Enhancing postural balance assessment through neural network-based lower-limb muscle strength evaluation with reduced markers.

Aiming to simplify the data acquisition process for balance diagnosis and focused on muscle, a direct factor affecting balance, to assess and judge postural stability. Utilizing a publicly available kinematic dataset, the research retained 3D coordinates and mechanical data for 8 markers on the lower limbs. By integrating this data with the musculoskeletal model in OpenSim, inverse kinematic calculations were performed to derive muscle forces. These forces, alongside the coordinates, were split into an 8:2 training and test set ratio. A neural network was then developed to predict muscle forces using normalized coordinate data from the training set as input, with corresponding muscle force data as training labels. The model's accuracy was confirmed on the test set, achieving coefficients of determination (R2) above 0.99 for 276 muscle forces. Furthermore, the Force Maximum Percentage Difference (FMPD) was introduced as a novel criterion to evaluate and visualize lower limb balance, revealing significant discrepancies between the patient and control groups. This study successfully demonstrates that the neural network model can precisely predict lower limb muscle forces using reduced markers and introduces FMPD as an effective tool for assessing limb balance, providing a robust framework for future diagnostic and rehabilitative applications.

Gender-specific Indian Paediatric and Adult Reference Data for Muscle Function Parameters Assessed Using Jumping Mechanography.

OBJECTIVE: To establish age and gender-specific paediatric and adult reference data for muscle function parameters assessed using Jumping Mechanography in the Indian population. METHODS: 2056 healthy individuals (1068 males), aged 5 to 60 years, performed 2 tests on a force platform (Leonardo Mechanograph, Novotec). Maximum power (Pmax) was assessed by single two legged jump and maximum force (Fmax) by multiple one legged hopping. LMS method was used to generate age and gender-specific reference curves for 5 - 20y group and mean ± SD and median ± IQR are presented for 21 - 60y group. RESULTS: In 5 - 20y group, Pmax and Fmax increased with age while in 21 - 60y group, the parameters declined with age. Females had lower Pmax values than males, consistently through all age groups. In children <15y, there were no intergender differences in Fmax, however, in further age groups, females had lower Fmax (p<0.001). Our participants showed lower Pmax and Fmax when compared with machine reference data based on German population (p<0.001). CONCLUSION: We present ethnicity-specific reference values for muscle function by Jumping Mechanography. These values are intended to help in clinical assessment of muscle function of Indian population and to identify those at risk of poor muscle function.

Gauging force by tapping tendons? Inaccurately in the human patellar tendon.

Accurately estimating in vivo tendon load non-invasively remains a major challenge in biomechanics, which might be overcome by shear-wave tensiometry. Shear-wave tensiometry measures the speed of mechanically induced tendon shear waves by skin-mounted accelerometers. To gauge the feasibility and accuracy of this novel technique, we obtained patellar tendon shear wave speeds via shear-wave tensiometry during sustained or ramp voluntary contractions of the knee extensors in two experiments (n = 8 in both). In experiment one, participants produced a constant knee extension torque of âˆ¼ 50 Nm at five different knee joint angles (i.e. variable tendon load), which resulted in estimated patellar tendon forces between 1005 ± 6N and 1182 ± 16 N. However, wave speed squared did not correlate with estimated tendon force within participants (rrm(31) = -0.19, p = 0.278). In experiment two, averaged correlation coefficients between normalized wave speed squared and torque of maximal and submaximal voluntary contractions across participants ranged between r = 0.43 and r = 0.94, while the time-varying correlation between these normalized signals ranged from r = -0.99 to r = 1.00. Further, the mean absolute errors (MAEs) between normalized wave speed squared and normalized torque across participants ranged between 0.03 and 0.54, which were larger than the MAEs between normalized torque and normalized summed EMG amplitude from the superficial quadriceps muscles (0.03-0.54 versus 0.06-0.26, respectively). In conclusion, there was no simple relation between shear wave speed squared and patellar tendon load, which severely limits the feasibility of shear-wave tensiometry for accurately estimating in vivo tendon load at the knee joint.

Effects of contrast water therapy on proprioception of the knee joint and degree of fatigue in sprinters after high intensity training.

