Correction of EMG Frequency Spectrum Using Physical Characteristics for Muscle Fatigue Estimation

Autosomal-dominant centronuclear myopathy (CNM) due to mutations in the dynamin 2 gene (DNM2) is a rare congenital myopathy histopathologically characterized by centrally located nuclei and a radial arrangement of sarcoplasmic strands around the central nuclei. A total of 1,582 consecutive muscle biopsies of adult patients (age ≥ 18 years) were screened for morphologically characteristic signs of CNM. Patients with CNM were screened for mutations in DNM2. Clinical data and complementary neurophysiologic, respiratory, cardiac, and muscle MRI data in these patients were analyzed. Six index patients had histopathological signs of CNM (0.38%). Three had the heterozygous p.R465W and 2 siblings the heterozygous p.E368K DNM2 mutation. In 2 patients mutational screening for DNM2, BIN1, MTM1, and RYR1 was negative. Apart from the siblings, there was no positive history, parental mutation screening in 2 cases was negative. Both the percentage of muscle fibers with centralized nuclei and the ratio of muscle fibers with centralized to internalized nuclei were higher in DNM2-CNM compared to non-DNM2-CNM (50% vs. 18% and 94% vs. 63%). The onset was already neonatal or in infancy in 3/5 patients with DNM2 mutation. Symptoms in DNM2-CNM included bilateral ptosis (n = 3), paresis of the external ocular muscles (n = 2), axonal neuropathy (n = 4), restrictive ventilatory involvement (n = 5), and contractures (n = 5), including muscular torticollis (n = 1) and masticatory muscles (n = 2). DNM2-CNM patients and non-DNM2-CNM patients could not be distinguished by clinical features. DNM2-CNM often shows de novo mutations. In addition to the feature of radial sarcoplasmic strands, the ratio of centrally to internalized nuclei might help to differentiate DNM2-CNM from other forms of CNM. Other genes than currently known seem to cause the clinical and histopathological phenotype of CNM.

AimTo assess the relation between muscle fibre hypertrophy and myonuclear accretion in relatively small and large muscle fibre size clusters following prolonged resistance exercise training in older adults.MethodsMuscle biopsies were collected before and after 12 weeks of resistance exercise training in 40 healthy, older men (70 ± 3 years). All muscle fibres were ordered by size and categorized in four muscle fibre size clusters: ‘Small’: 2000‐3999 µm2, ‘Moderate’: 4000‐5999 µm2, ‘Large’: 6000‐7999 µm2 and ‘Largest’: 8000‐9999 µm2. Changes in muscle fibre size cluster distribution were related to changes in muscle fibre size, myonuclear content and myonuclear domain size.ResultsWith training, the percentage of muscle fibres decreased in the Small (from 23 ± 12 to 17 ± 14%, P < .01) and increased in the Largest (from 11 ± 8 to 15 ± 10%, P < .01) muscle fibre size clusters. The decline in the percentage of Small muscle fibres was accompanied by an increase in overall myonuclear domain size (r = −.466, P = .002) and myonuclear content (r = −.390, P = .013). In contrast, the increase in the percentage of the Largest muscle fibres was accompanied by an overall increase in myonuclear content (r = .616, P < .001), but not in domain size.ConclusionProlonged resistance‐type exercise training induces a decline in the percentage of small as well as an increase in the percentage of the largest muscle fibres in older adults. Whereas the change in the percentage of small fibres is best predicted by an increase in overall myonuclear domain size, the change in the percentage of the largest fibres is associated with an overall increase in myonuclear content.

