At what time of day does physical performance peak? Original paper

Many factors can influence the timing of peak physical performance, including the time since prior physical activity, at what time a person usually exercises, food intake, sleep, environmental factors, and the biological circadian system, which optimally times physiological functions relative to the 24-hour environmental cycle. As such, there are specific times of day when physiological functions that directly impact performance (e.g., core body temperature and subjective alertness) reach their highest and lowest points.^[1][2] World records in sports are usually broken in the early evening. Of course, there is a bias for scheduling sporting events in the early evening, due to television demands, but it’s also the time of day when body temperature tends to be highest.^[3] Could later in the day be the best time to exercise?

This systematic review and meta-analysis of 63 randomized controlled trials investigated daytime variations in maximum endurance and strength performance. The outcomes assessed were performance on endurance exercise tests (e.g., time to exhaustion and time trials), the 30-second Wingate test (an anaerobic fitness test), handgrip strength tests, and jump height tests. Effects were calculated using the difference between the peak performance measurement (whenever it occurred) and the performance measurement reported between 8 and 10 a.m.

There was little evidence to suggest that there were variations in endurance exercise performance during the day: 1 study (out of 9) reported a significant difference, with higher performance in the evening compared with the morning. In contrast, peak performance on the Wingate and jump height tests occurred between 1 and 8 p.m. Eight of 12 studies that examined handgrip strength reported variations during the day; in these studies, peak performance occurred between 2 and 9 p.m.

The meta-analysis of 29 studies demonstrated that peak performance occurred later than 8 to 10 a.m. for each exercise test. The effect size was small for the endurance exercises and handgrip strength, medium for the Wingate test, and large for jump height.

The lackluster result for endurance exercise performance may be due to a wide variation in the exercise tests used among studies.

Since only one-fifth of the participants were women and the average age of participants from each study ranged from 18 to 33, the results may not be generalizable to women and older adults. Also, the risk of bias was moderate to high. Many studies failed to report basic participant characteristics, did not perform the tests in standardized conditions, and/or showed insufficient data reporting. Moreover, a sample size calculation was missing in almost every study. These issues reduce our confidence in the findings.