Exercise Timing and Circadian Rhythms

Older adults exercising ON TIME: protocol for a randomized controlled cross-over study to assess the effect of physical activity timing on insomnia severity

BACKGROUND

There are increased indications that physical activity timing, irrespective of intensity, impacts insomnia and circadian clock function. Here, we describe the rationale and design of a randomized cross-over study, called ON TIME, to examine the effects of (changing) physical activity timing on insomnia severity and on multiple exploratory outcomes that are linked to circadian clock function.

METHODS

We will conduct a randomized cross-over trial in 40 healthy older adults (aged 65 to 75 years) with subclinical or clinical insomnia (Insomnia Severity Index (ISI) scores of ≥ 10) from the Dutch municipality of Leiden and surroundings. Participants will undergo 3 intervention periods (14 days each) consecutively: one sedentary period and two periods of increased physical activity (one period with morning activity and one period with evening activity). The intervention periods are separated by a wash-out period of 1 week. In both active intervention arms, participants will follow coached or uncoached outdoor physical exercise sessions comprising endurance, strength, and flexibility exercises for 14 days. The primary outcome is change in insomnia severity as measured by the ISI. Additional exploratory outcomes include multiple components of objective sleep quality measured with tri-axial accelerometry and subjective sleep quality assessed by questionnaires as well as dim light melatonin onset and 24-h rhythms in heart rate, heart rate variability, breathing rate, oxygen saturation, mood, and objective emotional arousal and stress. Additionally, we will collect diary data on eating patterns (timing and composition). Finally, fasting blood samples will be collected at baseline and after each intervention period for measurements of biomarkers of metabolic and physiological functioning and expression of genes involved in regulation of the biological clock.

DISCUSSION

We anticipate that this study will make a significant contribution to the limited knowledge on the effect of physical activity timing. Optimizing physical activity timing has the potential to augment the health benefits of increased physical exercise in the aging population.

TRIAL REGISTRATION

Trial was approved by the Medical Ethics Committee Leiden, The Hague, Delft, The Netherlands (June, 2023). The trial was registered in the CCMO-register https://www.toetsingonline.nl/to/ccmo_search.nsf/Searchform?OpenForm under study ID NL82335.058.22 and named ("Ouderen op tijd in beweging" or in English "Older adults exercising on time"). At time of manuscript submission, the trial was additionally registered at ClinicalTrials.gov under study ID: NL82335.058.22 and is awaiting approval.

Alterations in Circadian Rhythms, Sleep, and Physical Activity in COVID-19: Mechanisms, Interventions, and Lessons for the Future

Although the world is acquitting from the throes of COVID-19 and returning to the regularity of life, its effects on physical and mental health are prominently evident in the post-pandemic era. The pandemic subjected us to inadequate sleep and physical activities, stress, irregular eating patterns, and work hours beyond the regular rest-activity cycle. Thus, perturbing the synchrony of the regular circadian clock functions led to chronic psychiatric and neurological disorders and poor immunological response in several COVID-19 survivors. Understanding the links between the host immune system and viral replication machinery from a clock-infection biology perspective promises novel avenues of intervention. Behavioral improvements in our daily lifestyle can reduce the severity and expedite the convalescent stage of COVID-19 by maintaining consistent eating, sleep, and physical activity schedules. Including dietary supplements and nutraceuticals with prophylactic value aids in combating COVID-19, as their deficiency can lead to a higher risk of infection, vulnerability, and severity of COVID-19. Thus, besides developing therapeutic measures, perpetual healthy practices could also contribute to combating the upcoming pandemics. This review highlights the impact of the COVID-19 pandemic on biological rhythms, sleep-wake cycles, physical activities, and eating patterns and how those disruptions possibly contribute to the response, severity, and outcome of SARS-CoV-2 infection.

