Thermoregulatory Responses To Repeated-sprint And Continuous Exercise

Abstract

While much research has investigated the thermoregulatory responses to continuous exercise, few studies have investigated the thermal strain of prolonged repeated-sprint exercise in the heat. PURPOSE The purpose of the present study (which had ethical approval) was to examine the physiological and metabolic responses to continuous and prolonged, repeated-sprint exercise in hot conditions (35 °C, RH 50%). METHODS Eight male, physically-active students (peak VO2: 51.9 ± 7.3 mL/kg/min) completed a graded exercise test (GXT), followed by 3 exercise trials. The initial exercise trial consisted of a 37-min repeated-sprint protocol divided into ∼2 min blocks consisting of a 4-s sprint, 100 s active recovery (35% peak VO2) and 20 s rest. The remaining two exercise trials (performed in a random order) were continuous in nature with workloads matched for either the same average mechanical work (Work) or the same estimated metabolic power (kJ) as that produced during the repeated-sprint protocol. Temperature measures (°C) were taken at rest and every 5 min during the repeatedsprint and continuous exercise protocols. RESULTS The intermittent exercise protocol was found to induce the highest rectal (Tre) and body (Tb) temperatures (38.4 ± 0.5°C, 37.9 ± 0.5°C), with the continuous work protocol eliciting the smallest Tre and Tb (37.7 ± 0.3°C, 37.3 ± 0.3°C). Significant differences in the Tre were found between the continuous work and both the continuous kJ and repeated-sprint exercise protocols after 20 min of exercise. Total oxygen consumption was significantly higher (P<0.05) during the continuous kJ exercise protocol (92.7 ± 5.5 L) when compared to both the repeated-sprint (82.9 ± 3.8 L) and the continuous work exercise protocols (68.7 ± 4.3 L). No Significant differences were found between exercise protocols in regards to skin temperature, muscle temperature or thermal gradient. CONCLUSIONS These results demonstrate that repeated-sprint exercise results in greater thermoregulatory strain than continuous exercise when matched for work, but not when matched for estimated metabolic heat production (kJ). While this indicates that repeated-sprint exercise may be less efficient than continuous exercise, further calculations suggest that this can be explained by the large energy expenditure during the recovery from repeated-sprint exercise.