Automatic analysis of EMG (T/A analysis) and invasive muscle fiber conduction velocity in situ (MFCV) were performed in 15 patients after traumatic lesions of the knee and immobilization with quadriceps atrophy. T/A analysis showed transient reduced number of turns, consistent with inhibition of quadriceps motoneurons, that recovered within the first 2 weeks after the plaster cast had been removed. MFCV was significantly slowed and showed a gradual improvement, reaching normal values after 6 weeks. These results suggest that decrement in activated motor units may be the cause of the disproportionate weakness of the quadriceps muscle on the first days after immobilization by the plaster cast. The recovery of MFCV was related with functional improvement of strength after the first weeks.
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