The time course of the effects of constant-angle and constant-torque stretching on the muscle-tendon unit

The purpose of the present study was to examine the time course of passive range of motion (PROM), passive torque (PAS(TQ)), and musculo-tendinous stiffness (MTS) responses during constant-angle (CA) and constant-torque (CT) stretching of the leg flexors. Eleven healthy men [mean +/- standard deviation (SD): age=21.5 +/- 2.3 years] performed 16 30-s bouts of CA and CT stretching of the leg flexors. PROM, PAS(TQ), and MTS were measured during stretches 1, 2, 4, 8, and 16. For PROM and PAS(TQ), there were no differences between CA and CT stretching treatments (P>0.05); however, there were stretch-related differences (P<0.001). PROM increased following one 30-s bout of stretching (collapsed across CA and CT stretching) with additional increases up to 8min of stretching. PAS(TQ) decreased following one 30-s bout of stretching (collapsed across CA and CT stretching) and continued to decrease up to 4min of stretching. In contrast, only the CT stretching treatment resulted in changes to MTS (P<0.001). MTS decreased after one 30-s bout of CT stretching, with subsequent decreases in MTS up to 6min of stretching. These results suggested that CT stretching may be more appropriate than a stretch held at a constant muscle length for decreasing MTS.