CAN AN EXTERNAL MUSCLE STIMULUS HELP THE LEARNING OF COMPLEX GROSS COORDINATE

MOTION?David O’Sullivan, Yong-hyun Park, Chul-soo Chung, and In-Sik Shin(Sports Biomechanics Lab, Seoul National University, Seoul, Korea)

Introduction Various methods are reported to be used in the instruction of different sporting techniques (e.g., demonstration, video analysis, visual (video, mirror) feedback, and working with a partner, and "hands-on segment manipulation) (1). Although many methods are used in the instruction of skill, a drawback is that specific muscles and timing the use of these muscles can not be well communicated. More importantly novice athletes are unable to correctly activate crucial muscles when learning a new technique. Lacking the ability to perform a new technique may then call for the instructor to adopt a more "hands-on" approach where the athlete's body segments are physically moved into the appropriate positions and desired timing. Within the sport of golf various teaching devices have been used, Power Swing Fan©(2), Golf Swing Coach©(3) and Links Walker Golf Swing Machine to aid in timing development. The current study seeks to investigate other teaching methods than a "hands-on" approach and will present the use of electrical muscle stimulation(ES). ES has been widely used in modern medicine by physiotherapists to aid in the re-learning of novel tasks (e.g., grasping control, gait and breathing) in patients struck by central and peripheral nervous system ailments, by sending messages to specific muscles and muscle groups via motor neuron activation (4,5,6,7). Yamada emphasized that hip extension should occur after the reversal point as the primary motion to be executed in unskilled participants (8). So, it is the kip motion, used in gymnastics, and the timing of hip extension that is to be analyzed and manipulated/taught via ES.

BackgroundKip MovementAfter swinging the body under the bar, at the point where the body is moving in a frontal direction the hip flexors are activated, and the lower extremities rise up. After hip flexion when the body is swinging backwards hip extension is required. This hip extension creates a counter reaction force in the trunk, resulting in an increase torque around the bar bringing the subject above the bar.

Understanding the Role of the Kip MovementAfter hip flexion the subject's COG becomes closer to the horizontal bar and this increases the speed of the swing. Maintaining angular momentum and reducing the distance from the COG to the fulcrum (horizontal bar) the swing speed increases and this augmented with a powerful hip extension creates enough speed and energy for the subject to rise above the bar. Viz if the kinetic energy and the energy created by the hip extension is sufficient the subject will be able to rise above the bar.

Prediction of Kip Movement SuccessPotential Energy above the bar < Total COG Potential Energy + Total Kinetic Energy passing under the bar

PurposeThe purpose of this study is to examine and compare the effects of conventional teaching methods(without ES) and teaching methods in conjunction with ES.

Method

Results & Discussion

Data collection Subjects: Twelve healthy male subjects participated in this study. Experiment Procedure After explaining experimental procedure and receiving signature of the consent form the participants prepared for participation. The participant’s warm up consisted of 10 minutes basic stretching and light jogging. After the attachment of reflective markers and electrodes (Kendal, Medi-trace Ag/AgCl) EMG and kinematic data were recorded with Noraxon wireless EMG system (Noraxon, USA) and 8 Oqus500 cameras (Qualysis, Sweden) at 1000Hz and 100Hz respectively. All EMG data were filtered with a band pass filter (10-500Hz), rectified and filter with a low pass filter at 3 Hz. Subjects for the final experiment were randomly assigned into two groups; a group to receive ES plus conventional training group and one group with only the conventional training(Control). The experiment was carried out on four separate days ES group day 1 and 2 and Control on days 3 and 4. Each subject was instructed to perform 6 trials on each day after showing expert motion data and a live demonstration of the required hip extension before the first trial. There was recovery time of 1 minute allocated between each trail and at this time further advice was given. For the ES group there were two separate external muscle stimuli; a hip flexion (lower abdominal) and hip extension(gluteus maximus). This stimulus timing was provided from the expert EMG data.

