Intramyocellular Lipid and Impaired Myofiber Contraction in Normal Weight and Obese Older Adults

Excess Intramyocellular Lipid Does Not Affect Muscle Fiber Biophysical Properties in Mice or People With Metabolically Abnormal Obesity

Observational studies have shown correlations between intramyocellular lipid (IMCL) content and muscle strength and contractile function in people with metabolically abnormal obesity. However, a clear physiologic mechanism for this association is lacking, and causation is debated. We combined immunofluorescent confocal imaging with force measurements on permeabilized muscle fibers from metabolically normal and metabolically abnormal mice and people with metabolically normal (defined as normal fasting plasma glucose and glucose tolerance) and metabolically abnormal (defined as prediabetes and type 2 diabetes) overweight/obesity to evaluate relationships among myocellular lipid droplet characteristics (droplet size and density) and biophysical (active contractile and passive viscoelastic) properties. The fiber type specificity of lipid droplet parameters varied by metabolic status and by species. It was different between mice and people across the board and different between people of different metabolic status. However, despite considerable quantities of IMCL in the metabolically abnormal groups, there were no significant differences in peak active tension or passive viscoelasticity between the metabolically abnormal and control groups in mice or people. Additionally, there were no significant relationships among IMCL parameters and biophysical variables. Thus, we conclude that IMCL accumulation per se does not impact muscle fiber biophysical properties or physically impede contraction.

ARTICLE HIGHLIGHTS

Nicotinamide N-methyltransferase inhibition mimics and boosts exercise-mediated improvements in muscle function in aged mice

Human hallmarks of sarcopenia include muscle weakness and a blunted response to exercise. Nicotinamide N-methyltransferase inhibitors (NNMTis) increase strength and promote the regenerative capacity of aged muscle, thus offering a promising treatment for sarcopenia. Since human hallmarks of sarcopenia are recapitulated in aged (24-month-old) mice, we treated mice from 22 to 24 months of age with NNMTi, intensive exercise, or a combination of both, and compared skeletal muscle adaptations, including grip strength, longitudinal running capacity, plantarflexor peak torque, fatigue, and muscle mass, fiber type, cross-sectional area, and intramyocellular lipid (IMCL) content. Exhaustive proteome and metabolome analyses were completed to identify the molecular mechanisms underlying the measured changes in skeletal muscle pathophysiology. Remarkably, NNMTi-treated aged sedentary mice showed ~ 40% greater grip strength than sedentary controls, while aged exercised mice only showed a 20% increase relative to controls. Importantly, the grip strength improvements resulting from NNMTi treatment and exercise were additive, with NNMTi-treated exercised mice developing a 60% increase in grip strength relative to sedentary controls. NNMTi treatment also promoted quantifiable improvements in IMCL content and, in combination with exercise, significantly increased gastrocnemius fiber CSA. Detailed skeletal muscle proteome and metabolome analyses revealed unique molecular mechanisms associated with NNMTi treatment and distinct molecular mechanisms and cellular processes arising from a combination of NNMTi and exercise relative to those given a single intervention. These studies suggest that NNMTi-based drugs, either alone or combined with exercise, will be beneficial in treating sarcopenia and a wide range of age-related myopathies.

Low handgrip strength is related to elevated echogenicity in patients with chronic kidney disease: A pilot, cross-sectional and exploratory study

OBJECTIVES

Evaluate associations between triceps braqui muscle ultrasound measures (TB US) and handgrip strength (HGS), and the sensibility of TB US for low HGS in non-dialysis-dependent chronic kidney disease (nd-CKD) patients.

PARTICIPANTS AND METHODS

This pilot, cross-sectional, and exploratory study evaluated TB cross-sectional images from A-mode US and processed by FIJI-Image J to obtain muscle thickness (MT), echogenicity (EI), cross-sectional area (CSA), pennation angle (PA), and fascicle length (Lf) associating them with absolute HGS by simple and, multiple linear regression. The HGS was normalized to body mass index (BMI) and separated into low HGS (HGS/BMI≤10p according to sex and age) and adequate HGS (HGS/BMI>10p) groups. The body composition was from multifrequency bioimpedance. ROC analysis verified the TB US diagnostic accuracy to low HGS.

RESULTS

Were included 42 (21M/21F) adults with 65.5 (60-70) y median age, 47.22% in 3b CKD stage. The low HGS group (45.23%) showed a higher fat mass (FM), TB muscle medium head's PA, and EI than adequate HGS (p<0.05). In crude model, a pixels increase in EI was associated with a 0.452kgf HGS reduction (p=0.019); adjusted for sex, age, and FM, a one-unit increase in EI was associated with a 0.510kgf HGS reduction (p=0.011). The EI also showed moderate diagnostic accuracy (AUC=0.730; CI 95%=0.589; 0.919) to low HGS and a sensitivity of 86.9% (cutoff≥13.52 pixels).

CONCLUSION

In nd-CKD patients, of all measurements from US, the EI was the most associated with HGS, and the only one sensitive to low HGS diagnosis.

Changes in lean body mass with glucagon-like peptide-1-based therapies and mitigation strategies

Weight loss induced by glucagon-like peptide-1 receptor agonists (GLP-1RAs) and dual glucagon-like peptide-1 receptor (GLP-1R)/glucose-dependent insulinotropic polypeptide receptor agonists is coming closer to the magnitudes achieved with surgery. However, with greater weight loss there is concern about potential side effects on muscle quantity (mass), health and function. There is heterogeneity in the reported effects of GLP-1-based therapies on lean mass changes in clinical trials: in some studies, reductions in lean mass range between 40% and 60% as a proportion of total weight lost, while other studies show lean mass reductions of approximately 15% or less of total weight lost. There are several potential reasons underlying this heterogeneity, including population, drug-specific/molecular, and comorbidity effects. Furthermore, changes in lean mass may not always reflect changes in muscle mass as the former measure includes not only muscle but also organs, bone, fluids, and water in fat tissue. Based on contemporary evidence with the addition of magnetic resonance imaging-based studies, skeletal muscle changes with GLP-1RA treatments appear to be adaptive: reductions in muscle volume seem to be commensurate with what is expected given ageing, disease status, and weight loss achieved, and the improvement in insulin sensitivity and muscle fat infiltration likely contributes to an adaptive process with improved muscle quality, lowering the probability for loss in strength and function. Nevertheless, factors such as older age and severity of disease may influence the selection of appropriate candidates for these therapies due to risk of sarcopenia. To further improve muscle health during weight loss, several pharmacological treatments to maintain or improve muscle mass designed in combination with GLP-1-based therapies are under development. Future research on GLP-1-based and other therapies designed for weight loss should focus on more accurate and meaningful assessments of muscle mass, composition, as well as function, mobility or strength, to better define their impact on muscle health for the substantial number of patients who will likely be taking these medications well into the future.

[Impact on weight loss and body composition of a food education intervention associated with Liraglutide treatment to address obesity]

Introduction

Introduction: clinical practice guidelines recommend considering pharmacological treatment of obesity only as a complement to lifestyle modification. Drugs alone are usually ineffective in the long term after discontinuation, so pharmacological weight loss strategies should always be accompanied by lifestyle modifications. Objective: to analyze the changes in weight, body mass index and body composition by means of electrical bioimpedance after a 32-week treatment with liraglutide in patients with obesity, associated or not with a food education program. Materials and methods: the study involved 68 patients who were randomly divided into 2 groups. One group received treatment with liraglutide 3.0 mg/day along with individual dietary education, and the other group was treated with liraglutide 3.0 mg/day and standard medical follow-up for 32 weeks. The data collected were weight (kg), height (m) (Seca® brand), body mass index (kg/m2) and body composition using multifrequency bioimpedance (SECA 112® brand). The variables were analyzed at the beginning and at the end of the treatment. Results: after 32 weeks of treatment, both study groups lost weight significantly. The group treated with liraglutide and individual dietary education had a reduction of 8.77 kg (9.08 %) (p < 0.001) and the group treated with liraglutide without education had a reduction of 3.55 kg (3.45 %) (p < 0.001). The BMI of the participants treated with liraglutide and education decreased by -4,04 kg/m2 (10.35 %) (p < 0.001) and in the group without education it decreased by -3.22 kg/m2 (8.30 %) (p = 0.003). In the educated group, fat mass decreased by -7.65 kg (15.89 %) (p < 0.001), although skeletal muscle mass also decreased by -1.62 kg (6.8 %) (p < 0.001). In those treated with liraglutide without education, a reduction in fat mass and skeletal muscle mass was also observed - fat mass by -4.72 kg (9.43 %) (p < 0.001) and skeletal muscle mass by -0.17 kg (0.70 %) (p < 0.001). Differences were also observed between groups, observing a greater reduction in weight, BMI, fat mass and skeletal muscle mass in the group with liraglutide and education compared to the group without education, although these differences were not statistically significant. Conclusions: dietary education associated with liraglutide treatment may contribute to increasing weight and fat mass losses. However, it was also associated with an unwanted loss of skeletal muscle mass, probably related to the greater intensity of weight loss, which will have to be reversed in future therapeutic approaches. Habit modification through multidisciplinary treatment, including nutritional education, combined strength and resistance exercise, and cognitive-behavioral therapy, could be an effective way to treat obesity and maintain weight, body composition, and adherence to a lifestyle.

