The underappreciated role of muscle in health and disease

The role of bone in energy metabolism: A focus on osteocalcin

Understanding the mechanisms involved in whole body glucose regulation is key for the discovery of new treatments for type 2 diabetes (T2D). Historically, glucose regulation was largely focused on responses to insulin and glucagon. Impacts of incretin-based therapies, and importance of muscle mass, are also highly relevant. Recently, bone was recognized as an endocrine organ, with several bone proteins, known as osteokines, implicated in glucose metabolism through their effects on the liver, skeletal muscle, and adipose tissue. Research efforts mostly focused on osteocalcin (OC) as a leading example. This review will provide an overview on this role of bone by discussing bone turnover markers (BTMs), the receptor activator of nuclear factor kB ligand (RANKL), osteoprotegerin (OPG), sclerostin (SCL) and lipocalin 2 (LCN2), with a focus on OC. Since 2007, some, but not all, research using mostly OC genetically modified animal models suggested undercarboxylated (uc) OC acts as a hormone involved in energy metabolism. Most data generated from in vivo, ex vivo and in vitro models, indicate that exogenous ucOC administration improves whole-body and skeletal muscle glucose metabolism. Although data in humans are generally supportive, findings are often discordant likely due to methodological differences and observational nature of that research. Overall, evidence supports the concept that bone-derived factors are involved in energy metabolism, some having beneficial effects (ucOC, OPG) others negative (RANKL, SCL), with the role of some (LCN2, other BTMs) remaining unclear. Whether the effect of osteokines on glucose regulation is clinically significant and of therapeutic value for people with insulin resistance and T2D remains to be confirmed.

Antioxidative, Glucose Management, and Muscle Protein Synthesis Properties of Fish Protein Hydrolysates and Peptides

The marine environment is an excellent source for many physiologically active compounds due to its extensive biodiversity. Among these, fish proteins stand out for their unique qualities, making them valuable in a variety of applications due to their diverse compositional and functional properties. Utilizing fish and fish coproducts for the production of protein hydrolysates and bioactive peptides not only enhances their economic value but also reduces their potential environmental harm, if left unutilized. Fish protein hydrolysates (FPHs), known for their excellent nutritional value, favorable amino acid profiles, and beneficial biological activities, have generated significant interest for their potential health benefits. These hydrolysates contain bioactive peptides which are peptide sequences known for their beneficial physiological effects. These biologically active peptides play a role in metabolic regulation/modulation and are increasingly seen as promising ingredients in functional foods, nutraceuticals and pharmaceuticals, with potential to improve human health and prevent disease. This review aims to summarize the current in vitro, cell model (in situ) and in vivo research on the antioxidant, glycaemic management and muscle health enhancement properties of FPHs and their peptides.

Shuttle Time for Seniors: The Impact of 8-Week Structured Badminton Training on Markers of Healthy Aging and Evaluation of Lived Experiences-A Quasi-Experimental Study

BACKGROUND/OBJECTIVES

Engagement in sport offers the potential for improved physical and psychological well-being and has been shown to be beneficial for promoting healthy aging. Opportunities for older adults to (re)engage with sport are limited by a paucity of age-appropriate introductory sports intervention programs. As such, the study evaluated the efficacy of a newly designed 8-week badminton training program (Shuttle Time for Seniors) on markers of healthy aging and the lived experiences of participation.

METHODS

Forty-three older adults assigned to a control (N = 20) or intervention group (N = 23) completed pre-post assessment of physical and cognitive function, self-efficacy for exercise, and well-being. Focus groups were conducted for program evaluation and to understand barriers and enablers to sustained participation.

RESULTS

Those in the intervention group increased upper body strength, aerobic fitness, coincidence anticipation time, and self-efficacy for exercise. Objectively improved physical and cognitive functions were corroborated by perceived benefits indicated in thematic analysis. Shuttle Time for Seniors was perceived as appropriate for the population, where the age-appropriate opportunity to participate with likeminded people of similar ability was a primary motivator to engagement. Despite willingness to continue playing, lack of badminton infrastructure was a primary barrier to continued engagement.

CONCLUSION

Shuttle Time for Seniors offered an important opportunity for older adults to (re)engage with badminton, where the physical and psychosocial benefits of group-based badminton improved facets important to healthy aging. Significance/Implications: Age-appropriate introductory intervention programs provide opportunity for older adults to (re)engage with sport. However, important barriers to long-term engagement need to be addressed from a whole systems perspective.

Free essential amino acid feeding improves endurance during resistance training via DRP1-dependent mitochondrial remodelling

BACKGROUND

Loss of muscle strength and endurance with aging or in various conditions negatively affects quality of life. Resistance exercise training (RET) is the most powerful means to improve muscle mass and strength, but it does not generally lead to improvements in endurance capacity. Free essential amino acids (EAAs) act as precursors and stimuli for synthesis of both mitochondrial and myofibrillar proteins that could potentially confer endurance and strength gains. Thus, we hypothesized that daily consumption of a dietary supplement of nine free EAAs with RET improves endurance in addition to the strength gains by RET.

METHODS

Male C57BL6J mice (9 weeks old) were assigned to control (CON), EAA, RET (ladder climbing, 3 times a week), or combined treatment of EAA and RET (EAA + RET) groups. Physical functions focusing on strength or endurance were assessed before and after the interventions. Several analyses were performed to gain better insight into the mechanisms by which muscle function was improved. We determined cumulative rates of myofibrillar and mitochondrial protein synthesis using 2H2O labelling and mass spectrometry; assessed ex vivo contractile properties and in vitro mitochondrial function, evaluated neuromuscular junction (NMJ) stability, and assessed implicated molecular singling pathways. Furthermore, whole-body and muscle insulin sensitivity along with glucose metabolism, were evaluated using a hyperinsulinaemic-euglycaemic clamp.

RESULTS

EAA + RET increased muscle mass (10%, P < 0.05) and strength (6%, P < 0.05) more than RET alone, due to an enhanced rate of integrated muscle protein synthesis (19%, P < 0.05) with concomitant activation of Akt1/mTORC1 signalling. Muscle quality (muscle strength normalized to mass) was improved by RET (i.e., RET and EAA + RET) compared with sedentary groups (10%, P < 0.05), which was associated with increased AchR cluster size and MuSK activation (P < 0.05). EAA + RET also increased endurance capacity more than RET alone (26%, P < 0.05) by increasing both mitochondrial protein synthesis (53%, P < 0.05) and DRP1 activation (P < 0.05). Maximal respiratory capacity increased (P < 0.05) through activation of the mTORC1-DRP1 signalling axis. These favourable effects were accompanied by an improvement in basal glucose metabolism (i.e., blood glucose concentrations and endogenous glucose production vs. CON, P < 0.05).

CONCLUSIONS

Combined treatment with balanced free EAAs and RET may effectively promote endurance capacity as well as muscle strength through increased muscle protein synthesis, improved NMJ stability, and enhanced mitochondrial dynamics via mTORC1-DRP1 axis activation, ultimately leading to improved basal glucose metabolism.

Protein Supplement Tolerability and Patient Satisfaction after Bariatric Surgery

PURPOSE

Disproportional fat-free mass loss often occurs post-bariatric surgery, partly due to insufficient protein intake during the post-surgery recovery phase. We compared five protein-enhancing strategies (PES) on patient tolerability, satisfaction and protein intake.

MATERIALS AND METHODS

Ninety-four participants, scheduled for bariatric surgery, were enrolled and allocated to either of the following: (1) whey powder, (2) hydrolysed collagen powder, (3) plant-based powder, (4) protein-rich products, (5) protein gel, or control. PES groups were instructed to add 30 g of powder or 2 gels or protein products to their diet. Patient satisfaction and tolerability were evaluated with questionnaires. Dietary intake was assessed prior to and during PES use.

RESULTS

Seven patients dropped out (i.e. loss of contact, personal reasons or post-surgery complications) yielding an analytical cohort of 87 participants. The majority of patients (61%) did not experience dietary complaints from PES and could use PES ≥ 5 days of the week. PES non-usage was mainly related to taste dislike (58%). Hydrolysed collagen scored highest on tolerability and satisfaction: 86% of the participants could use HC ≥ 5 days and 71% were satisfied with the product. PES increased protein intake from 54.7 ± 21.5 g/day to 64.7 ± 23.4 g/day during the intervention (p = 0.002), which differed from the control group (+ 10.1 ± 24.5 g/day vs. - 6.3 ± 23.8 g/day for controls, p = 0.019). Whey showed the highest increase, namely + 18.3 ± 16.3 g/day (p = 0.009).

CONCLUSION

PES were tolerated by the majority of participants, and an improved protein intake with PES use was seen. However, the taste of the products could be improved to further enhance satisfaction and tolerability.

Molecular mechanisms of cancer cachexia. Role of exercise training

Cancer-associated cachexia represents a multifactorial syndrome mainly characterized by muscle mass loss, which causes both a decrease in quality of life and anti-cancer therapy failure, among other consequences. The definition and diagnostic criteria of cachexia have changed and improved over time, including three different stages (pre-cachexia, cachexia, and refractory cachexia) and objective diagnostic markers. This metabolic wasting syndrome is characterized by a negative protein balance, and anti-cancer drugs like chemotherapy or immunotherapy exacerbate it through relatively unknown mechanisms. Due to its complexity, cachexia management involves a multidisciplinary strategy including not only nutritional and pharmacological interventions. Physical exercise has been proposed as a strategy to counteract the effects of cachexia on skeletal muscle, as it influences the mechanisms involved in the disease such as protein turnover, inflammation, oxidative stress, and mitochondrial dysfunction. This review will summarize the experimental and clinical evidence of the impact of physical exercise on cancer-associated cachexia.