Muscle injury following experimental intraoperative irradiation

Successive injections in MDX mice of myoblasts grown with bFGF

This study aimed to investigate the association between spine-specific sarcopenia, assessed using magnetic resonance imaging measurements of the multifidus muscle, and the risk of osteoporotic vertebral compression fractures in older adults. This retrospective study included 85 patients aged 60 years or older who underwent both lumbar spine magnetic resonance imaging and bone mineral density measurement between January 2020 and 2025. Patients were assigned to fracture (n=43) or control (n=42) groups according to the presence of osteoporotic vertebral compression fractures. Spine-specific sarcopenia was evaluated using the cross-sectional area and fat infiltration of the multifidus and psoas muscles. The percentage of muscle fibers was calculated by subtracting the fat area from the total cross-sectional area. Statistical analyses compared demographic, radiological, and clinical parameters between groups. There were no significant differences between groups regarding age, sex, Body mass index, or psoas index. However, spinal T-scores were significantly lower in the fracture group. The cross-sectional area of the multifidus muscle at L4–5 and L5–S1 levels was significantly higher in the fracture group. Notably, the percentage of muscle fibers of the multifidusmuscle was significantly lower in the fracture group at both levels, indicating increased fat infiltration. Multivariate analysis demonstrated that reduced percentage of muscle fibers was independently associated with an increased risk of osteoporotic vertebral compression fractures, regardless of bone mineral density. Reduced muscle fiber percentage and increased fat infiltration in the multifidus muscle are significant risk factors for osteoporotic vertebral compression fractures independent of bone mineral density. These findings highlight the importance of assessing paraspinal muscle quality for the evaluation and management of osteoporotic fracture risk in the elderly.Keywords: spine-specific sarcopenia, osteoporotic vertebral fracture, bone mineraldensity, magnetic resonance imaging, paraspinal muscle.

The effect of the thyroxine administration on body weight and on some physicochemical and histological characteristics of the Longissimus dorsi muscle was evaluated in gilts at 70 days of gestation. Twenty middle-sisters gilts, daughters of F1 females with a ¾ Landrace X ¼ Large White, male were used. At 150 days of age, i.e., before first heat, the animals were randomly distributed into two groups: treated (n = 10) and control (n = 10). The treated group received a daily dose of 400 μ g of L-thyroxine (T4) in the diet until three days before slaughter and the control group received only diet. Before artificial insemination, blood was collected for determination of plasma total T4. The gilts were inseminated in the second estrus and slaughtered at 70 days of gestation. The initial and final body weight, daily weight gain and pH, water retention, and percentage of muscle fibers and stroma in the Longissimus dorsi muscle were studied. The means of all variables were compared by the Student t-test. Before insemination, the gilts showed clinical signs of hyperthyroidism, characterized by significant increase in plasma levels of T4, mild exophthalmos, and behavioral change characterized by aggression and agitation. There was not significant difference among groups according to the studied parameters. It was concluded that the daily administration of 400µg of thyroxine does not change the daily weight gain during the gestation, as well the pH, the water retention, and the percentage of muscle fibers and stroma of the

This study investigates the effectiveness of a wearable exosuit using shape memory alloys (SMAs) in reducing muscle fatigue and energy expenditure during repetitive lifting tasks. Designed to support the lumbar region without relying on motors or batteries, the SMA-based exosuit offers a lightweight and flexible solution suitable for industrial environments requiring mobility and comfort. Five healthy adult males participated in controlled experiments comparing physiological responses between conditions with and without the exosuit. Each participant performed a 10-min repetitive lifting task involving a 13[Formula: see text]kg load, and various indicators of physical exertion were measured to evaluate the performance of the exosuit. Key physiological metrics included blood lactate concentration, energy expenditure, respiratory exchange ratio (RER), and muscle fatigue. The results showed that the post-task blood lactate concentration increased significantly in the nonexosuit condition (mean 10.5[Formula: see text]mmol/L), while the increase was notably smaller (mean 5.5[Formula: see text]mmol/L) when the exosuit was worn, indicating reduced anaerobic metabolism and muscle fatigue. Similarly, energy expenditure decreased by approximately 16.4% with the exosuit, and improvements were observed in RER values, suggesting a more balanced use of carbohydrate and fat as energy sources. This indicates that the exosuit enhances metabolic efficiency during physically demanding tasks. Muscle fatigue was assessed through median frequency (MF) analysis of surface electromyography (sEMG) signals from key trunk muscles (thoracic and lumbar erector spinae, multifidus). In the exosuit condition, the decline in MF over time was less severe, and final MF values were consistently higher compared to the nonexosuit condition, confirming the exosuit’s role in reducing muscular strain during prolonged lifting. These findings demonstrate that SMA-based exosuits can meaningfully reduce physical fatigue and improve efficiency in repetitive work environments. Their motorless, battery-free design provides advantages in terms of weight and wearability, making them well-suited for industrial applications. While the study was limited by a small and homogeneous sample, effect size calculations supported the practical relevance of the observed benefits. Future research should involve larger and more diverse populations and evaluate long-term usability in real industrial settings. Continued development of SMA technology, including improved thermal response and adaptive control, could further enhance the applicability of exosuits across various occupational and rehabilitative contexts.

