Sand vs. Track. Surface-based training integration enhances vertical jumping peak power in U-15 track and field female athletes.

Purpose: Exercising on sand surfaces holds unique beneficial characteristics for athletic performance, such as augmenting pre-stretch mechanisms and stability in the quadriceps and calf muscles, increasing motor unit recruitment, and improving postural control, ultimately leading to optimized jumping mechanics. The purpose of this study was to inquire about the promising yet underutilized inclusion of sand- based training to enhance bio-motor development of the lower-limbs in youth female athletes. Methods: We recruited 15 female track and field competitors at the U-15 national level (age 14 ± 1.1 years, height 162 ± 3.8 cm, body mass 52 ± 4.8 kg, World Athletics scoring tables of 634 ± 61), randomly and equally dividing them in 3 groups (i.e., sand, track, and mixed). The training intervention consisted of 7 weeks (two sessions per week, 1h per session) of supplementary training, along with the usual regime of training and conditioning which was the same for the whole sample of participants. The surface-based training intervention consisted in a periodized bodyweight circuit, focused on plyometrics and power development of the lower limbs. Relative peak power (RPP, W / kg) performed in the counter movement jump test (CMJ) was employed as a measure of pre-post training intervention, and was calculated with a novel approach using the Physics Toolbox smartphone app. Results: Wilcoxon signed rank test for matched pairs indicated that the median RPP in CMJ was significantly higher post-training than pre-training for the sand group (48 (0.8) vs. 43.1 (2.3), W = 13, p < 0.05, effect size r = 0.74), and the mixed group (47.8 (4.8) vs. 41.2 (3.8), W = 14, p < .05, effect size r = 0.76), while no pre-post differences were found within the track group (43.7 (3.1) vs. 42.9 (1.4), W 0.5= , p = 0.44, effect size r = 0.42). It is worth mentioning the narrower distribution (IQR) of the sand group from pre to post-training intervention. Kruskal-Wallis test indicated statistically significant differences among groups only post-training intervention (H (2)= 15.18, p < 0.05, effect size ε2 = 0.66 ), further suggesting that the whole sample had similar baseline levels of RPP. Post-hoc analysis with Bonferroni adjustment revealed that significant differences (p < 0.05) were present between the sand vs. track groups, 48 (0.8) vs. 43.7 (3.1) W/kg, and between the mixed vs. track groups, 47.8 (4.8) vs. 43.7 (3.1) W/kg , with no significant differences between the sand vs. track groups. Conclusions: Even a relatively brief exposition to sand-based training may elicit profitable adaptations in maximal muscular power of developing female athletes. Integrating an exclusive training routine on sand also seems to "tighten" the power performance distribution across athletes of similar level. This information could be used in future research designs for both performance enhancement and injury prevention purposes.