Compound Trunk Extension
Sagittal Plane Trunk Motion
During normal activities such as lifting and bending, compound movement of lumbar spine, pelvis and hip joints is required. This is COMPOUND TRUNK EXTENSION or LUMBOPELVIC RHYTHM
From full trunk flexion, lumbar extensors (erector spinae and multifidus) and hip extensors (gluteals and hamstrings) work together to rotate the trunk about 180º in the sagittal plane. Lumbar movement is 72º of this motion and hip and pelvis motion accounts for the other 108º. It is assumed that the larger hip extensors generate more of this latter force.
The pelvis is free to move during lifting and bending activities, so it is assumed that the lumbar muscles (small) play a minor role in trunk extension. They are thus considered a weak link in trunk extension movements.
Exercises which isolate the lumbar spine with pelvic stabilization force the lumbar extensors to become the primary trunk extensors, providing overload stimulus for strength gains. Dynamic progressive resistance exercises on devices which stabilize the pelvis have produced large gains in lumbar extension strength, even with a training frequency of once per week. Such exercises have also been shown to reduce low back pain.
NOTE: LOW BACK PAIN can have, among other causes, the following:
- Deconditioned lumbar spine
- Poor Posture
- Prolonged mechanical loading
- Poor body mechanics at home, work or sport activities
- One common mechanism of disc herniation is forceful flexion and rotation of lumbar spine