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Abstract Context Previous investigations on skeletal muscle health in type 1 diabetes (T1D) have generally focused on later stages of disease progression where comorbidities are present and are posited as a primary mechanism of muscle dysfunction. Objective To investigate skeletal muscle function and morphology across the adult lifespan in those with and without T1D. Design Participants underwent maximal contraction (MVC) testing, resting muscle biopsy, and venous blood sampling. Setting Procedures in this study were undertaken at the McMaster University Medical Centre. Participants Sixty-five healthy adult (18-78 years old) men/males and women/females (T1D = 34; control = 31) matched for age/biological sex/body mass index; self-reported physical activity levels were included. Main Outcome Measures Our primary measure in this study was MVC, with supporting histological/immunofluorescent measures. Results After 35 years of age (“older adults”), MVC declined quicker in T1D subjects compared to controls. Loss of strength in T1D was accompanied by morphological changes associated with accelerated aging. Type 1 myofiber grouping was higher in T1D, and the groups were larger and more numerous than in controls. Older T1D females exhibited more myofibers expressing multiple myosin heavy chain isoforms (hybrid fibers) than controls, another feature of accelerated aging. Conversely, T1D males exhibited a shift toward type 2 fibers, with less evidence of myofiber grouping or hybrid fibers. Conclusions These data suggest impairments to skeletal muscle function and morphology exist in T1D. The decline in strength with T1D is accelerated after 35 years of age and may be responsible for the earlier onset of frailty, which characterizes those with diabetes.

Paraspinal muscle dysfunction is associated with spinal degeneration, yet our understanding of the specifics of this muscle dysfunction is incomplete. Muscles consist of thousands of individual fibres, but little is known about the variability in functional capability amongst these fibres, particularly in muscles that display pathological features. This study investigated individual muscle fibre contractile function variability within paraspinal muscle biopsies from 19 chondrodystrophic canines undergoing surgery for intervertebral disc extrusion, and a control group of 10 healthy rats. Specific force, active modulus, and rate of force redevelopment (KTR) were tested in an average of 20 fibres from each biopsy. Correlations were computed between means and both standard deviations (absolute variability) and coefficient of variations (relative variability) for each contractile variable. Across contractile variables, canine muscle fibres demonstrated greater relative variability and lower means compared to rat controls, confirming pathological impairment. Notably, most relationships demonstrated negative correlations between contractile performance and relative variability, consistent with the hypothesis that more impaired muscles exhibit greater fibre-level heterogeneity. Interestingly, two canines demonstrated unusually high KTR in type 1 fibres, suggesting possible compensatory adaptation. These findings highlight altered within-muscle contractile function in spinal pathology and underscore the importance of fibre-level analysis for understanding muscle dysfunction.

Background Adipose infiltration and lipid droplet accumulation are implicated in metabolic diseases and are known to limit skeletal muscle repair and regeneration. However, their role in skeletal muscle injury, particularly volumetric muscle loss (VML), remains unclear. We aimed to characterize early lipid and adipokine responses following direct (i.e., VML) and indirect (i.e., denervation) traumatic injuries. Methods Adult male and female C57Bl/6J mice ( n  = 36) were randomized to VML injury to the posterior hindlimb, tibial nerve denervation, or remained injury Naïve. Three days post, in vivo muscle function was assessed. Serum and gastrocnemius muscle tissue were assessed for histological and biochemical analyses. Results A decrease in total myofiber number occurred post-VML with a reduction in force and increased fatigue. Lipid droplet-associated proteins displayed injury- and myofiber type-specific changes, with VML exhibiting accumulation of perilipin 5 localized to the injury site. Lipid droplets in the muscle remaining were significantly greater post-VML compared to denervation. The pro-inflammatory adipokine IL-6 and growth factor IGF-1 were markedly increased in the muscle remaining post-VML, while circulating metabolic regulators, adiponectin and leptin, were suppressed. Conclusions These findings underscore lipid droplet dynamics and adipokine signaling disruptions following indirect and direct traumatic injuries in a preclinical model. Future work should be done to explore aspects of lipid droplet regulation temporally following skeletal muscle injuries, as early accumulation may suggest an additional etiology in the pathological sequelae of injury.

