This study measured peak force (PF), peak rate of force development (PRFD), peak power (PP), concentric impulse, and eccentric impulse during static jump (SJ), countermovement jump (CMJ), and drop jump (DJ) in youth athletes to examine changes in vertical jump power with progressively greater eccentric preloading in relation to age, maturity, and muscle mass. Twenty-one males ranging from 6 to 16 years old performed the following vertical jumps in a random order: SJ, CMJ, and DJ from drop heights of 20, 30, and 40 cm (DJ20, DJ30, and DJ40, respectively). Measurements included PF, PRFD, PP, eccentric impulse, and concentric impulse for each vertical jump condition. Maturity offset was calculated, while ultrasound images quantified thigh muscle cross-sectional area (CSA). PF and PRFD increased from CMJ to DJ20. PP increased from SJ to CMJ. Concentric impulse remained unchanged, but eccentric impulse increased systematically from across jumps. The change in PP from SJ to CMJ was correlated with age, height, weight, maturity offset, and CSA. The CMJ resulted in the greatest concentric PP with the least amount of eccentric preloading. The inability of young athletes to translate the energy absorbed during the eccentric phase of the stretch-shortening cycle of DJs may be influenced by growth and development.

Purpose This study examined changes in vertical jump performance with progressively greater eccentric pre-loading in relation to growth and development in young female athletes. Methods Twenty young female athletes ranging from 9 to 17 years old performed the following vertical jumps in random order: static jumps (SJs), counter-movement jumps (CMJs), and drop jumps (DJs) from drop heights of 20, 30, and 40 cm (DJ20, DJ30, and DJ40, respectively). Measurements included peak force (PF), peak rate of force development (RFD), peak power (PP), eccentric impulse (ECC), and concentric impulse (CON). Measurements of growth included age, maturity offset, height, body mass, fat-free mass, and thigh muscle cross-sectional area (CSA). Results PF increased from the SJ-DJ20 (P ≤ 0.009), then plateaued from DJ20-DJ40 (P = 1.000). RFD remained the same from SJ-CMJ (P = 1.000), increased from CMJ-DJ20 (P < 0.001), and plateaued from DJ20-DJ40 (P = 0.874). PP increased from the SJ-CMJ (P < 0.001), then plateaued from the CMJ-DJ40 (P ≥ 0.486). CON remained the same across all vertical jumps (P = 1.000), while ECC increased from the SJ-DJ40 (P ≤ 0.038). Jump height (JH) increased from the SJ-CMJ (P < 0.001), decreased from CMJ-DJ20 (P < 0.001), and plateaued from DJ20-DJ40 (P = 1.000). The change in PP from the SJ-CMJ (ΔCMJ-SJ) was related to all measurements of growth except CSA (r = 0.558-0.815). Conclusion Young females produced greater power during the CMJ than SJ, but equivalent power from the CMJ-DJ40, despite increases in ECC. Additionally, ΔCMJ-SJ was not related to CSA, which suggests other underlying mechanisms affect stretch-shortening cycle utilization in young female athletes.

Gillen, ZM, Miramonti, AA, McKay, BD, Leutzinger, TJ, and Cramer, JT. Test-retest reliability and concurrent validity of athletic performance combine tests in 6-15-year-old male athletes. J Strength Cond Res 32(10): 2783-2794, 2018-Athletic performance combine tests are used by high school, collegiate, and professional American football programs to evaluate performance; however, limited evidence is available on performance combine test results in youth athletes. The purposes of this study were to report test-retest reliability statistics and evaluate concurrent validity among combine performance tests in 6-15-year-old male athletes. Sixty-nine young male athletes (mean ± SD; age = 10.9 ± 2.1 years, height = 154.4 ± 13.6 cm, body mass = 46.8 ± 16.0 kg) were divided into 3 age groups: 6-9 years (n = 16), 10-11 years (n = 26), and 12-15 years (n = 27). Participants completed 2 attempts of the vertical jump (VJ), broad jump (BJ), pro-agility (PA), L-cone (LC) drill, and 10-, 20-, 40-yd dashes. The results indicated that the older age groups performed better on most performance assessments compared with the 6-9-year group (p ≤ 0.05). The combine tests demonstrated consistently adequate reliability for all age groups, except for the 10-yd dash, which was deemed unreliable. Evidence of concurrent validity, and possible measurement redundancy were observed in the VJ vs. BJ, PA vs. LC, and 20 vs. 40 yd, but zero- and first-order partial correlations suggested that only the PA and LC were redundant, and the PA may be superior for this age group over the LC. Although the VJ and BJ provide independent performance information regarding lower-body power, questions regarding the redundancy of the 20 vs. 40 yd remain unanswered from a measurement perspective.

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