The influence of muscle stretch on tension of its twitch, unfused and fused tetanus in rat medial gastrocnemius

The relationships between muscle stretch and muscle tension generated in non-potentiated and potentiated twitches, unfused and fused tetani, were investigated in 11 rats under pentobarbital anaesthesia. Highest tensions of twitches and of fused tetani were reached when the muscle was stretched up to a similar tension (of about 0.5 N). The highest tension of unfused tetani required a stronger stretch of the muscle (about 0.7 N). This phenomenon can be explained by a prolonged contraction accompanying muscle stretching. This prolongation increases the fusion of tetani as well as its tension. Moreover, the experiments showed that twitches potentiated by a preceding stimulation developed highest tension id a significantly less stretched muscle than non-potentiated twitches. The results show that optimal mal muscle stretch may depend on the fusion of muscle fiber tetani and can change in relation to the potentiation of tension.