Physical Education-Based Stretching During Warm-Up, Cool-Down, or Both on Back-Saver Sit-and-Reach Scores in Schoolchildren

<b>Objectives:</b> The aim of this study was to compare the effects of eight-week hamstring stretching programs, implemented at different times during physical education classes (i.e., warm-up, cool-down, and both periods), on primary schoolchildren's back-saver sit-and-reach scores. <b>Methods:</b> A total of 275 schoolchildren (141 females and 134 males; age 8.82 ± 1.63 years) were divided into four groups: the WUG performed stretching during warm-up, the CDG during cool-down, and the MXG during both. The NSG followed the standard classes of physical education without any stretching. During physical education classes WUG, CDG, and MXG performed a 4 min stretching program twice a week. Hamstring extensibility was assessed before and after the program using the back-saver sit-and-reach test. <b>Results:</b> The CDG is the one that achieved statistically significant improvements compared with the WUG, MXG, and NSG (<i>p</i> ≤ 0.01; d = 0.50-0.71). Moreover, the CDG statistically increased the percentage of schoolchildren achieving healthy hamstring extensibility from pre-intervention (49%) to post-intervention (66%). <b>Conclusions:</b> This knowledge could guide teachers to design programs that guarantee feasible and effective development of hamstring extensibility in the physical education setting.