An Investigation of the Immediate Effect of Static Stretching on the Morphology and Stiffness of Achilles Tendon in Dominant and Non-Dominant Legs

Aims: This study was undertaken to investigate the immediate effect of static stretching on normal Achilles tendon morphology and stiffness, and the different effect on dominant and non-dominant legs; and to evaluate inter-operator and intra-operator reliability of using shear-wave elastography in measuring Achilles tendon stiffness. Methods: 20 healthy subjects (13 males, 7 females) were included in the study. Thickness, cross-sectional area and stiffness of Achilles tendons in both legs were measured before and after 5-min static stretching using grey-scale ultrasound and shear-wave elastography. Inter-operator and intra-operator reliability of tendon stiffness measurements of six operators were evaluated. Results: Result showed that there was no significant change in the thickness and cross-sectional area of Achilles tendon after static stretching in both dominant and non-dominant legs (p > 0.05). Tendon stiffness showed a significant increase in non-dominant leg (p 0.05). The inter-operator reliability of shear-wave elastography measurements was 0.749 and the intra-operator reliability ranged from 0.751 to 0.941. Conclusion: Shear-wave elastography is a useful and non-invasive imaging tool to assess the immediate stiffness change of Achilles tendon in response to static stretching with high intra-operator and inter-operator reliability.