Interactive effects of drop height and visual deprivation on kinematic and electromyographic characteristics during single-leg landing in individuals with functional ankle instability.

UNLABELLED: To investigate the interactive effects of landing height and visual feedback on the kinematic and electromyographic (EMG) strategies of functional ankle instability (FAI) individuals during single-leg drop landings.

METHODS

Twelve male participants with unilateral FAI performed single-leg drop landings from three heights (15, 30, and 45 cm) under visual presence (VP) and visual deprivation (VD). Kinematics and EMG activity of the vastus lateralis (VL), semitendinosus (ST), tibialis anterior (TA), and lateral gastrocnemius (LHG) were analyzed using a 2 × 2 × 3 (Limb × Vision × Height) repeated-measures ANOVA.

RESULTS

Three-way interactions were identified in knee flexion at initial contact, pre-landing hip angular velocity, and pre-activation of the VL and TA (p < 0.05). Under VD, the unstable side failed to modulate knee flexion and TA pre-activation between 15 cm and 30 cm, whereas the stable side maintained distinct height-dependent gradients. ST and LHG activation primarily exhibited height main effects (p < 0.05), although a Vision × Height interaction was found for LHG (p = 0.013), with higher activation under VD at 30 cm. Post-landing, TA exhibited a "phase-reversal," with significantly higher activation under VD than VP (p < 0.001). Furthermore, the stable side demonstrated significantly higher post-landing TA activation and ankle co-contraction than the unstable side under VD conditions (p < 0.05).

CONCLUSION

Visual deprivation disrupts feedforward preparation and height-modulation strategies in FAI individuals, particularly at moderate mechanical loads (30 cm). The observed temporal shift from proactive pre-activation to reactive feedback-driven compensation, coupled with bilateral asymmetries, highlights a maladaptive sensorimotor reorganization that may increase the risk of recurrent injury.