Effects of time of day on resistance exercise-induced anabolic signaling in skeletal muscle

The Clockwork of Champions: Influence of Circadian Biology on Exercise Performance

Exercise physiology and circadian biology are distinct and long-standing fields. Recently they have seen increased integration, largely due to the discovery of the molecular components of the circadian clock and recognition of human exercise performance differences over time-of-day. Circadian clocks, ubiquitous in cells, regulate a daily tissue specific program of gene expression that contribute to temporal patterns of physiological functions over a 24-hour cycle. Understanding how circadian clock function in skeletal muscle, as well as other tissues contribute to exercise performance is still in the very early stages. This review provides background on this emerging field with a review of early exercise and time-of-day studies in both human and animals. We then move into the role of the circadian clock and its daily program of gene expression in skeletal muscle with a focus on specific metabolic and physiological outputs that vary over time-of-day. Lastly, we discuss the recognition that the timing of exercise communicates with the skeletal muscle circadian clock to adjust its phase settings and why this maybe important for performance and health.

Anabolic myokine responses and muscular performance following 8 weeks of autoregulated compared to linear resistance exercise in recreationally active males

BACKGROUND

To date, no studies, to our knowledge, have compared the efficacy of autoregulated periodized and linear resistance exercises on anabolic myokines and muscular performance among recreationally active individuals. This study aimed to compare the effects of an 8-week autoregulated periodized resistance exercise (APRE) program with a linear resistance exercise (LRE) program on insulin-like growth factor-1 (IGF-1), follistatin (FST), myostatin (MST), body composition, muscular strength, and power in recreationally active males.

METHODS

Thirty males were randomly assigned to either the APRE group (n = 15) or the LRE group (n = 15). Participants completed training three times a week for 8 weeks. The outcome measures included serum IGF-1, FST, MST, muscular strength (isometric knee extension and handgrip), power (vertical jump), lean body mass, and fat mass.

RESULTS

IGF-1 circulating levels increased over time following APRE (34%) and with no significant change following LRE (~-1%). There were no significant differences over time or between groups for FST or MST. Muscular strength (knee extension [21.5 vs. ~16%] and handgrip [right: 31 vs. 25%; left: 31.7 vs. 28.8%]) and power (~ 33 vs. ~26%) significantly increased to a greater extent following APRE compared to LRE. Interestingly, the results revealed that lean body mass increased over time only after APRE (~ 3%), but not LRE.

CONCLUSION

These findings suggest that APRE may be more effective than LRE in increasing muscular strength, power, and lean body mass, as well as circulating IGF-1 levels, in recreationally active males. The observed differences may be attributed to the increased training volume associated with APRE. However, further research is needed to directly assess muscle protein synthesis.

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.

Time Course Evaluation of Mitogen-Activated Protein Kinase Phosphorylation to Resistance Exercise: A Systematic Review

ABSTRACT

Lee, CJ and Nicoll, JX. Time course evaluation of mitogen-activated protein kinase phosphorylation to resistance exercise: a systematic review. J Strength Cond Res 37(3): 710-725, 2023-Resistance exercise (RE) can increase the signaling activities of mitogen-activated protein kinases (MAPKs), specifically extracellular signal-regulated kinases 1/2 (ERK1/2), p90 ribosomal S6 kinases (p90RSK), c-Jun NH2-terminal kinases (JNK), and p38-MAPK. These RE-induced responses contribute to various intracellular processes modulating growth and development in skeletal muscles, playing an essential role in resistance training adaptations. The time course of MAPK phosphorylation to different RE conditions, such as training experience and varying loads, remains ambiguous. A systematic review was conducted to determine the effects of different post-RE recovery time points on the MAPK signaling cascade. In addition, the effects of loading and training statuses on MAPK responses were also investigated. The review was performed according to the preferred reporting items for systematic reviews and meta-analyses guidelines with a literature search incorporating 3 electronic databases. A modified version of the Downs and Black checklist was used to evaluate the methodological quality of the studies. The signaling responses were measured within a time range between immediately post-RE and >6 hours post-RE. Forty-four studies met the inclusion criteria, and all were classified as good-to-moderate methodological quality. Mitogen-activated protein kinase phosphorylation increased to different levels after RE, with the highest near the cessation of exercise. Although overall signaling was attenuated among trained individuals likely because of training adaptations, greater MAPK responses can be attributed to moderate loads of 65-85% 1RM regardless of the training experience. However, specific training-induced responses remain equivocal, and further investigations are required to determine the ideal training parameters to optimize anabolic intramuscular signaling, which may likely optimize resistance training adaptations.

