The acute effects of dynamic and static stretching during warm-up on muscle architecture and performance in children

Background There is insufficient evidence regarding the acute effects of warm-up with dynamic stretching (DS) and static stretching (SS) on children. Objective The aim of this study was to explore how two common warm-up protocols—DS and SS—acutely influence muscle architecture and key physical performance, including explosive strength and flexibility, in children. Methods Twenty-one healthy children (age: 10.6 ± 0.73 years) voluntarily participated in this study. Each participant completed two warm-up sessions on separate days, consisting of 3 min of light jogging followed by either a DS or SS protocol. Assessments included biceps femoris muscle architecture (fascicle length, pennation angle and muscle thickness), 50-meter sprint (SPR50m), standing long jump (SLJ), and sit-and-reach (SR) tests. All variables were measured at four time points: before stretching, immediately after stretching, and at 10- and 30-min post-stretching. Results Results showed an increase in SPR50m, SLJ, and SR performance after warm-up with DS, lasting for 10 min ( p < 0.01). SPR50m, SLJ, and muscle pennation angle decreased after SS ( p < 0.05), while SR and muscle fascicle length increased ( p < 0.05). Immediately after warm-up, SR and muscle fascicle length were higher in SS than DS ( p < 0.05), while SPR50m, SLJ, and pennation angle were lower in SS ( p < 0.01). Conclusions Similar to adults, warm-up with DS is more suitable for activities that require explosive power and strength in children. In contrast, when the primary goal is to improve flexibility, warm-up with SS can be selectively used. Therefore, the selection of warm-up stretching for children should be guided by the specific performance demands of the subsequent activities