ABSTRACT

The effect of H/Q ratio in balance on the dynamic stability of the upper limbs when drop landing

Jun, Hee-Sub
Advisor : Prof. Lee, koung-il, Ph. D.
Department of Physical Education,
Graduate School of Chosun University


This study identified the effect of H/Q ratio in drop landing on dynamic stability of the lower limbs and analysed it bio-mechanically to prevent risk factors which cause injury in the lower limbs and to obtain basic and qualitative data which are helpful for future instructors.
The subjects of the study were 13 soccer players from C university in G city who were aged 20-23 and had no injuries in the lower limbs and whole body for the recent six months. With a use of isokinetic sporting goods(60 deg/s) before the drop landing test, imbalance of H/Q ratio(Hamstring / Quadriceps ratio) was measured. the group with above 69% of H/Q ratio was classified as a dominant group and the group with below 69% of H/Q ratio as a recessive group. Before the test, all the subjects wore elastic exercise suits in their barefoot and had more than 5 times of warm-up and drop landing for 10 minutes. For drop landing, they jumped off from the 50cm-chair to the force platform with one feet and landed successfully on the ground twice without losing balance or hands touching on the ground. Five pieces of high definition Motion Master 200 (Bisol, Gwangmyong) were used to analyse images and 1 force platform(AMTI ORG-6, AMTI), and 2 pieces of AMTI ORG-6, AMTI were used to deal with image signal and ground force signals. Kwon3D XP was used to analyse the image data and ground force, and a Mann-whitney test and a Spearman correlations analysis were used to compare the two groups with a use of SPSS 18.0. All the significance level was p<.05.
As a result of the test, in drop landing according to the imbalance of H/R ratio, there were significant differences in means of a loading factor. GRF, and EMG between the dominant group and the recessive group(p<.05) while there was no significant difference in maximum knee curve angles, maximum vertical ground force, COM displacement, GRF, and maximum EMG between the two groups. In respect to the correlations between H/Q ratio and biomechanic variables, there were reverse correlations in loading factor, means and maximum EMG while there were correlations in maximum vertical ground force, loading factor, maximum knee curve angles, the right and left centers, the right and left displacement, maximum and mean EMG. It indicates that the higher H/Q ratio is, the loading factor and the maximum EMG decrease. In respect to the correlations in dynamic variables, the higher the maximum ground force, the loading factor increases. As the knee joint curve angle increases, outside ground force and the body center move right. As the right and left displacement of the body center increases, myoelectrical activities of hamstring decreases.