EMG characteristics of lower extremities during movement of white crane spreads its wings in Tai Chi Quan / 医用生物力学

Objective To analyze how the athletes control postural balance through observing their joint angular motion change，center of pressure (COP) change and EMG activities of lower extremities for both athletes and beginners when performing the movement of white crane spreads its wings in Tai Chi Quan. Methods Twenty subjects were divided into 2 groups as 10 athletes and 10 beginners of Tai Chi Quan in each. When performing the movement of white crane spreads its wings, their EMG activities of 10 skeletal muscles, two-dimensional angular motion of 3 large joints in bilateral lower extremities, and COP displacements in lateral and anterior-posterior directions were recorded. Each performing trial took 8 seconds and repeated 5 times. All data were statistically processed for EMG, motion and balance analysis, and the EMG data were normalized to compare the differences between the athletes and beginners of Tai Chi Quan. Results The EMG activities of tibialis anterior(Ta), biceps femur(bF), gluteus medium(Gm) in support leg of athletes were significantly greater than those of the ipsilateral muscles in support leg of beginners, and the same was the EMG activities of gastrocnemius (G) and rectus femur（rF) in virtual leg of athletes compared with the beginners. The maximal average angular motion of 3 large joints and the coxa -joint motion of support leg in athletes were both significantly greater than that in beginners, but the anterior-posterior COP displacement in athletes was significantly smaller than that in beginners. Conclusions When performing the movement of white crane spreads its wings in Tai Chi Quan, athletes could oppose the COP change by enhancing muscle activities to maintain the postural balance, while beginners couldn’t make such active muscle activities against the uncontrolled anterior-posterior COP displacement. This may preliminarily explain the reason why Tai Chi Quan exercise can improve the muscle strength in lower extremities and enhance the ability of postural control.

Effect of passive motion of from lower extremity on muscle fatigue when the back under head-down tilting / 医用生物力学

Objective To study the effect of passive motion from lower extremity on electromyography (EMG) activity of major muscles when the back under head down tilting state. Methods Thirty healthy subjects were selected. The EMGs of erector spinal and trapezius muscles were recorded and analyzed when human body was under head-down tilting at angel of 0°, 10°, 20° and 27° in static mode, respectively, in sway mode (along the axis of Z with frequencies of 120 and 140/min， respectively) and in vibration mode (along the axis of Y with frequency of 680/min) with the help of multifunctional test bed. Results In the static mode, the median frequency (MF) decreased with the increase of head-down titling angle; in the sway mode, the MF at each of 4 head-down tilting angles was smaller than that in the static mode. When the frequency was 120/min, the MF decreased with head-down tilting angle increasing, but when the frequency reached 140/min, the variation of MF became irregular. In the vibration mode, the MF increased with the increase of head-down tilting angle and was larger than that in the static mode. Conclusions In the static mode, the muscle fatigue increased with the head down tilting angle increasing; in the vibration mode, smaller head-down tilting angle should be selected to achieve better treatment effect; but in the sway mode, larger head-down tilting angle would be better, and the sway frequency should be set lower than 120/min to avoid potential damage due to excessive muscle fatigue.

Movement of trunk and surface electromyography under symmetric loading and unloading with static posture / 医用生物力学

Objective To observe the electromyography (EMG) activities and kinematic characteristics of the back, abdomen and hip muscles under the static symmetric loading and unloading with the flexion and extension posture. Methods Six healthy male subjects stood on a specially designed testing platform, doing flexion/extension under symmetric loading and unloading, respectively. Each trial lasted 4 seconds and was repeated 3 times. The EMG activities of 10 muscles(rectus abdominis，obliquus externus abdominis，erector spinae，multifidus，gluteus Medius), the 3D angular movement, the plantar COP (center of pressure) were recorded during the trial.The normalized EMG, trunk angle and COP displacement were calculated, and statistical analyses of all data were made. Results Muscle activities of the back were greater (10.47~16.94) with flexion both under loading and unloading. Muscle activities of the abdomen were greater with extension under unloading, and those of the back (3.70~17.95) and hip (6.64~11.52) were increasing under loading, with muscle activities of the abdomen decreasing (10.66~4.18). The flashing trunk numbers was increased with the increase of loading, especially 1.55-time increase in the trunk angle. The COP displacement in anterior posterior direction was shifted greater than that in lateral direction, and this shift was more during flexion (14.60) than that during extension (7.65).Conclusions Extension increases the activities of back muscles, especially for multifidus, and it also increases the torso angular displacement and flashing trunk numbers, especially under loading.