Muscular Co-Activation of the Knee Flexor-Extensor Muscles During Multi-Directional Perturbations

Aim: The purpose of this study was to investigate co contraction pattern of knee flexor-extensor muscles during multidirectional destabilizing knee perturbations. Thirteen healthy men (mean ± SD; age = 24.2 ± 2.2 yr) without previous knee injury participated in the study. Surface EMG signals were recorded from seven locations distributed over the knee flexor and extensor muscles by circular AgAgCl surface electrodes (Ambu Neuroline, conductive area 28 mm ) during unexpected knee perturbation in backward-forward, 2 medial-lateral and downward directions. Results revealed that muscle reflex activity was dependent on muscle (P <0.05) perturbation direction (P <0.05) and interaction between muscle and perturbation direction (P <0.05). The amplitude of EMG in backward direction was significantly larger than other directions (P < 0.05). The amplitude of EMG of the lateral head of gastrocnemius, semitendinosus, vastus lateralis and vastus medialis muscle were larger in backward direction compared with four other directions (P < 0.05). Likewise, vastus lateralis, semitendinosus and the lateral head of gastrocnemius produced larger EMG amplitude in forward direction (P <0.05). However the EMG activity of the knee muscle was not significantly different between medial, lateral and downward perturbations (P > 0.05). In conclusion these results indicate that central nervous system use different neural strategies in activating muscles around knee joint during postural perturbation in the saggital plan that challenges knee stability.