OBJECTIVE: To investigate the effect of contrast water therapy on proprioception of the knee joint and indicators associated with fatigue in sprinters after high intensity training. METHODS: A total of 40 sprinters were selected and divided into an observation group and a control group. The observation group got 14 minutes of contrast water therapy, while the control group took 14 minutes of sitting rest after training. The knee position sense, muscle force sense, joint reaction angle to release, knee joint function, and indictors associated with fatigue were evaluated before and after exercise at different time points. RESULTS: At 24 h, 48 h, and 72 h after exercise, the active position sense and muscle force sense of the control group were significantly lower than those of the observation group (all P<0.05). At 48 h after exercise, the passive position sense of the control group was significantly lower than that of the observation group (all P<0.05). At 24 h and 48 h after exercise, the joint reaction angle to release of the control group was significantly greater than that of the observation group (all P<0.05). Additionally, the IKDC2000 and Lysholm scores after interference in the observation group were greater than those of the control group (all P<0.05). The indicators associated with fatigue after interference in the observation group were significantly lower than those of the control group (all P<0.05). CONCLUSION: Contrast water therapy can effectively alleviate muscle force sense, promote muscle proprioception, improve knee joint function, and enhance recovery from fatigue.

Integrated Wearable System for Monitoring Skeletal Muscle Force of Lower Extremities.

Continuous monitoring of lower extremity muscles is necessary, as the muscles support many human daily activities, such as maintaining balance, standing, walking, running, and jumping. However, conventional electromyography and physiological cross-sectional area methods inherently encounter obstacles when acquiring precise and real-time data pertaining to human bodies, with a notable lack of consideration for user comfort. Benefitting from the fast development of various fabric-based sensors, this paper addresses these current issues by designing an integrated smart compression stocking system, which includes compression garments, fabric-embedded capacitive pressure sensors, an edge control unit, a user mobile application, and cloud backend. The pipeline architecture design and component selection are discussed in detail to illustrate a comprehensive user-centered STIMES design. Twelve healthy young individuals were recruited for clinical experiments to perform maximum voluntary isometric ankle plantarflexion contractions. All data were simultaneously collected through the integrated smart compression stocking system and a muscle force measurement system (Humac NORM, software version HUMAC2015). The obtained correlation coefficients above 0.92 indicated high linear relationships between the muscle torque and the proposed system readout. Two-way ANOVA analysis further stressed that different ankle angles (p = 0.055) had more important effects on the results than different subjects (p = 0.290). Hence, the integrated smart compression stocking system can be used to monitor the muscle force of the lower extremities in isometric mode.

Consensus for experimental design in electromyography (CEDE) project: Application of EMG to estimate muscle force.

Skeletal muscles power movement. Deriving the forces produced by individual muscles has applications across various fields including biomechanics, robotics, and rehabilitation. Since direct in vivo measurement of muscle force in humans is invasive and challenging, its estimation through non-invasive methods such as electromyography (EMG) holds considerable appeal. This matrix, developed by the Consensus for Experimental Design in Electromyography (CEDE) project, summarizes recommendations on the use of EMG to estimate muscle force. The matrix encompasses the use of bipolar surface EMG, high density surface EMG, and intra-muscular EMG (1) to identify the onset of muscle force during isometric contractions, (2) to identify the offset of muscle force during isometric contractions, (3) to identify force fluctuations during isometric contractions, (4) to estimate force during dynamic contractions, and (5) in combination with musculoskeletal models to estimate force during dynamic contractions. For each application, recommendations on the appropriateness of using EMG to estimate force and justification for each recommendation are provided. The achieved consensus makes clear that there are limited scenarios in which EMG can be used to accurately estimate muscle forces. In most cases, it remains important to consider the activation as well as the muscle state and other biomechanical and physiological factors- such as in the context of a formal mechanical model. This matrix is intended to encourage interdisciplinary discussions regarding the integration of EMG with other experimental techniques and to promote advances in the application of EMG towards developing muscle models and musculoskeletal simulations that can accurately predict muscle forces in healthy and clinical populations.

Effect of Warm-Up Exercise on Functional Regulation of Motor Unit Activation during Isometric Torque Production.