Does Taking a Break Matter-Adaptations in Muscle Strength and Size Between Continuous and Periodic Resistance Training

We aimed to compare the effects of periodic resistance training (RT) and continuous RT on muscle strength and size. Fifty-five healthy, untrained participants (age 32 ± 5 years) were randomized to periodic (PRT, n = 20 completed the study, 45% females) or continuous (CRT, n = 22 completed the study, 45% females) groups. PRT completed a 10-week RT, a 10-week detraining, and a second identical 10-week RT. CRT began with a 10-week non-RT, followed by a 20-week RT. RT included twice-weekly supervised whole-body RT sessions. Leg press (LP) and biceps curl (BC) one repetition maximum (1RM), countermovement jump (CMJ) height, muscle cross-sectional area (CSA) of vastus lateralis (VL), and biceps brachii (BB) using ultrasound imaging were measured twice at the beginning and every fifth week during the intervention. Both groups increased (p < 0.001) 1RM in LP and BC, CSA in VL and BB, and CMJ height with no differences between the groups. In PRT, 1RM in LP and BC, CSA in VL and BB, and CMJ height decreased during detraining (p < 0.05). During the first 5 weeks of retraining in PRT, increases in LP 1RM, and VL and BB CSA were greater than in CRT during Weeks 10-15 of their CRT (p < 0.01). PRT and CTR ended up in similar postintervention adaptations, as decreased muscle strength and size during detraining in PRT regained rapidly during retraining. Our results therefore suggest that trainees should not be too concerned about occasional short-term training breaks in their daily lives when it comes to lifelong strength training. Trial Registration: ClinicalTrials.gov identifier: NCT05553769.

Incretin-Based Weight Loss Pharmacotherapy: Can Resistance Exercise Optimize Changes in Body Composition?

This narrative review highlights the degree to which new antiobesity medications based on gut-derived nutrient-stimulated hormones (incretins) cause loss of lean mass, and the importance of resistance exercise to preserve muscle. Glucagon-like peptide 1 receptor agonists (GLP-1RA) induce substantial weight loss in randomized trials, effects that may be enhanced in combination with glucose-dependent insulinotropic polypeptide (GIP) receptor agonists. Liraglutide and semaglutide (GLP-1RA), tirzepatide (GLP-1 and GIP receptor dual agonist), and retatrutide (GLP-1, GIP, and glucagon receptor triple agonist) are peptides with incretin agonist activity that induce ∼15-24% weight loss in adults with overweight and obesity, alongside beneficial impacts on blood pressure, cholesterol, blood glucose, and insulin. However, these agents also cause rapid and significant loss of lean mass (∼10% or ∼6 kg), comparable to a decade or more of aging. Maintaining muscle mass and function as humans age is crucial to avoiding sarcopenia and frailty, which are strongly linked to morbidity and mortality. Studies indicate that supervised resistance exercise training interventions with a duration >10 weeks can elicit large increases in lean mass (∼3 kg) and strength (∼25%) in men and women. After a low-calorie diet, combining aerobic exercise with liraglutide improved weight loss maintenance compared with either alone. Retaining lean mass during incretin therapy could blunt body weight (and fat) regain on cessation of weight loss pharmacotherapy. We propose that tailored resistance exercise training be recommended as an adjunct to incretin therapy to optimize changes in body composition by preserving lean mass while achieving fat loss.

Is fat mass a better predictor of 6-month survival than muscle mass among African children aged 6-59 months with severe pneumonia?

BACKGROUND

Pneumonia remains the leading cause of mortality among children under 5 years. Poor nutritional status increases pneumonia mortality. Nutritional status assessed by anthropometry alone does not provide information on which body composition element predicts survival. Body composition proxy measures including arm-fat-area (AFA), arm-muscle-area (AMA), and arm-muscle-circumference (AMC) could be useful predictors.

OBJECTIVE

To compare the ability of fat and muscle mass indices to predict 6-month survival among children with severe pneumonia.

METHODS

This prospective cohort study was nested in the COAST-Nutrition trial (ISRCTN10829073, 06/06/2018) conducted between June 2020 and October 2022 in Uganda and Kenya. We included children aged 6-59 months hospitalized for severe pneumonia with hypoxemia. Children with severe malnutrition, known chronic lung or cardiac diseases were excluded. Anthropometry and clinical status were assessed at enrolment and at follow-up to day 180. We examined Receiver Operator Characteristic (ROC) curves of fat and muscle mass indices with 6-month survival as the outcome, and compared the areas under the curve (AUCs) using chi-square tests. Cox survival analysis models assessed time-to-mortality.

RESULTS

We included 369 participants. The median age was 15-months (IQR 9, 26), and 59.4% (219/369) of participants were male. The baseline measurements were: median MUAC 15.0 cm (IQR 14.0,16.0); arm-fat-area 5.6cm2 (IQR 4.7, 6.8); arm-muscle-area 11.4cm2 (IQR 10.0, 12.7); and arm-muscle-circumference 12.2 cm (IQR 11.5, 12.9). Sixteen (4.3%) participants died and 4 (1.1%) were lost-to-follow-up. The AUC for Arm-Fat-Area was not significantly higher than that for Arm-Muscle-Area and Arm-Muscle-Circumference [AUC 0.77 (95%CI 0.64-0.90) vs. 0.61 (95%CI 0.48-0.74), p = 0.09 and 0.63 (95%CI 0.51-0.75), p = 0.16 respectively], but was not statistically different from MUAC (AUC 0.73 (95%CI 0.62-0.85), p = 0.47). Increase in Arm-Fat-Area and Arm-Muscle-Circumference significantly improved survival [aHR 0.40 (95%CI 0.24-0.64), p = < 0.01 and 0.59 (95%CI 0.36-1.06), p = 0.03 respectively]. Survival prediction using Arm-Fat-Area was not statistically different from that of MUAC (p = 0.54).

CONCLUSIONS

Muscle mass did not predict 6-month survival better than fat mass in children with severe pneumonia. Fat mass appears to be a better predictor. Effects of fat and muscle could be considered for prognosis and targeted interventions.

How Can Promoting Skeletal Muscle Health and Exercise in Children and Adolescents Prevent Insulin Resistance and Type 2 Diabetes?

Skeletal muscle secretome, through its paracrine and endocrine functions, contributes to the maintenance and regulation of overall physiological health. We conducted a narrative review on the role of skeletal muscle and exercise in maintaining glucose homeostasis, driving insulin resistance (IR), and preventing type 2 diabetes in pediatric populations, especially in the context of overweight and obesity. Myokines such as interleukin (IL)-6, IL-8, and IL-15, as well as irisin, myonectin, and myostatin, appear to play a crucial role in IR. Skeletal muscle can also become a target of obesity-induced and IR-induced inflammation. In the correlation between muscle, IR, and inflammation, the role of infiltration of the immune cells and the microvasculature may also be considered. It remains unclear which exercise approach is the best; however, combining aerobic exercise with resistance training seems to be the most effective strategy for managing IR, with high-intensity activities offering superior metabolic benefits and long-term adherence. Encouraging daily participation in enjoyable and engaging exercise is key for long-term commitment and effective glucose metabolism management. Promoting physical activity in children and adolescents must be a top priority for public health, not only in terms of individual quality of life and well-being but also for community health.

Adults born preterm have lower peripheral skeletal muscle area and strength

Prematurity is associated with lower exercise capacity, which relies on the integrity of the cardiovascular, pulmonary, and skeletal muscle systems. Our animal model mimicking prematurity-associated conditions showed altered muscle composition and atrophy in adulthood. This study aimed to compare muscle composition and strength in adults born preterm versus full-term controls. This observational cohort study recruited 55 adults born preterm, ≤ 29 weeks' of gestation and 53 full-term controls who underwent musculoskeletal ultrasound imaging to assess morphology of the rectus femoris at rest and during a maximal voluntary contraction. Maximal voluntary contraction of the hands and legs were measured by manual dynamometry. In adults born preterm, there was lower muscle strength (handgrip: - 4.8 kg, 95% CI - 9.1, - 0.6; knee extensor: - 44.6 N/m, 95% CI - 63.4, - 25.8) and smaller muscle area (- 130 mm2, 95% CI - 207, - 53), which was more pronounced with a history of bronchopulmonary dysplasia. Muscle stiffness was increased in the preterm versus term group (0.4 m/s, 95% CI 0.04, 0.7). Prematurity is associated with alterations in skeletal muscle composition, area, and function in adulthood. These findings highlight the necessity to implement preventive and/or curative approaches to improve muscle development and function following preterm birth to enhance overall health in this population.

Association of the systemic inflammation and anthropometric measurements with cancer risk: a prospective study in MJ cohort

Objective

To investigate the specific role of inflammation in the connection between obesity and the overall incidence of cancer.

Methods

A total of 356,554 participants in MJ cohort study were included. Systemic inflammation markers from blood samples and anthropometric measurements were determined using professional instruments. The Cox model was adopted to evaluate the association.

