Author(s): BRIGHT, T., LAKE, J., MUNDY, P., THEIS, N., HUGHES, J., Institution: CARDIFF METROPOLITAN UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 907

INTRODUCTION:
Young athletes participating in regular strength and conditioning programmes inclusive of resistance and plyometric training have enhanced strength and power capabilities [1]. Considering the natural development and trainability of the stretch-shortening cycle during childhood [2], training methods that target this mechanism are of interest. While dumbbell accentuated eccentric loading (AEL) has shown promise in improving vertical jump heights during drop jumps in adolescent athletes [3], its acute effects during a countermovement vertical jump (CMVJ) remain unexplored. Therefore, the aim of this study was to explore the differences between force-time characteristics during a body weight CMVJ (CMVJBW) and a CMVJ with dumbbell AEL (CMVJAEL).
METHODS:
Eight male youth soccer players (age: 15.57 ± 1.53y; height: 173.76 ± 4.87cm; mass: 58.66 ± 7.26kg) volunteered to participate in the study. After familiarisation, participants completed 3 trials of CMVJBW and CMVJAEL using dumbbells at 20% of body mass using two parallel force platforms (Kistler type 9286AA, Kistler Instruments Inc., Amherst, NY, USA; 1000 Hz). Both the CMVJBW and CMVJAEL force-time data were filtered [4] and processed using published guidelines [5] to obtain the following variables: jump height, reactive strength index modified, time to take-off, countermovement depth, force at zero velocity and time, force and velocity characteristics for the unweighting, yielding, braking and propulsion phases. To account for the change in body mass as a result of the dumbbell release during CMVJAEL, backward integration was also undertaken[6]. A series of paired sample t-tests were conducted to determine the differences between CMVJBW and CMVJAEL. Hedge’s g effect sizes were used to examine the magnitude of the differences between conditions.
RESULTS:
Significantly greater jump height, velocity at take-off, unweighting peak velocity, yielding mean velocity, braking mean velocity and propulsion peak velocity were observed in the CMVJAEL condition (p < 0.05; g = 0.79-2.35). Yielding time was reduced during the CMVJAEL condition (p < 0.05; g = 0.79), while unweighting time and minimum force were moderately higher in the CMVJAEL condition (g = 0.66). All other effect sizes were trivial to small.
CONCLUSION:
This sample of youth soccer players were able to realise a greater jump height during the CMVJAEL condition. Furthermore, the CMVJAEL facilitated greater velocities during the unweighting, yielding, braking and propulsion phases without a significant change in countermovement depth. Collectively, these results suggest that practitioners can utilise CMVJAEL through dumbbells to target the stretch-shortening cycle in youth soccer players. Future research should investigate the acute effects of CMVJAEL at 30 and 40% of body mass to identify the changes in force-time characteristics at greater loads.