In this study, we tested several hypotheses related to changes in motor unit activation patterns after warm-up exercise. Fifteen healthy young men participated in the experiment and the main task was to produce voluntary torque through the elbow joint under the isometric condition. The experimental conditions consisted of two directions of torque, including flexion and extension, at two joint angles, 10° and 90°. Participants were asked to increase the joint torque to the maximal level at a rate of 10% of the maximum voluntary torque. The warm-up protocol followed the ACSM guidelines, which increased body temperature by approximately 1.5°C. Decomposition electromyography electrodes, capable of extracting multiple motor unit action potentials from surface signals, were placed on the biceps and triceps brachii muscles, and joint torque was measured on the dynamometer. The mean firing rate and the recruitment threshold of the decomposed motor units were quantified. In addition, a single motor unit activity from the spike train was quantified for each of five selected motor units. The magnitude of joint torque increased with the warm-up exercise for all the experimental conditions. The results of the motor unit analyses showed a positive and beneficial effect of the warm-up exercise, with an increase in both the mean firing rate and the recruitment threshold by about 56% and 33%, respectively, particularly in the agonist muscle. Power spectral density in the gamma band, which is thought to be the dominant voluntary activity, was also increased by the warm-up exercise only in the high threshold motor units.

Long-term monitoring of stimulated lower leg skeletal muscle forces compared with voluntary contractions in myopathy patients - A five-year follow-up report on 5 adults.

OBJECTIVE: Long-term assessments of lower leg muscle forces in ambulant patients with distal myopathies. METHODS AND MATERIALS: Over a five-year period, we measured involuntary, nerve-stimulated, isometric torques of the ankle dorsiflexors in a group of ambulant patients with myopathies and compared results with voluntary Manual Muscle Tests (MMT). RESULTS: From ten recruited patients, five could finish the five-year protocol. Twenty-seven force measurements sessions (one per year; 1,5 hours duration each) were performed. These patients exhibited low, stable torques or increased minimally (0.2 Newtonmeter, versus 0.1 Nm, ns; 0.7 vs. 1.0, ns; 3.4 vs. 3.5, ns; 0.2 vs. 0.1, ns; 0.8 vs. 1.5, P 0.0004 initial values vs. 5-year values, [norm: 3.9-5.7 Nm]). A 6th patient, eliciting low torque values (0.1 Nm) early passed away. Contraction times inversely correlated with MMT. MMT provided similar overall force abilities. CONCLUSIONS: Long-term monitoring of lower leg muscle forces in ambulant patients is limited by the patient's health status. In a small group of patients, stimulated lower leg forces did not worsen over many years relative to their diagnosed myopathies. Tracking involuntary forces, could be a useful monitoring providing phenotypic information, in addition to MMT. Future devices should be small and be simply self-applying, designed for subjects' domestic use and web-based data transfer. CLINICALTRIALS: gov NCT00735384.

Peripheral muscle force balance/imbalance in neurological binary control of bladder function and dysfunction.

Bladder control is not from the bladder itself but from muscles and ligaments outside of it. Bladder control is binary, either closed or open. Control is exerted cortically, directly and via a peripheral pelvic mechanism comprising three reflex pelvic muscles which contract (variously) against pubourethral ligaments (PULs) anteriorly and uterosacral ligaments (USLs) posteriorly. Directed efferent impulses from the cortex close the urethra, open it, and stretch the vagina in opposite directions to prevent urothelial impulses inappropriately activating micturition (urge incontinence). Normally, the opposite muscles are equivalent in force, and balance at the bladder neck. Weak PULs weaken the forward closure force: the posterior forces become relatively more powerful; balance shifts behind bladder neck; the posterior urethral wall is pulled open like a trapdoor, and urine is lost on effort (stress urinary incontinence). Weak USLs weaken the posterior muscle forces; the balance of forces shifts forwards, and the urethra is closed relatively more tightly by slow-twitch forward muscle vector forces (pubococcygei), which stretch each side of the distal vagina forwards to compress the posterior urethral wall; in consequence, the weakened posterior muscle forces cannot easily open the posterior urethral wall; the bladder has to contract against a relatively unopened urethra, perceived as "obstructed micturition". Nor can weakened posterior forces stretch the vagina sufficiently to support the urothelial stretch receptors from below; these may fire off excess afferent impulses to cause urgency. As bladder control is strictly binary, in women with urgency, control swings between open and closed modes. This condition is known as an "unstable bladder", which is defined symptomatically as "overactive bladder", and urodynamically as "detrusor overactivity". In summary, bladder control is binary, either closed or open. How the cortex integrates and computes multiple inputs determines the type of closure, opening or unstable control which is experienced by the patient.

