The circadian clock regulates metabolic responses to physical exercise

Effect of timed exercise interventions on patient-reported outcome measures: A systematic review

BACKGROUND

Exercising at a specific time of day has the potential to mitigate the negative effects of disrupted circadian rhythms caused by irregular work and sleep schedules on the development of chronic diseases. Afternoon/evening exercise is postulated to be superior to morning exercise for various health outcomes, but patient acceptance of timed exercise remains unclear. The aim of this systematic review was to assess the impact of exercise timing on patient-reported outcomes (PROMs).

METHODS

We conducted a systematic review, following Cochrane and PRISMA guidelines (PROSPERO: CRD42022322646). We systematically searched databases including MEDLINE, SCOPUS, Embase, APA PsycInfo, CINAHL, and Web of Science, to identify studies which reported on PROMs related to timed exercise interventions: either acutely after a bout of exercise or following extended training (>1 month). Studies were included if they reported primary data from randomized or non-randomized experiments of timed exercise interventions (against any comparator), published in English until August 2023 and reporting on any PROM. Machine-learning software (AR Reviews) was used to aid in abstract screening. Subsequently, two independent reviewers reviewed the included full texts, extracted study details (participants, interventions, outcomes), and evaluated the risk of bias using Cochrane tools (ROB-2 and ROBINS-I). Exercise interventions were summarized using the TIDieR reporting method and results were presented in accordance with the Synthesis Without Meta-analysis (SWiM) guidelines for systematic reviews.

RESULTS

Seventeen studies with 403 participants were included in the review. The interventions varied widely in exercise modality, duration, and participant characteristics, contributing to substantial heterogeneity in the findings. Most studies found no significant impact of exercise timing on PROMs. There was some inconsistency between studies for certain outcomes.

DISCUSSION

The review suggests that there are no clear detrimental effects of afternoon or evening exercise on PROMs compared to morning exercise. However, the lack of homogeneity in study populations and small sample sizes resulting in low power for PROM outcomes are major limitations of the research in this field. If future research confirms the metabolic advantages of afternoon/evening exercise, this may be an acceptable alternative for individuals.

Wearables in Chronomedicine and Interpretation of Circadian Health

Wearable devices have gained increasing attention for use in multifunctional applications related to health monitoring, particularly in research of the circadian rhythms of cognitive functions and metabolic processes. In this comprehensive review, we encompass how wearables can be used to study circadian rhythms in health and disease. We highlight the importance of these rhythms as markers of health and well-being and as potential predictors for health outcomes. We focus on the use of wearable technologies in sleep research, circadian medicine, and chronomedicine beyond the circadian domain and emphasize actigraphy as a validated tool for monitoring sleep, activity, and light exposure. We discuss various mathematical methods currently used to analyze actigraphic data, such as parametric and non-parametric approaches, linear, non-linear, and neural network-based methods applied to quantify circadian and non-circadian variability. We also introduce novel actigraphy-derived markers, which can be used as personalized proxies of health status, assisting in discriminating between health and disease, offering insights into neurobehavioral and metabolic status. We discuss how lifestyle factors such as physical activity and light exposure can modulate brain functions and metabolic health. We emphasize the importance of establishing reference standards for actigraphic measures to further refine data interpretation and improve clinical and research outcomes. The review calls for further research to refine existing tools and methods, deepen our understanding of circadian health, and develop personalized healthcare strategies.

Circadian rhythm in sportspersons and athletic performance: A mini review

Circadian rhythms in the physiological and behavioral processes of humans play a crucial role in the quality of living and also in the magnitude of success and failure in various endeavors including competitive sports. The rhythmic activities of the body and performance in sportspersons do have a massive impact on their every cutthroat competition. It is essential to schedule sports activities and training of players according to their circadian typology and time of peak performance for improved performance and achievement. In this review, the focus is on circadian rhythms and diurnal variations in peak athletic performance in sportspersons. Accuracy and temporal variability in peak performance in an individual could be attributed to various factors, namely chronotype, time of the day, body temperature, jetlag, hormones, and prior light exposure. Circadian rhythm of mood, alertness, T-core, and ultimately athletic performance is not only affected by sleep but also by circadian variations in hormones, such as cortisol, testosterone, and melatonin. There are, however, a few reports that are not consistent with the conclusions drawn in this review. Nevertheless, circadian rhythm and performance among sportspersons and athletes are important areas of research. This review might be useful to the managers and policymakers associated with competitive sports and athletic events.

Skeletal muscle gene expression dysregulation in long-term spaceflights and aging is clock-dependent

The circadian clock regulates cellular and molecular processes in mammals across all tissues including skeletal muscle, one of the largest organs in the human body. Dysregulated circadian rhythms are characteristic of aging and crewed spaceflight, associated with, for example, musculoskeletal atrophy. Molecular insights into spaceflight-related alterations of circadian regulation in skeletal muscle are still missing. Here, we investigated potential functional consequences of clock disruptions on skeletal muscle using published omics datasets obtained from spaceflights and other clock-altering, external (fasting and exercise), or internal (aging) conditions on Earth. Our analysis identified alterations of the clock network and skeletal muscle-associated pathways, as a result of spaceflight duration in mice, which resembles aging-related gene expression changes observed in humans on Earth (e.g., ATF4 downregulation, associated with muscle atrophy). Furthermore, according to our results, external factors such as exercise or fasting lead to molecular changes in the core-clock network, which may compensate for the circadian disruption observed during spaceflights. Thus, maintaining circadian functioning is crucial to ameliorate unphysiological alterations and musculoskeletal atrophy reported among astronauts.

Chronotype at the beginning of secondary school and school timing are both associated with chronotype development during adolescence

The misalignment between late chronotypes and early school start times affect health, performance and psychological well-being of adolescents. Here we test whether, and how, the baseline chronotype (i.e. chronotype at the beginning of secondary school) and the school timing affect the magnitude and the direction of the developmental change in chronotype during adolescence. We evaluated a sample of Argentinian students (n = 259) who were randomly assigned to attend school in the morning (07:45 a.m.–12:05 p.m.), afternoon (12:40 p.m.–05:00 p.m.) or evening (05:20 p.m.–09:40 p.m.) school timings. Importantly, chronotype and sleep habits were assessed longitudinally in the same group of students along secondary school (at 13–14 y.o. and 17–18 y.o.). Our results show that: (1) although chronotypes partially align with class time, this effect is insufficient to fully account for the differences observed in sleep-related variables between school timings; (2) both school timing and baseline chronotype are independently associated with the direction and the magnitude of change in chronotype, with greater delays related to earlier baseline chronotypes and later school timings. The practical implications of these results are challenging and should be considered in the design of future educational timing policies to improve adolescents’ well-being.