Results

Over a median follow-up of 8.2 years, 9,048 cancer cases were identified. For individual systemic inflammation biomarkers, the overall cancer risk significantly escalated as blood C-reactive protein (CRP) (hazard ratio (HR)=1.036 (1.017-1.054)) and globulin (GLO) (HR=1.128 (1.105-1.152)) levels increased, and as hemoglobin (HEMO) (HR=0.863 (0.842-0.884)), albumin (ALB) (HR=0.846 (0.829-0.863)) and platelets (PLA) (HR=0.842 (0.827-0.858)) levels decreased. For composite indicators, most of them existed a significant relationship to the overall cancer risk. Most indicators were correlated with the overall cancer and obesity-related cancer risk, but there was a reduction of association with non-obesity related cancer risk. Most of indicators mediated the association between anthropometric measurements and overall cancer risk.

Conclusions

Systemic inflammatory state was significantly associated with increased risks of cancer risk. Inflammation biomarkers were found to partly mediate the association between obesity and cancer risk.

Muscle-enriched microRNA-486-mediated regulation of muscular atrophy and exercise

The objectives of this review were to understand the impact of microRNA-486 on myogenesis and muscle atrophy, and the change of microRNA-486 following exercise, and provide valuable information for improving muscle atrophy based on exercise intervention targeting microRNA-486. Muscle-enriched microRNAs (miRNAs), also referred to as myomiRs, control various processes in skeletal muscles, from myogenesis and muscle homeostasis to different responses to environmental stimuli such as exercise. MicroRNA-486 is a miRNA in which a stem-loop sequence is embedded within the ANKYRIN1 (ANK1) locus and is strictly conserved across mammals. MicroRNA-486 is involved in the development of muscle atrophy caused by aging, immobility, prolonged exposure to microgravity, or muscular and neuromuscular disorders. PI3K/AKT signaling is a positive pathway, as it increases muscle mass by increasing protein synthesis and decreasing protein degradation. MicroRNA-486 can activate this pathway by inhibiting phosphatase and tensin homolog (PTEN), it may also indirectly inhibit the HIPPO signaling pathway to promote cell growth. Exercises regulate microRNA-486 expression both in blood and muscle. This review focused on the recent elucidation of sarcopenia regulation by microRNA-486 and its effects on pathological states, including primary muscular disease, secondary muscular disorders, and age-related sarcopenia. Additionally, the role of exercise in regulating skeletal muscle-enriched microRNA-486 was highlighted, along with its physiological significance. Growing evidence indicates that microRNA-486 significantly impacts the development of muscle atrophy. MicroRNA-486 has great potential to become a therapeutic target for improving muscle atrophy through exercise intervention.

Resistance training-induced changes in muscle proteolysis and extracellular matrix remodeling biomarkers in the untrained and trained states

PURPOSE

Resistance training (RT) induces muscle growth at varying rates across RT phases, and evidence suggests that the muscle-molecular responses to training bouts become refined or attenuated in the trained state. This study examined how proteolysis-related biomarkers and extracellular matrix (ECM) remodeling factors respond to a bout of RT in the untrained (UT) and trained (T) state.

METHODS

Participants (19 women and 19 men) underwent 10 weeks of RT. Biopsies of vastus lateralis were collected before and after (24 h) the first (UT) and last (T) sessions. Vastus lateralis cross-sectional area (CSA) was assessed before and after the experimental period.

RESULTS

There were increases in muscle and type II fiber CSAs. In both the UT and T states, calpain activity was upregulated and calpain-1/-2 protein expression was downregulated from Pre to 24 h. Calpain-2 was higher in the T state. Proteasome activity and 20S proteasome protein expression were upregulated from Pre to 24 h in both the UT and T. However, proteasome activity levels were lower in the T state. The expression of poly-ubiquitinated proteins was unchanged. MMP activity was downregulated, and MMP-9 protein expression was elevated from Pre to 24 h in UT and T. Although MMP-14 protein expression was acutely unchanged, this marker was lower in T state. TIMP-1 protein levels were reduced Pre to 24 h in UT and T, while TIMP-2 protein levels were unchanged.

CONCLUSION

Our results are the first to show that RT does not attenuate the acute-induced response of proteolysis and ECM remodeling-related biomarkers.

Strengths and Limitations of BMI in the Diagnosis of Obesity: What is the Path Forward?

PURPOSE OF REVIEW

This review aims to discuss strengths and limitations of body mass index (BMI) in diagnosing obesity, the use of alternative anthropometric measurements, and potential new technology that may change the future of obesity diagnosis and management.

RECENT FINDINGS

The diagnosis of obesity requires the anthropometric assessment of adiposity. In clinical settings, this should include BMI with confirmation that elevated BMI represents excess adiposity and a measure of fat distribution (i.e., waist circumference (WC), waist to height ratio (WHtR), or WC divided by height0.5 (WHR.5R). Digital anthropometry and bioelectric impedance (BIA) can estimate fat distribution and be feasibly employed in the clinic. In addition, the diagnosis should include a clinical component assessing the presence and severity of weight-related complications. As anthropometric measures used in the diagnosis of obesity, BMI is generally sufficient if confirmed to represent excess adiposity, and there are advantages to the use of WHtR over WC to assess fat distribution. BIA and digital anthropometry have the potential to provide accurate measures of fat mass and distribution in clinical settings. There should also be a clinical evaluation for the presence and severity of obesity complications that can be used to stage the disease.

Preservation of Muscle during Treatment for Obesity in Adults with Intellectual Disabilities

OBJECTIVES

Adults with intellectual disabilities will frequently experience sedentary behavior and excessive weight, which may cause or exacerbate a multitude of medical and behavioral problems. This study examined a program to encourage increased activity and weight loss in an outpatient service for adults with intellectual disabilities.

METHODS

Behavioral methods were used to treat obesity in 33 male and 21 female adults with intellectual disabilities for a mean of 9 months. They were retrospectively analyzed to determine the effects of treatment on muscle and adiposity using body composition analysis.

RESULTS

The 54 participants of the original 122 (44.3%) who did not drop out were divided into three groups: weight loss ≥3 kg/3% (n = 20, 37%), weight loss <3 kg/3% (n = 17, 31.5%), and no weight loss or weight gain (n = 17, 31.5%). Only men and women who lost ≥3 kg/3%, demonstrated significant gain of relative muscle mass. Those who gained weight lost muscle mass.

CONCLUSIONS

If motivation remains high and follow-up is reasonably long, then a multicomponent obesity treatment program can lead to significant weight loss with preservation of muscle in adults with intellectual disabilities.

Increased Neuromuscular Activity, Force Output, and Resistance Exercise Volume When Using 5-Minute Compared with 2-Minute Rest Intervals Between the Sets

ABSTRACT

McMahon, G, Best, N, Coulter, T, and Erskine, RM. Increased neuromuscular activation, force output and resistance exercise volume when using 5-minute compared with 2-minute rest intervals between the sets. J Strength Cond Res 38(9): 1527-1534, 2024-Longer rest intervals between resistance exercise (RE) sets may promote greater muscle hypertrophy and strength gains over time by facilitating the completion of greater training volume and intensity. However, little is known about the acute neuromuscular responses to RE sets incorporating longer vs. shorter rest intervals. Using a within-subject, crossover design, 8 healthy, young subjects completed 2 separate acute bouts of 4 sets of 8 × 3-s maximal isometric contractions using either a 2-minute (REST-2) or 5-minute (REST-5) rest interval between sets. Peak torque (PT) and electromyography (EMG) were measured pre and 5 minutes postexercise. Peak torque and mean torque (MT), EMG, mean, and median frequencies were measured during each set, whereas blood lactate (BLa), heart rate (HR), and rating of perceived exertion (RPE) were measured following each set. Peak torque and MT were lower ( p < 0.05) in sets 3 and 4, and sets 2-4 in REST-2 compared with REST-5, respectively. Electromyography and BL were lower and higher, respectively, in REST-2 vs. REST-5. There was no main effect of condition on HR or RPE. Pre-to-post exercise reductions in PT (-17 ± 9% vs. -4 ± 7%) and EMG (-29 ± 14% vs. -10 ± 7%) were greater ( p < 0.001) in REST-2 vs. REST-5. Total exercise volume was less in REST-2 vs. REST-5 (9,748 ± 2296 N·m -1 vs. 11,212 ± 2513 N·m -1 , p < 0.001). These results suggest that incorporating 5-minute between-set rest intervals into a resistance exercise session facilitates improved neuromuscular function, increased exercise volume, and less metabolic stress compared with 2-minute rest intervals. Thus, 5-minute rest intervals may be more efficacious for promoting muscle hypertrophy and strength gains in a chronic resistance training program.

The Anabolic Response to Protein Ingestion During Recovery From Exercise Has No Upper Limit in Magnitude and Duration In Vivo in Humans: A Commentary

A comprehensive recent study by Trommelen et al. demonstrated that muscle tissue exhibits a greater capacity to incorporate exogenous exogenous protein-derived amino acids into bound muscle protein than was previously appreciated, at least when measured in "anabolically sensitive," recreationally active (but not resistance-trained), young men following resistance exercise. Moreover, this study demonstrated that the duration of the postprandial period is modulated by the dose of ingested protein contained within a meal, that is, the postexercise muscle protein synthesis response to protein ingestion was more prolonged in 100PRO than 25PRO. Both observations represent important scientific advances in the field of protein metabolism. However, we respectfully caution that the practical implications of these findings may have been misinterpreted, at least in terms of dismissing the concept of protein meal distribution as an important factor in optimizing muscle tissue anabolism and/or metabolic health. Moreover, based on emerging evidence, this idea that the anabolic response to protein ingestion has no upper limit does not appear to translate to resistance-trained young women.

