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1 School of Human Movement Studies, Charles Sturt University, Bathurst, NSW, Australia
2 MRC/UCT Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
* To whom correspondence should be addressed. E-mail: fmarino{at}csu.edu.au.
There is evidence that athletes of (East) African ancestry currently outperform Caucasian runners in distance running. To date there are no published studies examining the performance of African and Caucasian runners in different ambient conditions. Accordingly, the purpose of this study was to examine the running performances and associated thermoregulatory responses of African and Caucasian runners in cool and warm conditions. On two separate occasions 12 (N = 6 African, N = 6 Caucasian) highly trained men ran on a motorized treadmill at 70% of peak treadmill running velocity followed by an 8 km self-paced performance run (PR) in cool (15 °C) or warm (35 °C) humid (60% relative humidity) conditions. Time to complete the PR in the cool was not different between groups (~27 min) but was significantly longer in warm conditions for Caucasian (33.0 ± 1.6 min) compared to African (29.7 ± 2.3 min, P < 0.01) runners. Rectal temperatures were not different between groups but were higher during warm conditions compared to cool conditions. During the 8km performance run in warm conditions sweat rates for African runners (25.3 ± 2.3 mL.min-1) were lower compared to Caucasian runners (32.2 ± 4.1 mL.min-1; P < 0.01). Relative rates of heat production were significantly less in African than in Caucasian runners when running in the heat. The finding that African runners ran faster only in the heat despite similar thermoregulatory responses as Caucasian runners is compatible with an exercise model in which performance during exercise in the heat is regulated by a feed-forward control of motor unit recruitment, the goal of which is to ensure an optimal rate of heat storage without the development of dangerous hyperthermia. According to this model, the superior running performance in the heat of this group of African runners can be partly attributed to their smaller size and hence their capacity to run faster in the heat whilst storing heat at the same rate as heavier Caucasian runners.
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