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submaximal work rate may more practically represent daily activities for average individuals, as opposed to maximal trials performed on highly fit individuals in stressful environments. Furthermore, LBI represents a more practical and accessible method of precooling for individuals with mobility constraints and very little tolerance for increases in Tc, such as many MS pa- tients.

METHODS Subjects

Eleven healthy men (subject characteristics in Table 1) volunteered to participate. Data were collected in a dry temperate climate (22°C, 20% relative humidity, and elevation 1,300 m). The protocol was approved by the Uni- versity of Utah Human Subjects Review Board, and all sub- jects provided written, informed consent.


Temperature. Skin temperature (Tsk) was measured by attaching banjo-type surface temperature probes (Yellow Springs Instruments) to the calf, thigh, chest, and arm. Rectal temperature (Tre) was measured via general use ther- mistor (Yellow Springs Instruments) inserted 10 cm past the anal sphincter. All temperature probes were connected to a digital thermistor readout unit (Digitec).

Metabolic and cardiovascular. Heart rate was monitored c o n t i n u o u s l y b y u s i n g a h e a r t r a t e m o n i t o r ( P o l a r ) . O x y g e n ˙ consumption (VO2) was measured by using indirect calorimetry

via an automated metabolic cart (ParvoMedics).

Participant perception. The Borg 6-20 point scale of rating of perceived exertion (RPE) was used to determine the par- ticipantsperception of exercise intensity. Nine-point ther- mal sensation (0 very cold to 8 very hot), five-point thermal discomfort (1 comfortable to 5 intolerable), and five-point sweating sensation scales (1 not at all to 5 maximally) were used to determine the participantsthermal

comfort during the protocol (8). Calculations Temperature calculations. Four Tsk

sites were used and

weighted according to the following equation: mean Tsk 0.3(Tsk chest Tsk arm) 0.2(Tsk thigh Tsk calf) (23). Mean Tb





was calculated

  • (0.65 Tc)

    • (5)


via the following weighting

  • (0.35 meanTsk), where Tc

system: mean is indexed by

˙˙ ˙ S . S w a s e s t i m a t e d v i a t h e f o l l o w i n g f o r m u l a : S 0.97 mass (Tb/t)/AD, where Tb is the change in mean

body temperature, /t is the change in time, and AD is body surface area (in m2) (13).

˙˙ M . M w a s c a l c u l a t e d a c c o r d i n g t o t h e f o l l o w i n g f o r m u l a ˙ ˙ (10): M [0.23(R) 0.77] (5.873/VO2) (60/AD), where R is

respiratory exchange ratio.

Table 1. Subject characteristics

Age, yr Height, cm Weight, kg

BSA, m2 ˙


, ml kg1

  • min1

25 2 180 8 78.0 10.6

    • 1.97


    • 52.5



Each participant reported to the laboratory three times over the course of the experiment: for a pretest session and for two randomly ordered precooling trials of either LBI or WBI. Each session was separated by 1 wk and was performed at the same time of day. During the pretest session, physical characteristics were measured and subjects performed a m a x i m a l g r a d e d e x e r c i s e t e s t o n a M o n a r c h c y c l e e r g o m e t e r t o d e t e r m i n e m a x i m a l O 2 u p t a k e ( V ˙ O 2 m a x ) . T h e w o r k r a t e 2 max ˙ corresponding to 60% VO was calculated and used for the

subsequent submaximal exercise trials described below.

Each precooling trial consisted of four 30-min phases: baseline, immersion, exercise, and recovery. Each phase was separated by 10 min for subject and instrument transition. During the baseline period, each subject, dressed in shorts and shoes, rested on a reclining chair in a thermoneutral environment (22°C, 20% relative humidity). During WBI and LBI, subjects were seated in cool water (20°C), immersed to the level of the clavicle and iliac crest, respectively. The e x e r c i s e p h a s e c o n s i s t e d o f c y c l i n g a t a w o r k r a t e c o r r e s p o n d - ˙ ing to 60% VO2 max in an environmental chamber at 30.3

0.2°C and 31.9 0.7% relative humidity. After exercise, subjects rested in a semireclined position in a thermoneutral environment throughout the recovery phase.


Descriptive statistics (means SE) are reported for de- pendent variables. Two-way (treatment vs. time) ANOVAs with repeated measures were used to evaluate thermoregu- latory responses during each experimental phase. When sig- nificant main effects were observed, post hoc Tukeys analy- ses were performed to determine where treatment and/or time differences existed.


Thermoregulatory Responses

During immersion, significant time and time treatment (LBI vs WBI) effects were observed for Tre (P 0.001). Post hoc analysis indicated that, during WBI, Tre was significantly lower than baseline at min- utes 2430 (Fig. 1).

During the exercise phase, Tre, mean Tsk, and mean





  • 0.001)




both LBI and WBI conditions. Significant treatment 0.002), (P differences also observed for T were re m e a n T s k ( P 0 . 0 3 4 ) , a n d m e a n T b ( P 0 . 0 0 9 ) throughout exercise. After WBI, Tre was significantly lower than LBI for the first 24 min of exercise (P 0.05, post hoc Tukeys test). Mean Tsk and mean Tb were also lower during exercise after WBI compared with LBI, but the treatment differences were no longer

significant after 1˙4 min (mean Tb) of exercise. S rates were between WBI and LBI during

Tsk) and 16 min (mean significantly different immersion (P 0.002)

(P 0.003) (Fig. 2). and phases exercise However, net ˙ changes in S over the entire experimental protocol did

not differ significantly between conditions.

Metabolic Responses

˙ Values are means SD. BSA, body surface area; VO2max

, maximal

˙ There were no significant differences in M or heart

O2 uptake.

rate between LBI and WBI during baseline or recovery J Appl Physiol VOL 94 MARCH 2003 www.jap.org

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