Effect of antispastic drugs on rapid force generation of spastic muscle

The effect of antispastic drugs, dantrolene sodium and baclofen, on the initiation of rapid knee extension was examined in 8 normal subjects and 8 patients with spastic hemiparesis. Three biomechanical variables, the latency between EMG onset of the rectus femoris and rise of tension (TLT), that between the rise of tension and the maximum tension of knee extension (FTmax) and the maximum tension attained (Fmax), were measured before and after administration of one of the drugs. Dantrolene sodium increased TLT, but did not change FTmax or Fmax. The increase of TLT was remarkable in the normal subjects and the non-affected side, compared to the affected side of the patients. Baclofen did not modify TLT or FTmax, but decreased Fmax. The decrease of Fmax was definite in the normal subjects while it was negligible in the affected side of the patients. Clinical implications and pathophysiological mechanisms of these results were discussed.