Author(s): MACHIZUKA, S., JO, I., YOON, J., LEE, H., Institution: MASTER DEGREE STUDENT, Country: KOREA, SOUTH, Abstract-ID: 2018

INTRODUCTION:
Counter movement jump (CMJ) is widely used to evaluate lower limb muscle performance. During the CMJ, the ankle plantar flexors are responsible for generating and maintaining concentric force until push-off (1). Considering the force-length relationship, the ankle joint becomes less capable of exerting force as it approaches maximum dorsiflexion. (over 25 degrees) (2). Therefore, the aim of this study is to identify the angle-specific ankle joint torque contributing to the difference in CMJ height between good jumpers (GJ) and bad jumpers (BJ).
METHODS:
Fourteen male participants were divided into two groups based on their CMJ height: the GJ group with heights of 50cm or more, and the BJ group with heights of less than 50cm. The participants took part in an experiment consisting of sessions for measuring maximal CMJ height and maximum voluntary contractions (MVC) of isometric ankle torque, which were conducted using a dynamometer at five different angles (-15, 0, 10, 20, 25 degrees). Lower extremity joint kinematic and kinetic data were obtained using the musculoskeletal program (OpenSim4.1). Statistical analysis was conducted using independent t-tests.
RESULTS:
Jump height (GJ: 54.0±3.2cm, BJ:45.7±3.6cm), peak GRF (GJ:2.5±0.1, BJ:2.2±0.2), and peak GRF after onset of ankle plantar flexion (GJ:2.6±0.3, BJ:2.2±0.2) were significantly higher in GJ compared to BJ. However, there were no significant differences observed in positive work, negative work, mechanical power, and all joint kinematic and kinetic data. On the other hand, in ankle joint MVC, joint peak torque at -15 degrees (GJ: 1.2±0.1, BJ: 1.0±0.2), 20 degrees (GJ: 2.2±0.4, BJ: 1.8±0.2), and 25 degrees (GJ: 2.0±0.3, BJ: 1.6±0.2) showed significantly higher values in GJ.
CONCLUSION:
The difference in ankle joint torque at 20 and 25 degrees between GJ and BJ suggests the importance of exerting and maintaining force during dorsiflexion from the peak of GRF until the peak of GRF following the onset of ankle joint plantar flexion. Therefore, the ankle joints ability to maintain the negative work acquired up to the beginning of the propulsive phase while exerting additional force during push-off at the ankle joint may be a determining factor in jump performance. Especially within this interval, which can be predicted to be situated near the descending limb of the force-length relationship, our results suggest the necessity of ankle joint-specific training closer to the actual angle where the concentric phase begins to enable force exertion near optimal length.