Muscle fatigue analysis in isometric contractions using geometric features of surface electromyography signals

Successful Compensation for Dystrophin Deficiency by a Helper-dependent Adenovirus Expressing Full-length Utrophin

Skeletal muscle fatigue is defined as a `any reduction in the maximal capacity to generate force or power output`, and is the reduction of oxygen consumption and by-product of metabolism. For the muscle fatigue therapy, low level laser has been introduced that leads the mitochondrial respiratory and attributes the muscle fatigue recovery. This study analyzed the muscle fatigue signals from electromyography(EMG) during low-level laser therapy (LLLT). Healthy subjects performed voluntary elbow flexion-extension excercise and received placebo LLLT and active LLLT using a 830 nm laser diode. Then, EMG were measured for the evaluation of muscle fatigue. The acquired EMG data were analyzed with median frequency and short time fourier transform methods. The results showed that the LLLT had a significant symptomatic relief of muscle fatigue based on the EMG frequency analysis. Therefore, the muscle fatigue analysis with EMG signals can be applied to quantitative evaluation for the monitoring of LLLT effects.

The main objective of this systematic review was to examine the effect of reduced muscle activity on the relative number of type 1 muscle fibers (%) in the human vastus lateralis muscle. Other objectives were changes in type 2A and 2X percentages and muscle fiber cross-sectional area. We conducted systematic literature searches in eight databases and included studies assessing type 1 fiber percentage visualized by ATPase or immunohistochemical staining before and after a period (≥14days) of reduced muscle activity. The reduced muscle activity models were detraining, leg unloading, and bed rest. Forty-two studies comprising 451 participants were included. Effect sizes were calculated as the mean difference between baseline and follow-up and Generic Inverse Variance tests with random-effects models were used for the weighted summary effect size. Overall, the mean type 1 muscle fiber percentage was significantly reduced after interventions (-1.94%-points, 95% CI [-3.37, -0.51], P=.008), with no significant differences between intervention models (P=.86). Meta-regression showed no effect of study duration on type 1 fiber percentage (P=.98). Conversely, the overall type 2X fiber percentage increased after reduced muscle activity (P<.001). The CSA of the muscle fiber types decreased after the study period (all P-values<0.001) with greater reductions in type 2 than type 1 fibers (P<.001). The result of this meta-analysis display that the type 1 muscle fiber percentage decrease as a result of reduced muscle activity, although the effect size is relatively small.

The aim of the study was to determine the effect of the muscle load and fatigue on the values of the parameters calculated on the basis of the time, frequency (Fourier transform) and time-frequency (wavelet transform) analysis of the EMG signal, for low levels of load. Fifteen young men took part in the study. The EMG signal was registered from right side biceps brachii (BB) and trapezius (TR) muscles in static conditions, at load 10%, 20% and 30% MVC (maximal voluntary contraction). On the basis of the analysis there were selected parameters sensitive to force (RMS) and parameters sensitive to fatigue but simultaneously insensitive to force (MPF--mean power frequency determined on the basis of Fourier transform, CMPFdb5--mean power frequency determined on the basis of the wavelet transform). The results indicate that CMPFdb5 can show similar (muscle BB) or greater (muscle TR) sensitivity to fatigue than MPF. It can suggest that, for low levels of load, the wavelet transform parameters can be more effective in assessing muscle fatigue than the parameters based on the Fourier transform. The obtained results can allow for a more precise analysis of muscle fatigue at low levels of load. Further analysis for a greater number of muscles activated at low levels of load, with the usage of the parameters tested is desirable.

