(9) THE LEARNING EFFECT ON LOWER LIMB KINETICS WHEN SINGLE-LEG HOPPING IN DIFFERENT DIRECTIONS: A JOINT-SPECIFIC LOADING ANALYSIS

Purpose: The current study aimed to quantify the learning effects on hip, knee, and ankle kinetics during jumping when single-leg hopping forward, vertical, and backward, focusing on the knee joint. Methods: Forty-five injury-free volunteers (21.0 ± 0.7 years old, 1.7 ± 0.1 m, 68.9 ± 11.9 kg) performed ten single-leg forward, vertical, and backward hopping on one leg. Participants hopped for maximum performance. Motion and force data were collected through infrared cameras (Vicon, 120 Hz) and a force plate (Bertec, 1200 Hz). Hopping performance, peak power and work of hip, knee, and ankle joints during jumping were calculated. To quantify learning effects, ten trials were grouped as one practice, Block 1 (average of trials 2-4), Block 2 (average of trials 5-7), and Block 3 (average of trials 8-10). Such arrangements were based on previous studies, which commonly reported an average of three trials with a single practice at the beginning of the testing. Three-by-three repeated-measures ANOVAs were applied. Results: For the hopping direction (Table 1), single-leg backward hopping showed the smallest hip/ankle power and work (p< 0.047) while the greatest knee power and work (p< 0.030), regardless of the blocks. For learning effects (Table 1), the greatest hopping performance (p< 0.003) and hip work (p< 0.015) were found in Block 3 for all tasks. Hopping performance increased over trials in forward and backward hopping (p< 0.003), while no significant improvement in peak knee power was observed among all tasks. Conclusions: Single-leg backward hopping demonstrated significantly greater knee kinetics compared to vertical and forward hopping, suggesting it may be a more demanding task for assessing knee function and quadricep strength. In addition, forward and backward hopping performance significantly improved over trials, whereas vertical jump height remained consistent. This may be because vertical jumping is more common in daily activities, making it a more familiar movement pattern. The improvement in hopping performance is likely contributed to increased peak hip power and work over trials. Furthermore, knee involvement remained consistent across blocks, while peak ankle power decreased in both vertical and backward hopping. The decreased ankle kinetics might be explained by possible fatigue after several jumps. Practical Applications: Single-leg backward hopping may serve as a more effective and challenging task for assessing knee function and quadriceps deficits in clinical settings. Incorporating a single practice trial may be sufficient when using hopping performance to evaluate knee function and quadriceps strength. For example, physical therapists could use backward hopping distance as a functional measure to track knee function and quadriceps strength during rehabilitation following anterior cruciate ligament injuries. Acknowledgements: This work was supported by the New Faculty Research Development Award from the University of Kansas.