A form of the sliding filament model is presented to simulate the experimentally observed phenomena when a contracting muscle is subjected to mechanical stretches. It is assumed that the cross bridges can be extended to provide extra tension and that they can be broken if a critical limit of extension IS exceeded. Passive components, including non-linear parallel elasticity are incorporated in the model. Such effects as short-range stiffness, the slip effect and excess tension after mechanical stretch can be simulated. The simulations are compared with our own experimental tests on frog sartorious muscle and with previously reported results from other muscle preparations.