| Popis: |
Fast pushing like forms of knee extension were previously studied (van Ingen Schenau, 1994, Bobbert 1994). From these the role of mono and bi-articular muscles was established for this type of pushing like motion patterns. The way whipping like forms of knee extension are controlled is however less understood. This study investigated the impact of skill level in modulating fast forms of knee extension. The investigation was carried out by using a Taekwondo fast front kicking action, mean peak leg angular velocity 18.65 rads/s, as the subject task. A total of 40 healthy male and female participants volunteered to take part in this study. Of these, 20 were skilled martial arts athletes while the remaining 20 were unskilled. Expert and novice groups were randomly divided into treatment and control groups. A ten week intervention program aimed at increasing the skill level of participants of the expert and novice groups was conducted. The kinematic profile of the execution of a fast front kick performed under various settings of velocity, range of motion and degrees of freedom was obtained by a high speed camera. The myoelectrical activity of selected muscle units was simultaneously obtained while kicks were video recorded. Expert and novice participants were tested pre and post intervention program. Of the available kinematic variables such as segmental angular velocities, joint linear velocities and intersegmental timing and coordination, it was found that only: peak ankle linear and leg angular velocities, intersegmental timing, thigh to leg peak angular velocity ratio and a calculated performance index, have the potential to discriminate differences in skill level in this form of kicking. Pre and post intervention differences between groups were assessed from these variables. It was of interest to this study to identify the sources of these differences. To this end, an inverse dynamics analysis of the interaction between segments during the execution of a front kick was performed. It was found that the interaction between segments evolves with increases in skill level. Expert athletes utilize a i) precursor knee flexion moment to assist hip flexion moment during the initial stages of the kicking action and ii) a late hip flexion moment to assist further increases of kicking speed. These moments were absent in the execution of a front kick by novice athletes. These findings were also obtained form an optimization approach to the analysis of interactive moments during kicking. An important conclusion from these analyses is that the view of a front kick as a proximal to distal motion pattern is inadequate. Evidence from this study suggests that this action is best defined as a distal-proximal-distal motion pattern in an expert population. It then indicates that skill gains rely on the utilization of intrinsic muscle properties to assist the execution of tasks like a front kick. |
