The Dependence of Tension Relaxation in Skeletal Muscle on the Number of Sarcomeres in Series

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Abstract
Mulieri reported that the depths of both latency and tension relaxation changed only insignificantly when about half of a fiber bundle is wound tightly around a small glass rod and he concluded that the tension relaxation is not correlated with the number of sarcomeres in series in a frog muscle fiber. The dependency of the tension relaxation on the number of sarcomeres in series was reinvestigated with Rana temporaria using Mulier''s method and other independent methods. When Mulieri''s experimental procedure was repeated, his result was reproduced. In the other methods used the tension relaxation was proportional to the number of sarcomeres in series which were activated initially. This result was also obtained by introducing a slight modification to the procedure used by Mulieri. The results could be understood equally well if the latency relaxation was caused by a definite elongation rather than an increase in compliance of the fiber.