Time-based effects of different duration stretching on hamstring muscle strength.

BACKGROUND Stretching is believed to decrease muscle strength. The aim of this paper was to examine the time course (immediate, and 10- and 20-minutes post-stretching) for the effects of 2, 4, and 8 minutes of static-stretching (SS) on the isometric maximum voluntary contraction force (MVCF) of hamstring muscles with a pretest-post-test experiment design. METHODS A total of 14 subjects with a mean age of 25 years participated in three experimental trials on three different days. Day I for static stretching for 2 minutes (SS 2 ), day II for 4 minutes (SS 4 ), and day III for 8 minutes (SS 8 ). Testing was conducted before (pre), immediately after (post), and at 10- and 20-minutes post-stretching. MVCF was measured using the strain gauze as the main outcome measure. RESULTS MVCF increased with SS 2 at 0 minutes (1.31%), 10 minutes (3.4%), and 20 minutes (4.1%) postintervention. MVCF increased with SS 4 at 0 minutes (1.13%), 10 minutes (9.6%) and 20 minutes (7.1%) postintervention. MVCF decreased with SS 8 at 0 minutes (2.9%), but increased at 10 minutes (1.86%) and 20 minutes (0.99%) postintervention. All these changes were not statistically significant (P>0.05). CONCLUSIONS In hamstring stretching, 2, 4 and 8 minutes increased MVCF, but results were not statistically significant. Thus, 2 to 8 minutes long-duration stretching exercises could safely be performed before a strength-training session.