r n i b l e e f fec t on the r a t e of hea t a c c l i m a t i o n . The h ighly condi t ioned s u b j e c t s showed l e s s phys io log ica l s t r a i n , p a r t i c u l a r l y d u r i n g the f i r s t few hea t e x p o s u r e s , and m a i n t a i n e d s o m e r e l a t i v e advan tage t h roughou t the s e r i e s of I0 e x p o s u r e s . Body s ize , in the r a n g e s tudied, a p p e a r e d to e x e r t l i t t l e in f luence on the amount of t h e r m a l s t r a i n . "