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Effects Of Contract-relax Versus Static Stretching On Strength Loss And The Length-tension Relationship

Sidse S. Balle1, S. Peter Magnusson, FACSM2, Malachy P. McHugh, FACSM1.

It is known that static stretching (SS) and contract-relax stretching (CRS) results in stretch-induced strength loss. After SS strength loss occurs at short, but not long muscle lengths, which is consistent with a shift in the length-tension relationship. Since CRS places additional stretch on the tendon we hypothesized that there would be a greater muscle length-specific effect of CRS versus SS.

PURPOSE: To determine the acute effects of SS versus CRS on strength loss and the length-tension relationship.

METHODS: 20 healthy people volunteered. Isometric hamstring strength was measured at 4 different knee joint angles (90°, 70°, 50° and 30° of flexion) before and after SS and CRS. One leg received SS and the contralateral received CRS, with side (right vs. left) and test order (SS vs. CRS) alternated using a Latin square randomized order. Stretching and strength testing took place in a dynamometer chair; back rest at 90°, test thigh elevated 50° from horizontal. SS was performed as 6 sets of 1 min with leg extended to maximal stretch tolerance. CRS was initiated with a 10 s submaximal (70%) isometric contraction performed at the point of maximal stretch tolerance and then held at this joint angle for a further 50 s. Effect of stretch technique on strength loss and the length-tension relationship was assessed using repeated measures ANOVA.

RESULTS: SS resulted in significant strength loss (p=0.025), which was more apparent at short versus long muscle length (Stretching*angle p<0.001; 11.7% at 90° p<0.01; 5.6% at 70° ns; 1.3% at 50° ns; -3.7% at 30° ns). CRS also resulted in significant strength loss (p<0.001), which was also more apparent at short versus long muscle length (stretching*angle p<0.001; 17.7% at 90°, 13.4% at 70°, 11.4% at 50°, all p<0.01, 4.3% at 30° ns). Stretch-induced strength loss (averaged across all angles) was greater (p=0.015) after CRS (11.7%) versus SS (3.7%). The muscle length effect on strength loss (length-tension relationship) was not different between CRS and SS (stretching*angle*stretching technique p=0.43).

CONCLUSIONS: Both SS and CRS resulted in stretch-induced strength loss, which was most apparent at short muscle lengths. 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.

Author affiliations:

1 Nicholas Institute of Sports Medicine and Athletic Trauma, Lenox Hill Hospital, New York, NY.

2 Institute of Sports Medicine Copenhagen, Bispebjerg Hospital, Copenhagen, Denmark.

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