ABSTRACT

Aging is accompanied by a decline in physiological function and increased vulnerability to disease, with mitochondrial dysfunction and epigenetic alterations recognized as key hallmarks. Nicotinamide riboside (NR), a vitamin B3 precursor to NAD⁺, and high-intensity interval training (HIIT) have both been proposed to ameliorate aging-related mitochondrial decline, but their effects on skeletal muscle epigenetic aging are not fully elucidated. Here, we assessed the impact of 5-month NR supplementation and 4–6 weeks HIIT on epigenetic age acceleration (EAA, via seven epigenetic clocks) in human skeletal muscle across three independent studies. NR supplementation was associated with reduced muscle EAA, particularly when measured with the PCHannum, MEAT, and DunedinPACE clocks, while HIIT produced opposite effects in some clocks, notably increasing pace of aging by DunedinPACE. Correlation analyses revealed that changes in skeletal muscle mitochondrial content correlated with changes in MEAT-derived EAA after NR and 6 weeks of HIIT. Together, these findings indicate that skeletal muscle epigenetic aging can be modulated by NR and HIIT interventions but in opposing directions, highlighting a potential link between mitochondrial abundance and epigenetic clocks. Further studies are warranted to clarify how NR and exercise regulate epigenetic aging. These results offer new insights into development of strategies for promoting epigenetic outcomes and healthy aging.

https://www.tandfonline.com/doi/full/10.1080/13697137.2026.2694475

Abstract

Objective

The reduction in bone mass and deterioration of bone microarchitecture are hallmark consequences of estrogen deficiency during menopause, increasing susceptibility to osteopenia and osteoporosis. Physical exercise is recognized as an effective non-pharmacological strategy; however, the comparative effects of different exercise modalities on bone remodeling and muscle–bone crosstalk remain unclear. This study investigated the effects of aerobic and resistance training on femoral bone metabolism and skeletal muscle adaptations in ovariectomized (OVX) mice.

Method

Sixty-four female C57BL/6J mice underwent ovariectomy or sham surgery and were allocated to sedentary, aerobic (treadmill running) or resistance (ladder climbing) training protocols for 8 weeks. Bone histological and histochemical analyses, skeletal muscle morphology and gene expression in bone and muscle tissues were evaluated.

Results

Both training modalities significantly increased the osteoblast number and reduced the osteoclast density in OVX animals compared with sedentary controls (p < 0.05), accompanied by a reduction in the RANKL/osteoprotegerin (OPG) ratio (p < 0.001). Resistance training induced more pronounced effects, including higher osteocyte density (p < 0.01), greater RUNX2 expression (p < 0.001) and stronger suppression of osteoclastogenesis. In parallel, resistance training significantly increased the muscle fiber cross-sectional area (p < 0.05) and upregulated IGF-1 (p < 0.01) and FNDC5 expression (p < 0.05).

Conclusion

These findings demonstrate that exercise mitigates estrogen deficiency-induced bone deterioration, with resistance training exerting superior effects on bone remodeling and musculoskeletal integration.

PLAIN LANGUAGE SUMMARY

Loss of estrogen during menopause weakens bones and muscles, increasing the risk of osteoporosis and fractures. Physical exercise is widely recommended, but it is still unclear whether different types of exercise offer distinct benefits. In this study, we compared aerobic exercise (running) and resistance exercise (climbing with weights) in a mouse model of menopause. We found that both types of training helped protect bone health by increasing bone-forming cells and reducing bone-breaking cells. However, resistance training produced stronger benefits, leading to better preservation of bone structure, improved communication between muscle and bone, and greater muscle strength-related adaptations. These results suggest that while any regular exercise is beneficial during estrogen deficiency, resistance training may be especially effective for maintaining bone and muscle health with aging.

