Tehran University Medical Journal

Background: One of the most important concerns in orthopedic medicine is the low back. Considering the importance of muscle function in preventing LBT by controlling too much load and stress applied on the spinal joints and ligaments.

Materials and Methods: The aim of this research was to determine the timing and level of activities of lumbopelvic muscles in response to postural perturbations caused by unexpected loading of the upper limbs in standing on three different supporting surfaces (neutral, positive slope, negative slope) in 20 healthy females 18 to 30 years old ( = 23.20 SD = 2.55 ). The electromyographic signals were recorded from the deltoid, gluteus maximus, internal oblique abdominis and lumbar paraspinal muscles of the dominant side of the body to evaluate the onset time, end time, level of muscle activity (RMS) and duration of different muscles in one task and one muscle in different tasks.

Results: The results showed that the agonists (posterior muscles) activated at first to compensate the flexor torque caused by loading and then the antagonists (anterior muscles) switched-on to compensate the reaction forces caused by agonist activities. With regards to continuous activity of internal oblique and its attachments via thoracalumbar fascia to the transverse processes of the lumbar vertebrae, it can be considered as one of the major stabilizer muscles of the trunk .

Conclusion: Finally the results indicated that supporting surface type didn’t have any effect on timing and scaling of muscle activities in different tasks suggesting that probably spinal and trunk priprioceptors are just responsible for triggering postural responses and they don’t have any role in determining timing and scaling.

Background: Joint trauma and injury are the most common causes of dynamic instability. Dynamic instability has a great effect on the lumbar spine, due to its three-dimensional motions. The greatest amounts of compression and shearing force are imposed at the points of maximum torque and velocity. The changes in these phase angles upon bearing various loads can cause some pathologic conditions. In this study, we examined the phase angle at maximum torque and velocity in the three planes of movement and then estimated their displacement upon external loads.

Methods: Using the B200 isoinertial dynamometer, 13 subjects were tested in three stages as follows: 1) Familiarization with tests and apparatus. 2) Warm-up and three maximum isometric tests, with a rest interval between each test, in the three axes of lumbar motion including: flexion/extension, rotation to right/left, lateral flexion to the right/left. 3) Five dynamic tests in these three axes of motion without load, with 25% maximum voluntary torque, and with 50% maximum voluntary torque. Special software was used to analyze the raw data and detect the occurrence of maximum torque and velocity in the dynamic range of motion at each of the three axes.     

Results: When the load was increased, the maximum dynamic torque in each of the three axes increased (P<0.05). The increase in load shifted the phase angles toward the maximum torque and velocity (P<0.05), with a positive correlation between changes in torque and velocity phase angles (P<0.05).

Conclusions: Rather than being a function of the biomechanical pattern, the changes in maximum torque and velocity of the phase angles following an increase in motion resistance to the outer range of the three axes are actually a control behavior in the motion processing system in dynamic movement.