Linear Motor Driven Leg-Press Dynamometer for Testing, Training, and Rehabilitation: A Scoping Review with a Focus on the Concept of Serial Stretch Loading

Background: The purpose of this scoping review was to analyze the evidence of acute and long-term effects of the application of leg-press strength training with or without serial stretch-loading stimuli on various biomechanical and physiological outcomes. Methods: This review was performed in accordance with PRISMA for Scoping Reviews recommendations, and two researchers independently searched the following databases: PubMed, Web of Science, Scopus, ScienceDirect, ProQuest, Cochrane, and Google Scholar. All studies that used unique leg-press device for testing, acute responses and long-term adaptation were included in this review, irrespective of the measured outcomes. A total of 13 studies were included in this review, with 5 focused on the testing capabilities of the device and acute training responses and 8 focused on the long-term adaptations in various physical and physiological outcomes. Results: Regarding the acute responses after leg-press strength training with or without serial stretch-loading stimuli, visible changes were observed in the muscle force, rate of force development, and hormonal concentrations between pre- and postmenopausal women (only one study). Long-term studies revealed different training adaptations after performing leg-press strength training with unique serial stretch-loading stimuli. A positive trend for leg-press strength training with serial stretch-loading was recorded in the young population and athletes; however, more variable training effects favoring one or the other approach were achieved in the older population. Conclusions: In summary, this review shows the uniqueness and usability of a leg-press device that is capable of various exercising modes, including special serial stretch-loading stimuli. The use of this device can serve as a positive addition to training regiments, and the main application appears to be suitable for rehabilitation needs.

Circadian rhythms modulate the effect of eccentric exercise on rat soleus muscles

We investigated whether time-of-day dependent changes in the rat soleus (SOL) muscle size, after eccentric exercises, operate via the mechanistic target of rapamycin (mTOR) signaling pathway. For our first experiment, we assigned 9-week-old male Wistar rats randomly into four groups: light phase (zeitgeber time; ZT6) non-trained control, dark phase (ZT18) non-trained control, light phase-trained, and dark phase-trained. Trained animals performed 90 min of downhill running once every 3 d for 8 weeks. The second experiment involved dividing 9-week-old male Wistar rats to control and exercise groups. The latter were subjected to 15 min of downhill running at ZT6 and ZT18. The absolute (+12.8%) and relative (+9.4%) SOL muscle weights were higher in the light phase-trained group. p70S6K phosphorylation ratio was 42.6% higher in the SOL muscle of rats that had exercised only in light (non-trained ZT6). Collectively, the degree of muscle hypertrophy in SOL is time-of-day dependent, perhaps via the mTOR/p70S6K signaling.

The effects of time of day-specific resistance training on adaptations in skeletal muscle hypertrophy and muscle strength: A systematic review and meta-analysis

The present paper endeavored to elucidate the topic on the effects of morning versus evening resistance training on muscle strength and hypertrophy by conducting a systematic review and a meta-analysis of studies that examined time of day-specific resistance training. This systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines with searches conducted through PubMed/MEDLINE, Scopus, and SPORTDiscus databases. The Downs and Black checklist was used for the assessment of the methodological quality of the included studies. Studies that examined the effects of time of day-specific resistance training (while equating all other training variables, such as training frequency and volume, between the groups) on muscle strength and/or muscle size were included in the present review. The random effects model was used for the meta-analysis. Meta-analyses explored (1) the differences in strength expression between morning and evening hours at baseline; (2) the differences in strength within the groups training in the morning and evening by using their post-intervention strength data from the morning and evening strength assessments; (3) the overall differences between the effects of morning and evening resistance training (with subgroup analyses conducted for studies that assessed strength in the morning hours and for the studies that assessed strength in the evening hours). Finally, a meta-analysis was also conducted for studies that assessed muscle hypertrophy. Eleven studies of moderate and good methodological quality were included in the present review. The primary findings of the review are as follows: (1) at baseline, a significant difference in strength between morning and evening is evident, with greater strength observed in the evening hours; (2) resistance training in the morning hours may increase strength assessed in the morning to similar levels as strength assessed in the evening; (3) training in the evening hours, however, maintains the general difference in strength across the day, with greater strength observed in the evening hours; (4) when comparing the effects between the groups training in the morning versus in the evening hours, increases in strength are similar in both groups, regardless of the time of day at which strength assessment is conducted; and (5) increases in muscle size are similar irrespective of the time of day at which the training is performed.

