Controlling rectal and muscle temperatures: Can we offset diurnal variation in repeated sprint performance?

ABSTRACT

The present study investigated whether increasing morning rectal temperatures (T_rec) to resting.evening levels, or decreasing evening T_rec or muscle (T_m) temperatures to morning values, would influence repeated sprint (RS) performance in a causal manner. Twelve trained males underwent five sessions [age (mean ± SD) 21.8 ± 2.6 yr, peak oxygen uptake ( peak) 60.6 ± 4.6 mL kg min⁻¹, stature 1.78 ± 0.07 m and body mass 76.0 ± 6.3 kg]. These included a control morning (M, 07:30 h) and evening (E, 17:30 h) session (5-min warm-up), and three further sessions consisting of a warm-up morning trial (M_E, on a motorised treadmill) until T_rec reached evening levels; and two cool-down evening trials (in 16–17°C water) until T_rec (E_Mrec) or T_m (E_Mmuscle) values reached morning temperatures, respectively. All sessions included a 3 × 3-s task-specific warm-up followed by 10 × 3-s RS with 30-s recoveries performed on a non-motorised treadmill. T_rec and T_m measurements were taken at the start of the protocol and following the warm-up or cool-down period. Values for T_rec and T_m were higher in the evening compared to morning values (0.45°C and 0.57°C, P < 0.05). RS performance was lower in the M for distance covered (DC), average power (AP) and average velocity (AV) (9–10%, P < 0.05). Pre-cooling T_rec and T_m in the evening reduced RS performance to levels observed in the morning (P < 0.05). However, an active warm-up resulted in no changes in morning RS performance. Diurnal variation in T_rec and T_m is not wholly accountable for time-of-day oscillations in RS performance on a non-motorised treadmill; the exact mechanism(s) for a causal link between central temperature and human performance are still unclear and require more research.

Keywords:

• Active warm-up
• passive cool down
• core temperature
• muscle temperature
• time-of-day
• repeated accelerations
• running

Acknowledgments

We would like to thank the participants who participated in the study. We would also like to acknowledge the intellectual input of Professor James M. Waterhouse who sadly passed away in October 2016.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.

Practical implications

Muscle force production and RS performance are higher in the evening than the morning. Our results showed no evidence that increasing morning rectal temperature (by an active warm-up) to evening resting values leads to a positive change in RS performance on a non-motorised treadmill. However, decreasing evening rectal and/or muscle temperatures (by immersion in a cool bath) to morning resting values leads to a negative effect. These findings help us to un-pick the contribution of core and muscle temperature to the diurnal variation in RS performance.