Gender Differences in the Impact of a High-Fat, High-Sugar Diet in Skeletal Muscles of Young Female and Male Mice

In the context of the increasing number of obese individuals, a major problem is represented by obesity and malnutrition in children. This condition is mainly ascribable to unbalanced diets characterized by high intakes of fat and sugar. Childhood obesity and malnutrition are not only associated with concurrent pathologies but potentially compromise adult life. Considering the strict correlation among systemic metabolism, obesity, and skeletal muscle health, we wanted to study the impact of juvenile malnutrition on the adult skeletal muscle. To this aim, 3-week-old C56BL/6 female and male mice were fed for 20 weeks on a high-fat. high-sugar diet, and their muscles were subjected to a histological evaluation. MyHCs expression, glycogen content, intramyocellular lipids, mitochondrial activity, and capillary density were analyzed on serial sections to obtain the metabolic profile. Our observations indicate that a high-fat, high-sugar diet alters the metabolic profile of skeletal muscles in a sex-dependent way and induces the increase in type II fibers, mitochondrial activity, and lipid content in males, while reducing the capillary density in females. These data highlight the sex-dependent response to nutrition, calling for the development of specific strategies and for a systematic inclusion of female subjects in basic and applied research in this field.

Perinatal HIV infection is associated with deficits in muscle function in children and adolescents in Zimbabwe

OBJECTIVES

To determine how muscle strength, power, mass, and density (i.e. quality) differ between children living with HIV (CWH) and those uninfected, and whether antiretroviral therapy (ART) regime is associated with muscle quality.

DESIGN

A cross-sectional study in Harare, Zimbabwe.

METHODS

The study recruited CWH aged 8-16 years, taking ART for at least 2 years, from HIV clinics, and HIV-uninfected children from local schools. Muscle outcomes comprised grip strength measured by hand-held Jamar dynamometer, lower limb power measured by standing long-jump distance, lean mass measured by dual-energy X-ray absorptiometry, and muscle density (reflecting intramuscular fat) by peripheral quantitative computed tomography. Linear regression calculated adjusted mean differences (aMD) by HIV status.

RESULTS

Overall, 303 CWH and 306 without HIV, had mean (SD) age 12.5 (2.5) years, BMI 17.5 (2.8), with 50% girls. Height and fat mass were lower in CWH, mean differences (SE) 7.4 (1.1) cm and 2.7 (0.4)kgs, respectively. Male CWH had lower grip strength [aMD 2.5 (1.1-3.9) kg, P  < 0.001], long-jump distance [7.1 (1.8-12.5) cm, P  = 0.006], muscle density [0.58 (0.12-1.05) mg/cm 3 , P  = 0.018, but not lean mass 0.06 (-1.08 to 1.21) kg, P  = 0.891) versus boys without HIV; differences were consistent but smaller in girls. Mediation analysis suggested the negative effect of HIV on jumping power in boys was partially mediated by muscle density ( P  = 0.032). CWH taking tenofovir disoproxil fumarate (TDF) had lower muscle density [0.56 (0.00-1.13)mg/cm 3 , P  = 0.049] independent of fat mass, than CWH on other ART.

CONCLUSION

Perinatally acquired HIV is associated, particularly in male individuals, with reduced upper and lower limb muscle function, not mass. Intra-muscular fat (poorer muscle quality) partially explained reductions in lower limb function. TDF is a novel risk factor for impaired muscle quality.

Exploring the Relationship between Ultrasonographic Measures of the Quadriceps and Knee Extensor Muscle Fitness in Endurance-Trained Individuals

Background

B-mode ultrasonography is an accessible and cost-effective method to assess muscle size and quality through muscle thickness (MT) and echo intensity (EI), respectively. Muscle thickness and EI have demonstrated relationships with maximal strength and local muscle endurance, providing a noninvasive and efficient modality to examine muscle fitness. However, these relationships have not been quantified in the individual quadriceps muscles of habitually endurance-trained populations, which may provide information to practitioners regarding rehabilitation and performance.

Methods

Twenty-three participants (males: N = 10; females: N = 13) underwent B-mode ultrasonography to assess MT, EI, and adipose tissue thickness-corrected echo intensity (cEI) in the vastus intermedius (VI), vastus lateralis (VL), and rectus femoris (RF). Muscle fitness was evaluated through maximal strength (1RM) and local muscle endurance (4 sets to failure at 50% 1RM) during dynamic knee extension. Relationships between ultrasonography outcomes and muscle fitness were examined through stepwise multiple linear regression.

Results

The results indicate that VI cEI is the strongest predictor of 1RM strength (r = -0.643), while no ultrasonography-derived measures significantly predicted local muscle endurance.

Conclusion

The study demonstrates that ultrasonography, specifically measures of cEI in the VI, has the greatest association with maximal strength in endurance-trained individuals. These findings suggest monitoring VI muscle size and quality may benefit practitioners who aim to improve knee extension strength for performance or following injury. In addition, the findings support the use of EI examinations in trained populations.

Association of skeletal muscle oxidative capacity with muscle function, sarcopenia-related exercise performance, and intramuscular adipose tissue in older adults

Muscle function and exercise performance measures, such as muscle endurance capacity, maximal strength, chair stand score, gait speed, and Timed Up and Go score, are evaluated to diagnose sarcopenia and frailty in older individuals. Furthermore, intramuscular adipose tissue (IntraMAT) content increases with age. Skeletal muscle oxidative capacity determines muscle metabolism and maintains muscle performance. This study aimed to investigate the association of skeletal muscle oxidative capacity with muscle function, exercise performance, and IntraMAT content in older individuals. Thirteen older men and women participated in this study. Skeletal muscle oxidative capacity was assessed by the recovery speed of muscle oxygen saturation after exercise using near-infrared spectroscopy from the medial gastrocnemius. We assessed two muscle functions, peak torque and time to task failure, and four sarcopenia-related exercise performances: handgrip strength, gait speed, 30-s chair stand, and Timed Up and Go. The IntraMAT content was measured using axial magnetic resonance imaging. The results showed a relationship between skeletal muscle oxidative capacity and gait speed but not with muscle functions and other exercise performance measures. Skeletal muscle oxidative capacity was not related to IntraMAT content. Skeletal muscle oxidative capacity, which may be indicative of the capacity of muscle energy production in the mitochondria, is related to locomotive functions but not to other functional parameters or skeletal fat infiltration.

Skeletal Muscle Compliance and Echogenicity in Resistance-Trained and Nontrained Women

ABSTRACT

Mongold, SJ, Ricci, AW, Hahn, ME, and Callahan, DM. Skeletal muscle compliance and echogenicity in resistance-trained and nontrained women. J Strength Cond Res 38(4): 671-680, 2024-Noninvasive assessment of muscle mechanical properties in clinical and performance settings tends to rely on manual palpation and emphasizes examination of musculotendinous stiffness. However, measurement standards are highly subjective. The purpose of the study was to compare musculotendinous stiffness in adult women with varying resistance training history while exploring the use of multiple tissue compliance measures. We identified relationships between tissue stiffness and morphology, and tested the hypothesis that combining objective measures of morphology and stiffness would better predict indices of contractile performance. Resistance-trained (RT) women (n = 11) and nontrained (NT) women (n = 10) participated in the study. Muscle echogenicity and morphology were measured using B-mode ultrasonography (US). Vastus lateralis (VL) and patellar tendon (PT) stiffness were measured using digital palpation and US across submaximal isometric contractions. Muscle function was evaluated during maximal voluntary isometric contraction (MVIC) of the knee extensors (KEs). Resistance trained had significantly greater PT stiffness and reduced echogenicity (p < 0.01). Resistance trained also had greater strength per body mass (p < 0.05). Muscle echogenicity was strongly associated with strength and rate of torque development (RTD). Patellar tendon passive stiffness was associated with RTD normalized to MVIC (RTDrel; r = 0.44, p < 0.05). Patellar tendon stiffness was greater in RT young women. No predictive models of muscle function incorporated both stiffness and echogenicity. Because RTDrel is a clinically relevant measure of rehabilitation in athletes and can be predicted by digital palpation, this might represent a practical and objective measure in settings where RTD may not be easy to measure directly.

Hand grip strength as a proposed new vital sign of health: a narrative review of evidences

Hand grip strength (HGS) serves as a fundamental metric in assessing muscle function and overall physical capability and is particularly relevant to the ageing population. HGS holds an important connection to the concept of sarcopenia, which encompasses the age-related decline in muscle mass, strength, and function. It has also been reported to indicate the health of an individual. We reviewed the interplay between HGS and various health parameters, including morbidity and mortality, by carrying out a literature search on PubMed, Scopus and Google Scholar between 10 and 30 August 2023, to identify the relevant papers on the relationship between health and HGS. We used several keywords like 'hand grip strength', 'muscle strength, 'sarcopenia', 'osteosarcopenia', 'health biomarker', 'osteoporosis', and 'frailty', to derive the appropriate literature for this review. This review has shown that the HGS can be measured reliably with a hand-held dynamometer. The cut-off values are different in various populations. It is lower in Asians, women, less educated and privileged, and those involved in sedentary work. Several diseases have shown a correlation with low HGS, e.g., Type 2 diabetes, cardiovascular disease, stroke, chronic kidney and liver disease, some cancers, sarcopenia and fragility fractures. The low HSG is also associated with increased hospitalization, nutritional status, overall mortality and quality of life. We believe that there is adequate evidence to show that HGS stands as an important biomarker of health. Its utility extends to the identification of diverse health issues and its potential as a new vital sign throughout the lifespan.

Cross-sectional area and fat infiltration of the lumbar spine muscles in patients with back disorders: a deep learning-based big data analysis

PURPOSE

Validated deep learning models represent a valuable option to perform large-scale research studies aiming to evaluate muscle quality and quantity of paravertebral lumbar muscles at the population level. This study aimed to assess lumbar spine muscle cross-sectional area (CSA) and fat infiltration (FI) in a large cohort of subjects with back disorders through a validated deep learning model.

