Evening workouts produce better endurance performance than morning sessions, but the size of that advantage depends on your chronotype and sleep timing. A study published in the European Journal of Applied Physiology finds that individual differences in circadian phenotype explain up to a quarter of the variation in how much better people perform later in the day.
What they found
Researchers at the University of Lancashire recruited 24 healthy young adults (12 men, 12 women) and asked each to complete a 10-minute cycling time trial on two separate occasions once in the morning (08:00-09:00) and once in the evening (17:00-18:00), in a randomized crossover design. Before each trial, the team standardized participants’ sleep, diet, and physical activity to isolate the effect of time of day.
The results were clear. Mean power output, peak power, and total distance covered were all significantly higher in the evening compared with the morning (p < 0.01 for all three measures). On average, participants cycled farther and generated more watts in the late afternoon, even though the effort felt the same to them. Their heart rate, blood lactate levels, and ratings of perceived exertion were statistically indistinguishable between the two time slots, meaning the evening advantage was not simply a matter of trying harder. Core body temperature was higher in the evening (p = 0.026), but this did not statistically explain the performance differences, suggesting other biological mechanisms such as circadian-driven changes in muscle metabolism, neuromuscular coordination, or fuel utilization are at work.
The study’s central contribution, however, is in linking these time-of-day performance swings to circadian phenotype. Each participant completed the Composite Morningness Questionnaire (a validated measure of chronotype) and wore an actigraphy watch for seven days to capture objective sleep timing, including sleep midpoint (the halfway point between sleep onset and wake time).
Chronotype correlated significantly with the magnitude of the morning-evening performance gap (r = -0.47, p = 0.019), accounting for 22 percent of the variance. Sleep midpoint was an even stronger predictor (r = 0.52, p = 0.003), explaining 27 percent of the variance. In practical terms, evening-type individuals showed larger evening performance advantages, while morning-type individuals showed a smaller boost perhaps because their natural peak is earlier in the day. The fact that the two markers, chronotype (a behavioral preference questionnaire) and sleep midpoint (an objective actigraphy measure), both independently predicted the gap strengthens the case that the association is real, not a measurement artifact.
Why it matters
The finding that circadian phenotype explains roughly a quarter of diurnal performance variability has practical implications for athletes, coaches, and clinicians. Exercise testing and prescription rarely account for what time of day a person trains or competes, let alone whether that timing aligns with their internal clock. These results suggest that both dimensions matter.
For athletes, scheduling key training sessions or competitions in the late afternoon or early evening could yield measurable performance benefits, especially for those who naturally lean toward eveningness. For coaches and sports scientists, the study underscores the value of assessing chronotype and sleep timing before making decisions about training schedules or interpreting fitness tests. A morning test may systematically underestimate an evening-type athlete’s true capacity.
The implications extend beyond elite sport. Sleep timing and chronotype are modifiable to some degree through light exposure, consistent sleep schedules, and phased training. Understanding that these factors account for meaningful performance variation opens the door to personalized exercise timing interventions rather than one-size-fits-all scheduling.
Limits
The study included only 24 participants, all healthy young adults, which limits generalizability to older populations, clinical groups, or elite athletes. The 10-minute cycling time trial is a controlled laboratory measure, not a full competition or field setting. The researchers note that performance in longer-duration events or different exercise modalities (strength, sprint, team sports) may follow different diurnal patterns. Additionally, while the study controlled for prior sleep and diet, the controlled laboratory environment itself may differ from real-world training conditions.
Bottom line
Evening endurance performance is systematically better than morning performance in young healthy adults, and individual circadian markers, chronotype and sleep midpoint, explain a substantial portion of the variation. Assessing a person’s internal clock could help optimize when they train and compete, and may improve the accuracy of exercise testing. For anyone who has ever wondered why their morning workout feels harder than their evening one, the answer may lie not in motivation or willpower but in the circadian program running inside every cell of their body.
Source
Singh A, Ahmed S, Hesketh SJ. Circadian phenotype is associated with diurnal variation in human exercise performance. European Journal of Applied Physiology. 2026. Online ahead of print. DOI: 10.1007/s00421-026-06352-0. PMID: 42455307.