EMG and kinematics of normal subjects performing trunk flexion/extensions freely in space

Ten normal subjects performed continuous trunk flexion/extensions (F/E) wit hout any restraining apparatus at free, 3, 2.25 and 1.5 s periods and a fat iguing task of FIE at 1.5 s period during 45 s. Kinematics of the trunk was obtained with bilateral electromyographic (EMG) activity of the erector sp inae (three levels), the abdominal oblique muscles and the rectus abdominis muscles. The free period chosen by the subjects was found to vary between 3.05 and 1.47 s. Lateral flexion of the spine was similar in each task but rotation about its longitudinal axis increased as the F/E period shortened. When left and right side EMG signals were grouped by level of recording, a significant difference in activity was found. Subjects who produced the sl owest free F/E displayed larger fatigue indexes derived from the EMG signal s for some of their back muscles than for other subjects. The flexion/relax ation phenomenon was considered present in a muscle if a level <10% of the maximum signal recorded during extension was detected. The phenomenon was f ound in >50% of the observations and occurred at a similar angle in each ta sk. Kinematics and several characteristics of the EMG signals of the trunk were statistically independent of the speed of motion. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.