Octopamine Rescues Endurance and Climbing Speed in Drosophila Clkout Mutants with Circadian Rhythm Disruption

Circadian rhythm disturbances are associated with various negative health outcomes, including an increasing incidence of chronic diseases with high societal costs. While exercise can protect against the negative effects of rhythm disruption, it is not available to all those impacted by sleep disruptions, in part because sleep disruption itself reduces exercise capacity. Thus, there is a need for therapeutics that bring the benefits of exercise to this population. Here, we investigate the relationship between exercise and circadian disturbances using a well-established Drosophila model of circadian rhythm loss, the Clkout mutant. We find that Clkout causes reduced exercise capacity, measured as post-training endurance, flight performance, and climbing speed, and these phenotypes are not rescued by chronic exercise training. However, exogenous administration of a molecule known to mediate the effects of chronic exercise, octopamine (OA), was able to effectively rescue mutant exercise performance, including the upregulation of other known exercise-mediating transcripts, without restoring the circadian rhythms of mutants. This work points the way toward the discovery of novel therapeutics that can restore exercise capacity in patients with rhythm disruption.

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.

Mechanisms of mechanical overload-induced skeletal muscle hypertrophy: current understanding and future directions

Mechanisms underlying mechanical overload-induced skeletal muscle hypertrophy have been extensively researched since the landmark report by Morpurgo (1897) of "work-induced hypertrophy" in dogs that were treadmill trained. Much of the preclinical rodent and human resistance training research to date supports that involved mechanisms include enhanced mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling, an expansion in translational capacity through ribosome biogenesis, increased satellite cell abundance and myonuclear accretion, and postexercise elevations in muscle protein synthesis rates. However, several lines of past and emerging evidence suggest that additional mechanisms that feed into or are independent of these processes are also involved. This review first provides a historical account of how mechanistic research into skeletal muscle hypertrophy has progressed. A comprehensive list of mechanisms associated with skeletal muscle hypertrophy is then outlined, and areas of disagreement involving these mechanisms are presented. Finally, future research directions involving many of the discussed mechanisms are proposed.

TimeTeller for timing health: The potential of circadian medicine to improve performance, prevent disease and optimize treatment

Circadian medicine, the study of the effects of time on health and disease has seen an uprising in recent years as a means to enhance health and performance, and optimize treatment timing. Our endogenous time generating system -the circadian clock- regulates behavioural, physiological and cellular processes. Disruptions of the clock, via external factors like shift work or jet lag, or internal perturbations such as genetic alterations, are linked to an increased risk of various diseases like obesity, diabetes, cardiovascular diseases and cancer. By aligning an individual's circadian clock with optimal times for performing daily routines, physical and mental performance, and also the effectiveness of certain therapies can be improved. Despite the benefits of circadian medicine, the lack of non-invasive tools for characterizing the clock limits the potential of the field. TimeTeller is a non-invasive molecular/digital tool for the characterization of circadian rhythms and prediction of daily routines, including treatment timing, to unlock the potential of circadian medicine and implementing it in various settings. Given the multiple known and potentially yet unknown dependent health factors of individual circadian rhythms, the utility of this emerging biomarker is best exploited in data driven, personalized medicine use cases, using health information across lifestyle, care, and research settings.

Sleep, circadian biology and skeletal muscle interactions: Implications for metabolic health

There currently exists a modern epidemic of sleep loss, triggered by the changing demands of our 21st century lifestyle that embrace 'round-the-clock' remote working hours, access to energy-dense food, prolonged periods of inactivity, and on-line social activities. Disturbances to sleep patterns impart widespread and adverse effects on numerous cells, tissues, and organs. Insufficient sleep causes circadian misalignment in humans, including perturbed peripheral clocks, leading to disrupted skeletal muscle and liver metabolism, and whole-body energy homeostasis. Fragmented or insufficient sleep also perturbs the hormonal milieu, shifting it towards a catabolic state, resulting in reduced rates of skeletal muscle protein synthesis. The interaction between disrupted sleep and skeletal muscle metabolic health is complex, with the mechanisms underpinning sleep-related disturbances on this tissue often multifaceted. Strategies to promote sufficient sleep duration combined with the appropriate timing of meals and physical activity to maintain circadian rhythmicity are important to mitigate the adverse effects of inadequate sleep on whole-body and skeletal muscle metabolic health. This review summarises the complex relationship between sleep, circadian biology, and skeletal muscle, and discusses the effectiveness of several strategies to mitigate the negative effects of disturbed sleep or circadian rhythms on skeletal muscle health.

