Age and Sex Effects on the Active Stiffness of Vastus Intermedius under Isometric Contraction

Cong-Zhi Wang,Yong-Ping Zheng,Tian-Jie Li,Wenxiu Shi,Yongjin Zhou,Jing-Yi Guo

doi:10.1155/2017/9469548

Abstract

Previously, a novel technique was proposed to quantify the relationship between the muscle stiffness and its nonfatigue contraction intensity. The method extended the measured range of isometric contraction to 100% maximum voluntary contraction (MVC) using an ultrasonic shear wave measurement setup. Yet, it has not been revealed how this relationship could be affected by factors like age or sex. To clarify these questions, vastus intermedius (VI) stiffness of 40 healthy subjects was assessed under 11 step levels of isometric contraction. The subjects were divided into four groups: young males, young females, elderly males, and elderly females (n = 10 for each). In a relaxed state, no significant difference was observed between the male and female subjects (p = 0.156) nor between the young and elderly subjects (p = 0.221). However, when performing isometric contraction, the VI stiffness of males was found to be significantly higher than that of females at the same level (p < 0.001), and that of the young was higher than the elderly (p < 0.001). Meanwhile, for two knee joint angles used, the stiffness measured at a 90° knee joint angle was always significantly larger than that measured at 60° (p < 0.001). Recognizing the active muscle stiffness of VI contributes to body stability, and these results may provide insight into the age and sex bias in musculoskeletal studies, such as those on fall risks.

Highlights

Skeletal muscle is the largest tissue within the fat-free human body mass
The results of the three-way analyses of variance (ANOVA) showed that the main effects of age (p = 0.01), sex (p < 0.001), and knee joint angle (p = 0.001) factors were all significant for the mean maximum voluntary contraction (MVC) torque
According to the estimated marginal mean values provided by the ANOVA method, the conclusion was that the mean MVC torque for males was larger than that for females; the values from young subjects were larger than those from elderly subjects; the values measured at the 90∘ knee joint angle were larger than those measured at 60∘

Summary

Introduction

Skeletal muscle is the largest tissue within the fat-free human body mass. The neuromuscular activity during muscle contraction has been studied in depth by means of electromyography (EMG) and mechanomyography (MMG) signals (e.g., [1, 2]). The higher risk of injury among females on their joints was found to be related to the sex differences of the skeletal muscle characteristics [9,10,11]. For voluntary muscle contraction under different joint angles, EMG activity and some morphology characteristics have been proved to change [12,13,14,15]. In addition to neuromuscular features and morphological characteristics, recently the mechanical properties of skeletal muscle have attracted more attention. Passive stiffness of muscle is important for the control of movement because it determines the muscle resistance to external perturbations, while active muscle stiffness plays a key role in both force generation and body movements

Methods

Results

Discussion

Conclusion