METHODS

T2 axial MRI images of 4434 patients (n = 2609 females, n = 1825 males; mean age: 56.7 ± 16.8) with back disorders, such as fracture, spine surgery or herniation, were retrospectively collected from a clinical database and automatically segmented. CSA, expressed as the ratio between total muscle area (TMA) and the vertebral body area (VBA), and FI, in percentages, of psoas major, quadratus lumborum, erector spinae, and multifidus were analyzed as primary outcomes.

RESULTS

Male subjects had significantly higher CSA (6.8 ± 1.7 vs. 5.9 ± 1.5 TMA/VBA; p < 0.001) and lower FI (21.9 ± 8.3% vs. 15.0 ± 7.3%; p < 0.001) than females. Multifidus had more FI (27.2 ± 10.6%; p < 0.001) than erector spinae (22.2 ± 9.7%), quadratus lumborum (17.5 ± 7.0%) and psoas (13.7 ± 5.8%) whereas CSA was higher in erector spinae than other lumbar muscles. A high positive correlation between age and total FI was detected (rs = 0.73; p < 0.001) whereas a negligible negative correlation between total CSA and age was observed (rs =  - 0.24; p < 0.001). Subjects with fractures had lower CSA and higher FI compared to those with herniations, surgery and with no clear pathological conditions.

CONCLUSION

CSA and FI values of paravertebral muscles vary a lot in accordance with subjects' sex, age and clinical conditions. Given also the large inter-muscle differences in CSA and FI, the choice of muscles needs to be considered with attention by spine surgeons or physiotherapists when investigating changes in lumbar muscle morphology in clinical practice.

Meta-Analysis on the Association between Echo Intensity, Muscle Strength, and Physical Function in Older Individuals

BACKGROUND

The use of ultrasonographic echo intensity (EI) to evaluate skeletal muscle quality and its effects on strength, explosive power, and physical function (PF) in older individuals remains unclear. This meta-analysis evaluated the associations among EI, muscle strength (MS), and PF in older individuals.

METHODS

We conducted a systematic search of the PubMed, Embase, Web of Science, SPORT Discus, and CINAHL databases through October 2022 to identify primary studies examining the association between EI and MS/PF. Effect sizes were computed using a random-effects model and presented using forest plots. Pearson correlation coefficient (r) and I2 statistics were used to measure heterogeneity.

RESULTS

This meta-analysis included 24 patients. EI demonstrated a negative association with maximal strength (r=-0.351; 95% confidence interval [CI], -0.411 to -0.288; p<0.001) and explosive power (r=-0.342; 95% CI, -0.517 to -0.139; p=0.001) in older individuals. Handgrip strength also showed a significant negative correlation with EI (r=-0.361; 95% CI, -0.463 to -0.249; p<0.001). However, we observed only a small and non-significant negative association between EI and gait speed (r=-0.003; 95% CI, -0.083 to -0.077; p=0.943), and a weak non-significant correlation with the chair stand test (r=0.072; 95% CI, -0.045 to 0.187; p=0.227).

CONCLUSION

Increased EI was associated with lower strength and power but not with gait speed or chair test performance in older individuals. Further large-sample studies with long-term follow-up are needed to improve frailty prediction and risk assessment in this population.

Low lean mass with obesity in older adults with hypertension: prevalence and association with mortality rate

BACKGROUND

The influence of sarcopenic obesity (SO) on overall survival in older adults with hypertension has not been addressed. The aim of this study was to investigate the prevalence and mortality predictive value of various body composition phenotypes, focusing mainly on SO, in older adults with hypertension.

METHODS

We included 1105 hypertensive patients aged ≥ 60 years from the National Health and Nutrition Examination Survey 1999-2004. Sarcopenia was broadly defined based on low lean mass (LLM; as measured by dual-energy X-ray absorptiometry), and was defined using appendicular lean mass (ALM) divided by height squared (ALM/height2), weight (ALM/weight), and body mass index (BMI; ALM/BMI), respectively. Obesity was defined as BMI ≥ 30 kg/m2, body fat percentage ≥ 30/42%, or waist circumference ≥ 102/88 cm. The prevalence of LLM with obesity was estimated according to each ALM index (ALMI). Multivariable Cox regression analysis and sensitivity analysis were used to examine the association between various body composition phenotypes and all-cause mortality.

RESULTS

In older adults with hypertension, the prevalence of LLM with obesity by the ALM/height2 index (9.8%) was lower relative to the ALM/weight (11.7%) and ALM/BMI indexes (19.6%). After a median follow-up of 15.4 years, 642 deaths occurred. In the fully adjusted models, LLM with obesity was significantly associated with a higher risk of all-cause mortality (hazard ratio [HR] 1.69, 95% confidence interval [CI] 1.14-2.49, P = 0.008; HR 1.48, 95% CI 1.04-2.10, P = 0.028; HR 1.30, 95% CI 1.02-1.66, P = 0.037; respectively) compared with the normal body phenotype, with no statistical differences found in individuals with LLM or obesity alone. Sensitivity analysis confirmed the robustness of the results.

CONCLUSIONS

The prevalence of LLM with obesity markedly differed in older adults with hypertension according to the 3 different ALMIs, varying from 9.8%, 11.7%, to 19.6%. Patients with both LLM and obesity had a higher risk of all-cause mortality. Further large, prospective, cohort studies are warranted to validate these findings and uncover underlying mechanisms.

Skeletal Muscle Function Is Altered in Male Mice on Low-Dose Androgen Receptor Antagonist or Estrogen Receptor Agonist

In males, skeletal muscle function may be altered by shifts in either circulating testosterone or estrogen. We examined the effect of acute (2-week) exposures to 17α-ethinyl estradiol (EE2), an estrogen receptor (ER) agonist, or flutamide, an androgen receptor (AR) antagonist, on the contractile function of individual skeletal muscle fibers from slow-contracting soleus and fast-contracting extensor digitorum longus muscles from adult male mice. Single fiber specific tension (force divided by cross-sectional area) was decreased with flutamide treatment in all myosin heavy chain (MHC) fiber types examined (I, IIA, and IIB); similar effects were observed with EE2 treatment but only in the fastest-contracting MHC IIB fibers. The decreases in maximally Ca2+-activated specific tension were primarily a result of fewer strongly bound myosin-actin cross-bridges, with flutamide treatment also showing lower myofilament lattice stiffness. Myosin-actin cross-bridge kinetics were slower in MHC IIA fibers in flutamide-treated mice, but faster in EE2-treated mice, indicating that contractile velocity may be affected differently in this fiber type, which is commonly expressed in human skeletal muscle. Importantly, these effects were observed in the absence of outcomes previously used to evaluate ER agonists or AR antagonists in rodents including weight of reproductive organs or mammary gland morphology. Our findings indicate that substantial shifts in skeletal muscle function occur in male mice following acute exposures to low doses of a pharmacological ER agonist and an AR antagonist. These results suggest that countermeasures to maintain physical function may be needed early in situations that induce similar ER agonist and AR antagonist conditions.

Slow or fast: Implications of myofibre type and associated differences for manifestation of neuromuscular disorders

Many neuromuscular disorders can have a differential impact on a specific myofibre type, forming the central premise of this review. The many different skeletal muscles in mammals contain a spectrum of slow- to fast-twitch myofibres with varying levels of protein isoforms that determine their distinctive contractile, metabolic, and other properties. The variations in functional properties across the range of classic 'slow' to 'fast' myofibres are outlined, combined with exemplars of the predominantly slow-twitch soleus and fast-twitch extensor digitorum longus muscles, species comparisons, and techniques used to study these properties. Other intrinsic and extrinsic differences are discussed in the context of slow and fast myofibres. These include inherent susceptibility to damage, myonecrosis, and regeneration, plus extrinsic nerves, extracellular matrix, and vasculature, examined in the context of growth, ageing, metabolic syndrome, and sexual dimorphism. These many differences emphasise the importance of carefully considering the influence of myofibre-type composition on manifestation of various neuromuscular disorders across the lifespan for both sexes. Equally, understanding the different responses of slow and fast myofibres due to intrinsic and extrinsic factors can provide deep insight into the precise molecular mechanisms that initiate and exacerbate various neuromuscular disorders. This focus on the influence of different myofibre types is of fundamental importance to enhance translation for clinical management and therapies for many skeletal muscle disorders.

Lifelong Fitness in Ambulatory Children and Adolescents with Cerebral Palsy I: Key Ingredients for Bone and Muscle Health

Physical activity of a sufficient amount and intensity is essential to health and the prevention of a sedentary lifestyle in all children as they transition into adolescence and adulthood. While fostering a fit lifestyle in all children can be challenging, it may be even more so for those with cerebral palsy (CP). Evidence suggests that bone and muscle health can improve with targeted exercise programs for children with CP. Yet, it is not clear how musculoskeletal improvements are sustained into adulthood. In this perspective, we introduce key ingredients and guidelines to promote bone and muscle health in ambulatory children with CP (GMFCS I-III), which could lay the foundation for sustained fitness and musculoskeletal health as they transition from childhood to adolescence and adulthood. First, one must consider crucial characteristics of the skeletal and muscular systems as well as key factors to augment bone and muscle integrity. Second, to build a better foundation, we must consider critical time periods and essential ingredients for programming. Finally, to foster the sustainability of a fit lifestyle, we must encourage commitment and self-initiated action while ensuring the attainment of skill acquisition and function. Thus, the overall objective of this perspective paper is to guide exercise programming and community implementation to truly alter lifelong fitness in persons with CP.

