Quantitative EMG analysis to investigate synergistic coactivation of ankle and knee muscles during isokinetic ankle movement. Part 1: time amplitude analysis.

Synergy generally refers to the coordinated action of several motor elements to produce a specific motor task, either intentionally or automatically. One example is motor irradiation, a sudden spread of synergistic muscular coactivation resulting from a forceful single joint movement. To investigate this type of synergy pattern, a quantitative EMG approach was employed to characterize explicit neuromuscular synergy in the ankle-knee complex during maximal ankle isokinetic contraction. In the present study, isokinetic ankle contractions, both dorsiflexion and plantarflexion, at four different speeds (30, 60, 120, and 240 degrees/s) were studied in a normal adult population (N=11) to assess synergistic coactivation of the prime movers (tibialis anterior and gastrocnemius) and irradiated muscles (ipsilateral and contralateral rectus femoris and biceps femoris) of the ankle-knee complex. Electromyographic signals were collected with surface EMG electrodes and processed with traditional time-amplitude analysis to examine specific neural control strategies. The data generally supported several empirical assumptions common to neurological facilitation techniques. (1) Motor irradiation to the knee muscles due to ankle muscle isokinetic contraction was strongly directionally dependent. (2) Motor irradiation to the ipsilateral knee muscles due to ankle isokinetic contraction was speed dependent. (3) The prime movers demonstrated a similar control strategy, irrespective of different contraction speeds.