Exercise performance tends to be better in the late afternoon/early evening (1–8 p.m.) than the morning (8–10 a.m.),[1] particularly for short-duration maximal exercise (e.g., a 30-second Wingate test or tests of jump height, repeated sprint ability, or maximal voluntary contraction).[2][3][1] Currently, there is limited evidence to suggest that a specific time of day is best for endurance exercise performance.[1]
The main mechanism that underlies this finding is core body temperature, which reaches a peak in the evening hours.[4][5] An increase in core body temperature may improve exercise performance by enhancing metabolic reactions, increasing the extensibility of connective tissue, reducing muscle viscosity, and increasing the conduction velocity of action potentials.[6] Moreover, using cold water immersion to decrease core body temperature before evening exercise has been shown to decrease muscular strength and repeated sprint ability.[7][8][9]
While exercise performance may be better in the evening than the morning at baseline, consistently training in the morning can offset this natural diurnal variation in performance. Indeed, long-term resistance exercise interventions that have participants train in the morning or evening report similar increases in strength and hypertrophy.[3] This suggests that training at a consistent time each day is more important than the time of day training takes place. Therefore, an individual interested in maximizing exercise adaptations should choose a time of day that suits their preferences and will facilitate long-term training adherence.
Besides consistently training in the morning, there are acute strategies that can diminish the natural diurnal variation in exercise performance, including exercising in a warm and humid environment,[10][11] performing an extended warm-up (e.g., 12 minutes of cycling at 50% of VO2max interspersed with brief accelerations of 5 seconds),[12][13][14] ingesting caffeine,[15][16] and listening to music.[17][18]