Author(s): CHENG, R., LI, Y., LI, M., ZHANG, Q., Institution: SHANGHAI UNIVERSITY OF SPORT, Country: CHINA, Abstract-ID: 678

INTRODUCTION:
The depth jump (DJ) serves as a common screening tool for lower limb injury risk. (1) Different movement initiation patterns (when leaving the raised platform) can create inconsistencies in actual drop height and touchdown velocity, thereby reducing the utility of the testing methodology. (2, 3) The study aimed to compare the biomechanical and performance outcomes when individuals used the step-off (SOF), single-leg jump (SLJ), and double-leg jump (DLJ) movement initiation patterns during the DJ.
METHODS:
Twenty-five well-trained male collegiate subjects (age= 20.85 ± 1.46 yrs, body mass= 74.41 ± 9.79 kg, stature= 179.16 ± 6.58 cm, training history= 5.95 ± 2.93 yrs) performed DJs with SOF, SLJ, and DLJ movement initiation patterns in a randomized order from box heights corresponding to ~50% (Low), ~75% (Medium), and ~100% (Maximum) of their maximum countermovement jump height. Rebound phase parameters (i.e., peak force [PF], peak power [PP], impulse [I]), actual drop height (DH), and subsequent jump height [JH] were obtained from the force-time data and compared between movement initiation patterns using a linear mixed model. Additionally, statistical non-parametric mapping (SnPM) analysis was used for time series comparisons on the force, velocity, power, and displacement data.
RESULTS:
The linear mixed model results showed that the different movement initiation patterns revealed varying DHs (p < 0.001). The SOF pattern resulted in a reduced DH (14.39 - 18.78%, p < 0.001, g = 1.61), which led to a significantly lower PF (all p < 0.001, g = 0.43 - 0.47), PP (all p < 0.001, g= 0.85 - 0.88), and I(all p <0.001, g = 0.44 - 0.73) during the braking phase, whereas the movement initiation pattern had no significant influence on the propulsive phase (p > 0.05). Conversely, the DLJ pattern facilitated superior JH (p < 0.001, g = 0.29), but it also resulted in an inflated DH (2.08 - 20.48%) and higher test variability (ICC = 0.74 - 0.89, SEM = 0.02 - 0.03 m). The SLJ pattern exhibited a closer approximation to the actual box height (-4.17 - 12.18%). Furthermore, SnPM analysis revealed that the different movement initiation patterns exhibited distinct force application characteristics (43.8 - 99.0%, p < 0.001), leading to different mechanical properties during the initial rebound phase (23.53-28.01%, p < 0.001).
CONCLUSION:
The movement initiation pattern in depth jumps is a critical variable determining their biomechanical characteristics and subsequent touchdown strategies. Consequently, for practitioners seeking to match the prescribed drop height accurately while obtaining highly reliable data, the SLJ movement initiation pattern offers a more robust and appropriate protocol for evaluating an athlete's bilateral touchdown abilities.
Reference
(1) Pedley et al., Journal of Science in Sport and Exercise, 2020
(2) McMahon et al., Biomechanics, 2021
(3) Wilder et al., Journal of Electromyography and Kinesiology, 2021