Abstract
1266 Adjustment in the combined activity of sympathetic and parasympathetic nervous systems (SNS and PNS) is a part of acclimation to heat. Spectral analysis of heart rate variability (HRV) was used to assess the changes in sympatho-vagal balance resulting during exercise-heat acclimation. HRV of eight healthy volunteers at the end of mild exercise (VO2≅1L O2/min) in heat (45 °C, 30% rh) and comfort (21 °C, 60% rh) conditions was compared before and after ten days of the exercise-heat acclimation. Spectral characteristics of HRV at the end of exercise were analyzed. Total power spectrum density (Pt) was divided to low (Pl) (0<Pl<O.15 Hz) and high (Ph) (0.15<Ph<0.5 Hz) bands. The ratios Pl/Ph and Ph/Pt were accepted as indices of SNS and PNS tone, respectively. TableTableThe results indicate that acclimation causes a shift towards the prevalence of SNS tone only during exercise in heat but not when exercising in comfortable conditions.
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