Passive Force, Angle, and Stiffness Changes after Stretching of Hamstring Muscles

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The purpose of this study was to investigate the influence of a 6-wk hamstring-stretching program on knee extension range of motion, passive resistive forces, and muscle stiffness.


A randomized control trial with repeated measures was undertaken with 43 school-age subjects. Hamstring extensibility was assessed by a passive knee extension test using a Kincom® isokinetic dynamometer. The intervention group participated in a 6-wk hamstring-stretching program. Stretches were performed 5 d·wk−1, once per day, held for 30 s, and for 3 repetitions. The control group did not stretch over the 6-wk intervention period. Measurements of hamstring extensibility were repeated at the end of the 6-wk intervention.


After the intervention period, significant (P < 0.05) increases in knee extension range of motion, passive resistive force, and stiffness were observed in the experimental group. No significant differences were observed in the control group’s findings for the same variables.


The findings of this study are consistent with other literature that shows periodic stretching programs over a 6-wk time frame produce significant changes in knee extension range of motion. The finding of increased stiffness in the new range of motion, gained as a result of the stretching program, provides some evidence that structural changes had occurred in the stretched muscles.

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