# Does a Greater Hamstring Muscle Thickness Mean a Greater Aponeurosis Thickness?
## 4 Discussion
### Hamstrings' Morphological Characteristics Varied Across Individuals  
The present results suggest significant interindividual (CV range 20.93-31-82%, Table 2) variability in aponeurosis thickness, as indicated by the density distribution plots. Similarly, [PERSON] et al. [13] reported up to a fourfold variability in the proximal BFlh  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Measurement Site** & \multicolumn{3}{c}{**Muscle**} & \multicolumn{3}{c}{**Superficial Aponeurosis**} & \multicolumn{3}{c}{**Deep Aponeurosis**} \\ \hline  & \multicolumn{2}{c}{**BFlh**} & \multicolumn{2}{c}{**ST**} & \multicolumn{2}{c}{**BFlh**} & \multicolumn{2}{c}{**ST**} & \multicolumn{2}{c}{**BFlh**} & \multicolumn{2}{c}{**ST**} \\ \cline{2-11}  & **Mean** & **Max** & **Mean** & **Max** & **Mean** & **Max** & **Mean** & **Max** & **Mean** & **Max** & **Mean** \\ \hline Proximal & 25.98 & 25.90 & 22.82 & 23.56 & 20.93 & 27.70 & 23.33 & 24.24 & 24.75 & 31.82 & 26.32 & 26.90 \\ \hline Proximal–Middle & 22.70 & 21.94 & 20.01 & 18.10 & 31.40 & 28.00 & 22.54 & 24.41 & 30.76 & 28.78 & 27.00 & 28.90 \\ \hline Middle & 21.26 & 17.11 & 14.53 & 13.97 & 26.64 & 26.48 & 19.37 & 21.10 & 29.86 & 25.31 & 23.22 & 21.22 \\ \hline Distal–Middle & 16.88 & 15.49 & 14.69 & 14.40 & 26.46 & 22.71 & 20.07 & 22.37 & 31.52 & 29.12 & 25.47 & 31.15 \\ \hline Distal & 21.20 & 19.54 & 17.45 & 16.49 & 22.19 & 29.69 & 24.88 & 21.32 & 24.75 & 28.68 & 24.64 & 27.25 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Coefficient of variation (%) for the mean and maximum measurements of the muscle as well as the superficial and deep aponeurosis thickness of the biceps femoris long head (BFlh) and semitendinosus (ST) muscles across five measurement sites (\(n=50\)).  
aponeurosis dimensions across individuals, suggesting a high degree of heterogeneity in structural characteristics that could potentially influence hamstring mechanics. This high degree of variability (Table 2) may further influence the overall correlation values between muscle and aponeurosis thickness and could help explain the generally low correlations observed in this study. The present results extend the previous findings by demonstrating that both the superficial and deep aponeuroses exhibit high variability across young males and females at different regions of the hamstring muscles.  
The variability observed in this study may reflect both intrinsic factors, such as muscle [19] and tendon architectural differences [21; 22], and extrinsic factors, including previous injuries, training background, and adaptive remodeling [13; 14; 15; 16]. For instance, [PERSON] et al. [15] identified significant increases in aponeurosis volume in previously injured limbs, likely due to scar formation or altered loading patterns following injury. From a clinical perspective, this interindividual variability complicates the establishment of universal criteria for aponeurosis size in injury risk prediction. Instead, our findings advocate for personalized evaluations that consider the unique structural and functional characteristics of an individual's muscle-aponeurosis complex.