Physiology-based dynamic muscle fatigue model for upper limbs during construction tasks

Background: Exoskeleton robots are emerging as a transformative technology in healthcare, rehabilitation, and industrial settings, providing significant benefits such as improving gait restoration and preventing injuries. These robots enhance mobility for individuals with neuromuscular disorders by providing muscular assistance and reducing physical strain, while also supporting workers in physically demanding tasks. They improve gait efficiency, muscle activation, and overall physical function, contributing to both rehabilitation and occupational health. Objective: This study aims to investigate the impact of exoskeleton use on muscle activation patterns, fatigue levels, and gait parameters in healthy individuals. Methods: Thirty-six participants engaged in a randomized sequence gait experiment on a treadmill for 30 min, both with and without an exoskeleton, with electromyography (EMG) and OptoGait measurements collected during the sessions. A one-week washout period was implemented before participants switched conditions. Results: In the Maximum voluntary contraction (MVC) analysis, significant differences were observed in the Rectus femoris (RF) and gastrocnemius(GM) when wearing the exoskeleton robot compared to not wearing it. At 10 min, 20 min, and 30 min, the differences were statistically significant (p < 0.05) for all muscles. In the muscle fatigue analysis, significant differences were observed in RF, GM, vastus medialis (VM), and hamstring(HS) at 10 min, 20 min, and 30 min (p < 0.05). In the step length and stride length analysis, significant differences were observed at 10 min and 30 min, but no differences were found at 20 min (p < 0.05). Conclusions: This study demonstrates that the use of the exoskeleton robot significantly impacts muscle activation, muscle fatigue, and gait parameters. The results emphasize the potential benefits of exoskeletons in enhancing mobility and reducing muscle strain, providing important insights for rehabilitation and occupational applications.

Recently, fuzzy dispersion entropy (DispEn) has attracted much attention as a new nonlinear dynamics method that combines the advantages of both DispEn and fuzzy entropy. However, it suffers from limitation of insensitivity to dynamic changes. To solve this limitation, we proposed fractional fuzzy dispersion entropy (FFDispEn) based on DispEn, a novel fuzzy membership function and fractional calculus. The fuzzy membership function was defined based on the Euclidean distance between the embedding vector and dispersion pattern. Simulated signals generated by the one-dimensional (1D) logistic map were used to test the sensitivity of the proposed method to dynamic changes. Moreover, 29 subjects were recruited for an upper limb muscle fatigue experiment, during which surface electromyography (sEMG) signals of the biceps brachii muscle were recorded. Both simulated signals and sEMG signals were processed using a sliding window approach. Sample entropy (SampEn), DispEn and FFDispEn were separately used to calculate the complexity of each frame. The sensitivity of different algorithms to the muscle fatigue process was analyzed using fitting parameters through linear fitting of the complexity of each frame signal. The results showed that for simulated signals, the larger the fractional order q, the higher the sensitivity to dynamic changes. Moreover, DispEn performed poorly in the sensitivity to dynamic changes compared with FFDispEn. As for muscle fatigue detection, the FFDispEn value showed a clear declining tendency with a mean slope of -1.658 × 10-3 as muscle fatigue progresses; additionally, it was more sensitive to muscle fatigue compared with SampEn (slope: -0.4156 × 10-3) and DispEn (slope: -0.1675 × 10-3). The highest accuracy of 97.5% was achieved with the FFDispEn and support vector machine (SVM). This study provided a new useful nonlinear dynamic indicator for sEMG signal processing and muscle fatigue analysis. The proposed method may be useful for physiological and biomedical signal analysis.