Quantitative analysis of variation in muscle internal parameters in crab-eating macaques (Macaca fascicularis)

Abstract

The internal parameters of muscle used to calculate physiological cross-sectional area (PCSA), i.e. muscle mass (MM), muscle fascicle length (MFL), and muscle pennation angle (Θ), were investigated for 23 forelimbs dissected carefully from 12 crab-eating macacques (Macaca fascicularis). The aims of this study were (1) to investigate how the postures of the limbs stored in formalin affect the muscle internal parameters (MM, MFL, Θ) required to calculate PCSA; (2) to quantify the variation in MM, MFL, Θ, and PCSA by determining the coefficient of variation (CV) for each parameter; (3) to validate evidence whether or not normalization using sarcomere length is valid considering the effects of differences in forelimb postures of specimens preserved in formalin on muscle internal parameters; (4) to validate evidence whether or not it is possible to compare MM, MFL, and PCSA values obtained here with those from previous similar studies; and finally (5) to devise a statistical criterion that can be applied to other studies. The results indicate that MM and Θ were not affected by differences in the positions of formalin-preserved specimens. In contrast, the values of MFL were strongly affected by the limb posture of the fixed specimen such as the elbow flexion or extension, the medial or lateral rotation of the arm, and supination or pronation of the forearm. The values of CV for the normalized MM, normalized MFL, and normalized PCSA were high, whereas that for cos Θ was low (around 5%). This indicates that the limb posture of the fixed specimen can be disregarded when measuring the muscle pennation angle. The muscle parameters obtained in the present study were compared with those in earlier studies and also discussed with reference to their data spread. © 2009 The Anthropological Society of Nippon.