Trunk-muscle strength during concentric and eccentric contraction: a comparison between healthy subjects and patients with chronic low-back pain.
The physical evaluation and exercise program of trunk muscles in patients with chronic low-back pain (CLBP) is still controversial. Many studies have been performed in the isometric and/or concentric contraction mode. Few data, however, have been reported on trunk-muscle strength during eccentric contraction, which plays a significant role in functional activities. To evaluate whether trunk-muscle strength on eccentric contraction could be applicable to the assessment and exercise of the patients with CLBP, trunk strength was measured in 20 healthy men and 16 healthy women, as well as 15 male and 10 female patients with CLBP. Maximum voluntary concentric and eccentric strength was measured during attempted flexion and extension in a seated position. In the healthy subjects, the maximum torque of extensors was greater than that of the flexors during both concentric and eccentric contraction (p less than 0.05). In flexors and extensors, maximum torque exerted on the eccentric contraction was always greater than that on the concentric contraction (p less than 0.05). Although strength was likely to be weaker in the patients with CLBP than in the healthy subjects, there were no statistical differences between the two groups. In terms of the flexor/extensor ratio of maximum torque, there were also no statistical significances between the two groups in either contraction mode. In the flexors, correlation coefficient (r) between concentric and eccentric torque was 0.84 for the healthy subjects and 0.48 for the CLBP subjects (p less than 0.05). In the extensors, the coefficient was 0.90 for the healthy patients and 0.71 for the CLBP patients.(ABSTRACT TRUNCATED AT 250 WORDS)