AdipoRon enhances healthspan in middle-aged obese mice: striking alleviation of myosteatosis and muscle degenerative markers

BACKGROUND

Obesity among older adults has increased tremendously. Obesity accelerates ageing and predisposes to age-related conditions and diseases, such as loss of endurance capacity, insulin resistance and features of the metabolic syndrome. Namely, ectopic lipids play a key role in the development of nonalcoholic fatty liver disease (NAFLD) and myosteatosis, two severe burdens of ageing and metabolic diseases. Adiponectin (ApN) is a hormone, mainly secreted by adipocytes, which exerts insulin-sensitizing and fat-burning properties in several tissues including the liver and the muscle. Its overexpression also increases lifespan in mice. In this study, we investigated whether an ApN receptor agonist, AdipoRon (AR), could slow muscle dysfunction, myosteatosis and degenerative muscle markers in middle-aged obese mice. The effects on myosteatosis were compared with those on NAFLD.

METHODS

Three groups of mice were studied up to 62 weeks of age: One group received normal diet (ND), another, high-fat diet (HFD); and the last, HFD combined with AR given orally for almost 1 year. An additional group of young mice under an ND was used. Treadmill tests and micro-computed tomography (CT) were carried out in vivo. Histological, biochemical and molecular analyses were performed on tissues ex vivo. Bodipy staining was used to assess intramyocellular lipid (IMCL) and lipid droplet morphology.

RESULTS

AR did not markedly alter diet-induced obesity. Yet, this treatment rescued exercise endurance in obese mice (up to 2.4-fold, P < 0.05), an event that preceded the improvement of insulin sensitivity. Dorsal muscles and liver densities, measured by CT, were reduced in obese mice (-42% and -109%, respectively, P < 0.0001), suggesting fatty infiltration. This reduction tended to be attenuated by AR. Accordingly, AR significantly mitigated steatosis and cellular ballooning at liver histology, thereby decreasing the NALFD activity score (-30%, P < 0.05). AR also strikingly reversed IMCL accumulation either due to ageing in oxidative fibres (types 1/2a, soleus) or to HFD in glycolytic ones (types 2x/2b, extensor digitorum longus) (-50% to -85%, P < 0.05 or less). Size of subsarcolemmal lipid droplets, known to be associated with adverse metabolic outcomes, was reduced as well. Alleviation of myosteatosis resulted from improved mitochondrial function and lipid oxidation. Meanwhile, AR halved aged-related accumulation of dysfunctional proteins identified as tubular aggregates and cylindrical spirals by electron microscopy (P < 0.05).

CONCLUSIONS

Long-term AdipoRon treatment promotes 'healthy ageing' in obese middle-aged mice by enhancing endurance and protecting skeletal muscle and liver against the adverse metabolic and degenerative effects of ageing and caloric excess.

Deciphering the "obesity paradox" in the elderly: A systematic review and meta-analysis of sarcopenic obesity

Aging and obesity are two global concerns in public health. Sarcopenic obesity (SO), defined as the combination of age-related sarcopenia and obesity, has become a pressing issue. This systematic review and meta-analysis summarize the current clinical evidence relevant to SO. PubMed, Embase, and Web of Science were searched, and 106 clinical studies with 167,151 elderlies were included. The estimated prevalence of SO was 9% in both men and women. Obesity was associated with 34% reduced risk of sarcopenia (odds ratio [OR] 0.66, 95% CI 0.48-0.91; p < 0.001). The pooled hazard ratio (HR) of all-cause mortality was 1.51 (95% CI 1.14-2.02; p < 0.001) for people with SO compared with healthy individuals. SO was associated with increased risk of cardiovascular disease and related mortality, metabolic disorders, cognitive impairment, arthritis, functional limitation, and lung diseases (all ORs > 1.0, p < 0.05). The attenuated risk of sarcopenia in elderlies with obesity ("obesity paradox") was dependent on higher muscle mass and strength. Apart from unifying the diagnosis of SO, more research is needed to subphenotype people with obesity and sarcopenia for individualized treatment. Meanwhile, the maintenance of proper body composition of muscle and fat may delay or attenuate the adverse outcomes of aging.

Metabolic reprogramming underlies cavefish muscular endurance despite loss of muscle mass and contractility

Physical inactivity is a scourge to human health, promoting metabolic disease and muscle wasting. Interestingly, multiple ecological niches have relaxed investment into physical activity, providing an evolutionary perspective into the effect of adaptive physical inactivity on tissue homeostasis. One such example, the Mexican cavefish Astyanax mexicanus, has lost moderate-to-vigorous activity following cave colonization, reaching basal swim speeds ~3.7-fold slower than their river-dwelling counterpart. This change in behavior is accompanied by a marked shift in body composition, decreasing total muscle mass and increasing fat mass. This shift persisted at the single muscle fiber level via increased lipid and sugar accumulation at the expense of myofibrillar volume. Transcriptomic analysis of laboratory-reared and wild-caught cavefish indicated that this shift is driven by increased expression of pparγ-the master regulator of adipogenesis-with a simultaneous decrease in fast myosin heavy chain expression. Ex vivo and in vivo analysis confirmed that these investment strategies come with a functional trade-off, decreasing cavefish muscle fiber shortening velocity, time to maximal force, and ultimately maximal swimming speed. Despite this, cavefish displayed a striking degree of muscular endurance, reaching maximal swim speeds ~3.5-fold faster than their basal swim speeds. Multi-omic analysis suggested metabolic reprogramming, specifically phosphorylation of Pgm1-Threonine 19, as a key component enhancing cavefish glycogen metabolism and sustained muscle contraction. Collectively, we reveal broad skeletal muscle changes following cave colonization, displaying an adaptive skeletal muscle phenotype reminiscent to mammalian disuse and high-fat models while simultaneously maintaining a unique capacity for sustained muscle contraction via enhanced glycogen metabolism.

Relative contribution of neuromuscular activation, muscle size, and muscle quality to maximum strength output of the thigh muscles in young individuals

This study aimed to investigate the relationship between maximal muscle strength and neuromuscular activation, muscle size, and quality of quadriceps (QF) and hamstring muscles (HM). The study included 24 young men and women. The neuromuscular activation parameter was recorded using a single-channel surface electromyography (EMG) with the root mean square (RMS) during maximal isometric knee extension and flexion from four muscles: rectus femoris and vastus lateralis for QF; biceps femoris and semitendinosus for HM. In addition, the peak torque was measured during the same session. B-mode ultrasonographic transverse images were obtained from the anterior, lateral, and posterior thighs. Furthermore, we calculated the muscle thickness (MT) and echo intensity (EI) of the four muscles as indicators of muscle size and quality. The averaged MT, EI, and absolute RMS of QF were calculated by averaging the values of the rectus femoris and vastus lateralis, and that of HM was calculated by averaging the values of the biceps femoris and semitendinosus. The knee extension peak torque was correlated with EI (r = -0.61, P < 0.01) and RMS (r = 0.53, P < 0.01) in the QF. In contrast, the knee flexion peak torque was correlated with RMS (r = 0.53, P < 0.05) but not with MT and EI in HM. In addition, EI and RMS in QF, and RMS in HM were selected as the major determinants of muscle strength in the stepwise regression analysis. These results suggest that muscle strength is moderately associated with different factors related to the thigh muscles in young individuals.

TrkB signaling is correlated with muscular fatigue resistance and less vulnerability to neurodegeneration

At the neuromuscular junction (NMJ), motor neurons and myocytes maintain a bidirectional communication that guarantees adequate functionality. Thus, motor neurons' firing pattern, which is influenced by retrograde muscle-derived neurotrophic factors, modulates myocyte contractibility. Myocytes can be fast-twitch fibers and become easily fatigued or slow-twitch fibers and resistant to fatigue. Extraocular muscles (EOM) show mixed properties that guarantee fast contraction speed and resistance to fatigue and the degeneration caused by Amyotrophic lateral sclerosis (ALS) disease. The TrkB signaling is an activity-dependent pathway implicated in the NMJ well-functioning. Therefore, it could mediate the differences between fast and slow myocytes' resistance to fatigue. The present study elucidates a specific protein expression profile concerning the TrkB signaling that correlates with higher resistance to fatigue and better neuroprotective capacity through time. The results unveil that Extra-ocular muscles (EOM) express lower levels of NT-4 that extend TrkB signaling, differential PKC expression, and a higher abundance of phosphorylated synaptic proteins that correlate with continuous neurotransmission requirements. Furthermore, common molecular features between EOM and slow soleus muscles including higher neurotrophic consumption and classic and novel PKC isoforms balance correlate with better preservation of these two muscles in ALS. Altogether, higher resistance of Soleus and EOM to fatigue and ALS seems to be associated with specific protein levels concerning the TrkB neurotrophic signaling.

Comparative Effect of Three Different Exercise Intensities in Combination with Diazoxide on Contraction Capacity and Oxidative Stress of Skeletal Muscle in Obese Rats

Simple Summary

Obesity is a growing public health problem worldwide. It is a pathological state that degrades the proper functioning of skeletal muscle. Diazoxide treatment and exercise have been shown to generally improve muscle function. However, the effect that each of the different exercise intensities has when combined with diazoxide on the contraction capacity, resistance to fatigue and oxidative stress levels in rat skeletal muscle is unknown. Therefore, this work focused on analyzing which exercise intensity was more efficient in combination with diazoxide in improving muscle tissue and its metabolic capacities. The best results were obtained with low- and moderate-intensity exercise when combined with the drug. These results expected to open a window of time that allows the implementation of a constant and prolonged exercise protocol that completely reverses the harmful effects of obesity on muscle tissue and obesity itself.

