Hopping, skipping, jumping and sprinting are common tasks in both active play and competitive sports. These movements utilise the stretch-shortening cycle (SSC), which is considered a naturally occurring muscle action for most forms of human locomotion. This muscle action results in more efficient movements and helps optimise relative force generated per motor unit recruited. Innate SSC development throughout childhood and adolescence enables children to increase power (jump higher and sprint faster) as they mature. Despite these improvements in physical performance, the underpinning mechanisms of SSC development during maturational years remain unclear. To the best of our knowledge, a comprehensive review of the potential structural and neuromuscular adaptations that underpin the SSC muscle action does not exist in the literature. Considering the importance of the SSC in human movement, it is imperative to understand how neural and structural adaptations throughout growth and maturation can influence this key muscle action. By understanding the factors that underpin functional SSC development, practitioners and clinicians will possess a better understanding of normal development processes, which will help differentiate between training-induced adaptations and those changes that occur naturally due to growth and maturation. Therefore, the focus of this article is to identify the potential underpinning mechanisms that drive development of SSC muscle action and to examine how SSC function is influenced by growth and maturation.

The purpose of this study was to compare the effectiveness of 6-week training interventions using different modes of resistance (traditional strength, plyometric, and combined training) on sprinting and jumping performances in boys before and after peak height velocity (PHV). Eighty school-aged boys were categorized into 2 maturity groups (pre- or post-PHV) and then randomly assigned to (a) plyometric training, (b) traditional strength training, (c) combined training, or (d) a control group. Experimental groups participated in twice-weekly training programs for 6 weeks. Acceleration, maximal running velocity, squat jump height, and reactive strength index data were collected pre- and postintervention. All training groups made significant gains in measures of sprinting and jumping irrespective of the mode of resistance training and maturity. Plyometric training elicited the greatest gains across all performance variables in pre-PHV children, whereas combined training was the most effective in eliciting change in all performance variables for the post-PHV cohort. Statistical analysis indicated that plyometric training produced greater changes in squat jump and acceleration performances in the pre-PHV group compared with the post-PHV cohort. All other training responses between pre- and post-PHV cohorts were not significant and not clinically meaningful. The study indicates that plyometric training might be more effective in eliciting short-term gains in jumping and sprinting in boys who are pre-PHV, whereas those who are post-PHV may benefit from the additive stimulus of combined training.

The purpose of this study was to examine relationships between functional movement screen scores, maturation and physical performance in young soccer players. Thirty males (11-16 years) were assessed for maturation, functional movement screen scores and a range of physical performance tests (squat jump, reactive strength index protocol and reactive agility cut). Older players significantly outperformed younger participants in all tests (P < 0.05; effect sizes = 1.25-3.40). Deep overhead squat, in-line lunge, active straight leg raise and rotary stability test were significantly correlated to all performance tests. In-line lunge performance explained the greatest variance in reactive strength index (adjusted R(2) = 47%) and reactive agility cut (adjusted R(2) = 38%) performance, whilst maturation was the strongest predictor of squat jump performance (adjusted R(2) = 46%). This study demonstrated that variation of physical performance in youth soccer players could be explained by a combination of both functional movement screen scores and maturation.

Radnor, JM, Lloyd, RS, and Oliver, JL. Individual response to different forms of resistance training in school-aged boys. J Strength Cond Res 31(3): 787-797, 2017-The aim of this study was to examine individual responses to different forms of resistance training on measures of jumping and sprinting performance in school-aged boys. Eighty boys were categorized into 2 maturity groups (pre- or post-peak height velocity [PHV]) and randomly assigned to a plyometric training, resistance training, combined training, or control group. Intervention groups participated in training twice weekly for 6 weeks, with measures of acceleration, maximal running velocity, squat jump height, and reactive strength index (RSI) collected preintervention and postintervention. In the pre-PHV cohort, plyometric training and combined training resulted in significantly more positive responders than the other 2 groups in both sprint variables (standardized residual values >1.96). In the post-PHV cohort, significantly more positive responders for acceleration and squat jump height resulted from traditional strength training and combined training groups, compared with other groups. Conversely, plyometric training and combined training resulted in a significantly greater number of positive responders than the other 2 groups for maximal velocity and RSI. Control participants rarely demonstrated meaningful changes in performance over the 6-week period. Irrespective of maturation, it would seem that combined training provides the greatest opportunity for most individuals to make short-term improvements in jump and sprint performance. Taking maturation into account, our data show that a plyometric training stimulus is important for individuals in the pre-PHV stage of development, whether as a stand-alone method or in combination with traditional strength training, when attempting to improve jumping and sprinting ability. However, individuals in the post-PHV stage require a more specific training stimulus depending on the performance variable that is being targeted for improvement.

Purpose: To determine the differences in muscle architecture of the lower limb in pre-peak height velocity (PHV), circa-PHV, and post-PHV boys. Method: Muscle architecture variables from both the gastrocnemius medialis (GM) and vastus lateralis (VL) were derived from ultrasonographic images in 126 school-aged boys. One-way analysis of variance using Bonferroni post hoc comparisons was employed to determine between-group differences, and effect sizes were calculated to establish the magnitude of these differences. Results: All muscle architecture variables showed significant small to large increases from pre-PHV to post-PHV, excluding GM fascicle length (d = 0.59–1.39; P < .05). More discrete between-group differences were evident as GM and VL muscle thickness, and physiological thickness significantly increased between pre-PHV and circa-PHV (d > 0.57; P < .05); however, only the VL muscle thickness and physiological thickness increased from circa-PHV to post-PHV (d = 0.68; P < .05). The post-PHV group also showed larger GM pennation angles than the circa-PHV group (d = 0.59; P < .05). Conclusion: The combined results showed that maturation is associated with changes in muscle morphology. These data quantify that the maturity-related changes in muscle architecture variables provide a reference to differentiate between training-induced adaptations versus changes associated with normal growth and maturation.