Physiological Effect of Pacing Tactics and Thermal Stress During 10-km Running

Abstract

When allowed to free choice, runners adopt a U shaped pattern of pacing during middle distance runs. In high level competition, runners may start at an unreasonably fast pace to stay with their competitors. Our understanding of how pace is regulated when the starting strategy is not freely chosen is incomplete. PURPOSE: We tested the hypothesis that running pace would change reciprocally with core temperature and [La-]. METHODS: Well-trained runners performed three experimental 10-km treadmill race simulations, one freely paced, one with increased starting pace and one with increased starting pace + increased heat stress. Gas exchange, core temperature, [La-] & RPE were measured. RESULTS: During the increased starting pace runs, subjects maintained pace for 2-4 km before slowing. During the final 5-km there was no difference in pace. Core temperature increased equally (37.5 ± 0.2 to 39.5 ± 0.5 °C) in all runs, With no differences in the last 5-km. VO2, HR, ventilation & [La-] increased more rapidly during the forced pace runs, but by 7-km was the same. VO2 averaged 85-90% of VO2max, and HR was >95%max during the last 6-km. By 5-km [La-] was constant between runs and was ∼8 mmol l-1 at the end. RPE was greater during the first 5-km of forced pace, but was not different during the last half. CONCLUSION: The hypothesis of reciprocal changes in pace vs core temperature and blood [La-] was supported. The data support the concept that exercise intensity is modulated in an anticipatory way to limit the magnitude of homeostatic disturbances and that slowing during mid-race may be a strategy to prevent a catastrophic collapse rather than a response to a homeostatic catastrophe.