The anabolic response to a ground beef patty and soy-based meat alternative: a randomized controlled trial

BACKGROUND

Soy-based meat alternatives (SBMA) are becoming increasingly popular, but it is unclear if they have the same anabolic effect on skeletal muscle as animal meat.

OBJECTIVES

We aimed to compare the stimulation of skeletal muscle protein synthesis by consumption of 1 or two 4 oz patties of SBMA with 4 oz (80% protein/20% fat) beef.

METHODS

The study design was a randomized controlled trial. Participants were aged 18-40 y of age and in good general health with a body mass index (kg/m2) between 20 and 32. Stable isotope tracer methods were used (L-[ring-2H5] phenylalanine, [U-13C9-15N]- tyrosine, and L-[ring-2H4] tyrosine) to quantify the response of muscle protein fractional synthetic rate (FSR) to consumption of a single beef (4 oz), single SBMA (4 oz), or two 4 oz SBMA patties (8 oz). Whole-body rates of protein synthesis, breakdown, and net balance, as well as plasma essential amino acid concentrations, were also measured.

RESULTS

The increase above basal in muscle protein FSR following consumption of the 4 oz beef patty (0.020 ± 0.016%/h) was significantly greater than the increase following consumption of 4 oz SBMA (P = 0.021; 0.003 ± 0.010%/h) but not 8 oz SBMA (P = 0.454; 0.013 ± 0.016%/h). The maximal essential amino acid concentration was significantly correlated (P = 0.046; r = 0.411) with the change in muscle FSR from the basal to the postprandial period. In addition, the change in muscle FSR from the basal to postprandial period was significantly correlated (P = 0.046; r = 0.412) with the corresponding change in whole-body protein synthesis.

CONCLUSIONS

Consumption of a 4 oz beef patty stimulates muscle and whole-body protein synthesis >4 oz SBMA patty and similarly to 8 oz of SBMA. This trial was registered at clinicaltrials.gov as NCT05197140.

Correlation Between Skeletal Muscle Mass and Fat-Free Mass in Infants Born Very Preterm

Assessing growth quality in preterm infants present challenges, particularly with the use of the standard fat-free mass measurement. We report here a moderate correlation between indirect skeletal muscle mass measurements using the D3-creatine dilution method and fat-free mass measured with air-displacement plethysmography. Skeletal muscle mass could serve as an indicator of growth quality.

Body fat percentage vs body mass index in estimating basal cell carcinoma

Background

The role of body mass index (BMI) in basal cell carcinoma (BCC) risk remains controversial, and limited information is available regarding the relationship between other physical measurements and BCC. Several recent studies have found a positive effect of adiposity on improved survival when obesity was determined solely by BMI (the "obesity paradox"). We hypothesize that body fat percentage (BFP) may serve as a more sensitive risk factor for BCC than BMI.

Methods

The study conducted a retrospective analysis of clinical data from two distinct centers in China. Individual patient-level data were obtained from medical record reviews spanning January 1, 2015, to December 31, 2022. Associations with outcomes were analyzed using univariate and stratified analyses and assessed using multiple logistic regression with adjustment for confounding factors. Additionally, we performed a meta-analysis to further test the observations in our study.

Results

A total of 337 patients, ranging in age from 50 to 91 years, with a mean age of 66.88 (standard deviation 10.16), were included. We observed no significant association between BMI and BCC after adjusting for confounders (OR: 0.71, 95 % CI: 0.36-1.40, P = 0.3186). There was also no convincing effect in a meta-analysis (n = 158,741) (OR: 0.99, 95 % CI: 0.93-1.06, P = 0.8). Furthermore, BFP was found to be associated with BCC (OR: 2.64, 95 % CI: 1.17-5.97, P = 0.0196), supported by strong clinical evidence.

Conclusions

Our study supports the hypothesis that BFP is superior to BMI in assessing BCC risk. Multiple logistic regression analyses, coupled with meta-analysis, provided robust evidence that BFP is a sensitive risk factor for BCC, while BMI appears unrelated to risk. According to these findings, routine healthcare practices could benefit from utilizing BFP measurements. The reduction of body fat percentage in low-fat diets may be beneficial for adjuvant treatment of BCC.

Association Between Indole-3-Pyruvic Acid and Change in Fat-Free Mass Relative to Weight Loss in Patients Undergoing Sleeve Gastrectomy

Sleeve gastrectomy typically leads to weight loss, including a reduction in fat-free mass (FFM). Studies have shown significant FFM loss within 1 year after the procedure but with individual variations. This study aimed to assess whether preoperative amino acid metabolite levels can predict FFM changes following sleeve gastrectomy. This study involved 42 patients. Body weight, fat mass (FM), and FFM were measured preoperatively and 3, 6, and 12 months postoperatively. All participants experienced weight loss, FM reduction, and FFM decrease for up to 3 months after surgery. However, the following distinct groups emerged from 3 to 6 months postoperatively: one showed FFM gain relative to weight loss, whereas the other exhibited continued FFM reduction relative to weight loss. This trend persisted for up to 12 months postoperatively and became more pronounced. The group with FFM gain had lower preoperative BMI and higher levels of indole-3-pyruvic acid (IPyA). Logistic regression and ROC curve analyses confirmed IPyA's ability to predict FFM gain between 3 and 6 months after sleeve gastrectomy, with a useful cutoff value of 20.205. Preoperative IPyA levels were associated with FFM gain relative to weight loss in the 3 to 6 months following sleeve gastrectomy. These findings suggest that IPyA may be a potential predictor for FFM changes during this period.

The Normal Weight Obesity (NWO) Problem-Prevalence and Time Changes in Children and Adolescents From Kraków (Poland)

OBJECTIVES

Normal weight obesity can be associated with an increased risk of metabolic abnormalities, systemic inflammation and mortality. The main aim of the study was to analyze the changes in the prevalence of normal weight obesity in 8-18-year-olds from Kraków (Poland) between 2010 and 2020.

METHODS

The study was based on two sets of cross-sectional, school-based data obtained in 2010 and 2020. Body height, weight, and fat percentage were obtained. Body mass index was calculated, and only normal-weight individuals were included. Normal weight obesity was defined as normal BMI with adiposity >85 percentile for age and sex.

RESULTS

The prevalence of normal weight obesity among Polish children and adolescents has been alarming for at least the last 10 years. Depending on the sex and age, normal weight obesity was present in more than 10% up to even more than 20% of the examined population.

CONCLUSIONS

Alarming numbers of Polish children and adolescents suffer from NWO and this problem seems to be present for at least the last decade. A need for a maximally universal definition and cut-offs to diagnose normal weight obesity should also be stressed, as it will be helpful in providing the best prophylaxis and help to persons already suffering from normal weight obesity.

Critical variables regulating age-related anabolic responses to protein nutrition in skeletal muscle

Protein nutrition is critical for the maintenance of skeletal muscle mass across the lifecourse and for the growth of muscle in response to resistance exercise - both acting via the stimulation of protein synthesis. The transient anabolic response to protein feeding may vary in magnitude and duration, depending on, e.g., timing, dose, amino acid composition and delivery mode, which are in turn influenced by physical activity and age. This review aims to: (i) summarise the fundamental metabolic responses of muscle to protein feeding, (ii) discuss key variables regulating muscle anabolic responses to protein feeding, and (iii) explore how these variables can be optimised for muscle anabolism in response to physical activity and ageing.

Deciphering the environmental chemical basis of muscle quality decline by interpretable machine learning models

BACKGROUND

Sarcopenia is known as a decline in skeletal muscle quality and function that is associated with age. Sarcopenia is linked to diverse health problems, including endocrine-related diseases. Environmental chemicals (ECs), a broad class of chemicals released from industry, may influence muscle quality decline.

OBJECTIVES

In this work, we aimed to simultaneously elucidate the associations between muscle quality decline and diverse EC exposures based on the data from the 2011-2012 and 2013-2014 survey cycles in the National Health and Nutrition Examination Survey (NHANES) project using machine learning models.

METHODS

Six machine learning models were trained based on the EC and non-EC exposures from NHANES to distinguish low from normal muscle quality index status. Different machine learning metrics were evaluated for these models. The Shapley additive explanations (SHAP) approach was used to provide explainability for machine learning models.

RESULTS

Random forest (RF) performed best on the independent testing data set. Based on the testing data set, ECs can independently predict the binary muscle quality status with good performance by RF (area under the receiver operating characteristic curve = 0.793; area under the precision-recall curve = 0.808). The SHAP ranked the importance of ECs for the RF model. As a result, several metals and chemicals in urine, including 3-phenoxybenzoic acid and cobalt, were more associated with the muscle quality decline.

CONCLUSIONS

Altogether, our analyses suggest that ECs can independently predict muscle quality decline with a good performance by RF, and the SHAP-identified ECs can be closely related to muscle quality decline and sarcopenia. Our analyses may provide valuable insights into ECs that may be the important basis of sarcopenia and endocrine-related diseases in United States populations.

