2007, Piran, Slovenia

Gravitational Physiology
THE EXERCISE-INDUCED SWEATING RESPONSE AFTER 35
DAYS OF HORIZONTAL BED REST
Igor B. Mekjavic 1 , Stelios Kounalakis 1,2 , Michail E. Keramidas 1,2 , Gianni Biolo 3 ,
Pietro E. di Prampero 4 , Marco Narici 5 , Rado Pisot 6 , and Ola Eiken 7
1 Jozef Stefan Institute, Ljubljana, Slovenia;
2 National and Kapodistrian University of Athens, Greece;
3 Università di Trieste - Ospedale di Cattinara, Trieste, Italy;
4 MATI Centro di Eccellenza - Università di Udine, Udine, Italy;
5 Manchester Metropolitan University, Alsager Campus, Cheshire, UK;
6 Institute for Kinesiology Research, University of Primorska, Koper, Slovenia;
7 Swedish Defence Research Agency, Karolinska Institutet, Stockholm, Sweden
Contact person: igor.mekjavic@ijs.si
INTRODUCTION
We have demonstrated that for a given combination of core and skin temperatures the
exercise sweating response may be modified by the magnitude of the relative work
rate (Eiken and Mekjavic 2004; Kacin et al. 2007). These studies were conducted by
manipulating the oxygen delivery to the working muscles either by experimentally
inducing ischaemia (Eiken and Mekjavic 2004), or with hypoxia (Kacin et al. 2007).
The aim of the present study was to evaluate whether the potentiation of the exercise
sweating response with increased relative work rate prevails, in conditions where the
ratio of relative:absolute work rate is changed while oxygen delivery to the working
muscles is not limited, either by perfusion or diffusion. The exercise sweating
response was compared prior to, and immediately after a 35-day horizontal bed rest
period, which induces cardiovascular and muscular deconditioning, resulting in a
decrease in aerobic capacity and muscle strength (Eiken and Mekjavic, 2002). By
conducting the exercise at the same absolute work rate, the post-bed rest exercise
induces a much greater relative work rate. If the potentiated sweating response
previously observed during ischaemic and hypoxic exercise is associated with
increased relative work rate per se, then the post-bed rest exercise sweating response
should be potentiated at given core and skin temperatures.
METHODS
Ten healthy male subjects with average ± SD age of 23.0±1.7 yrs, height 181.2±5.2
cm, body mass 76.3±9.0 kg, and V & O2max 4.1±0.7 L·min -1 participated in the study.
Following a medical examination they were housed in a ward at the Orthopaedic
Hospital Valdoltra. Subjects remained in a horizontal position for the entire 35-day
period, and were under 24-hour medical supervision during the study. Prior to the bed
rest, subjects conducted an incremental-rate exercise to exhaustion on a cycle
ergometer (Schiller CS-200, Switzerland), and a 40-min submaximal exercise test,
conducted at a work rate equivalent to 30% of the maximal work rate. Following the
bed rest, the subjects repeated the incremental-rate exercise to exhaustion, and also
conducted two submaximal exercises. One was conducted at the same absolute level
as in the pre-bed rest trial (Trial A), and the other at an absolute work rate, which
would induce the same amount of relative work rate in the post-bed rest exercise
(Trial R).
During the submaximal exercise we monitored rectal temperature (Tre; MSR 12,
Switzerland) 12 cm beyond the anal sphincter, skin temperatures (MSR 12,
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