Study design: This study investigated the effects of the intensive physical rehabilitation program on the trunk and knee extensor muscles in patients with chronic low back pain. At baseline and after 3 months, strength was measured and muscle biopsies were taken.
Objectives: To evaluate the effects of strength exercises on the structure of back muscles.
Summary of background data: Rehabilitation designed for chronic low back pain patients improves trunk muscle strength, mobility of the spine, and the patients' functional capacity. The effects of such programs on the structure of back muscles have not been reported previously.
Methods: Thirty patients with chronic low back pain volunteered to participate in the study. Biopsies were taken from the multifidus and vastus lateralis muscles. The sizes of Types 1 and 2 muscle fibers were measured. The peak-torques of isokinetic trunk and knee extension were determined at two different angular velocities.
Results: Strength increased by 19-22% (P < 0.05) in trunk extension and by 7-11% (P < 0.05) in knee extension. Type 1 fibers maintained their pre-exercise size. The size of Type 2 muscle fibers in men increased by 11% (P < 0.05) in the multifidus and by 8% (P < 0.05) in the vastus lateralis. In women, the corresponding increases were 11% (P = 0.16) and 11% (P < 0.05). The correlation between the size of Type 2 muscle fibers in the multifidus and the strength of trunk extension improved, especially in men at follow-up.
Conclusions: The results of the present study suggest that training with maximal or submaximal effort may reverse the selective atrophy of Type 2 fibers in the multifidus muscles in men. Intensive training also can significantly increase the trunk extension strength in women, but women may need a longer training period than men to achieve significant structural changes in their back muscles.