A multifaceted and inclusive methodology for the detection of sarcopenia in patients undergoing bariatric surgery: an in-depth analysis of current evidence

Bariatric surgery is widely recognized as the most effective intervention for obesity and offers benefits beyond weight loss. However, not all patients achieve satisfactory weight loss, balanced changes in body composition, and resolution of comorbidities. Therefore, thorough pre- and postoperative evaluations are important to predict success and minimize adverse effects. More comprehensive assessments require broadening the focus beyond body weight and fat measurements to consider quantitative and qualitative evaluations of muscles. Introducing the concept of sarcopenia is useful for assessing the degradative and pathological changes in muscles associated with cardiometabolic function, physical performance, and other obesity-related comorbidities in patients undergoing bariatric surgery. However, there is currently no consensus or definition regarding the research and clinical use of sarcopenia in patients undergoing bariatric surgery. Therefore, this review aimed to define the concept of sarcopenia applicable to patients undergoing bariatric surgery, based on the consensus reached for sarcopenia in the general population. We also discuss the methods and significance of measuring muscle mass, quality, and strength, which are key variables requiring a comprehensive assessment.

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.

Creatinine, cystatin C, muscle mass, and mortality: Findings from a primary and replication population-based cohort

BACKGROUND

Serum creatinine is used as initial test to derive eGFR and confirmatory testing with serum cystatin C is recommended when creatinine-based eGFR is considered less accurate due to deviant muscle mass. Low muscle mass is associated with increased risk of premature mortality. However, the associations of serum creatinine and cystatin C with muscle mass and mortality remain unclear and require further investigation to better inform clinical decision-making.

METHODS

We included 8437 community-dwelling adults enrolled in the Dutch PREVEND study and 5033 in the US NHANES replication cohort. Associations of serum creatinine and/or cystatin C with muscle mass surrogates and mortality were quantified with linear and Cox proportional hazards regression, respectively. Missing observations in covariates were multiply imputed using Substantive Model Compatible Fully Conditional Specification.

RESULTS

Mean (SD) age of PREVEND and NHANES participants (50% and 48% male) were 49.8 (12.6) and 48.7 (18.7) years, respectively. Median (Q1-Q3) serum creatinine and cystatin C were 71 (61-80) and 80 (62-88) μmol/L and 0.87 (0.78-0.98) and 0.91 (0.80-1.10) mg/L, respectively. Higher serum creatinine was associated with greater muscle mass, while serum cystatin C was not associated with muscle mass. Adjusting both markers for each other strengthened the positive relationship between serum creatinine and muscle mass and revealed an inverse association between serum cystatin C and muscle mass. In the PREVEND cohort, 1636 (19%) deaths were registered over a median follow-up of 12.9 (5.8-16.3) years with a 10-year mortality rate (95% CI) of 7.6% (7.1-8.2%). In the NHANES, 1273 (25%) deaths were registered over a median follow-up of 17.9 (17.3-18.5) years with a 10-year mortality rate of 13.8% (12.8-14.7%). Both markers were associated with increased mortality. Notably, when adjusted for each other, higher serum creatinine was associated with decreased mortality, while the association between serum cystatin C and increased mortality strengthened. The shapes of the associations in the PREVEND study and NHANES were almost identical.

CONCLUSIONS

The strong association between serum creatinine and muscle mass challenges its reliability as GFR marker, necessitating a more cautious approach in its clinical use. The minimal association between serum cystatin C and muscle mass supports its increased use as a more reliable alternative in routine clinical practice.

Effects of essential amino acid (EAA) and glutamine supplementation on skeletal muscle wasting in acute, subacute, and postacute conditions

Under optimal physiological conditions, muscle mass maintenance is ensured by dietary protein, which balances the amino acid loss during the post-absorption period and preserves the body's protein homeostasis. Conversely, in critical clinical conditions (acute, subacute or postacute), particularly those related to hypomobility or immobility, combined with malnutrition, and local/systemic inflammation, the loss of muscle mass and strength can be quantitatively significant. A decline of more than 1% in muscle mass and of more than 3% in muscle strength has been registered in subjects with aged 20-37 yr after just five days of bed rest, similarly to those observed during one year of age-related decline in individuals over the age of 50. Loss of muscle mass and strength can have a dramatic effect on subjects' functional capacities, on their systemic metabolic control and on the amino acid reserve function, all of which are fundamental for the maintenance of other organs' and tissues' cell processes. References available indicate that the average 1%-2% reduction per day of muscle mass in patients in the intensive care unit (ICU) could represent an independent predictor of hospital mortality and physical disability in the five years following hospitalization. After just a few days or weeks of administration, supplementation with EAAs and glutamine has shown significant effects in maintaining muscle size and strength, which are typically negatively affected by some acute/subacute or postacute critical conditions (muscle recovery after surgery, oncology patients, ICU treatments), especially in the elderly or in those with pre-existing degenerative diseases. In this review, we focused on the theoretical bases and the most relevant clinical studies of EAA and glutamine supplementation as a single compound, with the aim of clarifying whether their combined use in a blend (EAAs-glutamine) could be potentially synergistic to prevent disease-related muscle wasting and its impact on the duration and quality of patients' clinical course.

Skeletal muscle dysfunction with advancing age

As a result of advances in medical treatments and associated policy over the last century, life expectancy has risen substantially and continues to increase globally. However, the disconnect between lifespan and 'health span' (the length of time spent in a healthy, disease-free state) has also increased, with skeletal muscle being a substantial contributor to this. Biological ageing is accompanied by declines in both skeletal muscle mass and function, termed sarcopenia. The mechanisms underpinning sarcopenia are multifactorial and are known to include marked alterations in muscle protein turnover and adaptations to the neural input to muscle. However, to date, the relative contribution of each factor remains largely unexplored. Specifically, muscle protein synthetic responses to key anabolic stimuli are blunted with advancing age, whilst alterations to neural components, spanning from the motor cortex and motoneuron excitability to the neuromuscular junction, may explain the greater magnitude of function losses when compared with mass. The consequences of these losses can be devastating for individuals, their support networks, and healthcare services; with clear detrimental impacts on both clinical (e.g., mortality, frailty, and post-treatment complications) and societal (e.g., independence maintenance) outcomes. Whether declines in muscle quantity and quality are an inevitable component of ageing remains to be completely understood. Nevertheless, strategies to mitigate these declines are of vital importance to improve the health span of older adults. This review aims to provide an overview of the declines in skeletal muscle mass and function with advancing age, describes the wide-ranging implications of these declines, and finally suggests strategies to mitigate them, including the merits of emerging pharmaceutical agents.

Muscle Organoid and Assembloid Systems

Skeletal muscle is one of the most complex and largest tissues that perform important processes in the body, including performing voluntary movements and maintaining body temperature. Disruption of muscle homeostasis results in the development of several disorders, including diabetes and sarcopenia. To study the developmental and regenerative dynamics of skeletal muscle and the mechanism behind muscle diseases, it is important to model skeletal muscle and diseases in vitro. Since skeletal muscle has a complex structure and interaction with other tissues and cells that are required to perform their function, conventional 2D cultures are not sufficient to model the skeletal muscle with their interactions. Advances in the field of organoids and assembloids will enable the establishment of more complex and realistic tissue or disease models which cannot be fully recapitulated in conventional 2D culture systems for use in several areas, including disease research, regenerative, and tissue biology. To overcome these limitations, 3D organoid systems and assembloid systems are promising because of their success in recapitulating the complex structural organization, function, and cellular interactions of skeletal muscle.

mTORC1 and BMP-Smad1/5 regulation of serum-stimulated myotube hypertrophy: a role for autophagy

Protein synthesis regulation is critical for skeletal muscle hypertrophy, yet other established cellular processes are necessary for growth-related cellular remodeling. Autophagy has a well-acknowledged role in muscle quality control, but evidence for its role in myofiber hypertrophy remains equivocal. Both mammalian target of rapamycin complex I (mTORC1) and bone morphogenetic protein (BMP)-Smad1/5 (Sma and Mad proteins from Caenorhabditis elegans and Drosophila, respectively) signaling are reported regulators of myofiber hypertrophy; however, gaps remain in our understanding of how this regulation is integrated with growth processes and autophagy regulation. Therefore, we investigated the mTORC1 and Smad1/5 regulation of protein synthesis and autophagy flux during serum-stimulated myotube growth. Chronic serum stimulation experiments were performed on day 5 differentiated C2C12 myotubes incubated in differentiation medium [2% horse serum (HS)] or growth medium [5% fetal bovine serum (FBS)] for 48 h. Rapamycin or LDN193189 was dosed for 48 h to inhibit mTORC1 and BMP-Smad1/5 signaling, respectively. Acute serum stimulation was examined in day 7 differentiated myotubes. Protein synthesis was measured by puromycin incorporation. Bafilomycin A1 and immunoblotting for LC3B were used to assess autophagy flux. Chronic serum stimulation increased myotube diameter 22%, total protein 21%, total RNA 100%, and Smad1/5 phosphorylation 404% and suppressed autophagy flux. Rapamycin, but not LDN193189, blocked serum-induced myotube hypertrophy and the increase in total RNA. Acute serum stimulation increased protein synthesis 111%, Smad1/5 phosphorylation 559%, and rpS6 phosphorylation 117% and suppressed autophagy flux. Rapamycin increased autophagy flux during acute serum stimulation. These results provide evidence for mTORC1, but not BMP-Smad1/5, signaling being required for serum-induced myotube hypertrophy and autophagy flux by measuring LC3BII/I expression. Further investigation is warranted to examine the role of autophagy flux in myotube hypertrophy.NEW & NOTEWORTHY The present study demonstrates that myotube hypertrophy caused by chronic serum stimulation requires mammalian target of rapamycin complex 1 (mTORC1) signaling but not bone morphogenetic protein (BMP)-Smad1/5 signaling. The suppression of autophagy flux was associated with serum-induced myotube hypertrophy and mTORC1 regulation of autophagy flux by measuring LC3BII/I expression. Rapamycin is widely investigated for beneficial effects in aging skeletal muscle and sarcopenia; our results provide evidence that rapamycin can regulate autophagy-related signaling during myotube growth, which could benefit skeletal muscle functional and metabolic health.

