Abstract
[Purpose] Muscle quantity (e.g., cross-sectional area) and quality (e.g., muscle adipose tissue), which are muscle strength determinants, can be assessed using ultrasonography. The study aimed to investigate the changes in the quantity and quality of the peroneus longus and evaluate evertor strength in legs with chronic ankle instability (CAI). Furthermore, the associations among cross-sectional area, echogenicity, evertor strength, and frequency of ankle sprain were examined. [Participants and Methods] Nine males with CAI in unilateral legs were the voluntary participants in this study. The cross-sectional area of the peroneus longus, echogenicity, and evertor strength were measured for all the participants on the sides with CAI and that without. [Results] No significant difference in cross-sectional area was observed between the sides. Significant differences in echogenicity (higher on the CAI side) and evertor strength (lower on the CAI side) were observed between the sides. In addition, a moderate correlation was observed between echogenicity and increased sprain frequency on both sides. [Conclusion] Muscle adipose tissue increased, evertor strength decreased, and the cross-sectional area remained unchanged on the CAI side. The study results suggested that muscle adipose tissue increases with increasing frequency of ankle sprain.