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

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.