Thermoregulatory strategies during short-term exercise at different intensities

Authors

  • CAROLINE M. SCOTT,

    1. Centre for Equine Studies, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU
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  • D. J. MARLIN,

    Corresponding author
    1. Centre for Equine Studies, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU
      Centre for Equine Studies, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU
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  • R. C. SCHROTER

    1. Department of Biological and Medical Systems, Imperial College of Science, Technology and Medicine, London SW7 2BX, UK
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Centre for Equine Studies, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU

Summary

Previously we have observed a decline in sweating rate (SR) during high intensity exercise in an incremental test protocol. In man, the sweating sensitivity (SR/°C) has been shown to vary with exercise intensity. The aim of the present study was to determine if thermoregulatory responses in the horse, a prolific sweater with a high rate of metabolic heat production, were modified by exercise intensity. The effect of 3 separate exercise intensities (50 (S), 70 (M) and 90% (F) V̇o2Peak on neck (SRN) and gluteal sweating rate (SRG), pulmonary artery (TPA), rectal (TREC) and skin temperatures on the neck (TSK-N) and gluteal region (TSK-G) were investigated. Horses were exercised for ˜2 min at each exercise intensity in a randomised order. The rate of increase in TPA increased with exercise intensity (P<.05) (0.27 ± 0.05, 0.43 ± 0.04 and 0.77 ± 0.05°C/min during S, M and F, respectively. The TPA and TSK temperatures at the onset of sweating were not different between exercise intensities (P>0.05). Despite the increased rate of heat production with increasing exercise intensity, sweating sensitivity decreased on both the neck [(P<.05) (18.2 ± 3.4 (S), 12.0 ± 3.5 (M) and 2.9 ± 0.7 (g/m2/min)/°C (F)] and gluteal region [(P<.05) (8.9 ± 2.0 (S), 5.1 ± 1.7 (M) and 0.8 ± 0.3 (g/m2/min)/°C (F)]. During exercise at 90% V̇o2peak sweating sensitivity and the rate of increase in skin temperature were markedly reduced compared to at 70% V̇o2peak. The present investigation demonstrates that the drive to thermoregulate is overridden during short-term, high-intensity exercise, resulting in greater heat storage (TPA) as a result of a lower SR sensitivity.

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