The lower back, or trunk, has a functional muscular anatomy, frequently referred to as the core that is important to performance. Likewise, nearby musculature can have a strong influence on proper lower back function. Thus, it is not uncommon to have hypomobility (not much movement) in one segment of the lower back.
For example, the hamstring, even though it may be considered a lower extremity muscle group, can cause excessive forward flexion of the lumbar region due to the posterior pull on the pelvis. This is something I myself suffered with at one time, which resulted in excruciating pain when running. After many trips to the physician, it ended up in constant stretching and mobility exercises to help lengthen the hamstring muscle to stop the pulling on the pelvis.
Lower back pain responds well to spinal stabilisation exercise, posture correction and flexibility exercises. Proper assessment for either tightness or weakness of contributing musculature is essential, and common culprits are located in the hip such as; hip flexors, hip lateral rotators and hamstrings. The extensors of the lower back and abdominal muscles are essential in providing stability and support. Thus strengthening these areas will help greatly with the pain.
In general, when working with clients with lower back injuries, a proper assessment of flexibility or ROM (range of motion) should be conducted. Flexibility exercises to improve areas deficient in ROM may be done frequently and should not create pain, and may even need to become promoted in the opposite direction of painful motions. Establishing pain free lower back and neutral pelvic stabilisation exercises and body mechanics should be a primary strengthening goal, then progressing to trunk strengthening exercises and eventually more advanced stability and dynamic exercises.
Should the client have a considerable history of lower back pain or a lower back injury or experience an increase in symptoms, or if the personal trainer is unclear about the condition or status, you should immediately consult medical providers such as an athletic trainer, physical therapist or a physician.