Figure 3 demonstrates one of the other reasons for failure during the kip motion. Until the reversal point the all the elbow data is similar. However, after the reversal point and/or at the point of the hip extension only the expert group maintain their arms in extension. Whereas, for the ES and Control group subjects show the opposite pattern of elbow flexion with disrupts the direction of the reaction force created by the hip extension. Even with numerous verbal warnings between trials for the subjects not to flex their arms while or after kicking it tends to be a subconscious reaction.

ConclusionThe data from our data shows that the ES method of training could be helpful as the kip timing was more similar to the expert group than the Control. Elbow flexion during the kip movement was shown to dissipate the kip energy and inhibit the completion of the kip movement. One of the main restrictions of the ES method is that the reason the participant kicked at the time indicated by the external signal one cannot be verified. Another disadvantage is that because the subject is waiting for the signal that it could inhibit or interfere with other motions required. In future studies the ES and control group needs more subjects, more trials until the consistent success of the kip movement. As elbow flexion during the final stage inhibited the movement an ES to maintain elbow extension may have a positive effect.

References1. Petrofsky, et al. Med Bio Eng. Comput. 17:87-93,19792. http://www.GolfTrainingAids.com3. http://www.golf-swing-analysis.com4. Petrofsky, et al. Med Bio Eng. Comput. 16:302-308,19795. Petrofsky, et al. J. Neurol. Ortho. Surg. 9:165-175,19836. Kilgore, et al. IEEE Trans. Rehab. Eng. 7:1, 19997. Tiebin, et al. Stroke. 36:80-85, 20048. Yamada T, et al. Proceedings of the ISBS Conference, Spain, Abstract, 163-167, 2002.9. Eccles DW, et al. Psychology of Sport and Exercise, 10, 96-107 (2009).

Kinetic, potential and total energy

AcknowledgementsThis work was supported by the Korea Science and Engineering Foundation(KOSEF) grant funded by the Korea government(MOST) (No. R11-2007-028-02001-0).

Elbow flexion/extension timing according to angular position

With the timing of the kip motion being of crucial importance for success of the kip (6), Figure 2 shows the hip flexion/extension timing. Angular position (x-axis) is defined as the angle that a line connecting the bar and the right anterior superior iliac spine creates with the vertical axis. Figure 2 illustrates that the ES group tended to have a more similar pattern with the expert group than the control group.(expert group This can be viewed between day 1 and day 2 by the tendency of the ES group to extend the hip at the later. This improvement can be attributed to the ES as the Control groups’ timing even with verbal explanation did not tend to have any significant change. With the timing of the hip flexion/extension closer to the expert groups timing the kinetic energy while passing under the bar and comparing it to the potential energy above the bar was investigated to explain why did the ES group even with better timing fail?

Figure 3. A graph of the right arm elbow flexion and the angular position

Events

FLEXIONSTART REVERSAL POINT

COG BELOW BAR EXTENTION FINISH

Hip flexion/extension timing according to angular position

Figure 2. A graph highlighting the hip flexion/extension pattern of the relevant groups verses the angular position

Figure 1. Shows the motion and events of the kip movement on the horizontal bar and the timing of the EMS signal

Table 2. Energy comparison between groups and days

Table 1. Hip flexion timing according to angular position

In the introduction we made the hypothesis that the total energy of the COG while passing back under the bar would be larger than the target energy i.e. energy while above the bar. The percentage difference between the target energy and the total energy for the expert group was 15%. On observation of the COG’s velocity, the maximum point sometimes occurred after the COG was directly under the horizontal bar. For the ES group, there was a tendency for the total energy gap to decrease from 28-23%, whereas for the control group there was the opposite tendency an increase from 20-24%.

Groups Day 1 Day 2 Expert Flexion started at about 25º 　

ES Flexion started at about 0º Flexion started at about 20ºControl Flexion started at about 5º Flexion started at about 15º