Jul 2026· European Journal of Applied Physiology· 0 citations· 36 references
Medicine
TL;DR
It is demonstrated that endurance exercise performance is enhanced in the evening compared with the morning and suggested that behavioural markers of circadian phenotype are associated with the magnitude of diurnal variation in performance.
Abstract
Purpose
Time-of-day variation in exercise performance is well established, but the contribution of circadian phenotype to the magnitude of these differences remains unclear. This study examined diurnal variation in aerobic exercise performance and determined whether chronotype and sleep timing were associated with morning-evening differences in performance.
Methods
Twenty-four healthy young adults (12 male, 12 female) completed a randomised crossover protocol consisting of a 10-min cycling time trial performed in the morning (08:00-09:00) and evening (17:00-18:00). Pre-trial sleep, diet, and physical activity were standardised, and circadian phenotype was characterised using the Composite Morningness Questionnaire and 7-day actigraphy.
Results
Mean power, peak power, and distance covered were all significantly higher in the evening compared with morning (p < 0.01). Chronotype (r = - 0.47, p = 0.019) and sleep midpoint (r = 0.52, p = 0.003) were significantly associated with the magnitude of the diurnal performance difference, accounting for 22% and 27% of the variance, respectively. Heart rate, blood lactate, and perceived exertion responses were similar between conditions, indicating comparable physiological strain. Core temperature was higher in the evening (p = 0.026), but did not explain performance differences.
Conclusions
These findings demonstrate that endurance exercise performance is enhanced in the evening compared with the morning and suggest that behavioural markers of circadian phenotype are associated with the magnitude of diurnal variation in performance. Time-of-day and circadian phenotype should therefore be considered when optimising exercise testing and prescription.
Chronotype describes differences in the timing of daily rhythms, regulated by the circadian system. These patterns are classified as morning or evening chronotypes. Studies show increased impulsivity, poorer health behaviors, and greater cardiometabolic risk among evening chronotypes. However, few studies evaluate these effects relative to circadian biomarkers. Additionally, time of day may impact how chronotype affects behaviors. Participants completed an eating in the absence of hunger task during morning and evening sessions. Participants were served oatmeal, then given access to snack foods. Calories consumed from each snack type was the primary outcome. Participants fasted for ≥8 h before a 9 AM morning task. For the evening task, participants fasted for 2 h and completed an 8 PM task. Dim light melatonin onset (DLMO) was measured the day following the morning task. Covariate-adjusted models evaluated differences in caloric intake across food types and sessions, and tested associations between caloric intake and DLMO. 113 participants completed the protocol (57 female; age: M = 35.6, SD = 9.87). Significant time-of-day effects were observed, with lower intake of bland (B = -5.67, p < 0.001) and salty foods (B = -15.53, p = 0.015) in the evening. Order effects showed greater intake during the second administration for total calories and all categories (ps < 0.01). Later DLMO was linked to greater appetite ratings. These finding suggest that those with later circadian timing may have greater hedonic interest in food. Future research should explore interactions between chronotype, circadian timing, and environmental factors shaping eating behaviors.
Carson Hernandez, Steven E. Carlson, Bradley Appelhans et al.· Eating Behaviors· 0 citations
Objective Exercise timing may influence metabolic responses and body composition, but the extent to which circadian genetic variation contributes remains unclear. The PER3 rs228697 polymorphism has been linked to chronotype-related traits, although its relevance to exercise timing remains uncertain. This exploratory study examined whether body-composition responses to morning versus afternoon moderate-intensity continuous training (MICT) differed according to PER3 rs228697 genotype in overweight/obese university students. Methods In this 8-week supervised intervention, 31 overweight/obese university students performed MICT in the morning (7:00–10:00) or afternoon (16:00–19:00). Participants with the CC genotype were allocated to a morning training group (CC-AM) or an afternoon training group (CC-PM), and G-allele carriers were included in an afternoon group (G-PM). Body weight, body mass index (BMI), waist circumference, body fat percentage, total fat mass, and regional fat mass were assessed before and after the intervention. Circadian preference, physical activity, sleep quality, and fatigue were also evaluated. Because the G-PM subgroup was very small, findings for this subgroup were treated as exploratory. Results Across the overall sample, body weight, BMI, waist circumference, body fat percentage, and total fat mass decreased over the 8-week intervention. In descriptive subgroup analyses, the CC-PM group showed larger reductions in several body-composition outcomes, including body weight, BMI, waist circumference, body fat percentage, and total fat mass, than the CC-AM group. A similar pattern was observed for several regional fat measures, particularly trunk, android, and gynoid fat mass. By contrast, findings for G-allele carriers were difficult to interpret because of the very small subgroup size. Estimated between-group differences were generally modest and imprecise, and behavioral chronotype did not clearly correspond with PER3 genotype. Conclusions In this exploratory sample of overweight/obese university students, 8 weeks of MICT was associated with favorable changes in several body-composition outcomes. Among CC genotype carriers, afternoon training was associated with descriptively greater improvements than morning training; however, the estimates were imprecise and do not support strong conclusions regarding genotype-based exercise-time matching based on PER3 rs228697 alone. Larger, well-controlled studies with objective circadian phenotyping are needed to clarify the potential role of genotype-informed exercise timing in personalized weight management.