The purpose of this study was to investigate the effects of combining blood flow restriction training (BFRT) with electrical muscle stimulation (EMS) on muscle functions and sports performance in football players with knee osteoarthritis (KOA). This parallel randomized controlled trial was conducted on 64 football players diagnosed with KOA at Chengdu Sport University. Participants were enrolled based on predefined eligibility criteria and randomly allocated to four groups: the control group (CTR, n  = 16), BFRT-alone group (BFRT, n  = 16), EMS-alone group (EMS, n  = 16), and BFRT combined with EMS group (CMB, n  = 16). Data were gathered via the 10-meter sprint, 20-meter sprint, countermovement jump (CMJ), and Illinois agility test (IAT) to assess sports performance. Additionally, peak torque (PT) was used to measure muscle strength, the root mean square (RMS) was used to assess muscle activation, and the cross-sectional area (CSA) was used to evaluate muscle volume. The data were statistically analyzed via SPSS software, and a p -value < 0.05 was considered significant. Following the 8-week intervention, the CMB group showed a more pronounced change in the 10-m sprint compared to the CTR group ( p  < 0.001) and exhibited significant differences in the 20-m sprint (CTR: p  < 0.001, BFRT: p  = 0.015, EMS: p  < 0.001), CMJ (CTR: p  < 0.001, BFRT: p  = 0.019, EMS: p  < 0.001), and IAT (CTR: p  < 0.001, BFRT: p  = 0.009, EMS: p  = 0.018), outperforming the other three groups. To PT, the CMB groups demonstrated significant superiority over the other three groups (CTR: p  < 0.001, BFRT: p  < 0.001, EMS: p  < 0.001), while the BFRT group exhibited a notable difference in PT than the EMS group ( p  = 0.032). Concerning RMS, the EMS and CMB groups showed significant differences from the CTR (EMS: p  < 0.001, CMB: p  < 0.001) and BFRT (EMS: p  = 0.019, CMB: p  < 0.001) groups, whereas the change in the BFRT group was more significant than that in the CTR group ( p  = 0.007). For CSA, the BFRT and CMB groups presented notable differences from the CTR (BFRT: p  = 0.008, CMB: p  = 0.002)and EMS (BFRT: p  = 0.014, CMB: p  = 0.004) groups. In summary, the results suggest that BFRT combined with EMS can increase muscle strength in male football players with KOA through improving muscle volume and neuromuscular recruitment under low-intensity resistance training, thereby increasing explosive power and agility.

Inflammation and oxidative stress contribute to muscle dysfunction in patients with chronic obstructive pulmonary disease (COPD). Oxidants contained in cigarette smoke (CS) induce adverse effects on tissues through oxidative phenomena. To explore oxidative stress and inflammation in quadriceps of human smokers and in diaphragm and limb muscles of guinea pigs chronically exposed to CS. Muscle function, protein oxidation and nitration, antioxidants, oxidized proteins, inflammation, creatine kinase activity, and lung and muscle structures were investigated in vastus lateralis of smokers, patients with COPD, and healthy control subjects and in diaphragm and gastrocnemius of CS-exposed guinea pigs at 3, 4, and 6 months. Compared with control subjects, quadriceps muscle force was mildly but significantly reduced in smokers; protein oxidation levels were increased in quadriceps of smokers and patients with COPD, and in respiratory and limb muscles of CS-exposed animals; glycolytic enzymes, creatine kinase, carbonic anydrase-3, and contractile proteins were significantly more carbonylated in quadriceps of smokers and patients with COPD, and in respiratory and limb muscles of CS-exposed guinea pigs. Chronic CS exposure induced no significant rise in muscle inflammation in either smokers or rodents. Muscle creatine kinase activity was reduced only in patients with COPD and in both diaphragm and gastrocnemius of CS-exposed animals. Guinea pigs developed bronchiolar abnormalities at 4 months of exposure and thereafter. CS exerts direct oxidative modifications on muscle proteins, without inducing any significant rise in muscle inflammation. The oxidative damage to muscle proteins, which precedes the characteristic respiratory changes, may contribute to muscle loss and dysfunction in smokers and patients with COPD.

