Study design: Isokinetically measured muscle strength of the trunk and lower extremities was analyzed.
Objectives: The causes of the weak trunk muscle strength of subjects with low back pain were studied.
Summary of background data: Although it is a commonly accepted conclusion that subjects with low back pain have weaker trunk muscles than the normal population, there are no reports concerning muscle strength of the lower extremities in subjects with low back pain.
Methods: Ninety-eight male volunteers were divided into control groups and groups with low back pain. The total trunk strength and total knee strength were defined as the sum of the peak torques of trunk extension, flexion and rotation, and of bilateral knee extension and flexion, respectively.
Results: The total trunk and knee strength in the group with low back pain (281 +/- 170 and 301 +/- 132 Nm) were significantly lower than in the control group (543 +/- 124 and 441 +/- 123 Nm). The total trunk and knee strength were linearly correlated in both groups (r = 0.67 and 0.79).
Conclusions: In the group with low back pain, the muscles of the trunk and the lower extremities were similarly affected; this can be attributed to generalized muscular weakness or psychologic factors, such as fear of injury.