Results
Descriptive Data on Size of the MTU Components and Knee Flexor Strength. BFlh proximal aponeurosis area varied considerably (higher than fourfold) between participants ranging from 7.5 to 33.5 cm (20.4 ± 5.4 cm, CV = 26.6%). This was a reflection of the fact that aponeurosis length was variable (16.7 ± 2.8 cm, range = 10.5–22 cm or 43%–75% of muscle length), and muscle–aponeurosis contact interface distance was also variable along the aponeurosis length (Fig. 3).
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Figure 3.
Muscle–aponeurosis contact interface distance along the length of the BFlh muscle (interpolated data every 5% of muscle length). A. Three individual participants (maximum, minimum, and typical (midrange) aponeurosis area). The circles indicate the relative muscle length where the aponeurosis width measurement was performed on each individual. B. Group mean ± SD.
Individual aponeurosis width measurements using a previously published method appeared to occur at an arbitrary point along the aponeurosis (Fig. 3A, i.e., not at peak aponeurosis width or a consistent point along the aponeurosis). Aponeurosis width measured in this way was 0.43 ± 0.24 cm (range = 0.19–1.22 cm, CV = 56.4%).
Participants had a mean BFlh ACSAmax of 13.6 ± 2.2 cm (CV = 16.2%), whereas their BFlh muscle volume was 214.7 ± 37.2 cm (CV = 17.3%). BFlh muscle length was 29.3 ± 2.6 cm. Large interindividual variability was also found in proximal BFlh/ST tendon CSA (0.43 ± 0.14 cm, range = 0.25–0.91 cm, CV = 32.3%). In respect of the strength measurements, knee flexor isometric strength was 131.0 ± 19.9 N·m while eccentric strength was 134.3 ± 24.9 N·m at 50°·s and 118.2 ± 21.6 N·m at 350°·s.
Relationships Between the Size of the Different MTU Components. BFlh proximal aponeurosis area was not related to BFlh ACSAmax (r = 0.04, P = 0.830; Fig. 4) or volume (r = 0.35, P = 0.055). Consequently, the aponeurosis/muscle area ratio also exhibited high variability (sixfold), being 83% smaller in one individual than another (range, 0.53 to 3.09; CV = 32.5%). BFlh proximal aponeurosis area presented a weak correlation with proximal BFlh/ST tendon CSA (r = 0.36, P = 0.049).
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Figure 4.
A scatter plot of BFlh proximal aponeurosis area and BFlh ACSAmax (n = 30). The individuals with the lowest and highest aponeurosis size (7.5 vs 33.5 cm, more than fourfold difference) had very similar-sized BFlh muscles (ACSAmax, 14.1 vs 13.3 cm) and thus aponeurosis/muscle size ratios of 0.53 versus 2.52.
Relationships Between the Size of the MTU Components With Knee Flexor Strength. Although isometric strength was related to BFlh muscle ACSAmax and tendon CSA, there was no relationship with aponeurosis area (Fig. 5). Eccentric strength at both slow and fast velocities was related to BFlh muscle ACSAmax but not to aponeurosis area or tendon CSA (Table 1). Finally, overall hamstring ACSAmax was related to isometric strength as well as to eccentric strength at 50°·s and 350°·s (Table 1).
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Figure 5.
Scatter plots between knee flexor isometric strength and BFlh ACSAmax (A), BFlh proximal aponeurosis area (B), and BFlh/ST proximal tendon CSA (n = 30) (C).