As demonstrated in COPD, bronchiectasis patients may experience respiratory and peripheral muscle dysfunction. We hypothesized that respiratory and peripheral (upper and lower limbs) muscle function and nutritional status may be more significantly altered in female than in males for identical age and disease severity. In mild-to-moderate bronchiectasis patients (n = 150, 114 females) and 37 controls (n = 37, 21 females), radiological extension, maximal inspiratory and expiratory pressures (MIP and MEP), sniff nasal inspiratory pressure (SNIP), hand grip and quadriceps muscle strengths, body composition, and blood analytical biomarkers were explored. Compared to the controls, in all bronchiectasis patients (males and females), BMI, fat-free mass index (FFMI), fat tissue, upper and lower limb muscle strength, and respiratory muscle strength significantly declined, and FFMI, fat tissue, and quadriceps muscle function were significantly lower in female than male patients. In patients with mild-to-moderate bronchiectasis, respiratory and peripheral muscle function is significantly impaired and only partly related to lung disease status. Quadriceps muscle strength was particularly weakened in the female patients and was negatively associated with their exercise tolerance. Muscle weakness should be therapeutically targeted in bronchiectasis patients. Body composition and peripheral muscle function determination should be part of the comprehensive clinical assessment of these patients.

Muscle oximetry based on near-infrared spectroscopy (NIRS) and electromyography (EMG) techniques in adherent clothing might be used to monitor the muscular activity of selected muscle groups while exercising. The fusion of these wearable technologies in sporting garments can allow the objective assessment of the quality and the quantity of the muscle activity as well as the continuous monitoring of exercise programs. Several prototypes integrating EMG and NIRS have been developed previously; however, most devices presented the limitations of not measuring regional muscle oxyhemoglobin saturation and did not embed textile sensors for EMG. The purpose of this study was to compare regional muscle oxyhemoglobin saturation and surface EMG data, measured under resting and dynamic conditions (treadmill run and strength exercises) by a recently developed wearable integrated quadriceps muscle oximetry/EMG system adopting smart textiles for EMG, with those obtained by using two “gold standard” commercial instrumentations for EMG and muscle oximetry. The validity and agreement between the wearable integrated muscle oximetry/EMG system and the “gold standard” instrumentations were assessed by using the Bland-Altman agreement plots to determine the bias. The results support the validity of the data provided by the wearable electronic garment developed purposely for the quadriceps muscle group and suggest the potential of using such device to measure strength and endurance exercises in vivo in various populations.