Time-restricted feeding and cognitive function in sedentary and physically active elderly individuals: Ramadan diurnal intermittent fasting as a model

Objectives

This study aimed to investigate the effects of Ramadan diurnal intermittent fasting (RDIF) on cognitive performance, sleep quality, daytime sleepiness, and insomnia in physically active and sedentary elderly individuals.

Methods

A total of 58 participants (62.93 ± 3.99 years) were assigned to one of the following two groups: a sedentary group (control group) who observed Ramadan (n = 32) and a physically active group (n = 26) who continued to train while observing Ramadan. Participants were assessed 2 weeks before Ramadan and during the fourth week of Ramadan. On each occasion, participants completed a digital assessment of their cognitive performance and responded to the Pittsburgh sleep quality index (PSQI), the insomnia severity index (ISI) and the Epworth sleepiness scale (ESS) questionnaires to assess sleep parameters.

Results

Compared to before Ramadan, performance in executive function (p = 0.035), attention (p = 0.005), inhibition (p = 0.02), associative memory (p = 0.041), and recognition memory (p = 0.025) increased significantly during Ramadan in the physically active group. For the sedentary group, associative learning performance decreased (p = 0.041), whilst performances in the remaining domains remained unchanged during Ramadan. Global PSQI, ISI, and ESS scores indicated both groups suffered from poor sleep quality and excessive daytime sleepiness, with significantly higher negative effects of RDIF observed in the sedentary group.

Conclusion

Older adults who continue to train at least three times per week during Ramadan may improve their cognitive performance, despite the impairment of sleep quality. Future studies in older adults during Ramadan including objective measures of sleep (e.g., polysomnography, actigraphy) and brain function (e.g., functional magnetic resonance imaging) are warranted.

Chrono-Aerobic Exercise Optimizes Metabolic State in DB/DB Mice through CLOCK–Mitophagy–Apoptosis

Although the benefits of aerobic exercise on obesity and type 2 diabetes are well-documented, the pathogenesis of type 2 diabetes and the intervention mechanism of exercise remain ambiguous. The correlation between mitochondrial quality and metabolic diseases has been identified. Disruption of the central or peripheral molecular clock can also induce chronic metabolic diseases. In addition, the interactive effects of the molecular clock and mitochondrial quality have attracted extensive attention in recent years. Exercise and a high-fat diet have been considered external factors that may change the molecular clock and metabolic state. Therefore, we utilized a DB/DB (BSK.Cg-Dock7m +/+ Leprdb/JNju) mouse model to explore the effect of chrono-aerobic exercise on the metabolic state of type 2 diabetic mice and the effect of timing exercise as an external rhythm cue on liver molecular clock-mitochondrial quality. We found that two differently timed exercises reduced the blood glucose and serum cholesterol levels in DB/DB mice, and compared with night exercise (8:00 p.m., the active period of mice), morning exercise (8:00 a.m., the sleeping period of mice) significantly improved the insulin sensitivity in DB/DB mice. In contrast, type 2 diabetes mellitus (T2DM) increased the expression of CLOCK and impaired the mitochondrial quality (mitochondrial networks, OPA1, Fis1, and mitophagy), as well as induced apoptosis. Both morning and night exercise ameliorated impaired mitochondrial quality and apoptosis induced by diabetes. However, compared with morning exercise, night exercise not only decreased the protein expression of CLOCK but also decreased excessive apoptosis. In addition, the expression of CLOCK was negatively correlated with the expression of OPA1 and Fis1. In summary, our research suggests that morning exercise is more beneficial for increasing insulin sensitivity and promoting glucose transport in T2DM, whereas night exercise may improve lipid infiltration and mitochondrial abnormalities through CLOCK–mitophagy–apoptosis in the liver, thereby downregulating glucose and lipid disorders. In addition, CLOCK-OPA1/Fis1–mitophagy might be novel targets for T2DM treatment.

Circadian Clocks, Redox Homeostasis, and Exercise: Time to Connect the Dots?

