Neuromechanical Analysis of Loaded Plyometric Exercise on Lower Limbs in Elite Female Volleyball Players

[[abstract]]Neuromechanical Analysis of Loaded Plyometric Exercise on Lower Limbs in Elite Female Volleyball Players. Abstract Loaded plyometric exercise (LPE) is a type of power training method which combines the advantages of both weight training and plyometric training. The purposes of this study were to investigate the neuromechanical advantages and effects of the loaded counter-movement jump (LCMJ, a typical type of LPE) on lower-limb’s power output, neuromuscular activation, recruitment and firing frequency of motor units (MU) under varied loads. Twelve elite female volleyball players (age: 19.9±1.1, height: 171.8±6.8 cm, weight: 64.83±6.03 kg), who won the championship of University Volleyball Games in Taiwan in 2004, participated in this experiment. Firstly, maximal isometric force (MIF) of each subject on lower limbs was measured on Kistler’s Quattro Jump force plate, as the setting basis of different load intensity. They perform LCMJ and LSJ (loaded squat jump) on Smith Machine with different load (0%, 10%, 20%, 30%, and 40% of their MIF) randomly. Furthermore, force plate, displacement meter and Biovision’s EMG System were designed to synchronously collect the signals of force, displacement and EMG. Then relevant neuromechanical parameters were read for further analysis with DASYLab and Acqknowledge software. The collection of EMG’s data includes rectus femoris, vastus lateralis, soleus, gastrocnemius lateral head, hamstrings, and tibialis anterior. The standardizing root mean square of EMG (EMGrms) was aimed to assess the amount of MU recruited, and survey the recruit frequency and type of MU by median frequency (MDF). Statistical method adopted Two-way ANOVA to test the differences between different loads and motions on neuromechanical parameters. The result of this study shows: Loaded plyometric exercise has biomechanical advantage on power output. LCMJ is superior to LSJ evidently, and the advantage increases with increasing load. But in the advantage of neural innervations factor, it is affected by both load and movement speed, along with existent individual differences, which leads to the EMGrms of LCMJ showing no significant difference among different loads during concentric contraction. On the effects of neuromuscular activation, LCMJ and LSJ have not shown obvious difference on EMGrms during concentric phase, but LCMJ is higher significantly than LSJ on MDF due to the faster concentric velocity, and EMGrms of LCMJ increases with increasing load during eccentric phase. It is obvious, the main neuromechanical effect of the loaded plyometric exercise lies in increasing the recruitment of motor units during eccentric contraction, and activating the high-frequency fast-twitch muscles of motor units to participated in concentric contraction. In conclusion, weight load is the main decisive factor of MU recruited, and the firing frequency of MU depends on speed load mainly. Therefore, in order to inspire the best neuromechanical effects, strength training must give consideration to both the weight load that strengthens MU recruited and the speed load that intensifies higher MU firing frequency, and 30% of their MIF progressively was suggested when performs LPE. Keyword: plyometric training; plyometric weight training; electromyography; biomechanics; neuromechanics.