Achilles tendon and triceps surae muscle properties in athletes

Abstract

Purpose: The aim of this study was to investigate internal Achilles tendon (AT) displacement, AT shear wave velocity (SWV), and triceps surae (TS) muscle shear modulus in athletes. Methods: Internal AT displacement was assessed using ultrasound during isometric contraction. Shear wave elastography was used to assess AT SWV (m × s–1) at rest and TS muscle shear modulus (kPa) during passive ankle dorsiflexion. Results: A total of 131 athletes participated in this study. Athletes who had not exercised within two days had greater AT non-uniformity and mean anterior tendon displacement, and lower SWV at the proximal AT measurement site (mean difference [95% CI]: 1.8 mm [0.6–2.9], p = 0.003; 1.6 mm [0.2–2.9], p = 0.021; – 0.9 m × s–1 [– 1.6 to – 0.2], p = 0.014, respectively). Male basketball players had a lower mean AT displacement compared to gymnasts (– 3.7 mm [– 6.9 to – 0.5], p = 0.042), with the difference localised in the anterior half of the tendon (– 5.1 mm [– 9.0 to – 1.1], p = 0.022). Male gymnasts had a smaller absolute difference in medial gastrocnemius-minus-soleus shear modulus than basketball players (59.6 kPa [29.0–90.2], p < 0.001) and track and field athletes (52.7 kPa [19.2–86.3], p = 0.004). Intraclass correlation coefficients of measurements ranged from 0.720 to 0.937 for internal AT displacement, from 0.696 to 0.936 for AT SWE, and from 0.570 to 0.890 for TS muscles. Conclusion: This study provides a reliability assessment of muscle and tendon SWV. The relative differences in passive TS muscle shear modulus suggest sport-specific adaptation. Importantly, in healthy individuals, lower AT displacement after exercise may reflect the time required for tendon recovery.