Compelling research has documented how the circadian system is essential for the maintenance of several key biological processes including homeostasis, cardiovascular control, and glucose metabolism. Circadian clock disruptions, or losses of rhythmicity, have been implicated in the development of several diseases, premature ageing, and are regarded as health risks. Redox reactions involving reactive oxygen and nitrogen species (RONS) regulate several physiological functions such as cell signalling and the immune response. However, oxidative stress is associated with the pathological effects of RONS, resulting in a loss of cell signalling and damaging modifications to important molecules such as DNA. Direct connections have been established between circadian rhythms and oxidative stress on the basis that disruptions to circadian rhythms can affect redox biology, and vice versa, in a bi-directional relationship. For instance, the expression and activity of several key antioxidant enzymes (SOD, GPx, and CAT) appear to follow circadian patterns. Consequently, the ability to unravel these interactions has opened an exciting area of redox biology. Exercise exerts numerous benefits to health and, as a potent environmental cue, has the capacity to adjust disrupted circadian systems. In fact, the response to a given exercise stimulus may also exhibit circadian variation. At the same time, the relationship between exercise, RONS, and oxidative stress has also been scrutinised, whereby it is clear that exercise-induced RONS can elicit both helpful and potentially harmful health effects that are dependent on the type, intensity, and duration of exercise. To date, it appears that the emerging interface between circadian rhythmicity and oxidative stress/redox metabolism has not been explored in relation to exercise. This review aims to summarise the evidence supporting the conceptual link between the circadian clock, oxidative stress/redox homeostasis, and exercise stimuli. We believe carefully designed investigations of this nexus are required, which could be harnessed to tackle theories concerned with, for example, the existence of an optimal time to exercise to accrue physiological benefits.

Exercise as a Peripheral Circadian Clock Resynchronizer in Vascular and Skeletal Muscle Aging

Aging is characterized by several progressive physiological changes, including changes in the circadian rhythm. Circadian rhythms influence behavior, physiology, and metabolic processes in order to maintain homeostasis; they also influence the function of endothelial cells, smooth muscle cells, and immune cells in the vessel wall. A clock misalignment could favor vascular damage and indirectly also affect skeletal muscle function. In this review, we focus on the dysregulation of circadian rhythm due to aging and its relationship with skeletal muscle changes and vascular health as possible risk factors for the development of sarcopenia, as well as the role of physical exercise as a potential modulator of these processes.

Exercise-induced oxidative stress and melatonin supplementation: current evidence

Melatonin possesses the indoleamine structure and exerts antioxidant and anti-inflammatory actions and other physiological properties. Physical exercise can influence secretion of melatonin. Melatonin is used as a natural supplement among athletes to regulate sleep cycles and protect muscles against oxidative damage. Despite decades of research, there is still a lack of a comprehensive and critical review on melatonin supplementation and physical activity relationship. The aim of this literature review is to examine the antioxidant, anti-inflammatory and other biological functions played by melatonin with reference to the effect of physical exercise on melatonin secretion and the effect of this compound supplementation on exercise-induced oxidative stress in athletes. Evidence shows that intense exercises disturb antioxidant status of competitive athletes, whereas supplementation with melatonin strengthens antioxidant status in trained athletes in various sports as the compound showed high potency in reduction of the oxidative stress and inflammation markers generated during intense and prolonged exercise.

Exercise and health: historical perspectives and new insights

Since ancient times, the health benefits of regular physical activity/exercise have been recognized and the classic studies of Morris and Paffenbarger provided the epidemiological evidence in support of such an association. Cardiorespiratory fitness, often measured by maximal oxygen uptake, and habitual physical activity levels are inversely related to mortality. Thus, studies exploring the biological bases of the health benefits of exercise have largely focused on the cardiovascular system and skeletal muscle (mass and metabolism), although there is increasing evidence that multiple tissues and organ systems are influenced by regular exercise. Communication between contracting skeletal muscle and multiple organs has been implicated in exercise benefits, as indeed has other interorgan "cross-talk." The application of molecular biology techniques and "omics" approaches to questions in exercise biology has opened new lines of investigation to better understand the beneficial effects of exercise and, in so doing, inform the optimization of exercise regimens and the identification of novel therapeutic strategies to enhance health and well-being.

Circadian influence on post-exercise hypotension: a review

Circadian rhythm (CR) can influence the physiological and psychological parameters in every individual. There is a sinusoidal response to blood pressure brought about by the CR. A drop in blood pressure response immediately after an exercise is termed as post-exercise hypotension (PEH). The objective of the present paper is to review the influence of CR on PEH. Comparing the types of exercises, aerobic training showed a higher magnitude of the drop in PEH than resistance training. However, the majority of the studies have not considered the CR influence on PEH. With the evidence available, we can conclude that morning exercise shows the higher magnitude of the drop in PEH and could be sustained for a longer duration.