Virtual reality skateboarding training for balance and functional performance in degenerative lumbar spine disease.

BACKGROUND: Degenerative lumbar spine disease (DLD) is a prevalent condition in middle-aged and elderly individuals. DLD frequently results in pain, muscle weakness, and motor impairment, which affect postural stability and functional performance in daily activities. Simulated skateboarding training could enable patients with DLD to engage in exercise with less pain and focus on single-leg weight-bearing. The purpose of this study was to investigate the effects of virtual reality (VR) skateboarding training on balance and functional performance in patients with DLD. METHODS: Fourteen patients with DLD and 21 age-matched healthy individuals completed a 6-week program of VR skateboarding training. The motion capture and force platform systems were synchronized to collect data during a single-leg stance test (SLST). Musculoskeletal simulation was utilized to calculate muscle force based on the data. Four functional performance tests were conducted to evaluate the improvement after the training. A Visual Analogue Scale (VAS) was also employed for pain assessment. RESULTS: After the training, pain intensity significantly decreased in patients with DLD (p = 0.024). Before the training, patients with DLD took longer than healthy individuals on the five times sit-to-stand test (p = 0.024). After the training, no significant between-group differences were observed in any of the functional performance tests (p > 0.05). In balance, patients with DLD were similar to healthy individuals after the training, except that the mean frequency (p = 0.014) was higher. Patients with DLD initially had higher biceps femoris force demands (p = 0.028) but shifted to increased gluteus maximus demand after the training (p = 0.037). Gluteus medius strength significantly improved in patients with DLD (p = 0.039), while healthy individuals showed consistent muscle force (p > 0.05). CONCLUSION: This is the first study to apply the novel VR skateboarding training to patients with DLD. VR skateboarding training enabled patients with DLD to achieve the training effects in a posture that relieves lumbar spine pressure. The results also emphasized the significant benefits to patients with DLD, such as reduced pain, enhanced balance, and improved muscle performance.

Different Body Partialization Procedures Considering Maximum Strength and Explosiveness: Factorial Analysis Approach / Diferentes Procedimientos de Parcialización Corporal Considerando Fuerza Máxima y Explosividad: Enfoque de Análisis Factorial

SUMMARY: The aim of this study was to determine the sensitivity of different methods of partialization, in terms of different body component indices in relation to indicators of strength and explosiveness. The research involved 187 subjects who were divided into two groups based on sex. This research consisted of measuring body composition characteristics by multichannel bioimpedance analysis (BIA) InBody 720, as well as contractile characteristics of different muscle groups with tenziometric Dinamometry method. Based on the results of the factor analysis we found that regardless of the sex the most sensitive variable for partialization of absolute body isometric strength variable (ABiS) is partialization by allometric scaling (0.964 for females and 0.947 for males explained factor variance). However, in the case of absolute body isometric explosiveness (ABiE), the results of this study have demonstrated that partialization relative to skeletal muscle mass according to the body longitudinality - skeletal muscle mass index (SMMI) is the methodological choice disregarding the sex (0.982 for females and 0.980 for males explained factor variance). The results of the study have shown that for the purpose of scaling the maximal strength relative to body composition, the allometric method can be considered as a choice, while for the partialization of maximal isometric explosiveness skeletal muscle mass index is the best choice insensitive of the sex.

El objetivo de este estudio fue determinar la sensibilidad de distintos métodos de parcialización, en términos de diferentes índices de componentes corporales en relación a los indicadores de fuerza y explosividad. En la investigación participaron 187 sujetos que se dividieron según el sexo en dos grupos. Esta investigación consistió en medir las características de composición corporal mediante análisis de bioimpedancia multicanal (BIA) InBody 720, así como las características contráctiles de diferentes grupos musculares con el método de Dinamometría tenciométrica. Con base en los resultados del análisis factorial, encontramos que, independientemente del sexo, la variable más sensible para la parcialización de la variable de fuerza isométrica corporal absoluta (ABiS) fue la parcialización mediante escala alométrica (0,964 para las mujeres y 0,947 para los hombres). Sin embargo, en el caso de la explosividad isométrica corporal absoluta (ABiE), los resultados de este estudio han demostrado que la parcialización relativa a la masa del músculo esquelético según la longitudinalidad del cuerpo - índice de masa del músculo esquelético (SMMI) es la opción metodológica sin tener en cuenta el sexo (0,982 para las mujeres y 0,980 para los hombres). Los resultados del estudio han demostrado que para escalar la fuerza máxima en relación con la composición corporal, el método alométrico puede considerarse como una opción, mientras que para la parcialización de la explosividad isométrica máxima, el índice de masa del músculo esquelético es la mejor opción independiente del sexo.

