Background Trunk forward bending is one of the most common activities in daily living; it is a two-part movement involving the lumbar spine flexion and pelvis rotation at hip joint. The pattern of movement during forward bending was defined as the relative contribution of the lumbar spine to pelvis motion, and was expressed as the ratio between the ranges of lumbar spine motion to pelvis motion (L/P), which, calculated at certain degrees of trunk flexion during the entire movement, provides the lumbo-pelvic rhythm. This is associated with a specific pattern of activation for back and hip extensor muscles which was coined as flexion relaxation phenomenon, observed either in the erector spinae and biceps femoris (BF). It has been shown that in healthy people lumbopelvic pattern of movement for entire flexion varies, showing both lumbar spine dominant and pelvis dominant-patterns of movement.

Objectives To find out whether the variation in the lumbopelvic pattern of movement (lumbar spine or pelvis dominant) affects the appearance of the relaxation of the BF during trunk forward bending.

Methods Surface electrodes were applied to the skin on right BF, midway between ischial tuberosity and head of fibula to record EMG during a trunk flexion movement from the upright position. The EMG signal was full-wave rectified and averaged (40ms) to produce a linear envelope. An electrogoniometer measured the differential lumbar spine - pelvis sagittal angular displacement during trunk flexion in asymptomatic subjects. Both signals (EMG and degrees) were synchronously and continuously captured during the movement. Ranges of flexion (ROF) for the lumbar spine, pelvis and trunk motion were calculated for the entire movement. The subjects (both sexes) were assigned to group-L (n=11) and group-P (n=15) according to exhibiting lumbar spine and pelvis dominant patterns of movement (average age,24.5±3.3years).The myoelectric relaxation (MR) appearance was defined in terms of degrees of flexion where the electrical activity of the BF was less than that in upright posture (EMG basal), at this point the degrees of flexion for the pelvis and spine were determined; and their respective “range of motion” (ROM) was calculated and normalized to range of trunk flexion. One-way MANOVA was used to determine differences in range of flexion at the appearance of the myoelectric relaxation between groups.

Results ROF for MR of the BF was significantly greater in group-P (77,3%±3,4%) (p<0.01) than in group-L (47,8%±2,4%) for the pelvis, whereas ROF for the lumbar spine was significantly greater in group-L 95%±1,2% (p<0.01) than in group-P 40,41%±1,7%.

Conclusions In healthy subjects, differences in lumbopelvic patterns of movement during trunk flexion vary the appearance of the relaxation of the biceps femoris in the range of flexion. Present results show that the variance of the lumbar spine and pelvis Kinematics is associated with the neuromotor control of the biceps femoris.

Acknowledgements Grants supporting present study: Ref. FIS2001–0070–01, Ref. TIC2001–2786- C02–02, Ref. AP2001–376

Disclosure of Interest None declared