Per1/Per2-Igf2 axis-mediated circadian regulation of myogenic differentiation

Circadian rhythms regulate cell proliferation and differentiation, but circadian control of tissue regeneration remains elusive at the molecular level. Here, we show that proper myoblast differentiation and muscle regeneration are regulated by the circadian master regulators Per1 and Per2. Depletion of Per1 or Per2 suppressed myoblast differentiation in vitro and muscle regeneration in vivo, demonstrating their nonredundant functions. Both Per1 and Per2 were required for the activation of Igf2, an autocrine promoter of myoblast differentiation, accompanied by Per-dependent recruitment of RNA polymerase II, dynamic histone modifications at the Igf2 promoter and enhancer, and the promoter–enhancer interaction. This circadian epigenetic priming created a preferred time window for initiating myoblast differentiation. Consistently, muscle regeneration was faster if initiated at night, when Per1, Per2, and Igf2 were highly expressed compared with morning. This study reveals the circadian timing as a significant factor for effective muscle cell differentiation and regeneration.

Monitoring daytime differences in moderate intensity exercise capacity using treadmill test and muscle dissection

There is growing interest in medicine and sports in uncovering exercise modifiers that enhance or limit exercise capacity. Here, we detail a protocol for testing the daytime effect on running capacity in mice using a moderate intensity treadmill effort test. Instructions for dissecting soleus, gastrocnemius plantaris, and quadriceps muscles for further analysis are provided as well. This experimental setup is optimized for addressing questions regarding the involvement of daytime and circadian clocks in regulating exercise capacity.

For complete details on the use and execution of this protocol, please refer to Ezagouri et al. (2019).

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Exercise capacity is influenced by the time of day

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Protocol for determining moderate intensity exercise capacity using treadmill test

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Instructions for muscle dissection

Diurnal variations in the expression of core-clock genes correlate with resting muscle properties and predict fluctuations in exercise performance across the day

Objectives

In this study, we investigated daily fluctuations in molecular (gene expression) and physiological (biomechanical muscle properties) features in human peripheral cells and their correlation with exercise performance.

Methods

21 healthy participants (13 men and 8 women) took part in three test series: for the molecular analysis, 15 participants provided hair, blood or saliva time-course sampling for the rhythmicity analysis of core-clock gene expression via RT-PCR. For the exercise tests, 16 participants conducted strength and endurance exercises at different times of the day (9h, 12h, 15h and 18h). Myotonometry was carried out using a digital palpation device (MyotonPRO), five muscles were measured in 11 participants. A computational analysis was performed to relate core-clock gene expression, resting muscle tone and exercise performance.

Results

Core-clock genes show daily fluctuations in expression in all biological samples tested for all participants. Exercise performance peaks in the late afternoon (15–18 hours for both men and women) and shows variations in performance, depending on the type of exercise (eg, strength vs endurance). Muscle tone varies across the day and higher muscle tone correlates with better performance. Molecular daily profiles correlate with daily variation in exercise performance.

Conclusion

Training programmes can profit from these findings to increase efficiency and fine-tune timing of training sessions based on the individual molecular data. Our results can benefit both professional athletes, where a fraction of seconds may allow for a gold medal, and rehabilitation in clinical settings to increase therapy efficacy and reduce recovery times.

Regulation of Glucose Metabolism by MuRF1 and Treatment of Myopathy in Diabetic Mice with Small Molecules Targeting MuRF1