Exploring biomechanical variations in ankle joint injuries among Latin dancers with different stance patterns: utilizing OpenSim musculoskeletal models.

Background: Dancers represent the primary demographic affected by ankle joint injuries. In certain movements, some Latin dancers prefer landing on the Forefoot (FT), while others prefer landing on the Entire foot (ET). Different stance patterns can have varying impacts on dancers' risk of ankle joint injuries. The purpose of this study is to investigate the differences in lower limb biomechanics between Forefoot (FT) dancers and Entire foot (ET) dancers. Method: A group of 21 FT dancers (mean age 23.50 (S.D. 1.12) years) was compared to a group of 21 ET dancers (mean age 23.33 (S.D. 0.94) years), performing the kicking movements of the Jive in response to the corresponding music. We import data collected from Vicon and force plates into OpenSim to establish musculoskeletal models for computing kinematics, dynamics, muscle forces, and muscle co-activation. Result: In the sagittal plane: ankle angle (0%-100%, p < 0.001), In the coronal plane: ankle angle (0%-9.83%, p = 0.001) (44.34%-79.52%, p = 0.003), (88.56%-100%, p = 0.037), ankle velocity (3.73%-11.65%, p = 0.017) (94.72-100%, p = 0.031); SPM analysis revealed that FT dancers exhibited significantly smaller muscle force than ET dancers around the ankle joint during the stance phase. Furthermore, FT dancers displayed reduced co-activation compared to ET dancers around the ankle joint during the descending phase, while demonstrating higher co-activation around the knee joint than ET dancers. Conclusion: This study biomechanically demonstrates that in various stance patterns within Latin dance, a reduction in lower limb stance area leads to weakened muscle strength and reduced co-activation around the ankle joint, and results in increased ankle inversion angles and velocities, thereby heightening the risk of ankle sprains. Nevertheless, the increased co-activation around the knee joint in FT dancers may be a compensatory response for reducing the lower limb stance area in order to maintain stability.

Estimation of lower back muscle force in a lifting task using wearable IMUs.

Low back pain is commonly reported in occupational settings due to factors such as heavy lifting and poor ergonomic practices, often resulting in significant healthcare expenses and lowered productivity. Assessment tools for human motion and ergonomic risk at the workplace are still limited. Therefore, this study aimed to assess lower back muscle and joint reaction forces in laboratory conditions using wearable inertial measurement units (IMUs) during weight lifting, a frequently high-risk workplace task. Ten able-bodied participants were instructed to lift a 28 lbs. box while surface electromyography sensors, IMUs, and a camera-based motion capture system recorded their muscle activity and body motion. The data recorded by IMUs and motion capture system were used to estimate lower back muscle and joint reaction forces via musculoskeletal modeling. Lower back muscle patterns matched well with electromyography recordings. The normalized mean absolute differences between muscle forces estimated based on measurements of IMUs and cameras were less than 25 %, and the statistical parametric mapping results indicated no significant difference between the forces estimated by both systems. However, abrupt changes in motion, such as lifting initiation, led to significant differences (p < 0.05) between the muscle forces. Furthermore, the maximum L5-S1 joint reaction force estimated using IMU data was significantly lower (p < 0.05) than those estimated by cameras during weight lifting and lowering. The study showed how kinematic errors from IMUs propagated through the musculoskeletal model and affected the estimations of muscle forces and joint reaction forces. Our findings showed the potential of IMUs for in-field ergonomic risk evaluations.

Online prediction of sustained muscle force from individual motor unit activities using adaptive surface EMG decomposition.

