Impact of Surface Type on Single-Leg Jumping and Landing Mechanics using EMG, Kinematics, and Ground Reaction Force

Previous studies have found that athletes who need to jump in their sport often have asymmetry in their landing, resulting in a higher load on one leg. This can cause acute and chronic injuries to the knee such as ACL injuries, ligament injuries, stress fractures, and arthritis. PURPOSE: This project aims to measure the ground reaction force (GRF) of repetitive jumping of a single-leg on difference surfaces, identify key muscles and activation patterns, and understand the biomechanical kinematics of the jump sequence. By analyzing these aspects of repetitive jumping, and investigating the correlations and mutual influence, the effects of single-leg jumping and landing on firm surface versus sand can be determined. METHODS: Fifteen participants (7 male, 8 female) were taken through a 5-minute warm up on a cycle ergometer followed by familiarization jump trials. Afterwards, EMG sensors were placed on seven muscles of the dominant leg: gluteus maximus (GLUT), rectus femoris (RF), biceps femoris (BF), vastus lateralis (VS), vastus medialis (VM), gastrocnemius (GAST), and tibialis anterior (TA). Next, 7 retroreflective markers were placed on the lower body to measure joint kinematics. Video capture was recorded at 120fps in the frontal and sagittal plane. Participants were randomly assigned to start trials on a firm surface or on 10cm of sand. Using a force platform, participants were asked to jump five times on their dominant leg with a five second break in between each jump. The surface that participants started on was alternated, with a three-minute break in between each trial, ultimately completing two sand trials and two firm trials each. RESULTS: Significant differences were found in the muscle activation of the VL and BF between sand and firm surfaces (p < 0.05). The peak vertical force and internal rotation moment during a jump were significantly lower on the sand surface (p < 0.001). Average and maximum angular acceleration of the knee in the frontal plane was significantly lower on the sand surface (p < 0.05). CONCLUSION: These findings reveal that sand provides a lower total impact, and higher muscle activation environment for training compared to a firm surface. Clinicians can use these findings to better inform treatment protocols regarding stabilization during the landing phase of a jump.