Lower Extremity Joint Kinetics Do Not Differ Between Different Athletic Upper Body Positions

Abstract

Increased lower extremity injury risk has been speculated to relate with out-of-plane upper body position while performing running, cutting, and landing tasks. It remains poorly understood if athletic tasks that require different upper body positions do influence lower extremity kinetics. PURPOSE: To investigate if four different athletic upper body positions affect lower extremity joint kinetics. METHODS: Thirty healthy participants (23.4±4.3years, 1.70±0.11m, 72.8±14.9kg) volunteered for the study. Participants performed 5 landings from a 45cm box using four different upper body positions: 1) arms at chest level while holding a basketball (CH), 2) arms extended at chest level holding a basketball (FR), 3) arms extended straight up over head (UP), and 4) placing hands on hips (HIP). Forty markers were placed on the lower extremity. Trajectory and ground reaction force (GRF) data were collected at 200 and 1000Hz, respectively. Data were filtered with a 4th order Butterworth low pass filter with cutoff frequencies of 7 and 15Hz for trajectory and GRF data, respectively. Peak joint moments were attained between initial contact and minimum vertical displacement of center of mass; hip and knee flexor and extensor moments normalized to body mass and height (Nm/Kgm) were calculated. Peak vertical GRF was calculated for each arm position. Repeated measures ANOVAs and Bonferroni pairwise comparisons examined differences across conditions. RESULTS: CH position (-0.74±0.29 Nm/Kgm) presented lower knee flexor moment than UP (-0.81±0.26 Nm/Kgm) and HIP (-0.89±0.27 Nm/Kgm) positions (p0.05). CONCLUSIONS: Overall, It is noteworthy that when landing with the arms above the head and landing with the hands on the hips, the knee joint flexor moment significantly increased when compared with holding a ball at chest level. The higher knee flexor moment may increase the stress transmitted to the tibia, and result in a detrimental loading for the knee articular cartilage. When developing intervention strategies, health professionals should consider the effects of various arm positions on lower extremity kinetics to potentially minimize excessive knee joint loading.