Decoding movement intentions from motor unit (MU) activities to represent neural drive information plays a central role in establishing neural interfaces, but there remains a great challenge for obtaining precise MU activities during sustained muscle contractions. In this paper, we presented an online muscle force prediction method driven by individual MU activities that were decomposed from prolonged surface electromyogram (SEMG) signals in real time. In the training stage of the proposed method, a set of separation vectors was initialized for decomposing MU activities. After transferring each decomposed MU activity into a twitch force train according to its action potential waveform, a neural network was designed and trained for predicting muscle force. In the subsequent online stage, a practical double-thread-parallel algorithm was developed. One frontend thread predicted the muscle force in real time utilizing the trained network and the other backend thread simultaneously updated the separation vectors. To assess the performance of the proposed method, SEMG signals were recorded from the abductor pollicis brevis muscles of eight subjects and the contraction force was simultaneously collected. With the update procedure in the backend thread, the force prediction performance of the proposed method was significantly improved in terms of lower root mean square deviation (RMSD) of around 10% and higher fitness (R2) of around 0.90, outperforming two conventional methods. This study provides a promising technique for real-time myoelectric applications in movement control and health.

Scaling of buccal mass growth and muscle activation determine the duration of feeding behaviours in the marine mollusc Aplysia californica.

The mechanical forces experienced during movement and the time constants of muscle activation are important determinants of the durations of behaviours, which may both be affected by size-dependent scaling. The mechanics of slow movements in small animals are dominated by elastic forces and are thus quasistatic (i.e. always near mechanical equilibrium). Muscular forces producing movement and elastic forces resisting movement should scale identically (proportional to mass2/3), leaving the scaling of the time constant of muscle activation to play a critical role in determining behavioural duration. We tested this hypothesis by measuring the duration of feeding behaviours in the marine mollusc Aplysia californica whose body sizes spanned three orders of magnitude. The duration of muscle activation was determined by measuring the time it took for muscles to produce maximum force as A. californica attempted to feed on tethered inedible seaweed, which provided an in vivo approximation of an isometric contraction. The timing of muscle activation scaled with mass0.3. The total duration of biting behaviours scaled identically, with mass0.3, indicating a lack of additional mechanical effects. The duration of swallowing behaviour, however, exhibited a shallower scaling of mass0.17. We suggest that this was due to the allometric growth of the anterior retractor muscle during development, as measured by micro-computed tomography (micro-CT) scans of buccal masses. Consequently, larger A. californica did not need to activate their muscles as fully to produce equivalent forces. These results indicate that muscle activation may be an important determinant of the scaling of behavioural durations in quasistatic systems.

Cost function criteria using muscle synergies: Exploring the potential of muscle synergy hypothesis.

BACKGROUND AND OBJECTIVE: Solving the redundant optimization problem for human muscles depends on the cost function. Choosing the appropriate cost function helps to address a specific problem. Muscle synergies are currently limited to those obtained by electromyography. Furthermore, debate continues regarding whether muscle synergy is derived or real. This study proposes new cost functions based on the muscle synergy hypothesis for solving the optimal muscle force output problem through musculoskeletal modeling. METHODS: We propose two new computational cost functions involving muscle synergies, which are extracted from muscle activations predicted by musculoskeletal modelling rather than electromyography. In this study, we constructed a musculoskeletal model for simulation using the "Grand Challenge Competition to Predict In Vivo Knee Loads" dataset. Muscle synergies were obtained using non-negative matrix factorization. Two cost functions with muscle synergies were constructed by integrating the polynomial and min/max criterion. Two new functions were verified and validated in normal, smooth, and bouncy gaits. RESULTS: The muscle synergies based on normal gaits were classified into four modules. The cosine similarities of the first three modules were all >0.9. In the normal and smooth gaits, the forces in most muscles predicted using the two new functions were within three standard deviations of the root mean square error for electromyographic comparisons. Predicted muscle force curves using the four methods as well as characteristic points (i.e., time points in the gait cycle when the significant difference was observed between normal and bouncy gaits) were obtained to validate their predictive capabilities. CONCLUSIONS: This study constructed two new cost functions involving muscle synergies, verified and validated the ability, and explored the potential of muscle synergy hypothesis.

Mitochondrial Transplantation Therapy Ameliorates Muscular Dystrophy in mdx Mouse Model.

