The effects of different vertical jump height on electromyographic, kinematic and kinetic variables

Abstract

Countermovement jump (CMJ) is an element of many sports techniques and has an important role in the overall performance, both when performed at maximal and submaximal intensity. This paper aims to investigate changes in biomechanical and neuromuscular variables that are responsible for controlling different submaximal intensities of the CMJ. 8 healthy and uninjured volleyball players from the first league of the Republic of Serbia, average age 21.9 ± 1.9 years, average body height 191.6 ± 9.2 cm, average body weight 83.1 ± 7.1 kg were included in the study. Subjects performed CMJ at three different jump heights (approximately 65%, 80%, and 95% of the maximal height). For the analysis of electromyographic data, the value of root mean square analysis was used separately for the amortization phase and the jump phase, for the following muscles: m. gluteus maximus (GlutM), m. rectus femoris (RF), m. biceps femoris (BF), m. vastus lateralis (VL), m. tibialis anterior (TA) and m. gastrocnemius medialis(GastM).Kinematic and kinetic variableswere monitored: vertical center of mass displacement in the amortization phase [m], the center of mass height at take-off point [m], jump height [m], jump speed [m/s], angular displacement in the ankle, knee and hip joint [rad], maximal vertical ground reaction force [N/ kg], vertical stiffness [kN/m/kg], the torque of the ankle, knee and hip joint [Nm/kg]. The change in jump height (65, 80 and 95%) did not have a significant effect on the change in activation for most muscles (p≥0.05), except for GastM where a tendency towards increase was observed (p=0.066). During jump phase, the activation of VL, BF, GlutM, TA muscles significantly increased compared to the amortization phase (p≤0.05). The torque in the hip joint increased significantly with increasing jump height (65<80=95%) (p=0.028). During amortization phase, the values of vertical center of mass displacement increased significantl y between each jump height (65<80<95%) (p≤0.05), while the values of vertical stiffness decreased with increasing jump height, where significant differences were observed between 80% and 95% of maximal jump height (65=80<95%) (p=0.012). Angular displacements in the knee and hip joint increased significantly with increasing jump height (65<80<95%) (p≤0.05) while no changes in angular displacement in the ankle joint were observed (p≥0.05). The results of the research show that the increase in the jump height is related to an increase in the amortization phase, due to an increase in angular displacements in the knee and hip joint, as well as an increase in torque of the hip joint.