The muscle-specific ubiquitin ligase MuRF1 regulates muscle catabolism during chronic wasting states, although its roles in general metabolism are less-studied. Here, we metabolically profiled MuRF1-deficient knockout mice. We also included knockout mice for MuRF2 as its closely related gene homolog. MuRF1 and MuRF2-KO (knockout) mice have elevated serum glucose, elevated triglycerides, and reduced glucose tolerance. In addition, MuRF2-KO mice have a reduced tolerance to a fat-rich diet. Western blot and enzymatic studies on MuRF1-KO skeletal muscle showed perturbed FoxO-Akt signaling, elevated Akt-Ser-473 activation, and downregulated oxidative mitochondrial metabolism, indicating potential mechanisms for MuRF1,2-dependent glucose and fat metabolism regulation. Consistent with this, the adenoviral re-expression of MuRF1 in KO mice normalized Akt-Ser-473, serum glucose, and triglycerides. Finally, we tested the MuRF1/2 inhibitors MyoMed-205 and MyoMed-946 in a mouse model for type 2 diabetes mellitus (T2DM). After 28 days of treatment, T2DM mice developed progressive muscle weakness detected by wire hang tests, but this was attenuated by the MyoMed-205 treatment. While MyoMed-205 and MyoMed-946 had no significant effects on serum glucose, they did normalize the lymphocyte-granulocyte counts in diabetic sera as indicators of the immune response. Thus, small molecules directed to MuRF1 may be useful in attenuating skeletal muscle strength loss in T2DM conditions.

Effects of sleep deprivation on endothelial function in adult humans: a systematic review

Sleep deprivation is highly prevalent and is associated with increased cardiovascular disease (CVD) morbidity and mortality. Age-related alterations in sleep and chronobiology may exaggerate CVD susceptibility in older individuals. The mechanisms responsible for the association between sleep deprivation and CVD are not fully understood, but endothelial dysfunction may play a central role. Our objective was to conduct a systematic literature review to evaluate the evidence on the effects of sleep deprivation on endothelial function (EF). This review adhered to the PRISMA guidelines and was pre-registered with PROSPERO (#CRD42020192485, 07/24/2020). We searched PubMed, Web of Science, Embase, and Cochrane Library for articles published through May 1, 2020. Eligibility criteria included publication in English and use of well-established EF methodologies in adult humans. Two investigators independently performed the literature search, study selection, data extraction, risk-of-bias assessment, and qualitative data synthesis. Out of 3571 articles identified, 24 articles were included in the systematic review. Main findings include the following: (1) shorter sleep duration is associated with lower macrovascular EF; (2) not sleeping 7-9 h/night is linked with impaired microvascular EF; (3) sleep restriction impairs micro- and macrovascular EF; (4) acute total sleep deprivation impairs micro- and macrovascular EF but data on macrovascular EF are less consistent; and (5) shift work impairs macrovascular EF. In conclusion, sleep deprivation impairs EF, which may explain the link between insufficient sleep and CVD. Future investigations should fully elucidate the underlying mechanisms and develop strategies to combat the adverse endothelial effects of sleep deprivation across the lifespan.

Regulation of diurnal energy balance by mitokines

The mammalian system of energy balance regulation is intrinsically rhythmic with diurnal oscillations of behavioral and metabolic traits according to the 24 h day/night cycle, driven by cellular circadian clocks and synchronized by environmental or internal cues such as metabolites and hormones associated with feeding rhythms. Mitochondria are crucial organelles for cellular energy generation and their biology is largely under the control of the circadian system. Whether mitochondrial status might also feed-back on the circadian system, possibly via mitokines that are induced by mitochondrial stress as endocrine-acting molecules, remains poorly understood. Here, we describe our current understanding of the diurnal regulation of systemic energy balance, with focus on fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15), two well-known endocrine-acting metabolic mediators. FGF21 shows a diurnal oscillation and directly affects the output of the brain master clock. Moreover, recent data demonstrated that mitochondrial stress-induced GDF15 promotes a day-time restricted anorexia and systemic metabolic remodeling as shown in UCP1-transgenic mice, where both FGF21 and GDF15 are induced as myomitokines. In this mouse model of slightly uncoupled skeletal muscle mitochondria GDF15 proved responsible for an increased metabolic flexibility and a number of beneficial metabolic adaptations. However, the molecular mechanisms underlying energy balance regulation by mitokines are just starting to emerge, and more data on diurnal patterns in mouse and man are required. This will open new perspectives into the diurnal nature of mitokines and action both in health and disease.