Abstract

Obesity is a chronic disease that impairs skeletal muscle function, affects the ability to contract, and promotes the development of fatigue. For this reason, the study of treatments that seek to reduce the harmful effects of obesity on muscle tissue has been deepened. Diazoxide treatment and various exercise protocols have been proposed to protect skeletal muscle against oxidative stress and its effects. However, the intensity and duration of exercise combined with diazoxide that would obtain the best results for improving skeletal muscle function in obese rats is unknown. To this end, this study evaluated the effects of three different exercise intensities combined with diazoxide on contraction capacity, resistance to fatigue, markers of oxidative stress, lipid peroxidation, ROS, and glutathione redox status of skeletal muscle. The results showed that treatments with diazoxide and exercise at different intensities improved muscle contraction capacity by reducing oxidative stress during obesity, with the best results being obtained with low-intensity exercise in combination with diazoxide. Therefore, these results suggest that diazoxide and low-intensity exercise improve muscle function during obesity by decreasing oxidative stress with the same efficiency as a moderate-intensity exercise protocol.

Safety and feasibility of selective tongue fat reduction with injected ice‐slurry

Objectives

There is growing evidence that excess adipose tissue within the head and neck contributes to obstructive sleep apnea (OSA), particularly in obese patients. This subset of the population is often difficult to treat with surgical therapies. We theorized that a novel, transcervical method of injectable cryoablation using ice‐slurry can achieve low temperatures without causing neurovascular damage or airway distress in a swine model.

Methods

Four Yorkshire pigs were injected with ice‐slurry comprised of normal saline and 10% glycerol cooled to −6°C via a transcervical, ultrasound guided approach. Direct laryngoscopy was used to confirm accurate placement of the slurry. Thermocouple placement at the needle‐tip was used to measure temperatures at injection site. Swine were monitored for clinical signs of tongue necrosis and airway edema for 2 months, and then euthanized. Twelve biopsy samples from the base of the tongue were collected for histology. These were assessed for presence of tissue damage, inflammation and collagen formation by a blinded board‐certified pathologist.

Results

Tongue tissue temperature below 10°C was achieved for 13.5 ± 1.1 min. Minimum tissue temperature was −4 ± 0.6°C. There was no clinical or pathological evidence of tongue damage to include damage to the lingual nerve or artery. There was some histologic evidence of new collagen formation in areas of the tongue.

Conclusions

Transcervical ultrasound‐guided ice‐slurry injection is feasible, well‐tolerated at temperatures previously shown to be capable of selectively targeting adipose tissue in the base of the tongue in a preclinical swine model, without causing neurovascular damage or airway distress when properly injected.

Cellular and Molecular Variations in Male and Female Murine Skeletal Muscle after Long-Term Feeding with a High-Fat Diet

Current information regarding the effects of a high-fat diet (HFD) on skeletal muscle is contradictory. This study aimed to investigate the effects of a long-term HFD on skeletal muscle in male and female mice at the morphological, cellular, and molecular levels. Adult mice of the C57BL/6 strain were fed standard chow or an HFD for 20 weeks. The tibialis anterior muscles were dissected, weighed, and processed for cellular and molecular analyses. Immunocytochemical and morphometric techniques were applied to quantify fiber size, satellite cells (SCs), and myonuclei. Additionally, PCR array and RT-qPCR tests were performed to determine the expression levels of key muscle genes. Muscles from HFD mice showed decreases in weight, SCs, and myonuclei, consistent with the atrophic phenotype. This atrophy was associated with a decrease in the percentage of oxidative fibers within the muscle. These findings were further confirmed by molecular analyses that showed significant reductions in the expression of Pax7, Myh1, and Myh2 genes and increased Mstn gene expression. Male and female mice showed similar trends in response to HFD-induced obesity. These findings indicate that the long-term effects of obesity on skeletal muscle resemble those of age-related sarcopenia.

Impact of methionine restriction on muscle aerobic metabolism and hypertrophy in young and old mice on an obesogenic diet

Methionine restriction (MR) reduces inflammation and increases longevity. We studied the effects of MR (0.17% kCal methionine, 10% kCal fat) and MR + high-fat diet (HFD) (0.17% methionine, 45% kCal fat) and overload-induced hypertrophy on inflammation, angiogenesis and mitochondrial activity in the hind-limb muscle in 10- and 26-month-old male C57BL/6J mice. Plasma IL-6 concentrations were higher in old compared to young mice. M. plantaris hypertrophy was accompanied by increased p-Akt, without a significant change in Akt and VEGF levels. In young mice on a HFD or MR + HFD diet the SDH activity was higher than in those from mice on other diets, irrespective of overload. There were no significant differences in total NAD concentration in the m. gastrocnemius. MR enhanced the skeletal muscle hypertrophic response in old age that was accompanied with an increase in p-Akt without significant changes in muscle oxidative capacity, low-grade systemic inflammation, NAD, VEGF or Akt levels.

Importance of skeletal muscle lipid levels for muscle function and physical function in older individuals

The skeletal muscle contains lipids inside (intramyocellular lipids, IMCL) or outside (extramyocellular lipids, EMCL) its cells. The muscle lipid content increases with age; however, the characteristics of IMCL and EMCL in older individuals are not well known. We aimed to examine the characteristics of skeletal muscle lipids by investigating their relationship with muscle function and physical functions. Seven elderly men and 16 elderly women participated. The skeletal muscle lipid content, including IMCL and EMCL, was measured in the vastus lateralis by proton magnetic resonance spectroscopy. Isometric knee extension with maximal voluntary contraction (MVC) and time-to-task failure for knee extension with 50% MVC were measured as muscle functions. The participants performed six physical function tests: preferred gait speed, maximal gait speed, Timed Up and Go, chair sit-to-stand, handgrip strength, and stand from the floor. The time to knee extension task failure had a significant relationship with the IMCL (r_s = -0.43, P < 0.05), but not with the EMCL content. Significant relationships were confirmed in the EMCL content with the sit-to-stand (r_s = -0.48, P < 0.05) and stand-from-the-floor (r_s = 0.53, P < 0.05) tests. These findings indicated that muscle lipids are associated with muscle and physical functional performances in older individuals. Novelty: No relationship was confirmed between IMCL and EMCL in older individuals. Muscle endurance performance had a relationship with IMCL, but not with EMCL. Relationships between EMCL and physical functional tests (e.g., sit-to-stand and stand from the floor) were confirmed.

Development of Formulas for Calculating L3 Skeletal Muscle Mass Index and Visceral Fat Area Based on Anthropometric Parameters

Background

The anthropometric index is not accurate but shows a great advantage in accessibility. Simple body composition formulas should be investigated before proceeding with the universal nutrition screening.

Materials and Methods

Clinical data of patients with a malignant tumor of the digestive system were collected. SliceOmatic 5.0 software (TOMOVISION, Canada) was used to analyze abdominal CT images and taken as references. A linear regression analysis was adopted to establish the formula for calculating skeletal muscle index (SMI) and visceral fat area (VFA). In addition, the relweights function was adopted to measure the contribution of each variable.

Results

In total, 344 patients were divided into the training set and 134 patients into the validation set. The selected formulas were SMI.pre = 0.540 × weight (kg) – 0.559 × height (cm) – 13.877 × sex (male = 1, female = 2) + 123.583, and VFA.pre = 5.146 × weight (kg) – 2.666 × height (cm) + 1.436 × age (year) + 134.096, of which the adjusted R² were 0.597 and 0.581, respectively. The “weight” explained more than 80% of R² in the prediction of VFA. In addition, “sex” occupied approximately 40% of R² in the prediction of SMI. The paired t-test showed no significant difference between the real measured indices and the predicting ones (p = 0.123 for SMI and p = 0.299 for VFA). The logistic regression analysis exhibited similar diagnostic efficacy of the real measured parameters and formulas.

Conclusion

The SMI and VFA formulas were developed through basic indices, such as weight, height, sex, and age. According to the contribution of each variable, weight should always be focused on preserving appropriate muscle and adipose tissue.

The Pathological Links between Adiposity and the Carpal Tunnel Syndrome

An association between obesity and carpal tunnel syndrome is found in many epidemiological studies. Therefore, there is a need to evaluate the physiopathological links that could explain the association between these two entities. Ectopic adipose tissue is responsible for metabolic syndrome and inflammation, and is a major risk factor for diabetes and cardiovascular diseases. Taking these elements into consideration, we conducted an extensive literature revision of the subject, considering as ectopic fat-related mechanisms the following: (a) the direct compression and the association with the metabolic syndrome of the fat deposition around the wrist, (b) the insulin resistance, dyslipidemia, inflammatory, and oxidative mechanisms related to the central deposition of the fat, (c) the impaired muscle contraction and metabolism related to myosteatosis. Each section presents the cellular pathways which are modified by the ectopic deposition of the adipose tissue and the impact in the pathogeny of the carpal tunnel syndrome. In conclusion, the experimental and clinical data support the epidemiological findings. Efforts to reduce the obesity epidemics will improve not only cardio-metabolic health but will reduce the burden of the disability-free life expectancy due to the carpal tunnel syndrome.

Botox Injections in Paraspinal Muscles Result in Low Maximal Specific Force and Shortening Velocity in Fast but Not Slow Skinned Muscle Fibers

STUDY DESIGN

Basic science, experimental animal study.

OBJECTIVE

To determine the effects of Botulinum toxin type A (BTX-A) injections on the mechanical properties of skinned muscle fibers (cells) of rabbit paraspinal muscles.

