The effects of heat acclimation on physiological responses to sprint interval training at various pedal resistances

Abstract

Heat acclimation (HA) is an effective strategy used to prepare athletes for competing in hot conditions which aims to improve thermoregulation and reduce physiological stress. However, traditional HA modalities are time consuming. Therefore, implementing repeated sprint training into a HA protocol may provide an alternate time efficient strategy to acclimate. However, most studies investigating repeated sprint training use 0.075 kg·kg^-1 pedal resistance due to resistance as a variable being unexplored. Thus, the aim of the study was to compare the physiological responses of 0.075 kg·kg^-1 and 0.085 kg·kg^-1 sprint interval training (SIT) pedal resistances within a 3-week intermittent HA protocol. The study used a parallel groups design. Fourteen physically active adults completed an incremental time till exhaustion (TTE), Wingate test and a 15 min time trial at 38ºC and 30% relative humidity pre-intervention, control and post-intervention. For training, participants were stratified into a 0.075 kg·kg-1 pedal resistance training group (7.5TG; age: 21 ± 2 yrs, height: 181 ± 7 cm, body mass: 78 ± 13 kg, VO_2MAX: 50.0 ± 10.7 ml·kg·min-1) and a 0.085 kg·kg^-1 pedal resistance training group (8.5TG; age: 21 ± 3 yrs, height: 179 ± 10 cm, body mass: 79 ± 12 kg, VO_2MAX: 49.7 ± 12.6 ml·kg·min^-1) based on the 15 min time trial performance. Both groups completed 6 x 15 s cycle sprints with 30 s rest followed by a 30 min moderate cycle at 38ºC and 30% relative humidity three times a week for three weeks. The results show following HA, the 7.5TG induced no change in muscle oxygenation. Conversely, the 8.5TG during the repeated sprints saw a significant increase in the rate of the fast desaturation slope during sprint 1 (P = 0.05), and the duration of fast desaturation of sprint 6 decreased significantly (P = 0.03), with this change associated with greater power and lower heart rate. There was a significant increase in localised sweat rates in both groups (P = < 0.01). The incremental TTE maximal power in the 7.5TG saw significant improvements from pre-post HA (P = 0.01) and control-post HA (P = 0.01) however the 8.5TG saw a significant improvement from pre-post HA (P = 0.04) but not control-post HA (P = 0.15). Conversely, the Wingate test and 15 min time trial performance saw no change in both groups (P > 0.05). This study demonstrates intermittent HA can improve incremental TTE and sweat rate in the heat regardless of pedal resistance used however a heavier pedal resistance seems to offer a different training stimulus within the muscle. Therefore, pedal resistance within SIT should be considered in line with the needs of the athlete.

Date of Award	1 Mar 2024
Original language	English
Awarding Institution	Abertay University
Supervisor	John Babraj (Supervisor) & Andrew Marley (Supervisor)