The myonuclear DNA methylome in response to an acute hypertrophic stimulus

In addition to multi-nucleated muscle fibres, numerous resident and infiltrating mononuclear cells populate the muscle compartment. As most epigenetic assays in skeletal muscle are conducted on whole tissue homogenates, essentially nothing is known about regulatory processes exclusively within muscle fibres in vivo. Utilizing a novel genetically modified mouse model developed by our laboratory, we (1) outline a simple and rapid workflow for isolating pure myonuclei from small tissue samples via fluorescent activated cell sorting and extracting high-quality large-fragment DNA for downstream analyses, and (2) provide information on myonuclear and interstitial cell nuclear CpG DNA methylation via reduced representation bisulphite sequencing (RRBS) using mice that were subjected to an acute mechanical overload of the plantaris muscle. In 3-month-old mice, myonuclei are ~50% of total nuclei in sham and ~30% in 3-d overloaded muscle, the difference being attributable to mononuclear cell infiltration and proliferation with overload. In purified myonuclei, pathway analysis of hypomethylated promoter regions following overload was distinct from interstitial nuclei and revealed marked regulation of factors that converge on the master regulator of muscle growth mTOR, and on autophagy. Specifically, acute hypomethylation of Rheb, Rictor, Hdac1, and Hdac2, in addition to a major driver of ribosome biogenesis Myc, reveals the epigenetic regulation of hypertrophic signalling within muscle fibres that may underpin the long-term growth response to loading. This study provides foundational information on global myonuclear epigenetics in vivo using RRBS, and demonstrates the importance of isolating specific nuclear populations to study the epigenetic regulation of skeletal muscle fibre adaptation.

Diurnal Differences in Human Muscle Isometric Force In Vivo Are Associated with Differential Phosphorylation of Sarcomeric M-Band Proteins

We investigated whether diurnal differences in muscle force output are associated with the post-translational state of muscle proteins. Ten physically active men (mean ± SD; age 26.7 ± 3.7 y) performed experimental sessions in the morning (08:00 h) and evening (17:00 h), which were counterbalanced in order of administration and separated by at least 72 h. Knee extensor maximal voluntary isometric contraction (MVIC) force and peak rate of force development (RFD) were measured, and samples of vastus lateralis were collected immediately after exercise. MVIC force was greater in the evening (mean difference of 67 N, 10.2%; p < 0.05). Two-dimensional (2D) gel analysis encompassed 122 proteoforms and discovered 6 significant (p < 0.05; false discovery rate [FDR] = 10%) diurnal differences. Phosphopeptide analysis identified 1693 phosphopeptides and detected 140 phosphopeptides from 104 proteins that were more (p < 0.05, FDR = 22%) phosphorylated in the morning. Myomesin 2, muscle creatine kinase, and the C-terminus of titin exhibited the most robust (FDR < 10%) diurnal differences. Exercise in the morning, compared to the evening, coincided with a greater phosphorylation of M-band-associated proteins in human muscle. These protein modifications may alter the M-band structure and disrupt force transmission, thus potentially explaining the lower force output in the morning.

Coupled network of the circadian clocks: a driving force of rhythmic physiology

The circadian system is composed of coupled endogenous oscillators that allow living beings, including humans, to anticipate and adapt to daily changes in their environment. In mammals, circadian clocks form a hierarchically organized network with a 'master clock' located in the suprachiasmatic nucleus of the hypothalamus, which ensures entrainment of subsidiary oscillators to environmental cycles. Robust rhythmicity of body clocks is indispensable for temporally coordinating organ functions, and the disruption or misalignment of circadian rhythms caused for instance by modern lifestyle is strongly associated with various widespread diseases. This review aims to provide a comprehensive overview of our current knowledge about the molecular architecture and system-level organization of mammalian circadian oscillators. Furthermore, we discuss the regulatory roles of peripheral clocks for cell and organ physiology and their implication in the temporal coordination of metabolism in human health and disease. Finally, we summarize methods for assessing circadian rhythmicity in humans.

Time-of-day dependent effects of contractile activity on the phase of the skeletal muscle clock

Key points

Disruptions in circadian rhythms across an organism are associated with negative health outcomes, such as cardiometabolic and neurodegenerative diseases.

Exercise has been proposed as a time cue for the circadian clock in rodents and humans.

In this study, we assessed the effect of a single bout of endurance exercise on the skeletal muscle clock in vivo and a bout of muscle contractions in vitro.

Timing of exercise or contractions influences the directional response of the muscle clock phase in vivo and in vitro.

