Backrest Inclination Research Articles

Electromyographic investigation of extensor activity in cerebral-palsied children in different seating positions.

This study was designed to determine whether tonic myoelectric activity of low-back extensors of spastic cerebral-palsied children changed in response to changes in seating position, and if so, which position was coincident with the least extensor activity. Using two pairs of surface electrodes, the electrical activity of the lumbar erector spinae muscles was monitored in seven combinations of backrest inclinations (75 degrees, 90 degrees, 105 degrees and 120 degrees) and seat surface elevations (0 degrees and 15 degrees). Off-line analysis of action potential counts per second of recorded electromyographic signals showed that electrical activity was least when the seat surface elevation was 0 degrees and the backrest inclination 75 degrees. The results showed that differences existed in the activity of the low-back extensors in the seating positions that were assessed.

The Influence of Backrest Inclination and Lumbar Support on Lumbar Lordosis

The influence of backrest inclination and lumbar support on the shape of the lumbar spine in sitting positions has been studied radiographically on 38 healthy subjects. Four angles of backrest inclination and four different sizes of lumbar support were studied. In addition, the lumbar support was placed at three different lumbar levels. When sitting down from a standing position, the pelvis rotates and the lumbar lordosis decreases. Increases in the backrest-seat angle had only minor effect on the lumbar lordosis. A lumbar support, on the other hand, had a significant influence: the lordosis increased with increasing support. The location of the lumbar support with respect to the level of the spine did not significantly influence the measured angles.

The Sitting Posture: An Electromyographic and Discometric Study

The disc pressure of the third lumbar disc and the myoelectric activity of several muscles of the back were measured. Three standing and nine unsupported sitting positions were studied as well as eight support parameters and six sedentary tasks. 1. Myoelectric activity is about the same in standing and in relaxed unsupported sitting. In the unsupported sitting positions the highest level of activity is found in anterior sitting and the lowest in posterior sitting. In the muscles of the cervical and lumbar regions the activity is always lower than in the muscles of the thoracic region. The disc pressure is considerably higher in unsupported sitting than in standing. In the unsupported sitting positions the highest disc pressure is found in anterior sitting and the lowest in sitting straight. 2. Both the myoelectric activity and the disc pressure decrease when the back is supported. Of the support parameters, the backrest inclination is the most important, myoelectric activity and disc pressure both decreasing with an increase in inclination. The disc pressure is considerably reduced also when the lumbar support is increased and when armrests are used. 3. Myoelectric activity and disc pressure are both comparatively low in writing, higher in typing, and still higher in lifting. In the car driver's seat the disc pressure increases both when the gear is shifted and when the clutch pedal is depressed. When the gear is shifted, there is also an increase in myoelectric activity.