Lin-Hwa Wang

Comparison of segmental linear and angular momentum transfers in two-handed backhand stroke stances for different skill level tennis players.

The purpose of this study was to investigate the differences of momentum transfer from the trunk and upper extremities to the racket between open and square stances for different skill levels players in the two-handed backhand stroke. The motion capture system with twenty-one reflective markers attached on anatomic landmarks of the subject was used for two-handed backhand stroke motion data collection. Twelve subjects were divided into an advanced group and an intermediate group based on skill level. The three-dimensional linear and angular momentums of the trunk, upper arm, forearm, hand and racket were used for kinetic chain analysis. Results showed that all players with the square stance had significantly larger backward linear momentum contribution in trunk and upper arm than with the open stance (p<.05) irrespective of playing level. However, the external rotation angular momentum of the shoulder joint was significantly larger with an open stance than with a square stance (p=.047). Comparison of playing levels showed that the intermediate group performed higher linear momentum in three components of the trunk, upper arm backward linear momentum, and trunk right bending angular momentum than the advanced group significantly (p<.05). The advanced group reduces trunk linear movement to keep stability and applies trunk and linkage segment rotation to generate backhand stroke power. The advanced group also has a quick backswing for increasing acceleration and maintains longer in the follow-through phase for shock energy absorption. This information could improve training protocol design for teaching the two-handed backhand stroke and teaching players, especially beginners, how to make an effective stroke.

MULTIJOINT COORDINATION OF LOWER EXTREMITY IN TAI CHI EXERCISE

The goal of this study was to investigate the movement coordination among the hip, knee, and ankle joints during solo performance of the Tai Chi (TC) basic movements in order to understand its dynamic postural control. Nine male community-dwelling adults with experienced TC pushing hands participated in this cross-sectional study. The Eagle® motion analysis system with eight cameras was used to collect the trajectories of all reflective markers at sampling rate 100 Hz while the subject performed the ward-off, rollback, press, and push movements. Motion among the hip, knee, and ankle joints was highly coupled. Coupled joint motion, hip flexion-knee flexion-ankle dorsiflexion or reverse, existed in ward-off, rollback, and press phases for the front leg. However, in the push phase, the hip joint angle was kept almost constant with coupled knee and ankle motions. For the rear leg, coupled motion existed between the hip and the knee joints only. The ankle joint motion differed between the front and the rear legs during the basic movements of TC (p < 0.05). Basic characteristics were documented such as the forward knee never extending further than forward toe and both legs maintaining flexion during the full exercise cycle with hip and knee of front and rear legs having synchronized movements in opposite directions. The forward and backward shifts of TC basic movements have considerable contributions to the posture control in terms of the fine coordination of three lower extremity joints. This information could improve training protocol design for TC Chuan teaching and help beginners make an efficient and less damaging movement.

POSTURE AND GROUND REACTION FORCE RELATED INFLUENCES ON TAI CHI PUSHING MOVEMENT

The goal of this study was to investigate the differences in ground reaction force during a Tai Chi Chuan (TCC) pushing movement between those with and without TCC experience through a detailed 3D dynamic analysis of the lower extremities. Seven TCC practitioners who had practiced the TCC push-hands movement for 6.0 ± 4.8 years and eight males without any TCC experience were recruited in this study. An eight-camera Expert Vision Eagle motion analysis system and two Kistler force plates were used to collect kinematic data (100 Hz) and the ground reaction force (1000 Hz). About 34 retro-reflective markers were placed on anatomical significant locations that determine embedded axes for segments. Results showed that the angular motions of the knee joint were different between the two groups, both in pattern and magnitude. Compared with the TCC group, the non-TCC group had significantly smaller peak abduction angles at the ankle joint (p < 0.05). The magnitude of the vertical force of the TCC group was greater, whereas the medial and posterior shear forces were smaller. The significant difference in vertical force (p < 0.05) and fraction opponent force of vertical force were found significantly different (p < 0.05) between the two groups. The patterns of the anteroposterior component of the ground reaction force during pushing were different, but those for the other two components were similar. Different lower-limb kinematics and kinetics were found between those with and those without TCC experience during TCC pushing movement and it was also found that the TCC practitioners could generate more effective force transfer than the group with no prior TCC experience. It was further concluded that vertical force plays an important role in a pushing movement, and posterior force exerted from the opponent was absorbed and transformed into anterior force to help the TCC practitioners remain stable.