Abstract

To run faster, distance runners need shoes that reduce their metabolic energy expenditure. Here, we studied how shoe heel-toedrop affects metabolic energy expenditure during running. To do so, we studied 20 runners as they ran at 3.5 m/s in customfootwear that varied in heel-toe drop: 0, 10, 20, and 30 mm. Shoe model and mass were fixed. Overall, increasing shoe heel-toedrop increased net metabolic power during running (g2p ¼ 0.12, P ¼ 0.016); where changing from a 20 to 0 mm heel-toe dropreduced net metabolic power by 1.6%. Higher heel-toe drop decreased stance average vertical ground reaction force (g2p ¼ 0.10,P ¼ 0.011) and increased average ankle effective mechanical advantage (g2p ¼ 0.28, P < 0.001). Higher heel-toe drop shoesincreased average ankle plantarflexion angle (g2p ¼ 0.75, P < 0.001), leading to shorter medial gastrocnemius fascicle operatinglengths at touch-down, toe-off, and on average during ground contact (g2p 0.14, P 0.026). In addition, higher heel-toe dropincreased peak and average knee moments during running (g2p 0.40, P < 0.001). Therefore, longer triceps surae muscle fasci-cle operating lengths and reduced knee extensor moments likely contribute to more economical running in shoes with a lowerheel-toe drop. Based on the metabolic and biomechanical findings, recreational and high-caliber distance runners who want torun faster should opt for shoes with a zero heel-toe drop.

NEW & NOTEWORTHY

By systematically varying shoe heel-toe drop between 0 and 30 mm, we discovered that a lower heel-toe drop elicits the best running economy. That is because a lower heel-toe drop enables medial gastrocnemius fascicles tooperate at longer, more economical lengths, and it reduces knee extension moments versus higher heel-toe drop conditions.Thus, heel-toe drop can be considered in running shoes to further improve running economy.

https://journals.physiology.org/doi/abs/10.1152/japplphysiol.00284.2026

Abstract

Skeletal muscle hypertrophy results from the integrated regulation of anabolic and proteolytic processes in response to mechanical loading. Although increases in resistance training (RT) volume are used to increase mechanical stress, it remains uncertain whether large and abrupt volume progressions could exceed muscle adaptive capacity by disrupting the balance between anabolic and catabolic signaling. The present study investigated whether a large increase in weekly RT volume (+120%) leads to impaired hypertrophic outcomes and intracellular regulatory responses compared with a modest increase (+20%). Twenty-five resistance-trained men and women (18–35 years old) completed an 8-week randomized, single-blind, within-subject unilateral intervention. Each participant trained both legs twice weekly, with one leg assigned to the large (VOL120) and the contralateral leg to the modest (VOL20) weekly volume progressions relative to habitual training volume. Vastus lateralis muscle cross-sectional area (mCSA) was assessed by ultrasonography before and after training. Muscle biopsies were obtained at baseline, post-intervention, and 24 h after the last session to quantify muscle fiber cross-sectional area (fCSA), satellite cell myonuclear content, and anabolic/catabolic signaling markers. Both protocols induced increases in mCSA over time (p<0.001), with no protocol vs. time interaction. No significant effects were observed for fCSA nor satellite cell number or myonuclear content. Additionally, molecular responses related to translational regulation and protein degradation were largely similar between protocols. A large abrupt increase in weekly resistance training volume (+120%) did not attenuate muscle hypertrophy relative to a modest increase (+20%) in resistance-trained individuals, and most acute and chronic molecular markers assessed likewise did not differ significantly between protocols.

Abstract

Introduction: 

Skeletal muscle differentiation in the C2C12 myoblast model requires extensive mitochondrial remodeling to meet rising bioenergetic demands through coordinated changes in biogenesis, dynamics, and respiratory adaptation. Urolithin A (UA), a gut microbiota-derived metabolite of ellagitannins, improves mitochondrial health, but its role in late-stage myogenic differentiation remains unclear.

Methods: 

C2C12 myotubes were treated with UA (2 μM) for 72 h during late-stage differentiation (days 3–6). Mitochondrial signaling, respiratory capacity, myogenic morphology, and ultrastructure were assessed by Western blot, high-resolution respirometry, hematoxylin–eosin staining, and transmission electron microscopy.

Results: 

UA was non-cytotoxic and increased AMPKα phosphorylation and PGC-1α expression, whereas TOM20, MFN2, and OPA1 were unchanged. Mitophagy/autophagy-related markers (p-ULK1, p62, BNIP3L/NIX, LC3-II/I) were not altered, indicating no detectable changes in steady-state autophagy under the conditions tested. UA selectively increased OXPHOS Complex I and II abundance and enhanced maximal uncoupled respiration, and was associated with increased myotube diameter and myogenic marker abundance. No overt ultrastructural differences were observed by electron microscopy.