A standardized herbal combination of Astragalus membranaceus and Paeonia japonica promotes skeletal muscle hypertrophy in a treadmill exercise mouse model

Background

Maintaining a normal range of muscle mass and function is crucial not only for sustaining a healthy life but also for preventing various disorders. Numerous nutritional or natural resources are being explored for their potential muscle hypertrophic properties.

Aim

We aimed to evaluate the muscle hypertrophic effects of APX, a 1:1 mixture of Astragalus membranaceus and Paeonia japonica. In addition to the myotube differentiation cell assay, we utilized a weighted exercise-based animal model and evaluated changes in muscle hypertrophy using dual-energy X-ray absorptiometry (DXA) and histological analysis.

Results

The 8-week treadmill exercise led to notable decreases in body weight and fat mass but an increase in muscle mass compared to the control group. Administration of APX significantly accelerated muscle mass gain (p < 0.05) without altering body weight or fat mass compared to the exercise-only group. This muscle hypertrophic effect of APX was consistent with the histologic size of muscle fibers in the gastrocnemius (p > 0.05) and rectus femoris (p < 0.05), as well as the regulation of myogenic transcription factors (MyoD and myogenin), respectively. Furthermore, APX demonstrated a similar action to insulin-like growth factor 1, influencing the proliferation of C2C12 myoblast cells (p < 0.01) and their differentiation into myotubes (p < 0.05) compared to the control group.

Conclusion

The present study provides experimental evidence that APX has muscle hypertrophic effects, and its underlying mechanisms would involve the modulation of MyoD and myogenin.

Skeletal muscle immobilisation-induced atrophy: mechanistic insights from human studies

Periods of skeletal muscle disuse lead to rapid declines in muscle mass (atrophy), which is fundamentally underpinned by an imbalance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB). The complex interplay of molecular mechanisms contributing to the altered regulation of muscle protein balance during disuse have been investigated but rarely synthesised in the context of humans. This narrative review discusses human models of muscle disuse and the ensuing inversely exponential rate of muscle atrophy. The molecular processes contributing to altered protein balance are explored, with a particular focus on growth and breakdown signalling pathways, mitochondrial adaptations and neuromuscular dysfunction. Finally, key research gaps within the disuse atrophy literature are highlighted providing future avenues to enhance our mechanistic understanding of human disuse atrophy.

Glyphosate exposure, muscular health and functional limitations in middle-aged and older adults

BACKGROUND

Glyphosate is the most widely used herbicide worldwide, both in domestic and industrial settings. Experimental research in animal models has demonstrated changes in muscle physiology and reduced contractile strength associated with glyphosate exposure, while epidemiological studies have shown associations between glyphosate exposure and adverse health outcomes in critical biological systems affecting muscle function.

METHODS

This study used data from a nationally representative survey of the non-institutionalized U.S. general population (NHANES, n = 2132). Urine glyphosate concentrations were determined by ion chromatography with tandem mass spectrometry. Hand grip strength (HGS) was measured using a Takei Dynamometer, and relative strength estimated as the ratio between HGS in the dominant hand and the appendicular lean mass (ALM) to body mass index (ALMBMI) ratio. Low HGS and low relative HGS were defined as 1 sex-, age- and race-specific SD below the mean. Physical function limitations were identified as significant difficulty or incapacity in various activities.

RESULTS

In fully-adjusted models, the Mean Differences (MD) and 95% confidence intervals [95%CI] per doubling increase in glyphosate concentrations were -0.55 [-1.09, -0.01] kg for HGS in the dominant hand, and -0.90 [-1.58. -0.21] kg for HGS/ALMBMI. The Odds Ratios (OR) [95% CI] for low HGS, low relative HGS and functional limitations by glyphosate concentrations were 1.27 [1.03, 1.57] for low HGS; 1.43 [1.05; 1.94] for low relative HGS; 1.33 [1.08, 1.63] for stooping, crouching or kneeling difficulty; 1.17 [0.91, 1.50] for lifting or carrying items weighting up to 10 pounds difficulty; 1.21 [1.01, 1.40] for standing up from armless chair difficulty; and 1.47 [1.05, 2.29] for ascending ten steps without pause difficulty.

CONCLUSIONS

Glyphosate exposure may be a risk factor for decreased grip strength and increased physical functional limitations. More studies investigating the influence of this and other environmental pollutants on functional aging are needed.

Predicted body fat percentage, fat mass and lean body mass in relation to risk of prostate cancer: Results from the NHANES 1999 to 2010

The purpose of this study is to examine the relationship between fat mass (FM), body fat percentage (BF%), lean body mass (LM), and prostate cancer (PCa), and evaluate their potential impact on the risk of PCa. Data from the National Health and Nutrition Examination Survey (NHANES) of the United States were utilized. Adult male participants from 6 survey cycles between 1999 and 2010 were selected as the study sample. Multivariable logistic regression analysis was conducted to explore the association between BF%, LM, and PCa, while controlling for potential confounding variables. Among the 8440 participants, 359 cases of PCa were diagnosed. The relationship between BF%, LM, and PCa was nonlinear. In the multivariable logistic regression analysis, there was an independent association between BF% and PCa risk (OR: 1.04, 95% CI: 1.02-1.06), suggesting that higher BF% levels are associated with an increased risk of PCa. Conversely, higher LM levels were associated with a decreased risk of PCa (OR: 0.96, 95% CI: 0.95-0.98). The findings of this study demonstrate a correlation between BF% and LM with PCa, but do not provide direct evidence of a causal relationship. Higher BF% levels are associated with an increased risk of PCa, while higher LM levels are associated with a decreased risk. These results provide valuable insights for understanding and potentially preventing PCa, although further research is needed to fully comprehend the underlying mechanisms.

Impaired skeletal muscle regeneration in diabetes: From cellular and molecular mechanisms to novel treatments

Diabetes represents a major public health concern with a considerable impact on human life and healthcare expenditures. It is now well established that diabetes is characterized by a severe skeletal muscle pathology that limits functional capacity and quality of life. Increasing evidence indicates that diabetes is also one of the most prevalent disorders characterized by impaired skeletal muscle regeneration, yet underlying mechanisms and therapeutic treatments remain poorly established. In this review, we describe the cellular and molecular alterations currently known to occur during skeletal muscle regeneration in people with diabetes and animal models of diabetes, including its associated comorbidities, e.g., obesity, hyperinsulinemia, and insulin resistance. We describe the role of myogenic and non-myogenic cell types on muscle regeneration in conditions with or without diabetes. Therapies for skeletal muscle regeneration and gaps in our knowledge are also discussed, while proposing future directions for the field.

Proprietary alpha-amylase inhibitor formulation from white kidney bean (Phaseolus vulgaris L.) promotes weight and fat loss: a 12-week, double-blind, placebo-controlled, randomized trial

White kidney bean (Phaseolus vulgaris L.) extracts can aid weight management by reducing calorie intake from complex carbohydrates through alpha-amylase inhibition. We examined the impact of a proprietary aqueous extract from whole dried white kidney beans standardized by its alpha-amylase inhibitor activity (Phase 2 white kidney bean extract (WKBE)) on weight management in subjects with overweight and moderate obesity. In a randomized, double-blind, placebo-controlled fashion, 81 participants completed the study and ingested either a high dose of Phase 2 (1000 mg, WKBE HIGH), a low dose (700 mg, WKBE LOW), or a matching placebo (microcrystalline cellulose, PLA) three times a day, 30 min before meals, for 12 weeks during a calorie restricted diet. In a dose-dependent manner, Phase 2 significantly reduced body weight, fat mass, BMI, waist, hip and in the WKBE HIGH group thigh circumference. Phase 2 is an effective and safe supplement aiding weight and fat loss. ClinicalTrials.gov identifier NCT02930668.

