DataSet. Datos BSSR en Primaria.

The 3 experimental groups performed hamstring stretches for 4 minutes during each Physical Education class over a two-month period, 2 sessions per week (8 weeks, for a total of 16 PE sessions), with a stretch duration of 20 seconds, utilizing the static passive technique. The EG1 performed the stretching exercises during warm-up (4 minutes), the EG2 performed the stretching exercises during cool-down (4 minutes) and finally the EG3 performed the stretching exercises during warm-up (2 minutes) and cool-down (2 minutes) period.

The control group followed the standard class program of PE classes. Hamstring flexibility was measured using the BS-SR test before and after the program. The statistical significance level was set at p < 0.05.

All statistical analyses were performed using SPSS version 25.0 for Windows (IBM® SPSS® Statistics). Conclusion. The CDG that performed stretching in the cool down period is the one that achieved significant improvements ccompared with the WUG, MXG, and NSG (p ≤ 0.01; d = 0.50-0.71).