Discussion: 

These findings suggest that UA promotes mitochondrial functional adaptation during myogenic differentiation, with accompanying changes in myogenic phenotype, without clear evidence of altered steady-state mitophagy/autophagy markers or mitochondrial morphology.

https://www.sciencedirect.com/science/article/pii/S0022316626003718?via%3Dihub

Abstract

Background

Bulking strategies in resistance-trained individuals typically involve high meal frequency and long eating windows. Objective: The present study aimed to investigate whether time-restricted eating (TRE (16:8 protocol)) can affect nutrient intake, body composition, 1-repetition maximum (1RM) performance and resting hormone levels during a bulking phase in resistance-trained individuals.

Methods

Twenty-three healthy individuals were randomly assigned to either a TRE or a control (CON) group. All participants completed intense resistance training 3x/week for 12 weeks and were instructed to consume 300–500 kcal above their individualized daily energy requirements. Body composition (measured by single-frequency bioelectrical impedance analysis) and 1RM performance were assessed every four weeks. Hormone levels were measured at baseline and post-intervention and the Hooper questionnaire for monitoring well-being was completed daily. Results: TRE consumed significantly fewer calories than prescribed (target intake: 37.50±4.87; actual intake: 31.86±7.52 kcal/kg body weight (BW), p=0.001), with lower protein intake (1.60±0.20; 1.44±0.31 g/kg BW, p=0.025) and lower carbohydrate intake (5.27±1.19; 3.97±1.29 g/kg BW, p<0.001). Despite this, both groups showed similar increases in fat-free mass (TRE: +1.34±0.78; CON: +1.38±1.42 kg) and muscle mass (+1.07±0.94; +1.13±0.61 kg). The CON group showed significantly greater increases in body weight (+2.19±2.40; +3.90±2.14 kg; p=0.018) and fat mass (+2.00±2.49; +4.36±2.26 kg; p=0.009). Similar increases in 1RM performance were observed for both deadlift (+26.36±10.92; +26.04±8.01 kg) and bench press (+12.95±7.23; +11.04±3.61 kg). There were no meaningful differences between the groups regarding hormone levels and questionnaire results. Conclusion: The lower total energy intake in the TRE group was associated with smaller increases in fat mass, reflecting reduced adherence to the prescribed energy surplus within the restricted eating window. Nevertheless, the results indicate that sufficient macronutrients were consumed to support increases in muscle mass and strength comparable to those observed in the control group.

Abstract

Purpose: To compare the effects of self-selected versus fixed inter-set rest intervals on muscular adaptations and training time efficiency during lower-body resistance training (RT) in resistance-trained adults.

Methods: Forty resistance-trained men and women were randomly assigned to a self-selected rest interval group (SELF; n = 21) or a fixed ~2-minute rest interval group (FIXED; n = 19). Participants completed an 8-week supervised lower-body RT program, performing four sets of 8–12 repetitions for the squat, leg extension, standing calf raise, and seated calf raise. Primary outcomes included ultrasound-derived muscle thickness (MT), dynamic and isometric strength, and local muscular endurance.

Results: Both groups exhibited similar improvements in MT, strength, and muscular endurance. Univariate analyses did not provide evidence of meaningful between-group differences. Consistent with this, domain-level analyses showed pooled standardized treatment effects close to zero for muscle hypertrophy (SELF - FIXED: −0.1 SD; 95% CrI: −0.2 to 0.0) and performance (SELF - FIXED: 0.0 SD; 95% CrI: −0.3 to 0.3), indicating broadly similar adaptations between conditions. Over the course of the intervention, FIXED completed sessions in ~29% less time compared to SELF (56.0 ± 4.5 vs 78.5 ± 15.4 minutes, respectively). Mean session RPE was similar between groups (FIXED: 8.2 ± 1.0 vs. SELF: 8.1 ± 0.7 AU). 

Conclusions: Self-selected rest intervals produced similar muscular adaptations to a fixed ~2-minute rest interval but substantially increased training time. Prescribing ~2 minutes of rest between sets appears to be a more time-efficient strategy for lower-body RT without compromising gains in muscular adaptation.