SUMMARY OF BACKGROUND DATA

BTX-A has been widely used in the treatment of disorders of muscle hyperactivity, such as spasticity, dystonia, and back pain. However, BTX-A injection has been shown to cause muscle atrophy, fat infiltration, and decreased force output in target muscles, but its potential effects on the contractile machinery and force production on the cellular level remain unknown.

METHODS

Nineteen-month-old, male New Zealand White Rabbits received either saline or BTX-A injections into the paraspinal muscles, equally distributed along the left and right sides of the spine at T12, L1, and L2 at 0, 8, 12, 16, 20, and 24 weeks. Magnetic resonance imaging was used to quantify muscle crosssectional area and structural changes before and at 28 weeks following the initial injection. Skinned fibers isolated from the paraspinal muscles were tested for their active and passive force-length relationships, unloaded shortening velocity, and myosin heavy chain isoforms.

RESULTS

BTX-A injections led to significant fat infiltration within the injected muscles and a greater proportion of IIa to IIx fibers. Isolated fast fibers from BTX-A injected animals had lower active force and unloaded shortening velocity compared with fibers from saline-injected control animals. Force and velocity properties were not different between groups for the slow fibers.

CONCLUSION

Injection of BTX-A into the paraspinal rabbit muscles leads to significant alterations in the contractile properties of fast, but not slow, fibers.Level of Evidence: N/A.

Effects of 24 Weeks Combined Rehabilitation Exercise Program on Functional Recovery in Obsess High Tibial Osteotomy Patients

OBJECTIVES This study aims to investigate the effects of a 24 weeks combined rehabilitation exercise program on the subjective questionnaire, isokinetic muscle function test and dynamic balance test of high tibial osteotomy patients with normal weights and obese individuals.METHODS Sixteen tibial osteotomy patients were recruited in the study. They were divided into two groups(normal weight group[n=8] or obesity weight group[n=8]). A pre-test consisting of subjective questionnaire, isokinetic muscle function test and Y balance test. Using the same test in 12 weeks, 24 weeks after the surgery. All groups completed the rehabilitation exercise program for the duration of 24 weeks.RESULTS The significant interaction was observed between group and time on the involve bilateral flexor strength deficits (<i>p</i>=.045) and the posteromedial reach distance (<i>p</i>=.041).CONCLUSIONS These results suggest that a 24 weeks rehabilitation exercise program is needed after high tibial osteotomy in order to restore the same level of activity as before surgery.

Heterogeneity in resistance training-induced muscle strength responses is associated with training frequency and insulin resistance in postmenopausal women

BACKGROUND

In older adults, muscle strength (MS), a key component of sarcopenia, is essential to maintaining independence and physical capacity. The rate of muscle strength decline typically accelerates during the menopausal transition. Although MS has been shown to increase with resistance training (RT), the response to training is quite heterogeneous. Thus, if contributing factors to RT non-responsiveness to MS gains are identified, it may be possible to develop more effective and personalized ways to improve MS or identify individuals who may benefit from RT interventions. This study assessed potential factors that may contribute to MS response heterogeneity in postmenopausal women: training frequency, serum FSH and estrogen levels, adiposity, inflammation marker, and insulin resistance.

METHODS

One hundred and thirteen individuals participated in a 16-week program of supervised RT (3 sets, 8-12 repetitions, and 2-3 times/week). A control group (CTL, n = 63 - no performed the RT) was used as the comparator arm. Body composition (skinfold) and blood samples (metabolic and inflammatory indicators and hormones) were measured at baseline. Knee extensor strength (1RM) was measured at baseline, 8 weeks, and 16 weeks.

RESULTS

Only the RT group increased 1RM after 8 weeks (RT = 14 ± 12% vs. CTL = 6 ± 15%). Both groups increased 1RM after 16 weeks, with the RT group showing a greater increase than the CTL group (RT = 31 ± 23% vs CTL = 13 ± 25%). After 8 weeks of RT, 41 (36% of total) individuals were considered non-responders (based on control group responses) and 27 (24% of total) individuals after 16 weeks. At week 8, lower RT frequency (2 times/week vs. 3 times/week) was associated with higher odds of being non-responder (3 times, P = 0.048). At week 16, lower RT frequency (13 times, P = 0.009) and higher HOMA-IR (for every unit increase, odds increase by 40%, P = 0.022) were associated with higher odds of being non-responder. Higher QUICKI was associated with lower odds of being non-responder (for every unit increase, odds decrease by 16%, P = 0.039). Moreover, higher RT frequency (17 times, P = 0.028) and higher QUICKI (for every unit increase, odds increase by 41%, P = 0.017) were associated with higher odds of becoming a responder at week 16, being a non-responder at week 8.

CONCLUSION

Heterogeneity in RT-induced MS responses is associated with training frequency and insulin resistance in postmenopausal women.

High-fat diet affects measures of skeletal muscle contractile performance in a temperature specific manner but does not influence regional thermal sensitivity

The present study examined if 20-weeks high-fat diet (HFD) consumption had a temperature specific effect on the contractile performance and regional thermal sensitivity of isolated mouse soleus (SOL) and diaphragm (DIA) muscle. Four-week-old female CD-1 mice were randomly selected to consume either a standard laboratory diet or a standard laboratory diet in conjunction with a HFD for 20-weeks. Peripheral SOL and core DIA were isolated from each animal and maximal isometric force and work loop power were assessed at 20⁰C, 28⁰C, 35⁰C and 40⁰C. Increasing temperature to 35⁰C resulted in greater isometric stress, lower activation and relaxation time and higher work loop power in both muscles. A further increase in temperature to 40⁰C did not affect isometric force but increased work loop power output of the SOL. Conversely, isometric force of the DIA was reduced and work loop power maintained when temperature was increased to 40⁰C. HFD consumption resulted in greater isometric force and absolute work loop power of the SOL and reduced isometric stress of the DIA, effects that were less apparent at lower temperatures. When the relationship between temperature and each measure of contractile function was examined by linear regression, there was no difference in slope between the control or HFD groups for either SOL or DIA. These results indicate that whilst contractile function initially increases with temperature, the temperature to elicit maximal performance is muscle and contractile mode-specific. Furthermore, HFD effects on contractile function are temperature specific, but HFD does not influence the relationship between temperature and performance.

Effects of a 3-Week Inpatient Multidisciplinary Body Weight Reduction Program on Body Composition and Physical Capabilities in Adolescents and Adults With Obesity

Background

The aim of the present study was to examine the short-term changes in body composition and physical capabilities in subjects with obesity during a multidisciplinary inpatient body weight reduction program (BWRP).

Methods

One hundred thirty-nine adolescents (56 boys and 83 girls; BMI: 37.1 ± 6.5 kg/m²; Fat Mass, FM: 45.3 ± 7.2%) and 71 adults (27 males and 44 females; BMI: 44 ± 4.7 kg/m²; FM: 51.4 ± 4.7%) followed a 3-week inpatient BWRP consisting of regular physical activity, moderate energy restriction, nutritional education and psychological counseling. Before (T0) and after the end of the BWRP (T21), body composition was assessed with an impedancemeter, lower limb muscle power with Margaria Stair Climbing Test (SCT), lower limb functionality with Short Physical Performance Battery (SPPB), and the capacity of performing activity of daily living (ADL) with Physical Performance Test (PPT).

Results

At T21, obese adolescents showed a 4% reduction in body mass (BM) (p < 0.001), associated with a FM reduction in boys (−10%) and girls (−6%) (p < 0.001) and with a 3% reduction in fat-free mass (FFM) recorded only in boys (p = 0.013). Obese adults showed a 5% BM reduction (p < 0.001), associated with a 2% FFM and 9% FM reduction (p < 0.001) in males, and 7% FM reduction in females (p < 0.001). Regarding physical capabilities, at T21 in obese adolescents, PPT score increased by 4% (p < 0.001), SCT decreased by −5% (boys) and −7% (girls) (p < 0.001), while SPPB score did not change significantly. In obese adults at T21, PPT score increased by 9% (p < 0.001), SCT decreased by −16% (p < 0.001) only in females, and SPPB score increased by 7% (males) and 10% (females) (p < 0.01).

Conclusion

In conclusion, moderate energy restriction and regular physical activity determine a 4-5% BM reduction during a 3-week inpatient BWRP, improve physical capabilities and induce beneficial changes in body composition in adolescents and adults with obesity.

Trial registration

This study was approved by the Ethical Committee of the Istituto Auxologico Italiano (Milan, Italy; research code: 01C124; acronym: PRORIPONATFIS). Registered 11 November 2020 - Retrospectively registered.

Multimodal Diagnostic Approaches to Advance Precision Medicine in Sarcopenia and Frailty

Sarcopenia, defined as the loss of muscle mass, strength, and function with aging, is a geriatric syndrome with important implications for patients and healthcare systems. Sarcopenia increases the risk of clinical decompensation when faced with physiological stressors and increases vulnerability, termed frailty. Sarcopenia develops due to inflammatory, hormonal, and myocellular changes in response to physiological and pathological aging, which promote progressive gains in fat mass and loss of lean mass and muscle strength. Progression of these pathophysiological changes can lead to sarcopenic obesity and physical frailty. These syndromes independently increase the risk of adverse patient outcomes including hospitalizations, long-term care placement, mortality, and decreased quality of life. This risk increases substantially when these syndromes co-exist. While there is evidence suggesting that the progression of sarcopenia, sarcopenic obesity, and frailty can be slowed or reversed, the adoption of broad-based screening or interventions has been slow to implement. Factors contributing to slow implementation include the lack of cost-effective, timely bedside diagnostics and interventions that target fundamental biological processes. This paper describes how clinical, radiographic, and biological data can be used to evaluate older adults with sarcopenia and sarcopenic obesity and to further the understanding of the mechanisms leading to declines in physical function and frailty.

