Tension changes during and after stretch in frog muscle fibres.

1. Small fibre bundles from the semitendinosus muscles of the frog were stretched during tetanic stimulation, and the resulting tension changes were studied over a wide range of stretch velocities from 0.1 to 150 cm/sec (0.1-100 length/sec). The experiments were performed within the range of fibre lengths where the resting tension was negligible.2. With stretch velocities of more than 30 cm/sec (20 length/sec), the tension rose abruptly at first, and then started to fall while the stretch still continued, indicating the ;slip' of the contractile component. When the fibres were stretched at 80-150 cm/sec (70-100 length/sec), the tension fell quickly below the initial isometric level at the end of the stretch, and then began to rise again to the initial isometric value.3. Following stretches of 30-60 cm/sec (20-50 length/sec), the tension showed a delayed transient rise. The delayed rise of tension became more marked as the amount of stretch was increased.4. In some preparations, oscillatory tension changes were observed following stretches of 50-100 cm/sec (40-70 length/sec).5. The tension developed above the isometric level during moderate-velocity stretches of less than 15 cm/sec (10 length/sec) increased by lowering temperature, and showed a tendency to decay when the stretch velocity was suddenly reduced during a stretch.6. These results are discussed in relation to the sliding filament hypothesis, which provides an explanation for the findings of the present work.