Effects of contract-relax vs static stretching on stretch-induced strength loss and length-tension relationship

The purpose of this study was to determine the acute effects of contract-relax stretching (CRS) vs static stretching (SS) on strength loss and the length-tension relationship. We hypothesized that there would be a greater muscle length-specific effect of CRS vs SS. Isometric hamstring strength was measured in 20 healthy people at four knee joint angles (90 degrees, 70 degrees, 50 degrees, 30 degrees) before and after stretching. One leg received SS, the contralateral received CRS. Both stretching techniques resulted in significant strength loss, which was most apparent at short muscle lengths [SS: P=0.025; stretchingxangle P<0.001; 11.7% at 90 degrees P<0.01; 5.6% at 70 degrees nonsignificant (ns); 1.3% at 50 degrees ns; -3.7% at 30 degrees ns. CRS: P<0.001; stretchingxangle P<0.001; 17.7% at 90 degrees, 13.4% at 70 degrees, 11.4% at 50 degrees, all P<0.01, 4.3% at 30 degrees ns]. The overall stretch-induced strength loss was greater (P=0.015) after CRS (11.7%) vs SS (3.7%). The muscle length effect on strength loss was not different between CRS and SS (stretchingxanglexstretching technique P=0.43). Contrary to the hypothesis, CRS did not result in a greater shift in the length-tension relationship, and in fact, resulted in greater overall strength loss compared with SS. These results support the use of SS for stretching the hamstrings.