Purpose: The purposes of the this study were to determine whether stretch-induced strength loss was muscle length dependent (study 1) and whether passive stretching prior to eccentric exercise affected strength loss and pain on subsequent days (study 2). Methods: For study 1, knee flexion strength was measured isometrically (six angles) and isokinetically (eccentric and concentric) in 10 men (33 +/- 9 yr). The subjects then performed six 90-s static hamstring stretches, after which isometric and isokinetic strength were retested. For study 2, the dominant and nondominant legs of eight men (34 +/- 9 yr) were assigned to a stretch (six 60-s stretches) or control condition prior to eccentric hamstring exercise. Isometric strength and pain were assessed prior to, immediately after, and on the 3 d after exercise. Results: After stretching, strength was decreased by 17% at 80[degrees], 11% at 65[degrees], 5% at 50[degrees], 7% at 35[degrees], and 8% at 20[degrees], and it was increased by 6% at 5[degrees] (angle effect P < 0.01). Strength loss following eccentric exercise was less on the stretched versus the unstretched control limb at 37° (P < 0.05), but not at other angles (stretch by time by angle P < 0.01). Pain was not different between the stretched and the unstretched control limb (P = 0.94). Conclusion: Stretch-induced strength loss was dependent on muscle length, such that strength was decreased with the muscle group in a shortened position, but not with the muscle group in a lengthened position. Strength loss and pain after eccentric exercise were generally unaffected by prior stretching, with the exception that stretching prevented strength loss when assessed with the muscle in a lengthened position.
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