Adiponectin receptor agonist AdipoRon improves skeletal muscle function in aged mice

The loss of skeletal muscle function with age, known as sarcopenia, significantly reduces independence and quality of life and can have significant metabolic consequences. Although exercise is effective in treating sarcopenia it is not always a viable option clinically, and currently, there are no pharmacological therapeutic interventions for sarcopenia. Here, we show that chronic treatment with pan-adiponectin receptor agonist AdipoRon improved muscle function in male mice by a mechanism linked to skeletal muscle metabolism and tissue remodeling. In aged mice, 6 weeks of AdipoRon treatment improved skeletal muscle functional measures in vivo and ex vivo. Improvements were linked to changes in fiber type, including an enrichment of oxidative fibers, and an increase in mitochondrial activity. In young mice, 6 weeks of AdipoRon treatment improved contractile force and activated the energy-sensing kinase AMPK and the mitochondrial regulator PGC-1a (peroxisome proliferator-activated receptor gamma coactivator one alpha). In cultured cells, the AdipoRon induced stimulation of AMPK and PGC-1a was associated with increased mitochondrial membrane potential, reorganization of mitochondrial architecture, increased respiration, and increased ATP production. Furthermore, the ability of AdipoRon to stimulate AMPK and PGC1a was conserved in nonhuman primate cultured cells. These data show that AdipoRon is an effective agent for the prevention of sarcopenia in mice and indicate that its effects translate to primates, suggesting it may also be a suitable therapeutic for sarcopenia in clinical application.

Effects of Different Resistance Exercise Forms on Body Composition and Muscle Strength in Overweight and/or Obese Individuals: A Systematic Review and Meta-Analysis

Purpose

This study is a systematic review and meta-analysis to determine the effects of different forms of resistance training on body composition and muscle strength in overweight and/or obese people.

Method

Only randomized controlled trials (RCTs) were included by searching relevant databases such as a web of science, PubMed, and EBSCO, with search dates up to September 30, 2021. These trials performed resistance exercise training in overweight and/or obese people, and outcome indicators included evaluation of body composition and muscle strength, among other relevant indicators. The Cochrane evaluation tool was used to evaluate the methodological quality of the included literature, and statistical analysis was performed using the R analysis software.

Results

Fifteen studies, 18 trials, with a total of 669 participants meeting eligibility criteria were included in the final analysis, which included three resistance training types (own body weight, resistance bands, and free weight). The results showed that resistance bands improved body fat (BF; SMD −0.79, 95% CI −1.25 to −0.33, I2 = 0%) in overweight or obese people better than other resistance training types. Own body weight resistance training was better for increasing skeletal muscle mass in overweight or obese people (SMD 0.48, 95% CI 0.04–0.92, I2 = 0%). In addition, for muscle strength increase, although resistance exercise was shown to improve muscle strength, there was no significant difference between the three exercise forms compared.

Conclusion

Resistance bands can improve body composition by reducing BF. Resistance bands can improve body composition by reducing BF, while it is more effective in increasing muscle mass and own body weight. Therefore, for overweight and obese people, resistance bands resistance exercise can be taken for fat loss, and resistance exercise for own body weight for further muscle gain and maintenance of muscle mass, so as to achieve the purpose of improving body composition.

Association between quadriceps function, joint kinetics, and spatiotemporal gait parameters in young adults with and without obesity

BACKGROUND

Individuals with obesity have impaired gait and muscle function that may contribute to reduced mobility and increased fall risk.

RESEARCH QUESTIONS

(1) what is the difference in spatiotemporal gait parameters and joint kinetics between individuals with and without obesity; (2) what is the association between spatiotemporal gait parameters, joint kinetics, and quadriceps function?

METHODS

Forty-eight young adults with obesity (BMI = 33.0 ± 4.1 kg/m²) and 48 without obesity (BMI = 21.6 ± 1.7 kg/m²) completed assessments of quadriceps function (peak torque and early/late rate of torque development (RTD)) and walking biomechanics at self-selected speed. Spatiotemporal gait parameters (stance time, double support time, double support to stance ratio, step width, step length, cadence, and gait stability ratio (GSR)) and joint kinetics (total support moment, and relative contribution from extensor moments) were compared using one-way MANOVAs. Partial correlation examined the association between the total support moment and quadriceps function, and spatiotemporal gait parameters controlling for sex and speed.

RESULTS

Individuals with obesity walked with longer stance (p = 0.01), longer double-limb support (p < 0.001), wider steps (p < 0.001), lower cadence (p = 0.03), and a greater absolute (p < 0.001) but lesser normalized total support moment (p = 0.03) compared with adults without obesity. In those with obesity, greater PT was associated with less double limb support (p = 0.011) and smaller double support to stance ratio (p = 0.006); greater early RTD was associated with less double limb support (r = -0.455, p = 0.0021), less stance time (r = -0.384, p = 0.008), and a smaller double support to stance ratio (r = -0.371, p = 0.011). In those without obesity, a larger total support moment was associated with longer step length (r = 0.512, p < 0.001), lesser cadence (r = -0.497, p < 0.001), and smaller GSR (-0.460, p = 0.001).

SIGNIFICANCE

Individuals with obesity walk with altered spatiotemporal gait parameters and joint kinetics that may compromise stability. Extended periods of support may be a strategy used by individuals with obesity to increase stability during gait and accomodate insufficient quadriceps function.

Contractility of permeabilized rat vastus intermedius muscle fibres following high-fat, high-sucrose diet consumption

Obesity is a worldwide health concern associated with impaired physical function. It is not clear if contractile protein dysfunction contributes to the impairment of muscle function observed with obesity. The purpose of this study was to examine if diet-induced obesity affects contractile function of chemically permeabilized vastus intermedius fibres of male Sprague-Dawley rats expressing fast myosin heavy chain (MHC) IIa or slow MHC I. Rats consumed either a high-fat, high sucrose (HFHS) diet or a standard (CHOW) diet beginning as either weanlings (7-week duration: WEAN7 cohort, or 14-week duration: WEAN14 cohort) or young adults (12-week duration: ADULT12 cohort, 24-week duration: ADULT24 cohort). HFHS-fed rats had higher (P < 0.05) whole-body adiposity (derived from dual-energy X-ray absorptiometry) than CHOW-fed rats in all cohorts. Relative to CHOW diet groups, the HFHS diet was associated with impaired force production in (a) MHC I fibres in the ADULT24 cohort; and (b) MHC IIa fibres in the ADULT12 and ADULT24 cohorts combined. However, the HFHS diet did not significantly affect the Ca2+-sensitivity of force production, unloaded shortening velocity, or ratio of active force to active stiffness in any cohort. We conclude that diet-induced obesity can impair force output of permeabilized muscle fibres of adult rats. Novelty: We assessed contractile function of permeabilized skeletal muscle fibres in a rat model of diet-induced obesity. The high-fat, high-sucrose diet was associated with impaired force output of fibres expressing MHC I or MHC IIa in some cohorts of rats. Other measures of contractile function were not significantly affected by diet.

A High-Fat Diet Aggravates the Age-Related Decline in Skeletal Muscle Structure and Function

The age-related decline in muscle function is aggravated by a high-fat diet (HFD)-induced increase in fat mass. The hypothesis is that an HFD leads to a faster accumulation of intramyocellular lipids (IMCL) and an earlier onset of muscle dysfunction in old than in young-adult individuals. The IMCL accumulation is attenuated in young-adult organisms by an elevated oxidative capacity. Methionine restriction enhances mitochondrial biogenesis and is promising to combat obesity across the ages.

Energy cost of walking and body composition changes during a 9-month multidisciplinary weight reduction program and 4-month follow-up in adolescents with obesity

The purpose of the present study was to investigate changes in the energy cost of locomotion during walking (Cw) related to changes in body mass (BM, kg) and body composition in adolescents with obesity. Twenty-six (12 boys and 14 girls) obese adolescents (mean: body mass index, 33.6 ± 3.7 kg·m-2; 42.7 ± 4.5% fat mass (FM)) followed a 9-month multidisciplinary inpatient weight-reduction program consisting of lifestyle education, moderate energy restriction, and regular physical activity in a specialised institution. At baseline (M0), the end of the 9-month program (M9), and after the 4-month follow-up (M13), oxygen consumption and carbon dioxide production of the standardised activity program were assessed by whole-body indirect calorimetry over 24 hours, and body composition was assessed by dual-energy X-ray absorptiometry. At M9, adolescents showed an 18% reduction in BM (p < 0.001) and 40% in total FM, while fat-free mass (kg) remained stable in boys but decreased by ∼6% in girls (p = 0.001). Similarly, the mean Cw decreased by 20% (p < 0.001). At M13, BM, FM, and Cw were slightly higher compared with at M9. In conclusion, moderate energy restriction and regular moderate physical activities improved walking economy, improved exercise tolerance, and induced beneficial changes in the body composition of adolescents with obesity. Novelty: Reduction of FM in the trunk region, and consequently reducing the work carried out by respiratory muscles, contributes to reducing Cw in adolescents with obesity. A lower walking cost can be effective in improving exercise tolerance and quality of life in obese adolescents.

Tongue pressure waveform analysis for ascertaining the influence of tongue muscle composition on articulation

BACKGROUND

Rate force development is associated with performance and muscle composition in whole-body muscle. Although rate force development on tongue muscle can be examined using tongue pressure waveform, there have been only few investigations on this topic.