Our findings demonstrate that muscle contractions, as a component of exercise, can directly modulate the expression of muscle clock components in a time‐of‐day dependent manner.

Abstract

Exercise has been proposed to be a zeitgeber for the muscle circadian clock mechanism. However, this is not well defined and it is unknown if exercise timing induces directional shifts of the muscle clock. Our purpose herein was to assess the effect of one bout of treadmill exercise on skeletal muscle clock phase changes. We subjected PERIOD2::LUCIFERASE mice (n = 30F) to one 60 min treadmill exercise bout at three times of day. Exercise at ZT5, 5 h after lights on, induced a phase advance (100.2 ± 25.8 min; P = 0.0002), whereas exercise at ZT11, 1 h before lights off, induced a phase delay (62.1 ± 21.1 min; P = 0.0003). Exercise at ZT17, middle of the dark phase, did not alter the muscle clock phase. Exercise induces diverse systemic changes so we developed an in vitro model system to examine the effects of contractile activity on muscle clock phase. Contractions applied at peak or trough Bmal1 expression induced significant phase delays (applied at peak: 27.2 ± 10.2 min; P = 0.0017; applied at trough: 64.6 ± 6.5 min, P < 0.0001). Contractions applied during the transition from peak to trough Bmal1 expression induced a phase advance (49.8 ± 23.1 min; P = 0.0051). Lastly, contractions at different times of day resulted in differential changes of core clock gene expression, demonstrating an exercise and clock interaction, providing insight into potential mechanisms of exercise‐induced phase shifts. These data demonstrate that muscle contractions, as part of exercise, are sufficient to shift the muscle circadian clock phase, likely through changes in core clock gene expression. Additionally, our findings that exercise induces directional muscle clock phase changes confirms that exercise is a bona fide environmental time cue for skeletal muscle.

Disruptions in circadian rhythms across an organism are associated with negative health outcomes, such as cardiometabolic and neurodegenerative diseases.

Exercise has been proposed as a time cue for the circadian clock in rodents and humans.

In this study, we assessed the effect of a single bout of endurance exercise on the skeletal muscle clock in vivo and a bout of muscle contractions in vitro.

Timing of exercise or contractions influences the directional response of the muscle clock phase in vivo and in vitro.

Our findings demonstrate that muscle contractions, as a component of exercise, can directly modulate the expression of muscle clock components in a time‐of‐day dependent manner.

Functional and/or structural brain changes in response to resistance exercises and resistance training lead to cognitive improvements - a systematic review

BACKGROUND

During the aging process, physical capabilities (e.g., muscular strength) and cognitive functions (e.g., memory) gradually decrease. Regarding cognitive functions, substantial functional (e.g., compensatory brain activity) and structural changes (e.g., shrinking of the hippocampus) in the brain cause this decline. Notably, growing evidence points towards a relationship between cognition and measures of muscular strength and muscle mass. Based on this emerging evidence, resistance exercises and/or resistance training, which contributes to the preservation and augmentation of muscular strength and muscle mass, may trigger beneficial neurobiological processes and could be crucial for healthy aging that includes preservation of the brain and cognition. Compared with the multitude of studies that have investigated the influence of endurance exercises and/or endurance training on cognitive performance and brain structure, considerably less work has focused on the effects of resistance exercises and/or resistance training. While the available evidence regarding resistance exercise-induced changes in cognitive functions is pooled, the underlying neurobiological processes, such as functional and structural brain changes, have yet to be summarized. Hence, the purpose of this systematic review is to provide an overview of resistance exercise-induced functional and/or structural brain changes that are related to cognitive functions.

METHODS AND RESULTS

A systematic literature search was conducted by two independent researchers across six electronic databases; 5957 records were returned, of which 18 were considered relevant and were analyzed.

SHORT CONCLUSION

Based on our analyses, resistance exercises and resistance training evoked substantial functional brain changes, especially in the frontal lobe, which were accompanied by improvements in executive functions. Furthermore, resistance training led to lower white matter atrophy and smaller white matter lesion volumes. However, based on the relatively small number of studies available, the findings should be interpreted cautiously. Hence, future studies are required to investigate the underlying neurobiological mechanisms and to verify whether the positive findings can be confirmed and transferred to other needy cohorts, such as older adults with dementia, sarcopenia and/or dynapenia.