Influence of air flow and skin temperature on sweating at the onset, during and following exercise

Abstract

The influence of convective air flow (W_v), skin temperature (T¯_sk) and rapid changes in work rate on local and whole body evaporative sweat loss ([mdot]_sw) has been investigated in 4 healthy male subjects using the technique of resistance hygrometry. The results showed that changes in sweat rate, measured from a capsule placed on the chest or subscapular region of the mack [mdot],_w(cap), can be elicted rapidly (t_1/2< ls) at the onset and cessation of exercise through the response is dependent on T¯_stand the prior thermal slate of the subject. During exercise, [mdot]_sw and [mdot]_SW(cap) were correlated and the latter variable showed a close temporal relationship with the increase in core temperature measured either in the rectum (T_re) or oesophagus though the association could be affected by sudden changes in W_V. At low W_V the sensitivity of [mdot]_sw to changes in T_re and T¯_sk appeared to diminish. Sudden decreases in work rate by reducing running speeds from 16kmh^-1 to 8kmh ^-1 and 14 6kmh^-1 to 11 3kmh^-1 produce a transient increase in [mdot]_sw(cap) which persisted for some minutes. The rise in [mdot]_sw(cap) was associated with an increase in T_sk at the capsule site despite the maintenance of W_V at its high (45ms^-1) prior level. The responses of [mdot]_sw(cap) and [mdot]_swwere little affected by directional changes in W_V, they were the same irrespective of whether the subjects ran with a following, or against a head wind. It is concluded that during exercise the integrating and modulating effects of skin temperature from different regions of the body are responsible for the control of sweat loss under conditions of constant central thermal drive. The practical applications of these results are discussed in relation to running outdoors.