Lower Limb Loading in Step Aerobic Dance

Participation in aerobic dance is associated with a number of lower extremity injuries, and abnormal joint loading seems to be a factor in these. However, information on joint loading is limited. The purpose of this study was to investigate the kinetics of the lower extremity in step aerobic dance and to compare the differences of high-impact and low-impact step aerobic dance in 4 aerobic movements (mambo, kick, L step and leg curl). 18 subjects were recruited for this study. High-impact aerobic dance requires a significantly greater range of motion, joint force and joint moment than low-impact step aerobic dance. The peak joint forces and moments in high-impact step aerobic dance were found to be 1.4 times higher than in low-impact step aerobic dance. Understanding the nature of joint loading may help choreographers develop dance combinations that are less injury-prone. Furthermore, increased knowledge about joint loading may be helpful in lowering the risk of injuries in aerobic dance instructors and students.

Biomechanical effect of ankle Kinesio taping on the ground impacts during the vertical jump landing

The injuries in the lower limbs are common at the sports, and one of the most common injuries is ankle sprain. Kinesio taping is one of the useful treatments of ankle sprain. The objective of this study is to investigate the biomechanical effects of ankle Kinesio taping on ground impacts during the landing of vertical jump, and the effect of ankle Kinesio taping on vertical jump in functional instability. Two AMTI force plates and VICON motion analysis system were used to collect kinematic and kinetic data. The result of this study showed that the ankle Kinesio taping can reduce the functional instability groups time to ankle second peak ground reaction forces, and decrease the first peak vertical ground reaction forces and the integrated impulses after landing. There was no significant effect of ankle Kinesio taping on the biomechanical parameters of ground impact in the control group.

EFFECTS OF CAMBER ON PUSHRIM FORCE DURING WHEELCHAIR PROPULSION

INTRODUCTION The camber of the wheelchair plays an important role in many wheelchair exercises. There are many researches concerning about the design of wheelchairs and the parameters of physiology during propulsion, especially energy consumption. However, the literature on effects of wheel camber is not available. Therefore, the study aimed to investigate how the rear wheel camber affects the pushrim force during high-speed wheelchair propulsion.

GROUND REACTION FORCE AND POSTURAL ADAPTATION OF THE PUSH MOVEMENT IN TAI CHI

INTRODUCTION The basic principles of Tai Chi Chuan (TCC) are the same in spite of several different schools or styles [1]. For increasing ones skill, Tai Chi is practiced from single action to a complete boxing frame and learned from a single-practitioner practice to push-hands, two-person training. The push-hands in TCC is an important skill to make the opponents lose their own balance while practitioners still maintain the stability through changing defensive positions without losing ground. How do Tai Chi (TC) practitioners sense and adapt themselves to their opponent’s demands without losing their root? The purpose of this study was to investigate postural stability in terms of ground reaction forces during pushing hands in Tai Chi.

Joint loading of lower limbs in leg curl movement during high and low impact step aerobic dance

Study of the kinetics of lower limbs in step aerobic dance is helpful to the understanding the mechanism of injuries. This study implies that high impact situations not only create significant joint forces and moments, but high rates of axial and shear force application that could be associated with excessive joint wear.

Posture stability in lateral slope walking

Objective: To investigate the dynamic posture stability during lateral slop walking in terms of temporal distance parameters of gait cycle and the center of pressure (COP) and compare the differences between the side step and cross step. Materials & Methods: An EVaRT system with nineteen reflective markers, two force plates, and the foot switch sensors were used to measure the body movements, ground reaction forces and temporal parameters, respectively, during lateral walking on an inclined walkway with 5° tilt. Twelve normal subjects participated in this study. The subjects were instructed to walk with right leg leading from the bottom to the top of the slope at the self-selected speed using side step and cross step, respectively. The data were collected for 8 seconds for each trial. Results: Different gait pattern was found in the first and second force plate during the cross-step and the side-step walking. The result indicated that the increasing degree of inclination of the slope would cause the factor of unstable posture. The value of anterior/posterior deviation of the cross-step walking was larger than the side-step walking (P <.05). The maximal shift velocity of COP in the single-right foot stance phase during the side-step walking was much faster than in the cross-step walking (P <.05). The similar result was obtained in the single-left foot stance phase (P <.05). Conclusions: The primary finding of the study is that the cross-step walking is more unstable than the side-step walking. And the forward velocity of the cross-step walking is faster than the side-step walking. If there are unstable factors of cross-step walking concluded, the less smooth gait will be expected.