The Differences Between Jumpers And Non-jumpers On Biomechanical Performance During Landing And Drop-jump

PURPOSE:By comparing the isokinetic muscle strength（IMS） of the knee and the performance in drop jump & landing of female athletes with different training background, this study aimed to investigate the effect of eccentric training on the biomechanical outcomes of the lower limbs during impactive landing tasks. The finding could be used to explain the principle of the injury-prevention programs.METHODS:Twelve female athletes majoring in swimming（non-jumpers） and twelve female athletes majoring in tracking（jumpers） were recruited to perform the CMJ, step-off landing（40 cm）, and drop jump（40 cm）, 3 times of each. The surface EMG, 3D lower-limb kinematics and kinetics data were synchronously recorded. The EMG data of CMJ were processed as the basement for normalization. After that, the subjects performed the IMS testing in both eccentric and concentric pattern under 60°/s and120°/s, 3 times of each conditions. The independent t-test was applied to analyze the kinematics, kinetics, and EMG outcomes. The Mixed-design ANOVA of repeated measures was applied to analyze the outcomes of muscle strength. If interaction was found, the simple effect analysis was applied to investigate the differences between groups. The significant level was set as 0.05RESULTS:（1） No significant difference was found in the IMS in the concentric pattern. In the eccentric pattern, however, the jumpers performed higher extensors’ work than the non-jumpers did（P=0.003）. Also, the jumpers had greater flexors’ strength comparing with the non-jumpers（P=0.036）.（2） There were no much significant differences in the results of landing performance between jumpers and non-jumpers during landing. The only difference was found in the ankle joint, the jumpers had smaller ankle ROM（P=0.003） and greater ankle stiffness than the non-jumpers（P=0.032）.（3） Significant differences were found in the drop jumps. Specifically, the jumpers performed smaller joint ROM in the sagittal plane(PHip=0.006; P_Knee<0.001;P_Ankle<0.001), but larger loadrate in the V_GRF（ P =0.048） during buffering. The jumpers had greater extension torques in the knee(P_Knee=0.039) and anke(P_Ankle<0.001), greater ankle stiffness（P =0.003） than the non-jumpers. But, the jumpers had less total-work contribution of the knee comparing with the non-jumpers（P=0.001）. In the jumping phase, the jumpers performed greater concentric power in the ankle（P=0.001） and the hip（P=0.001）, less total-work contribution of the knee（P=0.001）, but greater total-work contribution of the ankle（P =0.003）. The jumpers toke less time（P<0.001）, but jumped higher than the non-jumpers did（P=0.002）.（4） No significant difference was found in any EMG-related outcomes.CONCLUSIONS:（1）Significant differences in landing performance were mainly found in drop jumps,but rarely existed in landing. This finding indicated that the differences in landing strategy and muscle strength became more obvious with the difficulty of the tasks increasing.（2）The jumpers performed greater concentric power, joint stiffness, and joint contribution of the ankle, which indicated that subjects received long-time eccentric training tended to adopt an “ankle strategy”. That is, by utilizing ankle muscles to absorb the impacts, the loading on the knee could be weakened to potentially reduce the risk of injury in the tissues around the knee.（3）There were no significant differences in the neuromuscular-control pattern in two groups, and that might be related to the higher knee-injury risks in females.