The Effect Of Arm Swings On Lower Limb Kinetics During Single-leg Hopping

Single-leg forward hopping for distance was widely used to evaluate knee functions and quadriceps strength following anterior cruciate ligament (ACL) injuries. Single-leg vertical hopping for height and backward hopping for distance were found to require more knee involvement compared to forward hopping. There is a lack of consistent task instruction for performing hopping tasks to sensitively monitor knee function following ACL injuries. PURPOSE: To quantify the effects of arm swings on lower limb kinetics during single-leg forward, vertical, and backward hopping with a focus on knee assessment. METHODS: 38 injury-free individuals (21.0 ± 2.3 yrs, 1.7 ± 0.1 m, 68.6 ± 12.9 kg) performed single-leg forward (FH), vertical (VH), and backward (BH) hopping with and without arm swings with motion and force data collected during jumping. Hopping performance, hip/knee/ankle work, and peak power were calculated and compared by three-by-two repeated-measures ANOVAs. RESULTS: BH showed the greatest peak knee power (p < 0.001), smallest hip/ankle work (p < 0.001), and smallest hip/ankle peak power (p < 0.001) compared to FH and VH, regardless of arm swings (Table 1). Arm swings significantly increased hopping performance (p < 0.001) among all tasks but decreased knee work (p = 0.004) in VH and BH (Table 1). CONCLUSION: The greatest peak knee power and smallest peak hip/ankle power and work in BH support the greater emphasis of the knee when hopping backward. Therefore, BH might be an additional task to assess the knee function following ACL injuries compared to FH and VH. Arm swings resulted in greater performance without significantly increasing knee emphasis during jumping. Standardized instructions on controlling arms are recommended when using performances from hopping tasks to assess knee function in rehabilitation progress in patients after ACL injuries. Future studies need to investigate the knee kinetics when hopping in different directions in patients after ACL injuries.