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enhancing activities such as exercise and rehabilitation programs (1, 22).

To date, the relative effectiveness of WBI and LBI precooling on thermoregulatory and metabolic re- sponses during submaximal exercise has not been in- vestigated. A direct comparison of the effects of these two immersion techniques during subsequent sub- maximal exercise performance was necessary to pre- scribe appropriate precooling recommendations for clinical populations.

The present study demonstrated that LBI and WBI precooling techniques 1) prevented excessive Tre in- c r e a s e s d u r i n g s u b s e q u e n t s u b m a x i m a l e x e r c i s e b y ˙ lowering initial Tc and 2) resulted in similar net S

Fig. 1. Rectal temperature (Tre) during lower body (LBI) and head- out whole body (WBI) immersion in 20°C water. Bracket indicates significant differences between conditions.

˙ phases. However, during immersion, M was nearly

twice as high for WBI compared with LBI (132 15 vs. 71 5 W/m2, respectively, at minute 30; P 0.01) (Table 2). Heart rate was also significantly higher during WBI compared with LBI (P 0.05) (Table 2). N o s i g n i fi c a n t t r e a t m e n t ( W B I v s . L B I ) d i f f e r e n c e s ˙ were observed for M or heart rate during exercise

(Table 3). Subjective Responses

There were no differences between treatments for sweat sensation, thermal sensation, or thermal dis- comfort during baseline and recovery phases. Thermal sensation throughout immersion was significantly lower (felt colder) during WBI compared with LBI (P 0.05). Similarly, thermal discomfort was significantly higher (less comfortable) for WBI throughout immer- sion (P 0.005) (Table 2).

During the exercise phase, sweat sensation scores increased significantly after both treatments. After WBI, sweat sensation scores were significantly lower than those after LBI through 20 min of exercise (P 0.05). Treatment differences were no longer apparent at 30 min for sweat sensation (Table 3).

changes over the experimental protocol. WBI produced a greater cooling effect compared with LBI, as demon- strated by significantly lower Tre during the first 24 m i n o f e x e r c i s e . H o w e v e r , t h i s l a r g e r c o o l i n g e f f e c t w a s ˙ accompanied by higher M and less thermal comfort

during cooling. LBI also produces significant physio- logical benefits but minimizes the metabolic and per- ceptual effects resulting from WBI.

During 30 min of cool-water immersion, heat in the body core was presumably conserved by peripheral vasoconstriction in the immersed extremities, reducing the skin-to-water temperature gradient. The magni- tude of heat loss during WBI was greater due to the larger skin surface area exposed to cooling, as well as greater heat flow from the trunk areas (14). This was demonstrated by a significant reduction in Tre com- pared with baseline during the last 6 min of immer- sion. By themselves, these observations would appear to suggest that WBI is a superior precooling method. However, the effectiveness of both precooling tech- niques became more evident during subsequent exer- cise when blood circulating through the cooled areas p r o d u c e d s i g n i fi c a n t i n i t i a l r e d u c t i o n s i n T r e . ˙ During WBI, M increased significantly to a value

nearly twice that achieved during LBI (Table 2). This corresponds well to the afferent stimulation provided

There were no significant treatment differences in RPE scores during exercise. However, RPE scores in- creased significantly (P 0.05) during exercise after both precooling treatments.


Our laboratory has previously demonstrated, in a small number of MS patients, that LBI precooling is tolerable, effective, and practical for use (25). Because many MS patients experience symptom worsening with small (0.5°C) increases in internal temperature, an effective precooling technique could have profound effects on preserving physical function during condi- tions that increase internal temperature. In turn, pre- cooling could facilitate greater participation in health-

Fig. 2. Body heat storage during immersion, exercise, and net pro- tocol (combined immersion and exercise phases) for LBI and WBI precooling treatments. NS, not significant.

J Appl Physiol VOL 94 MARCH 2003 www.jap.org

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