A new framework for analysis of three-dimensional shape and architecture of human skeletal muscles

A new framework is presented for comprehensive analysis of the three-dimensional shape and architecture of human skeletal muscles from magnetic resonance and diffusion tensor imaging data. The framework comprises three key features: (1) identification of points on the surface of and inside a muscle that have a correspondence to points on and inside another muscle, (2) reconstruction of average muscle shape and average muscle fibre orientations, and (3) utilization of data on between-muscle variation to visualize and make statistical inferences about changes or differences in muscle shape and architecture. The general use of the framework is demonstrated by its application to three datasets. Analysis of data obtained before and after eight weeks of strength training revealed there was little regional variation in hypertrophy of the vastus medialis and vastus lateralis, and no systematic change in pennation angle. Analysis of passive muscle lengthening revealed heterogeneous changes in shape of the medial gastrocnemius, and confirmed the ability of the methods to detect subtle changes in muscle fibre orientation. Analysis of the medial gastrocnemius of children with unilateral cerebral palsy showed that muscles in the more-affected limb were shorter, thinner and less wide than muscles in the less-affected limb, and had slightly more pennate muscle fibres in the central and proximal part of the muscle. Amongst other applications, the framework can be used to explore the mechanics of muscle contraction, investigate adaptations of muscle architecture, build anatomically realistic computational models of skeletal muscles, and compare muscle shape and architecture between species.

Alterations of Extracellular Matrix Mechanical Properties Contribute to Age-Related Functional Impairment of Human Skeletal Muscles

Aging of human skeletal muscles is associated with increased passive stiffness, but it is still debated whether muscle fibers or extracellular matrix (ECM) are the determinants of such change. To answer this question, we compared the passive stress generated by elongation of fibers alone and arranged in small bundles in young healthy (Y: 21 years) and elderly (E: 67 years) subjects. The physiological range of sarcomere length (SL) 2.5–3.3 μm was explored. The area of ECM between muscle fibers was determined on transversal sections with picrosirius red, a staining specific for collagen fibers. The passive tension of fiber bundles was significantly higher in E compared to Y at all SL. However, the resistance to elongation of fibers alone was not different between the two groups, while the ECM contribution was significantly increased in E compared to Y. The proportion of muscle area occupied by ECM increased from 3.3% in Y to 8.2% in E. When the contribution of ECM to bundle tension was normalized to the fraction of area occupied by ECM, the difference disappeared. We conclude that, in human skeletal muscles, the age-related reduced compliance is due to an increased stiffness of ECM, mainly caused by collagen accumulation.

Effect of Aerobic Exercise With Blood Flow Restriction on Mitochondrial Dynamics Proteins of Human Skeletal Muscles

Background: Aerobic exercise with Blood Flow Restriction (BFR) plays an important role in skeletal muscle adaptation; however, the effects of this type of exercise on mitochondrial dynamics proteins are unclear. Objective The purpose of this study was to investigate the effect of aerobic exercise with and without BFR on mitochondrial dynamics proteins of human skeletal muscles. Methods: Participants were 5 young men (mean age, 33.4±2.30 years; mean weight, 79.64±10.49 kg; BMI, 26.24±2.27 kg/m2). They performed aerobic exercise with BFR (AE+BFR) and without BFR (AE) in two separate days at five 2-min sessions and 1 min rest between the sessions. Western Blot method was used to measure the protein levels of Mitofusin 2 (MFN2) and Dynamin-Related Protein 1 (DRP1) in skeletal muscles. Findings: AE+BFR (1.02±0.05 vs. 0.77±0.03) and AE (0.65±0.08 vs 0.57±0.03) significantly increased the mean MFN2 protein level compared to the pre-test mean values (P<0.05). AE+BFR (3.54±0.46 and 5.01±0.66) and AE (3.38±0.38 vs. 2.82±0.59) also significantly reduced the mean DRP1 level (P<0.05). Moreover, AE+BFR had greater significant effect on the mean levels of MFN2 (0.24±0.01 vs. 0.08±0.04) and DRP1 (-1.46±0.22 vs. -0.33±0.12) compared to AE (P<0.05). Conclusion: It seems that aerobic exercise with BFR is a strong stimulant for the improvement of skeletal muscle mitochondrial dynamics.

Modeling and Controller Design for Pneumatic Artificial Muscle for Ankle-Foot Orthotic Device

In the present era Electric motors are most commonly used actuators for various robotic and bio-robotic applications. However, the functioning of electric motor is not similar to human skeletal muscles. Also, the electric motors are prone to harm human beings in case of failure. Hence, the present work has focused on exploring a bio-inspired actuator, which functions similar to human skeletal muscles and is safe for human beings. The literature review has revealed that such an actuator is pneumatic artificial muscle (PAM). In the present work the researchers have focused on developing an efficient model and control strategy for PAM in order to use it for biorobotic applications. An experimental setup has been prepared to analyze the behavior of PAM for different speeds of operation and different loading conditions during inflation/ deflation. Based on the experimental datasets an experimental model of PAM and Proportional Pressure Regulator (PPR) has been developed using polynomial curve fitting tool of MATLAB. Then a switched mode feedback PID control strategy has been developed for PAM which takes care for the hysteresis behavior of PAM. The control strategy has been simulated to achieve the trajectory angle tracking of ankle joint during the complete gait cycle. The simulation of the proposed control strategy with the developed model has shown that the proposed approach works fairly well and the error in the ankle joint movement could be limited in the range of -0.8° to 0.6° for the complete gait cycle. The result obtained in the present study is similar to the results as reported in the literature. However, this could be achieved with less system complexity using simpler modeling technique and “switched mode feedback PID controller”, which has not been reported by any researcher till date