Human Motor

HUMAN MOVEMENT STUDIES

by Professor Joung H Mun, Ph.D., Department of Biomechatronic Engineering, College of Life Science & Technology, Sungkyunwan University, Korea

The Biomedical Engineering Laboratory was established in March 2003, in the Department of Biomechatronics Engineering, College of Life Science and Technology, Sungkyunkwan University, Korea by Professor. Joung H Mun who specialized in human motion analysis in biomedical engineering at the University of Iowa (title of doctorate : "Human Gait Analysis Using Multi-body Dynamics and Contact Modeling"). This lab mainly focuses on the study of human movement. The lab team comprises one Ph.D. candidate and four master's students along with seven undergraduate students, and they are as follows.
· Kyoungkee Min, Ph.D candidate, instructor at the Dept. of Biomedical Engineering, College of Seoul Health, in rehabilitation
· Daeseop Lim, master's program in human body modeling
· Taeyong Sim, master's program in sports biomechanics
· Hyoshin Kim, master's program in knee modeling and spine FEM
· Yonghoon Leem, master's program in bio-robotics

A Vicon 460 motion analysis system was installed in the laboratory in December 2002 as part of the project "Frontier Center for Imaging Human Structures" (FCIHS) in the Sungkyunwhan University supported by the Ministry of Health and Welfare. The Vicon system, together with six MCam2 cameras with a maximum frame rate of 1000Hz (red visible strobe), is working in the lab with two AMTI force platforms and 16-channel electromyography, EMG (20 to 2,000Hz) from Motion Lab Systems, Inc. This installation became a focus for the study of kinematics during normal gait, gait analysis in clinic applications, sports biomechanics, ergonomics and human body modeling and other projects.

Gait applications
The ability to respond rapidly to environment is a vital function not only for survival but also to avoid unexpected dangers such as collisions[1]. In this sense, gait should initiate reaction to these situations effectively in a steady manner. Reaction in gait varies depending on age. A previous study shows that the delayed reaction time is observed in elderly people, which is due to aging in sensory and motor systems[1] and the lack of momentum generated during initiation.[2]. Therefore, this study was conducted to investigate reaction times and steady-state gait in older adults in terms of vertical reaction force and muscle activity after gait was initiated corresponding to such signals as "sudden" and "ready". EMG was used to quantify muscle activity in both left and right lower limb - Gastrocnemius (GA), tibialis anterior (TA), vastus medialis (VM), rectus femoris (RF), and biceps femoris (BF)[3]. In addition, the Vicon 460 and AMTI force platforms were used to evaluate kinematic motion analysis and vertical reaction force, respectively.

The results show that reaction time to a sudden signal was longer compared to the ready signal. In addition, steady-state gait in older adults was completed within the second step based on the vertical reaction force and EMG data.

As the combined study with gait analysis for clinic applications, a human study of spinal stenosis has also been conducted. In this study, it is found that low back pain and claudication induced by neuromuscular stimulus are the main causes of abnormal gait. Particularly, spine as well as lower limb showed different kinematic patterns from normal motion. In detail, patients diagnosed with these conditions showed motion stiffness and whole reduction of angle magnitude except for forward oblique of body with respect to spine kinematics contrary to the normal. This lab tests gait in patients with spinal stenosis with much more segmentation of upper limb based on the previous studies[4, 5, 6] by attaching more markers to the subjects than the Plug-in-Gait marker set.

Sports applications
Even just a decade ago, golf in Korea was known as a sport popular with only privileged social class members, but due to the recent economic growth and enhanced social welfare, its popularity has been boosted dramatically. Now the golfing population has reached three million and is expected to increase substantially and more rapidly. As in any other sport, golf requires reliable technique and reflexes, leading to good swings and an ability to adjust to every given situation. In addition, high speed, accuracy and consistency are essential for good swing. This lab is involved in a scientific analysis project aimed at the improvement of golf technique as follows.
(i)The relationship between muscles (selected by previous studies[7, 8, 9]) during golf swing;
(ii)The correlation between transition of upper body during down swing and swing velocity at impact.

fig. 2

Since the rotation of upper limb and transition from right to left of body mass centered on the lower limb occur regularly during golf swing (Figure 2), it is critical to examine the relationship of muscle function involved in the swing motion. Muscle activities were measured by EMG, X-factor, during the transition of upper body at top swing and impact phase, and the horizontal velocity of left hand at impact were analyzed using the Vicon 460 (120Hz) system.

