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°, 11% at 65°, 5% at 50°, 7% at 35°, and 8% at 20°, and it was increased by 6% at 5° (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.