Diurnal variation in repeated sprint performance cannot be offset when rectal and muscle temperatures are at optimal levels (38.5°C)

• Published in: Chronobiology international 2018-08, Vol.35 (8), p.1054-12
• Main Authors: Pullinger, Samuel A, Oksa, Juha, Clark, Liam F, Guyatt, Joe W F, Newlove, Antonia, Burniston, Jatin G, Doran, Dominic A, Waterhouse, James M, Edwards, Ben J
• Format: Article
• Language: English
• ISSN: 0742-0528; 1525-6073
• DOI: 10.1080/07420528.2018.1454938

The present study investigated whether increasing morning rectal temperatures (T ) to evening levels, or increasing morning and evening T to an "optimal" level (38.5°C), resulting in increased muscle temperatures (T ), would offset diurnal variation in repeated sprint (RS) performance in a causal manner. Twelve trained males underwent five sessions [age (mean ± SD) 21.0 ± 2.3 years, maximal oxygen consumption (V̇O max) 60.0 ± 4.4 mL.kg  min , height 1.79 ± 0.06 m, body mass 78.2 ± 11.8 kg]. These included control morning (M, 07:30 h) and evening (E, 17:30 h) sessions (5-min warm-up), and three further sessions consisting of a warm-up morning trial (M , in 39-40°C water) until T reached evening levels; two "optimal" trials in the morning and evening (M and E , in 39-40°C water) respectively, until T reached 38.5°C. All sessions included 3 × 3-s task-specific warm-up sprints, thereafter 10 × 3-s RS with 30-s recoveries were performed a non-motorised treadmill. T and T measurements were taken at the start of the protocol and following the warm-up periods. Values for T and T at rest were higher in the evening compared to morning values (0.48°C and 0.69°C, p