Figure 3 shows the relationship and its patterns of five muscles in the shape of an L, line, triangle, loop and T. Another experiment reveals that the transition of the upper body increased more during down swing; the more the swing velocity of left hand increased at impact between two groups with correlation coefficient at the same X-factor.
Based on these scientific swing motion analyses, it is believed to be a pointer towards enhanced performance.

fig 3

Ergonomics applications
Sit-to-stand is a common motion in daily lives, and although many researchers have studied each parameter including height of seat, foot position and potential existence of armrest, relationships between all of these parameters are still unknown. Therefore, the aim of this study is to discover the position that minimizes the moment of knee by representing maximum moment of knee as an equation of height of seat and angle of knee joint during sit-to-stand.

fig 4 Sit-to-stand. a means angle of knee joint

The frequency of EMG was set as 1080Hz, then attached to rectus femoris (RF), vastus medialis (VM) of muscles[10] - rectus femoris, vastus lateralis, vastus medialis and vastus intermedius, which is involved in the movements in reaching a position with legs apart. The force platform was sampled at the same frequency (1080Hz), and results were normalized by body weight. Height of seat was divided into 80%, 100% and 120% of knee height and foot position was classified as shown in Figure 5.

Data obtained in the above experiments were analyzed using a statistical method. In this analysis, height of seat and angle of knee joint (Figure 4) were considered. Results are being achieved quantitatively, relating to the position minimizing moment of knee by representing maximum moment of knee during sit-to-stand.

Likewise, sit-to-stand, and the motion of lifting are easily observed, for example, at a construction site, and it is hypothesized that this will correlate with a high incidence of low back pain. In numerous previous studies [11, 12, 13], low back pain is usually caused by external forces such as the motion of lifting. Therefore, the goal of this research is to minimize the risk of low back pain caused by the motion of lifting by investigating the relationship between muscle fatigue of paraspinal muscles and box size during frequent lifting.
The initial experimental condition was that the subjects had their feet set to coincide with shoulder width and knees straightened. Various sizes of boxes were used, and it was seen that muscle fatigue increased through an increase in the bending angle of the upper limbs as box size was varied larger or smaller than shoulder width. This concludes that low back pain can be minimized by lifting only shoulder width sized boxes.

fig 5

In conclusion, the Vicon 460 in the Biomedical Engineering Laboratory enables the study of gait analysis for clinic applications as well as normal gait, sports biomechanics and ergonomics. In addition, the modeling team developed 6DOF kinematic and kinetic model of knee joint so that it can be applied to the various studies described above. Finally, a study of FEM analysis of the spine will also be developed for the future.

References
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3. Okamoto T., Okamoto K., Andrew P. D., "Electromyographic developmental changed in one individual from newborn stepping to mature walking", Gait Posture, vol. 17, pp. 18-27, 2003
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8. John T. Kao, Marilyn Pink, Frank W. Jobe, Jaquelin Perry, "Electromyographic Analysis of the Scapular Muscles during a Golf Swing," American Orthopaedic Society for Sports Medicine, vol. 23, no.1, pp. 19-23, 1995.
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11. Darre E., Ammundsen A., Fabrin J., Hansen L. B., Thorstensson B., "Back", 1982.
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13. Riihimaki H., "Back pain and heavy physical work: a comparable study of concrete reinforcement workers and maintenance house painters", British Journal of Industrial Medicine, vol. 42, pp. 226-232, 1985.