Background Manual muscle testing (MMT8), the current gold standard for assessing muscle function in patients with idiopathic inflammatory myopathies (IIM), has notable limitations. This study had three aims (1) to compare MMT8 with inertial sensor-based gait analysis, (2) to evaluate patient-performed functional tests guided by shared decision-making (SDM), and (3) to investigate adherence to electronic patient-reported outcomes (ePROs). Methods Gold standard muscle function assessment (MMT8) was performed at baseline (T0) and three months (T1). Additionally, inertial-sensor-based gait analysis was completed at T0 and two standardized upper extremity (Modified Barré test; 10-time arm lift test) and two lower extremity muscle endurance tests (60-second Sit-to-Stand (STS) test; Mingazzini test) were presented to patients to choose from. Through shared decision-making, each patient selected one test for lower and upper extremities and opted to record weekly results on paper or through a medical app. Correlations between gait parameters, functional tests, and MMT8 were analyzed, while agreement between patient- and healthcare professional (HCP)-recorded results at T0 and T1 was assessed. Responsiveness to change was also evaluated. Results A total of 28 IIM patients (67.9% female; mean age 57.4 ± 12.9 years) were enrolled. Moderate correlations were observed between gait parameters and MMT8, such as walking speed ( r  = 0.545, p  = 0.004) and stride length ( r  = 0.580, p  = 0.002). All patients selected the Modified Barré test for assessing upper extremity function and 60.7% of patients chose the Mingazzini test for lower extremity function. Agreement between patient- and HCP-recorded functional test results was excellent at baseline and after three months (ICC 0.99–1.00). Functional tests demonstrated strong correlations with MMT8, particularly for the Mingazzini test ( r  = 0.762, p  = 0.002). Patients preferred app-based recording (82.1%) over paper-based methods and weekly ePROs were completed on average 6.9 out of 12 weeks (57.5%). Conclusion Patient-performed functional tests are reliable, scalable alternatives to MMT8, with gait analysis providing complementary insights. Digitally supported self-assessments can enhance clinical workflows, remote monitoring, and treat-to-target strategies, empowering patients and improving disease management.

Muscles, the fundamental components supporting all human movement, exhibit various signals upon contraction, including mechanical signals indicating tremors or mechanical deformation and electrical signals responsive to muscle fiber activation. For noninvasive wearable devices, these signals can be measured using surface electromyography (sEMG) and force myography (FMG) techniques, respectively. However, relying on a single source of information is insufficient for a comprehensive evaluation of muscle condition. In order to accurately and effectively evaluate the various states of muscles, it is necessary to integrate sEMG and FMG in a spatiotemporally synchronized manner. This study presents a flexible sensor for multimodal muscle state monitoring, integrating serpentine‐structured sEMG electrodes with fingerprint‐like FMG sensors into a patch approximately 250 μm thick. This design achieves a multimodal assessment of muscle conditions while maintaining a compact form factor. A thermo‐responsive adhesive hydrogel is incorporated to enhance skin adhesion, improving the signal‐to‐noise ratio of the sEMG signals (33.07 dB) and ensuring the stability of the FMG sensor during mechanical deformation and tremors. The patterned coupled sensing patch demonstrates its utility in tracking muscular strength, assessing fatigue levels, and discerning features of muscle dysfunction by analyzing the time‐domain and frequency‐domain characteristics of the mechanical–electrical coupled signals, highlighting its potential application in sports training and rehabilitation monitoring. A novel patterned mechanical–electrical coupled sensing patch is designed for the simultaneous temporal and spatial acquisition of electrical and mechanical signals in muscle activities, which provides an effective tool for comprehensive multimodal muscle function assessment (muscle strength, fatigue level, and muscle dysfunction) through the complementary time and frequency domain characteristics.

Purpose The purpose of this article is to present recommendations for new muscle strength and hop performance criteria prior to a return to sports after anterior cruciate ligament (ACL) reconstruction. Methods A search was made of relevant literature relating to muscle function, self-reported questionnaires on symptoms, function and knee-related quality of life, as well as the rate of re-injury, the rate of return to sports and the development of osteoarthritis after ACL reconstruction. The literature was reviewed and discussed by the European Board of Sports Rehabilitation in order to reach consensus on criteria for muscle strength and hop performance prior to a return to sports. Results The majority of athletes that sustain an (ACL) injury do not successfully return to their pre-injury sport, even though most athletes achieve what is considered to be acceptable muscle function. On self-reported questionnaires, the athletes report high ratings for fear of re-injury, low ratings for their knee function during sports and low ratings for their knee-related quality of life. Conclusion The conclusion is that the muscle function tests that are commonly used are not demanding enough or not sensitive enough to identify differences between injured and non-injured sides. Recommendations for new criteria are given for the sports medicine community to consider, before allowing an athlete to return to sports after an ACL reconstruction. Level of evidence IV.