Altered kinematics and muscle activities during half squats in people with ankle sprain history

To compare the lower limb angles and electromyogram (EMG) activities of lower limb muscles  during half squats and gait between copers and healthy controls.

Ten copers (21.6 ± 1.1 years, 3 females) and 10 controls (2.5 ± 2.8 years, 4 females) were included in the cross-sectional study. We compared angles of the thigh, shank, and foot calculated from inertial measurement units and EMG activities of the biceps femoris long head, rectus femoris, gastrocnemius, and tibialis anterior between copers and controls during half squats and gait. Statistical significance was set at ≤0.05 and 95% confidence intervals were used to identify the group differences. Cohen’s d effect sizes were calculated to evaluate the magnitude of the differences.

Copers had a previous ankle sprain an average of 4.9 ± 5.0 years ago. 

For half squats, copers demonstrated less thigh angle compared to healthy controls during decending phase (p ≦ 0.013) with an effect size of 0.67–1.35, whereas no significant differences for the shank and foot angles during decending phase (p≧ 0.054). Copers demonstrated less activity of biceps femoris long head, rectas femoris and tibialis anterior than healthy controls (p ≦0.022) with an effect size of 0.61–1.58. 

For gait, there were no significant group differences in lower limb angles and EMG  activities (p ≧ 0.106). 

Copers exhibited a restricted thigh rotational angle and less EMG activities compared with those exhibited by healthy controls during half squats, whereas no group differences in the lower limb angles and EMG activities during gait. Our study suggests the importance of assessing lower limb movements and EMG activities for copers to obtain efficient training effects, even if they do not experience instability and inconvenience in their daily lives.

When clinicians or coaches prescribe squatting exercises to copers, they need to determine whether copers are unintentionally restricting thigh rotation. By removing the unconscious restriction of thigh rotation, the targeted muscle activities of the intervention may increase, which may allow for more effective training.