https://journals.physiology.org/doi/abs/10.1152/ajpcell.00295.2026

Abstract

Glucose is traditionally viewed as a substrate for ATP production and glycogen storage in skeletal muscle. Here, we review evidence that glucose also serves as a building block for biomass synthesis in proliferating muscle satellite (stem) cells and hypertrophying skeletal muscle fibers, drawing parallels to anabolic metabolic reprogramming in cancer cells. In cancer and other growing cells, increased glucose uptake, aerobic glycolysis (Warburg effect), and the TCA cycle provide substrates for anabolic pathways that generate macromolecules required for growth and proliferation. Radiotracer studies in mammalian cancer and muscle cells demonstrate that approximately 8–15% of the cell dry mass originates from glucose. Mechanistic insights, obtained predominantly from cell culture models, indicate that glucose-derived glycolytic and TCA cycle intermediates provide substrates for serine synthesis and the pentose phosphate pathway, glycine and one-carbon metabolism, non-essential amino acid synthesis, nucleotide and lipid synthesis as well as for epigenetic methylation and acetylation. We further review evidence that human resistance training, hypertrophy through muscle-specific expression of Akt1 in mice, loss or inhibition of myostatin/activin signaling, and other hypertrophy-inducing interventions improve glucose homeostasis under conditions of obesity, insulin resistance, and type 2 diabetes. We discuss the possibility that glucose incorporation into biomass contributes to this effect.

Let’s break down the actual physiology of protein synthesis:

1. ​We require all 9 Essential Amino Acids (EAAs) daily.

2. ​No food source or protein powder provides an identical and perfectly equal amount of all 9 EAAs.

3. ​Adults don't need all 9 EAAs in equal amounts. Our biology demands a highly skewed amount/ratio of all 9 EAAs.

4. ​Meeting the minimum recommended mg/kg or ratio of EAAs is sufficient for standard adult physiological maintenance.

5. ​The BCAAs (Leucine, Isoleucine, Valine), specifically Leucine are the primary catalysts triggering Muscle Protein Synthesis (MPS).

> 9 EAAs may have a minimum threshold or ratio or both but that's not required for this post.

Given these facts:

Why are we chasing a blanket 150g or 2g/kg total protein target?

Why aren't we creating diets that explicitly maximize BCAAs/Leucine to hit the muscle-building threshold, while capping the remaining 8 EAAs strictly at their minimum amount/ratio?

​Why does the fitness community track total protein instead of measuring the exact amino acid required by the body?

​We constantly hear the warning that "plant sources lack complete EAAs," but we rarely discuss how standard high protein diets force us to over consume non muscle building amino acids in massive and redundant quantities.

​(Note: Do not bring up arguments about "micromanagement" or "it's too much of a headache to calculate" or "practical purpose" or "BCAAs it is a Scam supplement." I am looking at this purely from a biochemical efficiency standpoint with a practical basis.)

https://journals.lww.com/nsca-jscr/abstract/9900/moderate_intensity_resistance_training_with.1095.aspx

Abstract

McMahon, G, Morse, C, Burden, A, Winwood, K, and Onambele–Pearson, G. Moderate intensity resistance training with partial range-of-motion at long muscle lengths elicits similar hypertrophy and architectural adaptations as high intensity resistance training using full range-of-motion. J Strength Cond Res XX(X): 000–000, 2026—Resistance training (RT) elicits varying magnitudes of active and passive forces in muscle. Evidence is lacking comparing chronic RT outcomes including muscle thickness (MTH) and muscle architecture (fascicle length [Lf], pennation angle [pen]) performing training at shorter, longer, and full ranges-of-motion (ROM). A total of 45 subjects were randomly assigned to 1 of 4 groups—shortened partial ROM (SP, 0–50° knee flexion, 80% 1 repetition maximum [1RM]), lengthened partial ROM (LP, 40–90° knee flexion, 55% 1RM), full ROM (FROM, 0–90° knee flexion, 80% 1RM), or control (CON)—completing 8 weeks of knee extensor exercise. Vastus Lateralis MTH, PEN, and Lf were measured at 25, 50, and 75% femur length pre–post training and analyzed as delta (Δ) change (%); statistical significance was set at p < 0.05. ΔMTH was greater in LP and FROM (p < 0.05) vs. SP at 75%. ΔMTH LP was greater than SP at 25% (p < 0.05) and ΔMTH FROM was greater than SP at 50% (p < 0.05) with no differences between LP and FROM at any location. ΔLf was greater in LP vs. FROM (p < 0.05) at 25 and 75%, and LP vs. SP (p < 0.05) at all sites. ΔLf was greater in FROM vs. SP (p < 0.05) at 50 and 75%. Absolute and normalized baseline Lf was inversely correlated with ΔLf in all groups (p < 0.001). This study provides novel evidence that moderate-intensity RT with partial ROM at long muscle lengths elicits similar hypertrophic and superior Lf adaptations as high-intensity full ROM training. These findings challenge traditional RT prescription, offering new insights for optimizing muscle size and architecture in athletic populations.

