Load-strain characteristics of distal (deep) and proximal (superficial) aponeuroses were determined in vivo for human tibialis anterior muscle (TA). Seven male subjects exerted isometric dorsiflexion torque from relaxation to voluntary maximum while elongation of both aponeuroses of TA was determined by ultrasonography. Two positions (end of the muscle belly and a proximal part) and one position (distal part) were scanned for the deep and superficial aponeuroses, respectively, and tendinous movements of the respective positions were determined. Based on the tendinous movements, elongation of each aponeurosis was determined. Both aponeuroses were elongated significantly, and there was no significant difference in strain between the deep (3.3 ± 0.8%) and superficial (3.0 ± 0.5%) aponeuroses. In addition, there was a significant linear relationship between strain of deep and superficial aponeuroses. It was suggested that both aponeuroses similarly act as an elastic component in pennate muscles.
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