Effects of contract-relax vs static stretching on stretch-induced strength loss and length-tension relationship
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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; stretching x angle 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; stretching x angle 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 (stretching x angle x stretching 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.