Abstract
Elderly people often suffer from sarcopenia in their lower extremities, which gives rise to the increased susceptibility of fall. Comparing the mechanical properties of the knee extensor/flexors on elderly and young subjects is helpful in understanding the underlying mechanisms of the muscle aging process. However, although the stiffness of skeletal muscle has been proved to be positively correlated to its non-fatiguing contraction intensity by some existing methods, this conclusion has not been verified above 50% maximum voluntary contraction (MVC) due to the limitation of their measurement range. In this study, a vibro-ultrasound system was set up to achieve a considerably larger measurement range on muscle stiffness estimation. Its feasibility was verified on self-made silicone phantoms by comparing with the mechanical indentation method. The system was then used to assess the stiffness of vastus intermedius (VI), one of the knee extensors, on 10 healthy elderly female subjects (56.7±4.9 yr) and 10 healthy young female subjects (27.6±5.0 yr). The VI stiffness in its action direction was confirmed to be positively correlated to the % MVC level (R2 = 0.999) over the entire range of isometric contraction, i.e. from 0% MVC (relaxed state) to 100% MVC. Furthermore, it was shown that there was no significant difference between the mean VI shear modulus of the elderly and young subjects in a relaxed state (p>0.1). However, when performing step isometric contraction, the VI stiffness of young female subjects was found to be larger than that of elderly participants (p<0.001), especially at the relatively higher contraction levels. The results expanded our knowledge on the mechanical property of the elderly’s skeletal muscle and its relationship with intensity of active contraction. Furthermore, the vibro-ultrasound system has a potential to become a powerful tool for investigating the elderly’s muscle diseases.
Highlights
Sarcopenia refers to the degenerative decline of muscle strength in the elderly [1]
Since we found that the quadratic regression model had the best performance, the mean shear moduli across the ten subjects were fitted with the relative isometric contraction levels (% maximum voluntary contraction (MVC)) using a quadratic regression model
This demonstrated that the vibro-ultrasound system was feasible for measuring the stiffness of tissue-mimicking phantoms and could be used for monitoring the change of muscle stiffness in a large measurement range
Summary
Sarcopenia refers to the degenerative decline of muscle strength in the elderly [1]. It will significantly increase their risk of sudden falls and dramatically impact on their quality of life [2,3]. Fascicle length and pennation angle have been extensively investigated [4,5,6,7]. Some other studies applied biomedicine methods on elderly patients to investigate the fiber atrophy on different fiber types [8,9] and the phenomenon of ‘‘metabolic dysregulation’’, such as impaired oxidative defense and decreased mitochondrial function [10,11]
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