The human body operates on a circadian rhythm. This means that over a 24 hour period, various physiological processes will fluctuate that are influenced by environmental cues. For example, body temperature fluctuates throughout the day, as does hormone secretion, hunger and feelings of tiredness and alertness. When the sun goes down and it gets dark out, neurohormones are secreted in the brain to start preparing the body for sleep. When the sun rises and the body detects light, awakening is triggered. This circadian rhythm largely accounts for the feeling of “jet lag” when you cross time zones as you are suddenly out of whack.
As we develop a daily routine of eating, sleeping and training at the same time of day, the body adapts and tends to expect and prepare for this sequence of events. Naturally, this led to the hypothesis that sports performance is affected by habitual time of day training. In other words, if training regularly took place in the morning, then competition time would be better in the morning and worse at night. The same applies for habitual evening training.
A recent study published ahead of print in the European Journal of Applied Physiology tested this hypothesis. The researchers compared morning and evening time-trial performance, RPE and mood state in trained swimmers while factoring in habitual training times. The sample included 18 males and 8 females. Subjects performed 200 m time trials at 6:30am and 6:30pm in a randomized order.
When evaluated as a group, no significant differences were found between average 200 m performance time (p = 0.611). However, when the group was separated by habitual time of day training, significant differences were found in time of day testing. The athletes that typically trained in the mornings swam significantly faster during the morning 200 m time trial (p = 0.036) and vice versa (p = 0.011). In addition, lower RPE post warm-up, higher vigour and lower fatigue scores were documented in the morning session by the swimmers habituated to morning training.
The results indicate that habitual training time has a significant effect on diurnal variation in sports performance. This study is in support of several others that corroborate these findings. Additionally, this study further supports the notion that the body favors routine. Therefore, in an ideal setting, training times would be schedules at the same time of day as competition times. This of course can be difficult however if competition times vary or when dealing with athletes who have conflicting school and/or work schedules.
Rae, D. E., Stephenson, K. J., & Roden, L. C. (2015). Factors to consider when assessing diurnal variation in sports performance: the influence of chronotype and habitual training time-of-day. European Journal of Applied Physiology, 1-11.