The Effect Of Plyometric Training On Lower Extremity Biomechanics

Purpose: The purpose of this study was to compare the joint kinetics, joint contributions and co-activation of lower extremity during countermovement jump and identify the optimal loading when one wanted to promote lower extremity strength and power during plyometric weight training. We measured kinetics, kinematics and electromyogram data of lower extremity. We measured the same data during squat jump with different loads in order to clarify the effects of loads on kinetics, kinematics and muscle activity of lower extremity. Furthermore, in order to compare the pre-activation and determine the optimal drop height we measured kinetics and electromyogram data of lower extremity during drop jump with different height. Based on the above-mentioned context, we attempt to observe the effects of plyometric weight training on maximum muscle strength and power of lower extremity, to reveal the mechanism that how the muscle strength and power of lower extremity are promoted after plyometric weight training. So we compared the lower extremity kinetics, joint kinetics, co-activation and pre-activation pre-/post-training.The sense of this study was to provide reliable experimental data for athletes to select appropriate training mode in promoting lower extremity strength and power, to provide fundamental theory for spreading of plyometric weight training and practicing of plyometric weight training machine, and to provide practicing principles for coaches to make rational plans for training.Methods: Sixteen male basketball athletes were trained their lower extremities with plyometric training with the help of plyometric weight training machine. Initially, a 1-repetition maximum squat (1RM) resistance was determined for each subject and then the 0, 10, 20, 30, 40, 50, 60%1RM of each subject was calculated as different loading conditions. A KISTLER-3D force plate was used to collect kinetics data of lower extremity with a sampling rate of 1200Hz. Kinematic data of lower extremity were acquired using a VICON motion analysis system consisting of eight infra-red ray cameras with a sampling rate of 120Hz to detect the motion of reflective markers placed on skin over the left tubercle of iliac crest, anterior superior iliac spine, greater trochanter, medial and lateral epicondyle of knee, medial and lateral malleolus, first and fifth metatarsophalangeal joint, tiptoe. VISUAL3D image analysis system was used to reconstruct the marker 3D co-ordinates for data processing. Standard inverse dynamic calculations were used to determine the net joint moment. Leg stiffness and joint stiffness of hip, knee, and ankle were calculated using spring-mass model. An eight channel surface electromyogram was used to collect the electromyogram signal data of lower extremity synchronously with kinetics and kinematics data. The Gain was 1000, Common Mode Reaction Ratio was 12 dB and sampling rate was 1200Hz. Bipolar surface electrodes were placed over the muscle belly of the tibialis anterior, gastrocnemius lateralis, rectus femoris, vestus lateralis, and biceps femoris, 0 electrode on tibial tuberosity. DASYLab8.0 electromyographic signal analysis system was used for data processing after which the integrated electromyographic of each muscle and co-activation of rectus femoris/biceps femoris, gastrocnemius lateralis/vestus lateralis, and tibialis anterior/gastrocnemius lateralis were calculated.Results: (1) The analysis of lower extremity dynamics indicated that hip was the dominate contributor and knee is the least during plyometric weight training. (2) The comparison of lower extremity dynamics pre-/post- plyometric weight training indicated that the peak vertical ground reaction force and 1RM during concentric phase of countermovement jump, the impulse of concentric phase of squat jump, peak net joint moment and peak net joint moment power of hip and ankle during concentric phase of countermovement jump were significantly promoted. But the peak net joint moment and peak net joint moment power of knee were not influenced by this training. Leg stiffness and joint stiffness of hip and ankle were also significantly increased after plyometric weight training. The comparison of lower extremity muscle activity of pre-/post- plyometric weight training indicated that co-activations of hip and ankle significantly decreased and pre-activation was significantly increased.Conclusion: (1) During plyometric weight training action the joint contributions of hip and ankle is greater than knee, which indicated more demand of hip and ankle than knee. The result suggested that the role of hip and ankle was more important than knee during this kind of training, thus the muscle strength and power of hip and knee were mainly developed. (2) The fact that the peak net joint moment, peak joint moment power, and joint stiffness were promoted after plyometric weight training indicated that muscle strength and power of lower extremity were elevated through the increasing of hip and ankle muscle joint dynamics, then, the bounce and velocity of lower extremity were promoted. The fact that the co-activation decreased and pre-activation increased after plyometric weight training indicated that the adaptability and concordant of muscle were promoted, and then multijoint motor capacity increased. (3) From the analysis of lower extremity dynamics and muscle activity we concluded that plyometric weight training is an effective training mode for promoting muscle strength and power of lower extremity. It is applicable to the projects that highly demand bounce and velocity.