Sex differences in hamstring muscle and aponeurosis thickness

This study investigated the sex-related differences in aponeurosis and muscle thickness of the biceps femoris long head (BFlh) and semitendinosus (ST). Forty physically active individuals (20 males and 20 females) were recruited. Using ultrasound imaging, muscle and aponeurosis thickness was measured at six sites along the muscle length for both superficial and deep aponeuroses of the BFlh and ST in prone position. A computational image segmentation approach was used to analyze ultrasound images which generated ∼ 360 data points per participant. A two-way statistical parametric mapping (SPM) analysis was implemented to assess the sex and inter-muscular differences in aponeurosis and muscle thickness. SPM revealed no consistent significant sex-related differences in superficial or deep aponeurosis thickness of ST and BFlh (p > 0.05). Males presented greater overall muscle thickness throughout the thigh (p < 0.001), resulting in a higher muscle-to-superficial-aponeurosis and muscle-to-deep-aponeurosis ratios, particularly in the proximal regions p = 0.003-0.050 and p < 0.001-0.032, respectively). Inter-muscular differences were observed, with the ST exhibiting greater superficial aponeurosis thickness and lower muscle-to-aponeurosis ratio (p < 0.001-0.035), whereas no differences were detected in deep aponeurosis thickness (p > 0.05). Although males having greater muscle thickness, aponeurosis thickness did not differ between sexes, suggesting disproportionate scaling between muscle and connective tissues. These findings highlight the importance of considering sex-specific variations in aponeurosis morphology when designing prevention and rehabilitation strategies.