ABSTRACT
Objective To observe electromyography (EMG) activity and kinematic characteristics of the dorsal and ventral muscles during extension-flexion of the trunk． Methods Ten healthy male subjects stood on a test platform, performing the front and back lifting and lowering. The EMG activity of 10 muscles (rectus abdominus, external oblique, gluteus medius, erector spinae, multifidus), the angular movement, the plantar center of pressure (COP) were recorded at the same time. The average amplitude of EMG, contribution ratio of muscles, and COP displacement were calculated, and statistical analyses of all the data were conducted． Results During front lifting and lowering, the activity of dorsal muscles was greater than that of ventral muscles under both loading and unloading, and the contribution ratio of dorsal muscles was increasing with loading. During back lifting and lowering, the activity of ventral muscles was slightly greater, but the contribution ratio of both dorsal and ventral muscles was very close. The contribution ratio of ventral muscles was increasing with loading, while the activity of dorsal muscles decreased. The activity of gluteus medius was increasing with loading, but the contribution ratio was basically consistent under both loading and unloading. Conclusions During extension-flexion of the trunk, muscle activation varies with the load size and trunk position. Under loading at front, dorsal muscles are working as an agonist, while ventral muscles as antagonist; under loading at back, ventral muscles become an agonist and dorsal muscles as a co-activator. The activity of gluteus medius might play a role of stabilization during front and back lifting and lowering.
ABSTRACT
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.