Time for Exercise? Exercise and Its Influence on the Skeletal Muscle Clock

Disrupted rest-activity circadian rhythms are associated with all-cause mortality in patients with chronic kidney diseases

Circadian rhythms are important biological contributors to health. Rest activity rhythms (RAR) are emerging as biomarkers of circadian behavior that are associated with chronic disease when abnormal. RAR have not yet been characterized in chronic kidney diseases (CKD). Leveraging the National Health and Nutrition Examination Survey (2011-2014), patients with CKD (n = 1114; Mean [95% CI]: Age, 50 [58-61] y; 52% female) were compared with non-CKD individuals (n = 5885; Age, 47 [46-48] y; 52% female). Actigraphy data were processed for RAR parameters including rhythmic strength (amplitude), the rhythm adjusted mean (mesor), the timing of peak activity (acrophase), activity regularity (inter-daily stability), and activity fragmentation (intra-daily variability). Cox regression was performed to assess RAR parameters for the prediction of all-cause mortality. Compared to non-CKD adults, patients with CKD had a lower rhythmic amplitude and mesor, and exhibited greater fragmentation and less day-to-day stability in RAR (ps < 0.001). Among CKD patients, a lower rhythmic amplitude (HR [95% CI]: 0.88 [0.82-0.96]; p < 0.001), a lower rhythm adjusted mean (0.87 [0.81-0.95]; p = 0.002), and a higher daily activity fragmentation (1.87 [1.10-3.18]; p = 0.023) were associated with an increased risk of all-cause mortality. Patients with CKD showed dampened rhythmic amplitudes and greater fragmentation of activity that were associated with a higher risk of all-cause mortality. These findings demonstrate a relationship between circadian disruption and prognosis in patients with CKD.

Mechanisms of exercise intervention in type 2 diabetes: a bibliometric and visualization analysis based on CiteSpace

Objective

Type 2 diabetes (T2D) is a common chronic metabolic disease, and its prevalence is increasing globally. Exercise is crucial for T2D management, yet many aspects of its mechanisms remain unclear. This study employs CiteSpace to reveal research hotspots and frontier issues in exercise intervention for T2D.

Method

A literature review spanning from January 1, 2013 to December 31, 2022, was conducted using the Web of Science Core Collection (WoSCC), with keywords including "exercise," "type 2 diabetes," and "mechanisms." We analyzed network diagrams generated by CiteSpace, which depicted relationships among countries, authors, and keywords.

Results

This study includes 1,210 English papers from 555 journals, affiliated with 348 institutions across 80 countries/regions. Notably, the United States, China, and the United Kingdom account for nearly half of all publications. The University of Copenhagen leads in publication volume, followed by Harvard Medical School and the University of Colorado. Key authors include Kirwan, John P (Case Western Reserve University), Malin, Steven K (Rutgers University), and Pedersen, Bente Klarlund (University of Copenhagen). Based on co-occurrence analysis of keywords, it is evident that terms such as "disease," "glucagon-like peptide 1," and "cardiovascular risk factor" exhibit high intermediary centrality.

Conclusion

The analysis highlights ongoing investigations into molecular mechanisms, such as β-cell function enhancement, exerkines, and epigenetic mechanisms. Emerging areas include exercise response heterogeneity, circadian rhythm regulation, transcription factors, neurotrophic factors, and mitochondrial function. Future studies should prioritize understanding interactions between different exercise mechanisms and optimizing exercise prescriptions for T2D. Exercise prescriptions are crucial for effective interventions. Collaboration between countries and institutions is essential to understand the influences of different genetic backgrounds and environmental factors. Currently, a combination of aerobic and resistance training is considered the optimal form of exercise. However, considering time efficiency, high-intensity interval training (HIIT) has gained widespread attention and research due to its ability to achieve similar exercise effects in a shorter duration. Additionally, circadian rhythm regulation may affect the exercise outcomes of diabetic individuals at different times of the day, particularly concerning the specific types, doses, and intensities used for precision intervention in T2D.

Chronobioethics: Symphony of biological clocks observed by 7-day/24-hour ambulatory blood pressure monitoring and cardiovascular health

BACKGROUND

The high prevalence of desynchronized biological rhythms is becoming a primary public health concern. We assess complex and diverse inter-modulations among multi-frequency rhythms present in blood pressure (BP) and heart rate (HR).

SUBJECTS

and Methods: We performed 7-day/24-hour Ambulatory BP Monitoring in 220 (133 women) residents (23 to 74 years) of a rural Japanese town in Kochi Prefecture under everyday life conditions.

RESULTS

A symphony of biological clocks contributes to the preservation of a synchronized circadian system. (1) Citizens with an average 12.02-h period had fewer vascular variability disorders than those with shorter (11.37-h) or longer (12.88-h) periods (P<0.05), suggesting that the circasemidian rhythm is potentially important for human health. (2) An appropriate BP-HR coupling promoted healthier circadian profiles than a phase-advanced BP: lower 7-day nighttime SBP (106.8 vs. 112.9 mmHg, P=0.0469), deeper nocturnal SBP dip (20.5% vs. 16.8%, P=0.0101), and less frequent incidence of masked non-dipping (0.53 vs. 0.86, P=0.0378), identifying the night as an important time window.

