The purpose of this study was to evaluate the effect of asymmetric muscle force in lower extremity on dynamic balance during walking. Sixteen elementary students(age: 12.3±0.7 yrs, height: 149.4±9.7 cm, weight 40.6±7.8 kg) who have no musculoskeletal disorder were recruited as the subjects. Temporal parameters, M-L inclination angle of XCoM-CoP, M-L and A-P CoP, loading rate, and decay rate were determined for each trial. For each dependent variable, a independent-sample t-test was performed to test if significant difference existed between each conditions(p<.05). The displacement of antero-posterior COP during RTO-LHC1 in SG was siginificantly smaller than corresponding value in AG. In contrast, the displacement of medio-lateral COP during RTO-LHC1 in SG was greater than those of AG. It seems that imbalance of muscle force may result in increasing the medio-lateral stance in order to minimize the instability. We found that the asymmetric muscle force in the lower extremity may be a reason for the awkward control of impact force.

The purpose of this study was to evaluate the effect of angle change of forefoot's adhesive outsole on the electromyographic activity (EMG) of the erector spinae and selected lower limbs muscle during downhill walking over -20 o ramp. Thirteen male university students (age: 25.4±3.9 yrs, height: 176.2±5.1 cm, weight: 717.4±105.0 N) who have no musculoskeletal disorder were recruited as the subjects. To assess the myoelectric activities of selected muscles, six of surface EMG electrodes with on-site preamplification circuitry were attached to erector spinae (ES), rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), lateral gastrocnemius (LG), and medial gastrocnemius (MG). To obtain maximum EMG levels of the selected muscles for normalization, five maximum effort isometric contraction were performed before the experimental trials. Each subject walked over 0 o and 20 o ramp with three different forefeet's EVA outsole (0, 10, 20 o ) in random order at a speed of 1.2±0.1 m/s. For each trial being analyzed, five critical instants and four phases were identified from the recording. The results of this study showed that the average muscle activities of MG and LG decreased in 20 o shoes compared to 0 o and 10 o ones in the initial double limb stance (IDLS). In initial single limb stance (ISLS) phase, the average muscle activities of ES increased with the angle of forefoot's adhesive outsole, indicating that the increment of shoes' angle induce upper body to flex anteriorly in order to maintain balance of trunk. In terminal double limb stance (TDLS) phase, average muscle activities of TA significantly increased in 20 o outsole compared to 0 o and 10 o ones. There was no external forces acting on the right foot other than the gravity during terminal single limb stance (TSLS) phase, all muscles maintained moderate levels of activity.