Proteomics analysis of C2C12 myotubes treated with atrophy inducing cancer cell-derived factors

Cancer-associated cachexia is a wasting syndrome that results in dramatic loss of whole-body weight, predominantly due to loss of skeletal muscle mass. It has been established that cachexia inducing cancer cells secrete proteins and extracellular vesicles (EVs) that can induce muscle atrophy. Though several studies examined these cancer-cell derived factors, targeting some of these components have shown little or no clinical benefit. To develop new therapies, understanding of the dysregulated proteins and signaling pathways that regulate catabolic gene expression during muscle wasting is essential. Here, we sought to examine the effect of conditioned media (CM) that contain secreted factors and EVs from cachexia inducing C26 colon cancer cells on C2C12 myotubes using mass spectrometry-based label-free quantitative proteomics. We identified significant changes in the protein profile of C2C12 cells upon exposure to C26-derived CM. Functional enrichment analysis revealed enrichment of proteins associated with inflammation, mitochondrial dysfunction, muscle catabolism, ROS production, and ER stress in CM treated myotubes. Furthermore, strong downregulation in muscle structural integrity and development and/or regenerative pathways were observed. Together, these enriched proteins in atrophied muscle could be utilized as potential muscle wasting markers and the dysregulated biological processes could be employed for therapeutic benefit in cancer-induced muscle wasting.

Senolytic treatment does not mitigate oxidative stress-induced muscle atrophy but improves muscle force generation in CuZn superoxide dismutase knockout mice

Oxidative stress is associated with tissue dysfunctions that can lead to reduced health. Prior work has shown that oxidative stress contributes to both muscle atrophy and cellular senescence, which is a hallmark of aging that may drive in muscle atrophy and muscle contractile dysfunction. The purpose of the study was to test the hypothesis that cellular senescence contributes to muscle atrophy or weakness. To increase potential senescence in skeletal muscle, we used a model of oxidative stress-induced muscle frailty, the CuZn superoxide dismutase knockout (Sod1KO) mouse. We treated 6-month-old wildtype (WT) and Sod1KO mice with either vehicle or a senolytic treatment of combined dasatinib (5 mg/kg) + quercetin (50 mg/kg) (D + Q) for 3 consecutive days every 15 days. We continued treatment for 7 months and sacrificed the mice at 13 months of age. Treatment with D + Q did not preserve muscle mass, reduce NMJ fragmentation, or alter muscle protein synthesis in Sod1KO mice when compared to the vehicle-treated group. However, we observed an improvement in muscle-specific force generation in Sod1KO mice treated with D + Q when compared to Sod1KO-vehicle mice. Overall, these data suggest that reducing cellular senescence via D + Q is not sufficient to mitigate loss of muscle mass in a mouse model of oxidative stress-induced muscle frailty but may mitigate some aspects of oxidative stress-induced muscle dysfunction.

Obstructive sleep apnea (OSA) is associated with increased risk of early-onset sarcopenia and sarcopenic obesity: Results from NHANES 2015-2018

OBJECTIVE

This study aims to estimate the prevalence of early-onset sarcopenia and sarcopenic obesity in the United States and its relative risk due to obstructive sleep apnea (OSA).

METHODS

Data in this cross-sectional study were extracted from the National Health and Nutritional Examination Survey (NHANES) 2015-2018. Weighted multistage stratified probability sampling design was considered to estimate the prevalence of early-onset sarcopenia and sarcopenic obesity. Weighted multivariable logistic regression analyses and weighted multivariable mediation models were performed to evaluate the association between OSA and early-onset sarcopenia.

RESULTS

The prevalence of early-onset sarcopenia and early-onset sarcopenic obesity was estimated to be 5.5% and 4.6%, respectively. A higher prevalence of sarcopenia (12% V.S. 5.5%, P < 0.01) and sarcopenic obesity (10.3% V.S. 4.0%, P < 0.01) was observed among participants with OSA than those without OSA. Multivariable logistic regression models suggested that participants with OSA had higher odds ratios of suffering from early-onset sarcopenia [Odds Ratio (OR): 1.5, 95% confidence interval (CI):1.1-2.7] and early-onset sarcopenic obesity [OR: 1.8, 95% CI: 1.1-3.1] after adjusting for potential confounding variables. Mediation analyses suggested serum chronic reaction protein (CRP) mediated 23.7% (P < 0.01) & 26.2% (P < 0.01), homeostasis model assessment insulin resistance index (HOMA-IR) mediated 24.8% (P < 0.01) & 20.7% (P < 0.05), body mass index (BMI) mediated 46.4% (P < 0.05) & 49.9% (P < 0.01), HEI-2015 mediated 23.3% (P < 0.01) & 25.6% (P < 0.01), and Vitamin D mediated 7.5% (P < 0.01) & 8.5% (P < 0.01) of the potential effects of OSA on early-onset sarcopenia and sarcopenic obesity, respectively.

CONCLUSION

Early-onset sarcopenia and sarcopenic obesity were prevalent among young adults in the US. OSA is a significant independent risk factor and may induce muscle loss by unhealthy diet habits, higher BMI, chronic inflammation, insulin resistance, and Vitamin D. It was essential for clinicians to arrange appropriate screening and interventions for patients with OSA to prevent muscle loss as early as possible.

MicroRNA Expression Profile in Patients Admitted to ICU as Novel and Reliable Approach for Diagnostic and Therapeutic Purposes

The ability to detect early metabolic changes in patients who have an increased mortality risk in the intensive care units (ICUs) could increase the likelihood of predicting recovery patterns and assist in disease management. Markers that can predict the disease progression of patients in the ICU might also be beneficial for improving their medical profile. Although biomarkers have been used in the ICU more frequently in recent years, the clinical use of most of them is limited. A wide range of biological processes are influenced by microRNAs (miRNAs) that modulate the translation and stability of specific mRNAs. Studies suggest that miRNAs may serve as a diagnostic and therapeutic biomarker in ICUs by profiling miRNA dysregulation in patient samples. To improve the predictive value of biomarkers for ICU patients, researchers have proposed both investigating miRNAs as novel biomarkers and combining them with other clinical biomarkers. Herein, we discuss recent approaches to the diagnosis and prognosis of patients admitted to an ICU, highlighting the use of miRNAs as novel and robust biomarkers for this purpose. In addition, we discuss emerging approaches to biomarker development and ways to improve the quality of biomarkers so that patients in ICU get the best outcomes possible.

Postabsorptive and postprandial myofibrillar protein synthesis rates at rest and after resistance exercise in women with postmenopause

Feeding and resistance exercise stimulate myofibrillar protein synthesis (MPS) rates in healthy adults. This anabolic characterization of "healthy adults" has been namely focused on males. Therefore, the purpose of this study was to examine the temporal responses of MPS and anabolic signaling to resistance exercise alone or combined with the ingestion of protein in postmenopausal females and compare postabsorptive rates with young females. Sixteen females [60 ± 7 yr; body mass index (BMI) = 26 ± 12 kg·m-2] completed an acute bout of unilateral resistance exercise before consuming either: a fortified whey protein supplement (WHEY) or water. Participants received primed continuous infusions of L-[ring-13C6]phenylalanine with bilateral muscle biopsies before and after treatment ingestion at 2 h and 4 h in nonexercised and exercised legs. Resistance exercise transiently increased MPS above baseline at 0-2 h in the water condition (P = 0.007). Feeding after resistance exercise resulted in a late phase (2-4 h) increase in MPS in the WHEY condition (P = 0.005). In both conditions, resistance exercise did not enhance the cumulative (0-4 h) MPS response. In the nonexercised leg, MPS did not differ at 0-2 h, 2-4 h, or 0-4 h of the measurement periods (all, P > 0.05). Likewise, there were no changes in the phosphorylation of p70S6K, AMPKα, or total and phosphorylated yes-associated protein on Ser127. Finally, postabsorptive MPS was lower in premenopausal versus postmenopausal females (P = 0.023). Our results demonstrate that resistance exercise-induced changes in MPS are temporally regulated, but do not result in greater cumulative (0-4 h) MPS in postmenopausal women.NEW & NOTEWORTHY An adequate quality and quantity of skeletal muscle is relevant to support physical performance and metabolic health. Muscle protein synthesis (MPS) is an established remodeling marker, which can be hypertrophic or nonhypertrophic. Importantly, protein ingestion and resistance exercise are two strategies that support healthy muscle by stimulating MPS. Our study shows postmenopause modulates baseline MPS that may diminish the MPS response to the fundamental anabolic stimuli of protein ingestion and resistance exercise in older females.

Duchenne and Becker muscular dystrophy: Cellular mechanisms, image analysis, and computational models: A review

The muscle is the principal tissue that is capable to transform potential energy into kinetic energy. This process is due to the transformation of chemical energy into mechanical energy to enhance the movements and all the daily activities. However, muscular tissues can be affected by some pathologies associated with genetic alterations that affect the expression of proteins. As the muscle is a highly organized structure in which most of the signaling pathways and proteins are related to one another, pathologies may overlap. Duchenne muscular dystrophy (DMD) is one of the most severe muscle pathologies triggering degeneration and muscle necrosis. Several mathematical models have been developed to predict muscle response to different scenarios and pathologies. The aim of this review is to describe DMD and Becker muscular dystrophy in terms of cellular behavior and molecular disorders and to present an overview of the computational models implemented to understand muscle behavior with the aim of improving regenerative therapy.

