Effect of stretching on strength loss and pain after eccentric exercise.

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 degrees (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.

Effect of knee flexion angle on Achilles tendon force and ankle joint plantarflexion moment during passive dorsiflexion.

Early mobilization exercises are advocated following Achilles tendon (AT) repair, but forces on the repair during passive range of motion are unknown. The extent to which these forces change with flexion of the knee is also not known. Estimated AT forces were measured using 3 models: cadaveric, uninjured subjects, and in both legs of subjects 6 weeks following unilateral AT repair. For cadaveric testing, estimated AT force was recorded using a force transducer while cycling the ankle from 10 degrees plantarflexion to maximum dorsiflexion at 3 different knee flexion angles (0 degrees , 45 degrees , and 90 degrees ). For in vivo testing, subjects were seated in an isokinetic dynamometer, and their ankles passively cycled from plantarflexion to dorsiflexion with the knee extended and flexed 50 degrees . Passive plantarflexion moment recorded by the dynamometer was converted to AT force by estimating the AT moment arm. In the cadaveric model, knee flexion reduced estimated AT forces during dorsiflexion by more than 40% (P < .036). In vivo testing showed that estimated AT force was reduced in knee flexion in healthy subjects (P < .001) and in the uninvolved leg AT repair subjects (P = .021), but not in the AT repaired leg (P = .387). Normal AT showed a marked reduction in estimated AT force with knee flexion which was not present in repaired AT. This could be because of elongation of the repair, causing more slack in the tendon that would need to be taken up before force transmission occurs. ACFAS Level of Clinical Evidence: 4.