2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
of change in the sweating rate with increased exercise intensity is demonstrated to be almost
identical to the change in the rated perceived effort (Kondo et al., 2000; Yanagimoto et al.,
2002). These results imply that the sweating response to exercise, and the intensity-dependent
sweating response (Kondo et al., 2000; Yanagimoto et al., 2002, 2003), may result from a
change in central command. In contrast, it is reported that central command may attenuate
cutaneous vascular conductance (Shibasaki et al. 2006).
Peripheral reflexes in muscle: It has been reported that changes in sweating are influenced by
afferents signals from exercising muscle (Gisolfi and Robinson, 1970; Van Beaumont and
Bullard, 1963). In humans, sweating increases within a few seconds of exercise commencing,
and without a change in thermal factors, when sweating is already active (Van Beaumont and
Bullard, 1963). Kondo et al. (1997) indicated that the increase in the sweat rate was
significant during passive limb movement, which means that mechanoreceptors in working
muscle are stimulated predominately. In addition, the mechanoreceptors enhance sweating but
not cutaneous vascular conductance (Shibasaki et al., 2004). However, it is questioned
whether these earlier studies actually stimulated the mechanoreceptors, indicating that we
could perhaps observe effects of mechanoreceptors on heat loss responses in the future.
It has been reported that the sweat rates on the forearm and chest during post-exercise
ischemia were significantly higher than baseline rates (Crandall et al., 1998; Kondo et al.,
1999; Shibasaki et al., 2003). Since muscle metaboreceptor afferents are activated during
ischemia, while muscle relaxation eliminates both central command and the muscle
mechanoreceptor afferent, the sweating is modulated by afferent signals from muscle
metaboreceptors. In contrast, muscle metaboreceptors would inhibit cutaneous vascular
conductance by a reduction of the active vasodilator system (Crandall et al., 1998).
Since all the earlier studies of muscle metaboreceptors used isometric exercise, the effects of
these receptors on the heat loss responses during dynamic exercise remains unclear. Recently,
it was reported that sweating during dynamic exercise was greater in a condition where thigh
blood flow was partially occluded (50 mmHg pressure), in which muscle metaboreceptors
may be activated, than in the control condition (Eiken ad Mekjavic, 2004). We also confirmed
effects of muscle metaboreceptors on both sweating and cutanous vascular conductance using
similar methods (unpublished data). These results indicate that non-thermal factors associated
with ischemia in working muscle facilitate the sweating response, whilst simultaneously
inhibiting the cutaneous vascular response during dynamic exercise in humans.
Other non-thermal factors: Sweating and cutaneous vascular responses during exercise are
influenced by the baroreflex (Mack et al., 1995) and osmoreflex (Takamata et al., 1998).
Unloading the cardiopulmonary baroreceptors and an increasing plasma osmolality reduces
the sweating and skin blood flow responses during exercise. It is suggested that decreases in
plasma volume induce a reduction in the sensitivity of the heat loss responses to body
temperature changes, while an increased plasma osmolality changes the thresholds for
sweating and vasodilation (Takamata et al., 1998). Although it has been reported that
sweating at rest is influenced by emotional and mental stimulation (Kuno, 1956; Ogawa,
1975), it is not well known whether there are effects of emotional and mental stimulation on
heat loss responses during exercise.
From these results, a model of the heat loss responses during exercise is proposed (Figure 1).
Increases in thermal factors always have a positive effect on heat loss responses. On the other
hand, non-thermal factors facilitate the sweating response while simultaneously inhibiting
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