Answer
The tension generated by a muscle when it contracts, and therefore the force it produces, depends on how contracted or how stretched the muscle was prior to stimulation. If a fiber was already contracted to some degree before stimulation, its thick filaments would be closer to the Z-discs than they would be in an uncontracted resting muscle. The fiber would not be able to contract much farther before the thick filaments made contact with the Z-discs and stop moving : the resultant contraction would be weak. However, if before stimulation, a muscle fiber was extremely stretched , there would be very little overlap between thick and thin filaments in the relaxed state. In this situation, the myosin filaments would have difficulty grasping the thin filaments; again, the contraction that resulted would be weak.
Work Step by Step
The length of the muscle fiber for generating optimum tension obtains in a situation between these two extremes. -- with sarcomere 2,0 -2.5 um long. If before stimulation, the sarcomeres are at least 60% shorter or 125% longer than the optimal lengths , the myofibers would develop no tension in response to stimulation.
