Study of force development in resting and activated muscles during velocity dependent stretching

The time course in force development of gastrocnemius muscles isolated from frog (Rama esculenta) were investigated under the effect of stretching with different velocity and time characteristics. Time course of stretching were linear, parabolic and exponential. It was found that the changes in force development of both resting and activated muscles depend on the time characteristics of the stretching applied. Corresponding to data in literature, the length-tension curve of resting muscle in dynamic stretching differs from the length-tension curve measured in static circumstances, but the shape of the length-tension curve is not essentially affected by the change of the average rate of stretching with a duration of 0.1-0.4 s and constant size (0.2-0.25 lo, lo is the reference length). The results can be interpreted with the aid of a muscle model as well. In the case of a contracted muscle, if the stretching and the stimulation of the muscle begin at the same time, the active force development reaches its maximum approximately at about half-length of maximum stretch.