Effect of Tubocurarine on Human Soleus and Gastrocnemius Muscles

The effect of a bolus injection of tubocurarine (0.1‐0.13 mg × kg‐1 i. v.) was followed in six young male subjects by registration of the rectified smoothed electromyogram (rsEMG) from them. soleus (71±5.1 (s.e.mean) % slow twitch muscle fibers) and from the m. gastrocnemius (54±3.1% slow twitch muscle fibers). Volitional muscle strength was recorded in isometric plantar flexions with the knee fully (0°) extended where m. soleus and m. gastrocnemius both are active, and with the knee bent 90° where m. soleus is dominating force development. During maximal action of the drug, the rsEMG from the soleus muscle was reduced to 30±4.0% of the control value, while the rsEMG from the gastrocnemius muscle was reduced to 53±5.2% (P<0.01). Muscle strength with the knee extended showed 53±7.5% force left, while 44±6.4% of the muscle strength remained when the knee was bent (P<0.01). The results suggest that tubocurarine aflects human muscles in proportion to their slow twitch muscle fiber content.