Yuchen Wang, Chunyan Xu, Juan Tong· Frontiers in Physiology· 0 citations
This study aimed to compare subjective and objective circadian measures with a focus on sex differences and cognition in healthy older adults. A total of 126 participants (aged 65–90 years) completed the Horne & Ostberg Morning-Eveningness Questionnaire (MEQ) and the Circadian Type Inventory (CTI) to assess their morning-evening preference and four circadian traits: rigidity vs flexibility (CTI-FR) and languidity vs vigor (CTI-LV). These self-report measures were compared to actigraphy data from a sub-cohort of 63 individuals who wore wrist actigraphs for 24 hours a day over a 7-day period. Results showed that cognitively healthy older adults tend towards rigidity and vigor (on the CTI) and morningness (on the MEQ). Overall, the languid vs vigorous types and flexible vs rigid types displayed differences in MEQ scores. Sex moderated the association between the CTI-LV and MEQ with a steeper association in males than females (p = 0.012). Actigraphy data showed that males had less stable (interdaily stability, IS, p = 0.03) and more fragmented (interdaily variability, IV, p = 0.001) circadian rhythms than older females. Subjective MEQ scores were strongly predictive of acrophase time (p = 0.009) in males but not females. Using information processing speed (IPS) as a marker of cognitive function, we found that greater circadian rhythm fragmentation (IV) was linked to slower verbal IPS (p = 0.004) in males. Morning preference on the MEQ predicted faster spatial IPS in the overall sample (p < 0.001). These findings provide preliminary evidence of the relationship between subjective sleep preferences and objective circadian data in cognitively healthy older adults with notable sex differences in these relationships.
Natalie S Pandher, L. Yack, E. Li et al.· PLoS ONE· 0 citations
Study Objectives To develop and initially validate the Circadian Disruption Index (CDI), a self-report measure of circadian disruption, and obtain preliminary evidence of its responsiveness to circadian health education. Methods In Study 1, 244 participants completed a 22-item CDI version and external measures. The sample was randomly divided for exploratory and confirmatory factor analyses. Internal consistency, external associations, and discrimination of poor sleep quality were examined. In Study 2, 72 postgraduate students completed the CDI before and 1 week after a 16-hour circadian health education program in an uncontrolled pre-post design. Results Analyses yielded a 15-item, three-factor structure comprising rhythm stability and light exposure, behavioral habits and diet, and sleep quality and subjective complaints. Total-score internal consistency was acceptable (Cronbach's = 0.871). Confirmatory factor analysis showed a comparative fit index of 0.902 and a root mean square error of approximation of 0.072, although the Tucker-Lewis index was 0.882. CDI scores correlated with sleep quality, chronotype, corrected midsleep on free days, depression, and anxiety, but not social jetlag. The area under the curve for poor sleep quality was 0.807 (95% confidence interval, 0.753-0.862), with an exploratory cutoff of [≤] 23. In Study 2, CDI scores decreased from 22.26 to 19.88 (p = 0.002; Cohen's dz = 0.36). Conclusions The CDI demonstrated satisfactory internal consistency, a meaningful multidimensional structure, and responsiveness to short-term changes following circadian health education, supporting its potential utility for assessing circadian disruption and monitoring circadian-related behavioral changes.
Y. Fan, M. Tian, J. Xu et al.· medRxiv· 0 citations
Skin temperature showed promising feasibility for in-field circadian rhythm estimation after only three days, potentially facilitating research on circadian rhythms and health and validation against core body temperature and melatonin sampling is warranted.
Vaida T R Verhoef, K.C.H.J. Smolders, Geert Peeters et al.· Chronobiology International· 0 citations
In characterizing sleep and circadian health, the day-to-day regularity of sleep-wake timing strongly predicts health outcomes, outperforming short sleep duration in prospective associations with mortality and new-onset disease. It is unknown whether biological (e.g., sleep and circadian physiology) and sociocultural (e.g., exposures that affect sleep-wake timing) sex differences lead to differences in day-to-day sleep-wake regularity or modify its prospective associations with health outcomes. Here, we present findings from a UK Biobank study of 506,582 person-days of accelerometer recordings across 73,647 middle-aged adults preceding 549,009 person-years of follow-up. We compared SRI scores between males and females and evaluated whether all-cause, cardiovascular, and cancer mortality differed across SRI groups by sex. Custom contrasts were used to compare estimated marginal means across specific SRI-sex combinations. Females were overrepresented among very high (SRI [≥]90) and underrepresented among very low (SRI <60) groups. After adjustment for demographic, health, and behavioral covariates, males still had higher odds than females of exhibiting SRI <60. Low SRI and male sex were synergistically associated with higher mortality rate. Demographic, health, and behavioral covariate-adjusted models showed stronger and more dose-dependent associations between low SRI and mortality among males than females. Although the omnibus SRI x sex interaction terms were not statistically significant, the interaction contrast for SRI <60 versus [≥]90 differed by sex, suggesting a possible sex difference in mortality rates at very low SRI. Together, our findings suggest that males may be more vulnerable than females to the mortality risk associated with highly irregular sleep-wake schedules.
M. Czeisler, J. Leota, F. Le et al.· medRxiv· 0 citations