2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
420
THE EFFECTS OF PASSIVE HEATING AND HEAD-COOLING ON
EXERCISE IN THE HEAT
Shona Simmons 1, 2 , Toby Mündel 1, 3 and David Jones
1 2 3
University of Birmingham, Birmingham, UK. Unilever R&D, Wirral, UK, Massey
University, Palmerston North, New Zealand, 4 Manchester Metropolitan University, Alsager,
UK
Contact person: Shona.Simmons@Unilever.com
INTRODUCTION
The capacity to perform exercise is reduced in a hot environment when compared to cooler
conditions, and a limiting factor appears to be a higher core body temperature (Tcore). It has
been suggested that an elevated Tcore reduces the drive to exercise, this being reflected in
higher ratings of perceived exertion (RPE). Some of the unpleasant sensations associated with
an elevated Tcore can be modulated by cooling the skin, with cooling the head and face being
particularly effective. Results from our laboratory have shown that cooling the head and face
during exercise in the heat can attenuate the RPE without affecting Tcore, and that this may in
part be due to improved subjective thermal comfort (TC).
Exercise in the heat is also associated with a greater increase in muscle temperature, a
possible reduction in muscle blood flow and faster rates of muscle glycogen breakdown when
compared with exercise in cooler conditions. Therefore, it is difficult to distinguish between
the role that thermal and metabolic pathways play during exercise in the heat. Armada-da-
Silva et al. (2004) used a passive heating model to control for these metabolic factors in order
to investigate the role of an elevated Tcore per se on subsequent exercise in the heat. Subjects
performed two 14-minute bouts of cycling (~63% maximum power output) at 35°C separated
by a period of passive heating in a sauna to increase Tcore above 38.5°C. This design allowed
the comparison between exercise with Tcore at resting values and exercise where Tcore had been
elevated by ~1.5°C. They found that exercise following passive heating was accompanied by
a significantly greater RPE than when the exercise was performed before heating. The
relatively short duration of exercise and model of passive heating meant that metabolic factors
were unlikely to explain the increased RPE and it was concluded that hyperthermia during
exercise is a causative element of increased RPE. Furthermore, cooling the head and face
during exercise following passive heating reversed the hyperthermia-induced increase in RPE.
The purpose of the present study was to further the work of Armada-da-Silva et al. (2004) and
investigate whether these results could be replicated, if the head-cooling intervention occurred
during the passive heating, as previous results have indicated this to be effective in reducing
subjective discomfort without affecting Tcore (Nunneley et al. 1982; Mündel et al. 2006).
METHODS
Nine physically-active, non-heat-acclimated subjects (6 male, 3 female) volunteered for this
study. Written consent was obtained and the study was performed according to the
Declaration of Helsinki, following approval by the Local Ethics Committee. Subjects’ mean
(SD) physical characteristics were: age: 21 (1) yrs, body mass: 80 (13 kg), V . O2max: 4.0 (0.6)
L.min -1 , peak power output: 286 (43) W. All trials were conducted during winter (Nov. to
Feb.) during which time the subjects’ acclimation to heat would be at a natural nadir.
The experimental protocol is shown in Figure 1. Subjects performed two 12-minute constantload
cycling tests at 70% VO2max in a warm-dry environment (34 ± 1°C, relative humidity <
1, 4