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This study investigated the relationships between performance and force-velocity (F-v) parameters obtained from a ballistic lower limb (BLL) and a 30-m sprint test in 24 adolescent elite footballers (13.2–15.1 years old). In the BLL test, normal ground reaction force and velocity were recorded by two force plates and a linear encoder, respectively, and take-off velocity (vto) at 0% of body mass was considered as performance. In the 30-m sprint test, raw velocity-time data were measured using a radar, and 5, 10 and 30 m sprint times using a timing gate system. Theoretical maximal force (F0), velocity (v0) and power (Pmax) were determined using the Samozino’s method. All sprint times were significantly correlated with vto (p = 0.004 to p < 0.001; −0.57 to −0.72), but no significant correlation was found between the respective F-v parameters ;(p = 0.152 to 0.913). As both tests assess explosive performance, players who can produce a high vto will also perform best in short sprints. However, the F-v discrepancies highlight the complementarity of these tests: the BLL test minimises the coordination and technical influences that can affect sprint performance in adolescents. [ABSTRACT FROM AUTHOR]

Little is known about the influence of fatigue in repeated overground sprinting on force-velocity properties in children and adolescents, while this ability to repeat sprints is important for future progress in rugby union. Sprint time decline is commonly used to assess fatigability. However, it does not provide data on biomechanical aspects of sprint performance such as maximal power, force, and velocity production. As sprint time performance and force-velocity properties do not linearly change during adolescence, considering maturity status is important. This study aimed to assess the effect of fatigue on sprint time performance fatigability, force-velocity parameters, and mechanical effectiveness according to maturity status. A group of fifteen boys (12.5 ± 0.5 years) children and a group of seventeen boys (15.1 ± 0.6 years) adolescent rugby players completed seven blocks, consisting of a 30-meter sprint followed by five minutes of high-intensity exercise with one minute of passive recovery. The force-velocity parameters were calculated at each sprint, and performance decrement was assessed using a fatigue index. A main effect of block repetition was found for maximal power output, maximal force, maximal velocity, 30-meter sprint time, fatigue index and mechanical effectiveness parameters with large effect sizes (p <0.001; ηp2 = 0.19 to 0.47) and without a main effect of maturity status (p = 0.37 to 0.99; ηp2 = 0.00 to 0.05). This could be explained by the modalities (duration, intensity, recovery) of the protocol and the training level of the adolescent group. For both groups, the decrease in maximal power output was due more to a reduction in maximal velocity than force, and mechanical effectiveness was negatively impacted. Coaches could prioritize the training of horizontal force at high velocity under fatigue conditions, as this ability tends to be the most affected. They could also incorporate training on mechanical effectiveness as this is a determinant in team sports. [ABSTRACT FROM AUTHOR]