Duchenne muscular dystrophy is caused by loss of the dystrophin protein. This pathology is accompanied by mitochondrial dysfunction contributing to muscle fiber instability. It is known that mitochondria-targeted in vivo therapy mitigates pathology and improves the quality of life of model animals. In the present work, we applied mitochondrial transplantation therapy (MTT) to correct the pathology in dystrophin-deficient mdx mice. Intramuscular injections of allogeneic mitochondria obtained from healthy animals into the hind limbs of mdx mice alleviated skeletal muscle injury, reduced calcium deposits in muscles and serum creatine kinase levels, and improved the grip strength of the hind limbs and motor activity of recipient mdx mice. We noted normalization of the mitochondrial ultrastructure and sarcoplasmic reticulum/mitochondria interactions in mdx muscles. At the same time, we revealed a decrease in the efficiency of oxidative phosphorylation in the skeletal muscle mitochondria of recipient mdx mice accompanied by a reduction in lipid peroxidation products (MDA products) and reduced calcium overloading. We found no effect of MTT on the expression of mitochondrial signature genes (Drp1, Mfn2, Ppargc1a, Pink1, Parkin) and on the level of mtDNA. Our results show that systemic MTT mitigates the development of destructive processes in the quadriceps muscle of mdx mice.

Four-compartment muscle fatigue model to predict metabolic inhibition and long-lasting nonmetabolic components.

Introduction: Computational muscle force models aim to mathematically represent the mechanics of movement and the factors influencing force generation. These tools allow the prediction of the nonlinear and task-related muscle behavior, aiding biomechanics, sports science, and rehabilitation. Despite often overlooking muscle fatigue in low-force scenarios, these simulations are crucial for high-intensity activities where fatigue and force loss play a significant role. Applications include functional electrical stimulation, motor control, and ergonomic considerations in diverse contexts, encompassing rehabilitation and the prevention of injuries in sports and workplaces. Methods: In this work, the authors enhance the pre-existing 3CCr muscle fatigue model by introducing an additional component of force decay associated with central fatigue and a long-term fatigue state. The innovative four-compartment model distinguishes between the short-term fatigued state (related to metabolic inhibition) and the long-term fatigued state (emulating central fatigue and potential microtraumas). Results: Its validation process involved experimental measurements during both short- and long-duration exercises, shedding light on the limitations of the traditional 3CCr in addressing dynamic force profiles.

Comparison of Synergy Extrapolation and Static Optimization for Estimating Multiple Unmeasured Muscle Activations during Walking.

Background: Calibrated electromyography (EMG)-driven musculoskeletal models can provide great insight into internal quantities (e.g., muscle forces) that are difficult or impossible to measure experimentally. However, the need for EMG data from all involved muscles presents a significant barrier to the widespread application of EMG-driven modeling methods. Synergy extrapolation (SynX) is a computational method that can estimate a single missing EMG signal with reasonable accuracy during the EMG-driven model calibration process, yet its performance in estimating a larger number of missing EMG signals remains unclear. Methods: This study assessed the accuracy with which SynX can use eight measured EMG signals to estimate muscle activations and forces associated with eight missing EMG signals in the same leg during walking while simultaneously performing EMG-driven model calibration. Experimental gait data collected from two individuals post-stroke, including 16 channels of EMG data per leg, were used to calibrate an EMG-driven musculoskeletal model, providing "gold standard" muscle activations and forces for evaluation purposes. SynX was then used to predict the muscle activations and forces associated with the eight missing EMG signals while simultaneously calibrating EMG-driven model parameter values. Due to its widespread use, static optimization (SO) was also utilized to estimate the same muscle activations and forces. Estimation accuracy for SynX and SO was evaluated using root mean square errors (RMSE) to quantify amplitude errors and correlation coefficient r values to quantify shape similarity, each calculated with respect to "gold standard" muscle activations and forces. Results: On average, SynX produced significantly more accurate amplitude and shape estimates for unmeasured muscle activations (RMSE 0.08 vs. 0.15,r value 0.55 vs. 0.12) and forces (RMSE 101.3 N vs. 174.4 N,r value 0.53 vs. 0.07) compared to SO. SynX yielded calibrated Hill-type muscle-tendon model parameter values for all muscles and activation dynamics model parameter values for measured muscles that were similar to "gold standard" calibrated model parameter values. Conclusions: These findings suggest that SynX could make it possible to calibrate EMG-driven musculoskeletal models for all important lower-extremity muscles with as few as eight carefully chosen EMG signals and eventually contribute to the design of personalized rehabilitation and surgical interventions for mobility impairments.