Kinetics and Pre-activity Modulation of Lower Extremity Muscles within Different Heights of Drop Jump

Objective:The purpose of this study was to test kinematics and kinetics variables and measure surface electromyography(SEMG) of lower extremity muscles,and determine modulation of pre-activity related to drop jump(DJ) with different heights.Methods:Sixteen healthy young males without experience in deep jumps training,who participated in the study,from three different heights(low,optimal,high).SEMG device was used to estimate muscle activity(integral EMG signal-iEMG and maximal amplitude of EMG-AmaxEMG) of five muscles(tibialis anterior-TA,gastrocnemius medialis-GM,rectus femoris-RF,vestus lateralis-VL,biceps femoris-BF) within 150ms before touchdown.Contact time and flight time of DJ were measured to be used in output power calculation.Result:There is long flight time in drop jump of optimal drop height and high output power in drop jump of low drop height.All muscles,except GM,showed systematic increase in pre-activity when platform height was raised.For most of the lower extremity muscles,the most significant differences were between values of pre-activity obtained for low and high platforms.The amount of muscle pre-activity in DJ from the heights above and beneath the optimal one did not differ significantly from that generated in DJ from the optimal drop height.Conclusion:DJ from the heights above the optimal one are not adequate for adjusting muscle activity for the impact of ground reaction force.We recommend the DJ power output as the main criteria to train lower extremity for plyometric training purposes.DJ from the optimal drop height or beneath the optimal one should be used as plyometric training method in practice to elevate muscle strength of lower extremity.