CONCLUSION

Adaptation to irregular schedules in everyday life occurs unconsciously at night, probably initiated from the brain default mode network, in coordination with the biological clock system, including a reinforced about 12-hour clock, as "a biological clock-guided core integration system".

Move the night way: how can physical activity facilitate adaptation to shift work?

Shift work, involving night work, leads to impaired sleep, cognition, health and wellbeing, and an increased risk of occupational incidents. Current countermeasures include circadian adaptation to phase shift circadian biomarkers. However, evidence of real-world circadian adaptation is found primarily in occupations where light exposure is readily controlled. Despite this, non-photic adaptation to shift work remains under researched. Other markers of shift work adaptation exist (e.g., improvements in cognition and wellbeing outcomes) but are relatively unexplored. Timeframes for shift work adaptation involve changes which occur over a block of shifts, or over a shift working career. We propose an additional shift work adaptation timeframe exists which encompasses acute within shift changes in markers of adaptation. We also propose that physical activity might be an accessible and cost-effective countermeasure that could influence multiple markers of adaptation across three timeframes (Within Shift, Within Block, Within Work-span). Finally, practical considerations for shift workers, shift work industries and future research are identified.

Delaying early morning workouts to protect sleep in two-a-day athletes

Two-a-day training is common for endurance athletes with training sessions typically beginning at 6 a.m. and 3 p.m. or 4 p.m. However, the early morning workouts could contribute to significant sleep loss, especially for night owls. Chronic sleep loss over a season could result in impaired performance, as well as an increased risk of physical and mental illness. It is hypothesized that shifting the early morning workout to later in the day could have beneficial effects for these athletes. A number of obstacles could make this hypothesis difficulty to test and implement. However, such a change could have dramatic benefits for some athletes.

Nrf2 modulates the benefits of evening exercise in type 2 diabetes

Exercise has well-characterized therapeutic benefits in the management of type 2 diabetes mellitus (T2DM). Most of the beneficial effects of exercise arise from the impact of nuclear factor erythroid 2 related factor-2 (Nrf2) activation of glucose metabolism. Nrf2 is an essential controller of cellular anti-oxidative capacity and circadian rhythms. The circadian rhythm of Nrf2 is influenced by circadian genes on its expression, where the timing of exercise effects the activation of Nrf2 and the rhythmicity of Nrf2 and signaling, such that the timing of exercise has differential physiological effects. Exercise in the evening has beneficial effects on diabetes management, such as lowering of blood glucose and weight. The mechanisms responsible for these effects have not yet been associated with the influence of exercise on the circadian rhythm of Nrf2 activity. A better understanding of exercise-induced Nrf2 activation on Nrf2 rhythm and signaling can improve our appreciation of the distinct effects of morning and evening exercise. This review hypothesizes that activation of Nrf2 by exercise in the morning, when Nrf2 level is already at high levels, leads to hyperactivation and decrease in Nrf2 signaling, while activation of Nrf2 in the evening, when Nrf2 levels are at nadir levels, improves Nrf2 signaling and lowers blood glucose levels and increases fatty acid oxidation. Exploring the effects of Nrf2 activators on rhythmic signaling could also provide valuable insights into the optimal timing of their application, while also holding promise for timed treatment of type 2 diabetes.

Effects of exercise on circadian rhythms in humans

The biological clock system is an intrinsic timekeeping device that integrates internal physiology and external cues. Maintaining a healthy biological clock system is crucial for life. Disruptions to the body's internal clock can lead to disturbances in the sleep-wake cycle and abnormalities in hormone regulation, blood pressure, heart rate, and other vital processes. Long-term disturbances have been linked to the development of various common major diseases, including cardiovascular diseases, metabolic disorders, tumors, neuropsychiatric conditions, and so on. External factors, such as the diurnal rhythm of light, have a significant impact on the body's internal clock. Additionally, as an important non-photic zeitgeber, exercise can regulate the body's internal rhythms to a certain extent, making it possible to become a non-drug intervention for preventing and treating circadian rhythm disorders. This comprehensive review encompasses behavioral, physiological, and molecular perspectives to provide a deeper understanding of how exercise influences circadian rhythms and its association with related diseases.

Metabolic Adaptations to Morning Versus Afternoon Training: A Systematic Review and Meta-analysis

BACKGROUND

Some physiological responses such as circulating glucose as well as muscle performance show a circadian rhythmicity. In the present study we aimed to quantitatively synthesize the data comparing the metabolic adaptations induced by morning and afternoon training.