An Amino Acid Mixture to Counteract Skeletal Muscle Atrophy: Impact on Mitochondrial Bioenergetics

Skeletal muscle atrophy (SMA) is caused by a rise in muscle breakdown and a decline in protein synthesis, with a consequent loss of mass and function. This study characterized the effect of an amino acid mixture (AA) in models of SMA, focusing on mitochondria. C57/Bl6 mice underwent immobilization of one hindlimb (I) or cardiotoxin-induced muscle injury (C) and were compared with controls (CTRL). Mice were then administered AA in drinking water for 10 days and compared to a placebo group. With respect to CTRL, I and C reduced running time and distance, along with grip strength; however, the reduction was prevented by AA. Tibialis anterior (TA) muscles were used for histology and mitochondria isolation. I and C resulted in TA atrophy, characterized by a reduction in both wet weight and TA/body weight ratio and smaller myofibers than those of CTRL. Interestingly, these alterations were lightly observed in mice treated with AA. The mitochondrial yield from the TA of I and C mice was lower than that of CTRL but not in AA-treated mice. AA also preserved mitochondrial bioenergetics in TA muscle from I and C mice. To conclude, this study demonstrates that AA prevents loss of muscle mass and function in SMA by protecting mitochondria.

Effects of Resistance Exercise and Essential Amino Acid Intake on Muscle Quality, Myokine, and Inflammation Factors in Young Adult Males

BACKGROUND

Recently, many studies have been devoted to discovering nutrients for exercise-like effects. Resistance exercise and the intake of essential amino acids (EAAs) are known to be factors that can affect muscle mass and strength improvement. The purpose of this study was to investigate changes in muscle quality, myokines, and inflammation in response to resistance exercise and EAA supplementation.

METHODS

Thirty-four males volunteered to participate in this study. They were assigned to four groups: (1) placebo (CO), (2) resistance exercise (RE), (3) EAA supplementation, and (4) RE + EAA supplementation. Body composition, muscle quality, myokines, and inflammation were measured at baseline and four weeks after treatment.

RESULTS

Lean body fat had decreased in both RE and RE + EAA groups. Lean body mass had increased in only the RE + EAA group. In all groups except for CO, irisin, myostatin A, and TNF-α levels had decreased. The grip strength of the right hand and trunk flexion peak torque increased in the RE group. The grip strength of the left hand, trunk flexion peak torque, and knee flexion peak torque of the left leg were increased in RE + EAA.

CONCLUSIONS

RE, EAA, and RE + EAA could effectively improve the muscle quality, myokine, and inflammation factors of young adult males. This finding highlights the importance of resistance exercise and amino acid intake.

An Indian classical dance form, Kathak in maintaining handgrip strength symmetry and reducing the risk of hypertension

BACKGROUND

The present paper aimed to study handgrip strength (HGS) asymmetry and its association with hypertension in a sample of Kathak dancers and non-dancers of North India.

METHODS

Data on HGS and blood pressure were collected from 206 Kathak dancers and 235 age-matched controls, using standardized protocols. Pearson correlation coefficients assessed the association between HGS and hypertension, and binary logistic regression identified the risk of developing hypertension.

RESULTS

HGS asymmetry was higher among non-dancers. In Kathak dancers, systolic blood pressure (SBP) was positively correlated with HGS and negatively correlated with HGS asymmetry whereas diastolic blood pressure (DBP) was negatively correlated with both HGS and HGS asymmetry. Dancers with high HGS, have significantly reduced risk of developing hypertension. Non-dancers with HGS asymmetry were 1.8 times more likely to report hypertension, relative to dancers.

CONCLUSION

Kathak may be used as an alternative method for maintaining HGS symmetry and reducing the risk of developing hypertension.

Adding Branched-Chain Amino Acids and Vitamin D to Whey Protein Is More Effective than Protein Alone in Preserving Fat Free Mass and Muscle Strength in the First Month after Sleeve Gastrectomy

OBJECTIVES

Sleeve gastrectomy (SG) is one of the most commonly performed weight loss (WL) bariatric procedures. The main goal of WL is reducing total body weight (TBW) and fat mass (FM). However, TBW loss is systematically accompanied by a decline in fat-free mass (FFM), predominantly in the first post-surgical month, despite protein supplementation. Branched-chain amino acids (BCAAs) and vitamin D seem to attenuate loss of FFM and, thus, reduce the decline in muscle strength (MS). However, data on the role of an integrated supplementation with whey protein plus BCAAs plus vitamin D (P+BCAAs+Vit.D) vs. protein alone on total weight loss (TWL), fat mass (FM), fat-free mass (FFM), and (MS) in the first month after SG are lacking. Therefore, the present study aims to evaluate the impact of P+BCAAs+Vit.D vs. protein alone supplementation on TWL, FM, FFM, and MS in the first month after SG.

MATERIALS AND METHODS

Before SG and at 1 month afterward, we prospectively measured and compared TBW, FM, FFM, and MS in 57 patients who received either a supplementation with P+BCAAs+Vit.D (n = 31) or protein alone (n = 26). The impact of P+BCAAs+Vit.D and protein alone supplementation on clinical status was also evaluated.

RESULTS

Despite non-significant variation in TBW, FM decreased more significantly (18.5% vs. 13.2%, p = 0.023) with the P+BCAA+Vit.D supplementation compared to protein alone. Furthermore, the P+BCAA+Vit.D group showed a significantly lower decrease in FFM (4.1% vs. 11.4%, p < 0.001) and MS (3.8% vs. 18.5%, p < 0.001) compared to the protein alone group. No significant alterations in clinical status were seen in either group.

CONCLUSION

P+BCAA+Vit.D supplementation is more effective than protein alone in determining FM loss and is associated with a lower decrease in FFM and MS, without interfering with clinical status in patients 1 month after SG.

Impacts of protein quantity and distribution on body composition

The importance of meal distribution of dietary protein to optimize muscle mass and body remains unclear, and the findings are intertwined with age, physical activity, and the total quantity and quality of protein consumed. The concept of meal distribution evolved from multiple discoveries about regulating protein synthesis in skeletal muscle. The most significant was the discovery of the role of the branched-chain amino acid leucine as a metabolic signal to initiate a post-meal anabolic period of muscle protein synthesis (MPS) in older adults. Aging is often characterized by loss of muscle mass and function associated with a decline in protein synthesis. The age-related changes in protein synthesis and subsequent muscle atrophy were generally considered inevitable until the discovery of the unique role of leucine for the activation of the mTOR signal complex for the initiation of MPS. Clinical studies demonstrated that older adults (>60 years) require meals with at least 2.8 g of leucine (~30 g of protein) to stimulate MPS. This meal requirement for leucine is not observed in younger adults (<30 years), who produce a nearly linear response of MPS in proportion to the protein content of a meal. These findings suggest that while the efficiency of dietary protein to stimulate MPS declines with aging, the capacity for MPS to respond is maintained if a meal provides adequate protein. While the meal response of MPS to total protein and leucine is established, the long-term impact on muscle mass and body composition remains less clear, at least in part, because the rate of change in muscle mass with aging is small. Because direct diet studies for meal distribution during aging are impractical, research groups have applied meal distribution and the leucine threshold to protein-sparing concepts during acute catabolic conditions such as weight loss. These studies demonstrate enhanced MPS at the first meal after an overnight fast and net sparing of lean body mass during weight loss. While the anabolic benefits of increased protein at the first meal to stimulate MPS are clear, the benefits to long-term changes in muscle mass and body composition in aging adults remain speculative.

NASA SPRINT exercise program efficacy for vastus lateralis and soleus skeletal muscle health during 70 days of simulated microgravity

The efficacy of the NASA SPRINT exercise countermeasures program for quadriceps (vastus lateralis) and triceps surae (soleus) skeletal muscle health was investigated during 70 days of simulated microgravity. Individuals completed 6° head-down-tilt bedrest (BR, n = 9), bedrest with resistance and aerobic exercise (BRE, n = 9), or bedrest with resistance and aerobic exercise and low-dose testosterone (BRE + T, n = 8). All groups were periodically tested for muscle (n = 9 times) and aerobic (n = 4 times) power during bedrest. In BR, surprisingly, the typical bedrest-induced decrements in vastus lateralis myofiber size and power were either blunted (myosin heavy chain, MHC I) or eliminated (MHC IIa), along with no change (P > 0.05) in %MHC distribution and blunted quadriceps atrophy. In BRE, MHC I (vastus lateralis and soleus) and IIa (vastus lateralis) contractile performance was maintained (P > 0.05) or increased (P < 0.05). Vastus lateralis hybrid fiber percentage was reduced (P < 0.05) and energy metabolism enzymes and capillarization were generally maintained (P > 0.05), while not all of these positive responses were observed in the soleus. Exercise offsets 100% of quadriceps and approximately two-thirds of soleus whole muscle mass loss. Testosterone (BRE + T) did not provide any benefit over exercise alone for either muscle and for some myocellular parameters appeared detrimental. In summary, the periodic testing likely provided a partial exercise countermeasure for the quadriceps in the bedrest group, which is a novel finding given the extremely low exercise dose. The SPRINT exercise program appears to be viable for the quadriceps; however, refinement is needed to completely protect triceps surae myocellular and whole muscle health for astronauts on long-duration spaceflights.NEW & NOTEWORTHY This study provides unique exercise countermeasures development information for astronauts on long-duration spaceflights. The NASA SPRINT program was protective for quadriceps myocellular and whole muscle health, whereas the triceps surae (soleus) was only partially protected as has been shown with other programs. The bedrest control group data may provide beneficial information for overall exercise dose and targeting fast-twitch muscle fibers. Other unique approaches for the triceps surae are needed to supplement existing exercise programs.