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the intervertebral discs, the contact of the chin or rib cage with the legs, and the abdominal fat mass. Similarly, trunk extension is controlled by the stiffness of the anterior trunk muscles, the stiffness of the anterior trunk ligaments, the strength of the extensor muscles, the alignment of the vertebral bodies with the adjacent vertebrae, and the compressibility of the posterior portions of the intervertebral discs. In addition to the factors listed for flexion and extension, trunk lateral movement is controlled by the impingement of each vertebra’s transverse process on the adjacent transverse processes. Trunk rotation is limited by the stiffness of spinal ligaments, the strength of the muscles on the side of rotation, the stiffness of the muscles opposite the side of rotation, and body tissues and their dimensions. For instance, rotating to the left is limited by weak left-side muscles and tight right-side muscles.
    Many people who have stiff back muscles have discovered that stretching helps relieve some of the pain. The back muscles, or trunk extensors, are not the only lower-trunk muscles to influence back pain. Often people find relief from back pain by leaning back (trunk hyperextension) because this action stretches the abdominal muscles, the trunk flexors. This shows that flexible trunk flexors are also important. Moreover, numerous sporting activities such as golf, tennis, and throwing sports require twisting of the trunk. Twisting the trunk involves the trunk extensors, flexors, and lateral flexors. Improved range of motion of all lower-trunk muscles can increase the range of motion in trunk rotation and improve the performance in activities that involve these actions.
    Hyperextension (arching) and hyperflexion (bending) of the lower back are potentially dangerous, especially if you have weak abdominal, thigh, and buttocks muscles. Backward rolling movements are potentially dangerous to the cervical spine (neck). Potential injuries include excessively squeezing the spinal discs, jamming together the spinal joints, and pinching the spinal nerves emerging from the lumbar vertebrae. If you choose to perform these stretches, build up to them more gradually than most other stretches. Also, to keep pressure off the neck during back rolls, keep the shoulder blades in contact with the floor.
    Overstretching (very hard stretching) causes more harm than good. Sometimes the muscles become stiff from overstretching. Overstretching can reduce muscle tone, and the body compensates by making the loose muscle excessively tight. For each progression, start with the position that is the least stiff, and progress to the next position only when, after several days of stretching, you notice a consistent lack of stiffness during the exercise. This means you should stretch both the agonist and antagonist muscles. Also, remember that although there may be greater stiffness in one direction (right versus left), you should stretch both sides so you maintain proper muscle balance.
    Many of the stretches in this chapter are described for the left side of the body. Similar but opposite procedures would be used for the right side of the body. The stretches in this chapter are excellent overall stretches. However, not all these stretches may be completely suited to each person’s needs. To stretch specific muscles, the stretch must involve one or more movements in the opposite direction of the desired muscle’s movements. For example, if you want to stretch the left external oblique, perform a movement that involves trunk extension and right trunk lateral flexion. When a muscle has a high level of stiffness, you should use fewer simultaneous opposite movements. For example, to stretch a very tight external oblique, start by doing only trunk extension. As a muscle becomes loose, you can incorporate more simultaneous opposite movements.

Supine Lower-Trunk Flexor Stretch

Execution
     
Lie on the floor on your back.
Place a rolled-up towel