Morphological, molecular and hormonal adaptations to early morning versus afternoon resistance training

It has been clearly established that maximal force and power is lower in the morning compared to noon or afternoon hours. This morning neuromuscular deficit can be diminished by regularly training in the morning hours. However, there is limited and contradictory information upon hypertrophic adaptations to time-of-day-specific resistance training. Moreover, no cellular or molecular mechanisms related to muscle hypertrophy adaptation have been studied with this respect. Therefore, the present study examined effects of the time-of-day-specific resistance training on muscle hypertrophy, phosphorylation of selected proteins, hormonal concentrations and neuromuscular performance. Twenty five previously untrained males were randomly divided into a morning group (n = 11, age 23 ± 2 yrs), afternoon group (n = 7, 24 ± 4 yrs) and control group (n = 7, 24 ± 3 yrs). Both the morning and afternoon group underwent hypertrophy-type of resistance training with 22 training sessions over an 11-week period performed between 07:30-08:30 h and 16:00-17:00 h, respectively. Isometric MVC was tested before and immediately after an acute loading exclusively during their training times before and after the training period. Before acute loadings, resting blood samples were drawn and analysed for plasma testosterone and cortisol. At each testing occasion, muscle biopsies from m. vastus lateralis were obtained before and 60 min after the acute loading. Muscle specimens were analysed for muscle fibre cross-sectional areas (CSA) and for phosphorylated p70S6K, rpS6, p38MAPK, Erk1/2, and eEF2. In addition, the right quadriceps femoris was scanned with MRI before and after the training period. The control group underwent the same testing, except for MRI, between 11:00 h and 13:00 h but did not train. Voluntary muscle strength increased significantly in both the morning and afternoon training group by 16.9% and 15.2 %, respectively. Also muscle hypertrophy occurred by 8.8% and 11.9% (MRI, p < 0.001) and at muscle fibre CSA level by 21% and 18% (p < 0.01) in the morning and afternoon group, respectively. No significant changes were found in controls within these parameters. Both pre- and post-training acute loadings induced a significant (p < 0.001) reduction in muscle strength in all groups, not affected by time of day or training. The post-loading phosphorylation of p70S6Thr421/Ser424 increased independent of the time of day in the pre-training condition, whereas it was significantly increased in the morning group only after the training period (p < 0.05). Phosphorylation of rpS6 and p38MAPK increased acutely both before and after training in a time-of-day independent manner (p < 0.05 at all occasions). Phosphorylation of p70S6Thr389, eEF2 and Erk1/2 did not change at any time point. No statistically significant correlations were found between changes in muscle fibre CSA, MRI and cell signalling data. Resting testosterone was not statistically different among groups at any time point. Resting cortisol declined significantly from pre- to post-training in all three groups (p < 0.05). In conclusion, similar levels of muscle strength and hypertrophy could be achieved regardless of time of the day in previously untrained men. However, at the level of skeletal muscle signalling, the extent of adaptation in some parameters may be time of day dependent.

Effects of morning versus evening combined strength and endurance training on physical performance, muscle hypertrophy, and serum hormone concentrations

This study investigated the effects of 24 weeks of morning versus evening same-session combined strength (S) and endurance (E) training on physical performance, muscle hypertrophy, and resting serum testosterone and cortisol diurnal concentrations. Forty-two young men were matched and assigned to a morning (m) or evening (e) E + S or S + E group (mE + S, n = 9; mS + E, n = 9; eE + S, n = 12; and eS + E, n = 12). Participants were tested for dynamic leg press 1-repetition maximum (1RM) and time to exhaustion (Texh) during an incremental cycle ergometer test both in the morning and evening, cross-sectional area (CSA) of vastus lateralis and diurnal serum testosterone and cortisol concentrations (0730 h; 0930 h; 1630 h; 1830 h). All groups similarly increased 1RM in the morning (14%–19%; p < 0.001) and evening (18%–24%; p < 0.001). CSA increased in all groups by week 24 (12%–20%, p < 0.01); however, during the training weeks 13–24 the evening groups gained more muscle mass (time-of-day main effect; p < 0.05). Texh increased in all groups in the morning (16%–28%; p < 0.01) and evening (18%–27%; p < 0.001), however, a main effect for the exercise order, in favor of E + S, was observed on both testing times (p < 0.051). Diurnal rhythms in testosterone and cortisol remained statistically unaltered by the training order or time. The present results indicate that combined strength and endurance training in the evening may lead to larger gains in muscle mass, while the E + S training order might be more beneficial for endurance performance development. However, training order and time seem to influence the magnitude of adaptations only when the training period exceeded 12 weeks.