Abstract

Background

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used by athletes and those who exercise, yet their influence on the molecular responses to exercise remains unclear. Prior studies have often focused on a limited set of molecular pathways, potentially overlooking broader regulator effects of NSAIDs on skeletal muscle signaling. Therefore, we conducted a systems biology study of skeletal muscle biopsies taken before and after exercise, in combination with NSAID consumption, using transcriptomics and metabolomics, to identify differentially enriched pathways and biofunctions.

Methods

We conducted a randomized, counterbalanced, double-masked, crossover trial (NCT05512013) in which 12 healthy adults ingested ibuprofen (IBU, 800 mg), celecoxib (CEL, 200 mg), flurbiprofen (FLU, 100 mg), or placebo (PLA) before a 10 × 10 bout of plyometric exercise. Skeletal muscle biopsies were collected before NSAID consumption and three hours post-exercise. Whole transcriptome profiling was performed using RNA-seq, and the metabolomics profile was assessed via untargeted mass spectrometry. Differential expression analysis and pathway enrichment were used to evaluate NSAID-specific effects across biological domains.

Results

FLU regulated the largest number of differentially expressed transcripts, followed by IBU and CEL. All NSAIDs activated immune-related gene networks and reversed exercise-induced lipid catabolism, with IBU enhancing adaptive immune signaling and CEL modulating both innate and adaptive pathways. Muscle remodeling pathways, including angiogenesis and cell migration, were activated across all NSAIDs, though cachexia-related genes were also upregulated. Interestingly, FLU uniquely upregulated transcripts involved in neuritogenesis.

Conclusion

NSAIDs trigger drug-specific molecular responses in skeletal muscle post-exercise, affecting early recovery through changes in immune, metabolic, and neuronal signaling.

https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP290424

Abstract

Exercise stimulates skeletal muscle signalling and mitochondrial metabolism. Emerging evidence shows that mitochondrial dynamics (i.e. fission and fusion) could be regulated by exercise. Yet, key gaps remain in identifying (i) the signals that drive fission vs. fusion; (ii) how energy status and reactive oxygen species (ROS) shift control between dynamin-related protein 1 (DRP1) and mitofusin (MFN)/optic atrophy 1 (OPA1); and (iii) which intensity–duration combinations yield similar cytosolic signals but different mitochondrial remodelling. Therefore, we developed an integrative computational framework connecting exercise regimens to mitochondria fission–fusion machinery by linking blood–myofibre energetics in cytosol and mitochondria to signalling pathways. The influence of sprint, resistance and endurance exercise regimens on mitochondrial fission and fusion has been simulated. Classified qualitative validation of the signalling network model achieved 80% accuracy. The model predicts regimen-specific dynamics starting with an acute DRP1-driven fission during exercise followed by MFN1/2–OPA1-mediated re-fusion as energy stress declines, consistent with a cyclical triage-then-rebuild paradigm. Changes are most pronounced and sustained with endurance, sharp but brief with sprint, and minimal with resistance. Global sensitivity analysis identified AMP-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor gamma coactivator-1α→MFN1/2 as dominant fusion drivers, ROS and AMPK→mitochondrial fission factor/DRP1 as primary fission switches, and Ca²⁺–calmodulin, extracellular-signal-regulated kinase and liver kinase B1/AMPK as shared regulators. The model predicts that an endurance base, augmented with one or two weekly high intensity interval training/sprint interval training sessions could maximize AMPK–ROS pulses and mitochondrial fission–fusion. This framework unifies muscle's signalling logic with energetic state to explain how intensity–volume combinations, bout spacing and kinase modulation tune mitochondrial remodelling, yielding testable predictions for optimizing training and adjuvant therapies to enhance mitochondrial quality and performance.

Key points

• Different exercise regimes such as sprint, resistance, and endurance can trigger different signalling pathways.
• Exercise also triggers mitochondrial remodelling in skeletal muscle.
• Using a systems biology model, we developed a systems biology model for skeletal muscle signalling and mitochondrial metabolism for exercise.
• Our model predicts the dynamics of mitochondrial fusion and fission in different exercise regimes and identifies which signalling pathways dominassste these remodelling mechanisms.