Evaluation of Muscle Hardness by Indentation Method

―Dependence on Isometric Contractile Force and Effect of Muscle Fatigue―

Abstract

The purpose of this study was to investigate muscle hardness related to isometric contractile level and muscle fatigue by the indentation method. The first experiment involved fifteen healthy volunteers. Their upper arms were indented at elbow angles of 0, 45 and 90 degree varying isometric contractile force from 0 to 100% MVC, every 10%. The indentation depth, reaction force and isometric contractile force were recorded. The relationship between the indentation depth and the reaction force was approximated well with the proposed model and the elastic indices were estimated. The elastic indices were more proportional to the isometric contractile level than other indices using linear approximation of the force-indentation curve. The relationship between the elastic indices and isometric contractile levels did not depend on the elbow angle.

In the second experiment, the elastic indices and relative blood flow change after repetitive eccentric-concentric exercises (40% and 20% MVC) were investigated. Both the elastic indices and the relative blood flow change were high just after the exercises and then decreased. However the elastic indices decreased more rapidly than the relative blood flow change. The results of this study suggested that the blood flow change affected the muscle hardness but there would be other mechanisms to determine the muscle hardness.