OBJECTIVES

This study's main purpose was to investigate the reliability of tongue pressure waveform analysis and its relationship with articulation and tongue muscle composition. In addition, we also investigated the association between tongue muscle composition and articulation.

METHODS

Forty-five community-dwelling individuals aged >20 years participated. We analysed tongue pressure waveform, including maximum tongue pressure (MTP), time to peak, mean rate of tongue force development and peak rate of tongue force development (PRTFD). We also assessed oral diadochokinesis. Magnetic resonance imaging of the tongue provided data on tongue muscle composition, including tongue volume, fat mass, lean muscle mass and fat percentage. We evaluated the reliability of tongue pressure waveform analysis. Moreover, we examined the coefficients between tongue pressure waveform analysis, oral diadochokinesis and tongue composition.

RESULTS

We detected a high reliability of MTP and PRTFD. MTP and PRTFD were significantly correlated with tongue muscle composition. MTP was not significantly correlated with oral diadochokinesis. PRTFD was significantly positively correlated with oral diadochokinesis. Tongue fat mass and fat percentage were negatively correlated with oral diadochokinesis of /ta/ and /ka/.

CONCLUSIONS

Peak rate of tongue force development is a highly reliable method for tongue pressure analysis and is useful for elucidating the functional importance of tongue muscle function on articulation. We speculated that fatty infiltration of the tongue adversely affects articulation.

Higher body mass index and body fat percentage correlate to lower joint and functional strength in working age adults

As the prevalence of obesity grows worldwide, it becomes an increasing concern in working populations. Ergonomists are faced with the challenge of accommodating workplace layouts to include this worker demographic. This study investigated the relationship between shoulder and low back isometric joint strengths across body mass index (BMI) groups. Additionally, relationships between body fat percentage (BF%), absolute strength, and strength normalized to body mass were examined. Ninety, healthy, working age participants performed 11 functional and isometric joint strength exertions. BMI group influenced normalized strength, as the obese 2+ (BMI >35.0) group had up to 63.1% lower joint strength than all other BMI groups (p < 0.05). Significant strong to moderate negative linear relationships existed between BF% and normalized strength for both males and females, and relationships were stronger for females. These strength deficits highlight the importance of considering body composition during ergonomics analyses and configuration of occupational tasks.

Contribution of Intramyocellular Lipids to Decreased Computed Tomography Muscle Density With Age

Skeletal muscle density, as determined by computed tomography (CT), has been shown to decline with age, resulting in increased frailty and morbidity. However, the mechanism underlying this decrease in muscle density remains elusive. We sought to investigate the role of intramyocellular lipid (IMCL) accumulation in the age-related decline in muscle density. Muscle density was measured using computerized tomography (CT), and IMCL content was quantified using in vivo proton magnetic resonance spectroscopy (¹H-MRS). The study population consisted of 314 healthy participants (142 men, 32–98 years) of the Baltimore Longitudinal Study of Aging (BLSA). In addition to IMCL quantification, obesity-related covariates were measured, including body mass index (BMI), waist circumference, and circulating triglyceride concentration. Higher IMCL concentrations were significantly correlated with lower muscle density in older individuals, independent of age, sex, race, and the obesity-associated covariates (p < 0.01). Lower muscle density was also significantly associated with greater age-adjusted IMCL, a variable we constructed using LOESS regression (p < 0.05). Our results suggest that the accumulation of IMCL may be associated with a decrease in muscle density. This may serve to define a potential therapeutic target for treatment of age-associated decreased muscle function.

Effects of a 12-Week Suspension versus Traditional Resistance Training Program on Body Composition, Bioimpedance Vector Patterns, and Handgrip Strength in Older Men: A Randomized Controlled Trial

This investigation aimed to compare the effects of suspension training versus traditional resistance exercise using a combination of bands and bodyweight on body composition, bioimpedance vector patterns, and handgrip strength in older men. Thirty-six older men (age 67.4 ± 5.1 years, BMI 27.1 ± 3.3 kg/m²) were randomly allocated into suspension training (n = 12), traditional training (n = 13), or non-exercise (n = 11) groups over a 12-week study period. Body composition was assessed using conventional bioelectrical impedance analysis and classic and specific bioelectric impedance vector analysis, and handgrip strength was measured with a dynamometer. Results showed a significant (p < 0.05) group by time interaction for fat mass, fat-free mass, total body water, skeletal muscle index, classic and specific bioelectrical resistance, classic bioelectrical reactance, phase angle, and dominant handgrip strength. Classic and specific vector displacements from baseline to post 12 weeks for the three groups were observed. Handgrip strength increased in the suspension training group (p < 0.01, ES: 1.50), remained stable in the traditional training group, and decreased in the control group (p < 0.01, ES: -0.86). Although bodyweight and elastic band training helps to prevent a decline in muscle mass and handgrip strength, suspension training proved more effective in counteracting the effects of aging in older men under the specific conditions studied.

Predictive equation for assessing appendicular lean soft tissue mass using bioelectric impedance analysis in older adults: Effect of body fat distribution

BACKGROUND

Low muscle mass is associated with sarcopenia and increased mortality. Muscle mass, especially that of the limbs, is commonly estimated by dual-energy X-ray absorptiometry (DXA) or bioimpedance analysis (BIA). However, BIA-based predictive equations for estimating lean appendicular soft tissue mass (ALST) do not take into account body fat distribution, an important factor influencing DXA and BIA measurements.

OBJECTIVES

To develop and cross-validate a BIA-based equation for estimating ALST with DXA as criterion, and to compare our new formula to three previously published models.

METHODS

One-hundred eighty-four older adults (140 women and 44 men) (age 71.5 ± 7.3 years, body mass index 27.9 ± 5.3 kg/m²) were recruited. Participants were randomly split into validation (n = 118) and cross-validation groups (n = 66). Bioelectrical resistance was obtained with a phase-sensitive 50 kHz BIA device.

RESULTS

A BIA-based model was developed for appendicular lean soft tissue mass [ALST (kg) = 5.982 + (0.188 × S² / resistance) + (0.014 × waist circumference) + (0.046 × Wt) + (3.881 × sex) - (0.053 × age), where sex is 0 if female or 1 if male, Wt is weight (kg), and S is stature (cm) (R² = 0.86, SEE = 1.35 kg)]. Cross validation revealed r² of 0.91 and no mean bias. Two of three previously published models showed a trend to significantly overestimate ALST in our sample (p < 0.01).

CONCLUSIONS

The new equation can be considered valid, with no observed bias and trend, thus affording practical means to quantify ALST mass in older adults.

Examination of the confounding effect of subcutaneous fat on muscle echo intensity utilizing exogenous fat

We aimed to provide an unbiased estimate of the confounding effect of subcutaneous fat thickness on ultrasound echo intensity (EI) measures of muscle quality. The effect of fat thickness on EI was verified for an approximate range of 0 to 3 cm of fat using exogeneous layers of pork fat over the human tibialis anterior muscle. Sonograms were obtained (i) with focus constant across fat thickness conditions, and (ii) with focus position adjusted to the muscle region of interest (ROI) position for each fat thickness level. In agreement with our hypothesis, increasing fat between the probe and the ROI resulted in a decrease in EI. This overestimating effect of fat on muscle quality differs between sonograms with constant focus and sonograms with focus position adjusted to the vertical displacement in ROI position that occurs for different levels of fat thickness. Correcting equations to account for the overestimating effect of fat on muscle quality are provided for both focus conditions. This is the first study to systematically analyze the confounding effect of fat thickness as an independent factor and the provided equations can be used for improved accuracy in estimates of muscle quality in obese/overweight subjects/patients.

Novelty: The independent confounding effect of subcutaneous fat thickness on ultrasound (US) estimates of muscle quality was quantified. US estimates of muscle quality depend on whether focus is adjusted to the muscle region of interest or not. Equations for correcting muscle quality estimates are provided.

The combined effects of obesity and ageing on skeletal muscle function and tendon properties in vivo in men

PURPOSE

We investigated the combined impact of ageing and obesity on Achilles tendon (AT) properties in vivo in men, utilizing three classification methods of obesity.

METHOD

Forty healthy, untrained men were categorised by age (young (18-49 years); older (50-80 years)), body mass index (BMI; normal weight (≥18.5-<25); overweight (≥25-<30); obese (≥30)), body fat% (normal adipose (<28%); high adiposity (≥28%)) and fat mass index (FMI; normal (3-6); excess fat (>6-9); high fat (>9). Assessment of body composition used dual-energy X-ray absorptiometry, gastrocnemius medialis (GM)/AT properties used dynamometry and ultrasonography and endocrine profiling used multiplex luminometry.

RESULTS

Older men had lower total range of motion (ROM; -11%; P = 0.020), GM AT force (-29%; P < 0.001), stiffness (-18%; P = 0.041), Young's modulus (-22%; P = 0.011) and AT stress (-28%; P < 0.001). All three methods of classifying obesity revealed obesity to be associated with lower total ROM (P = 0.014-0.039). AT cross sectional area (CSA) was larger with higher BMI (P = 0.030). However, after controlling for age, higher BMI only tended to be associated with greater tendon stiffness (P = 0.074). Interestingly, both AT CSA and stiffness were positively correlated with body mass (r = 0.644 and r = 0.520) and BMI (r = 0.541 and r = 0.493) in the young but not older adults. Finally, negative relationships were observed between AT CSA and pro-inflammatory cytokines TNF-α, IL-6 and IL-1β.

CONCLUSIONS

This is the first study to provide evidence of positive adaptations in tendon stiffness and size in vivo resulting from increased mass and BMI in young but not older men, irrespective of obesity classification.