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cise, an overall Tre increase of 1°C was observed after both WBI and LBI. This magnitude of change in Tre is consistent with other studies that have utilized the same relative workload (25, 26). Because precooling does not appear to alter the slope of temperature in- creases during 30 min of submaximal exercise (Fig. 3), t h e r e d u c t i o n i n T r e p r o d u c e d b y p r e c o o l i n g l a r g e l y d e t e r m i n e s t h e n e t T r e i n c r e a s e a b o v e n o r m a l b a s e temperature. In a study that compared LBI precooling to no cooling in MS patients, LBI produced an after- drop of 0.8°C (25). As in the present study, 30 min of l i n e

˙ exercise at 60% VO2 max resulted in overall Tre in-

creases of 0.9°C for LBI and noncooled conditions. During the noncooled trial, a Tre of 0.5°C above base- line was reached at 22 min of exercise. In contrast, LBI produced no net increase in Tre at the end of 30 min of exercise (25).

Similarly, in healthy men, LBI precooling produced a reduction in Tre of 1°C, noted by 68 min of exercise at

˙ 60% VO2 max

. The time required to produce a 0.5°C Tre

increase was 33 min for the precooled condition com- pared with 15 min for the noncooled condition (26). In the present study, WBI and LBI produced similar de- lays in the time to increase Tre by 0.5°C (24 and 28 min of exercise for LBI and WBI, respectively). Variability in the studies cited above was due to differing immer- sion temperatures (16°C for Ref. 26, and 20°C for the present study) and ambient conditions during exercise (2123°C for Ref. 26, and 30°C for the present study). Immersion temperature for the present study was based on observations suggesting WBI in 16°C water would not be tolerated well (4, 18).

Throughout WBI, thermal sensation scores were sig- nificantly lower (colder) and thermal discomfort scores were significantly higher (more uncomfortable) com- pared with LBI. Although the differences in thermal comfort and thermal sensation were statistically sig- nificant, one might question the practical interpreta- tion of a one-point difference on these perceptual scales. However, this small perceptual benefit com- bined with the greater accessibility of LBI (which can be accomplished in a regular bath tub by using tap water) may indicate the use of LBI precooling as a practical means to delay heat stress during subsequent physical activity, be it exercise or activities of daily living.

During exercise, subjective measures assessed after WBI and LBI were similar. There were no treatment differences in RPE throughout exercise. This observa- tion is consistent with Booth et al. (4) and Wilson et al. (26), but it differs from that of White et al. (25). This discrepancy is likely due to differing subject popula- tions. The latter study examined MS patients who experienced symptom worsening with increased Tc. Greater difficulty with motor control and other neuro- logical signs may explain the increased perception of effort.

Sweat sensation was significantly lower after WBI through minute 20 of exercise, suggesting that sweat production may have been reduced. This is consistent with our laboratorys previous work that demonstrated that precooling significantly delayed onset of sweating and led to decreased sweat loss during 60 min of submaximal exercise (26).

Fig. 3. Tre (top), mean skin tempera- ture (Tsk; middle), and mean body tem- perature (Tb; bottom) responses during submaximal cycling exercise after LBI and WBI in 20°C water. Brackets indi- cate significant differences between conditions.

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

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