METHODS

PubMed, SCOPUS, and Web of Science databases were systematically searched for studies comparing the metabolic adaptations (> 2 weeks) between morning and afternoon training. A meta-analysis was performed using random-effects models with DerSimonian-Laird methods for fasting blood glucose, hemoglobin A1c (HbAc1), homeostatic model assessment (HOMA), insulin, triglycerides, total cholesterol, low-density lipoprotein (LDL), and high-density lipoprotein (HDL).

RESULTS

We identified 9 studies with 11 different populations (n = 450 participants). We found that afternoon exercise was more effective at reducing circulating triglycerides [standardized mean difference (SMD) - 0.32; 95% confidence interval (CI) - 0.616 to - 0.025] than morning training. Moreover, afternoon tended to decrease fasting blood glucose (SMD - 0.24; 95% CI - 0.478 to 0.004) to a greater extent than morning training.

CONCLUSION

Metabolic adaptations to exercise may be dependent on the time of day. Morning training does not show superior effects to afternoon exercise in any of the analyzed outcomes. However, afternoon training is more effective at reducing circulating triglyceride levels and perhaps at reducing fasting blood glucose than morning training. The study was preregistered at PROSPERO (CRD42021287860).

Inflammation o'clock: interactions of circadian rhythms with inflammation-induced skeletal muscle atrophy

Circadian rhythms are ∼24 h cycles evident in behaviour, physiology and metabolism. The molecular mechanism directing circadian rhythms is the circadian clock, which is composed of an interactive network of transcription-translation feedback loops. The core clock genes include Bmal1, Clock, Rev-erbα/β, Per and Cry. In addition to keeping time, the core clock regulates a daily programme of gene expression that is important for overall cell homeostasis. The circadian clock mechanism is present in all cells, including skeletal muscle fibres, and disruption of the muscle clock is associated with changes in muscle phenotype and function. Skeletal muscle atrophy is largely associated with a lower quality of life, frailty and reduced lifespan. Physiological and genetic modification of the core clock mechanism yields immune dysfunction, alters inflammatory factor expression and secretion and is associated with skeletal muscle atrophy in multiple conditions, such as ageing and cancer cachexia. Here, we summarize the possible interplay between the circadian clock modulation of immune cells, systemic inflammatory status and skeletal muscle atrophy in chronic inflammatory conditions. Although there is a clear disruption of circadian clocks in various models of atrophy, the mechanism behind such alterations remains unknown. Understanding the modulatory potential of muscle and immune circadian clocks in inflammation and skeletal muscle health is essential for the development of therapeutic strategies to protect skeletal muscle mass and function of patients with chronic inflammation.

Best Time of Day for Strength and Endurance Training to Improve Health and Performance? A Systematic Review with Meta-analysis

BACKGROUND

Current recommendations for physical exercise include information about the frequency, intensity, type, and duration of exercise. However, to date, there are no recommendations on what time of day one should exercise. The aim was to perform a systematic review with meta-analysis to investigate if the time of day of exercise training in intervention studies influences the degree of improvements in physical performance or health-related outcomes.

METHODS

The databases EMBASE, PubMed, Cochrane Library, and SPORTDiscus were searched from inception to January 2023. Eligibility criteria were that the studies conducted structured endurance and/or strength training with a minimum of two exercise sessions per week for at least 2 weeks and compared exercise training between at least two different times of the day using a randomized crossover or parallel group design.

RESULTS

From 14,125 screened articles, 26 articles were included in the systematic review of which seven were also included in the meta-analyses. Both the qualitative synthesis and the quantitative synthesis (i.e., meta-analysis) provide little evidence for or against the hypothesis that training at a specific time of day leads to more improvements in performance-related or health-related outcomes compared to other times. There was some evidence that there is a benefit when training and testing occur at the same time of day, mainly for performance-related outcomes. Overall, the risk of bias in most studies was high.

CONCLUSIONS

The current state of research provides evidence neither for nor against a specific time of the day being more beneficial, but provides evidence for larger effects when there is congruency between training and testing times. This review provides recommendations to improve the design and execution of future studies on this topic.

REGISTRATION

PROSPERO (CRD42021246468).

Rhythms in barriers and fluids: Circadian clock regulation in the aging neurovascular unit

The neurovascular unit is where two very distinct physiological systems meet: The central nervous system (CNS) and the blood. The permeability of the barriers separating these systems is regulated by time, including both the 24 h circadian clock and the longer processes of aging. An endogenous circadian rhythm regulates the transport of molecules across the blood-brain barrier and the circulation of the cerebrospinal fluid and the glymphatic system. These fluid dynamics change with time of day, and with age, and especially in the context of neurodegeneration. Factors may differ depending on brain region, as can be highlighted by consideration of circadian regulation of the neurovascular niche in white matter. As an example of a potential target for clinical applications, we highlight chaperone-mediated autophagy as one mechanism at the intersection of circadian dysregulation, aging and neurodegenerative disease. In this review we emphasize key areas for future research.

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.