Reproducibility of dynamometric and non-dynamometric trunk extensor muscle tests in patients with chronic low back pain

Background and Aims:
Literature describes several dynamometric and non-dynamometric tests to assess trunk extensor muscle performances. In patients with chronic low back pain (CLBP), reproducibility of such assessments remains understudied. The purpose of this study was to compare reproducibility of two dynamometric tests and of the widely used Sorensen test.

Methods:
44 patients (22 men, 22 women; age range: 30-60 years) with CLBP (mean Roland-Morris disability scores reaching 6 ± 3.4) were randomized into two groups attending two assessment sessions. Group 1 (12 men and 12 women) underwent two tests (i.e. a maximal strength test (figure 1) and a static endurance test requiring to maintain as long as possible a torque of 50 percent of maximal strength previously determined (figure 2)) performed on a specific trunk extensor dynamometer (David Back). Group 2 (10 men and 10 women) was submitted to the non-dynamometric Sorensen test (lifting the upper trunk and maintaining the horizontal position) (figure 3). For both groups, tests were performed twice (spaced by 15 minutes) during the first session (intra-session reproducibility) and once during the second session (inter-session reproducibility) happening 2 to 7 days later.

Results:
Mean torques reached 2.67 ± 0.63 Nm/Kg (women) and 3.66 ± 0.75 Nm/Kg (men) for the strength test. Mean maintaining times were 83 ± 34 s for the endurance test and 99 ± 28 s for the Sorensen test.
The Table presents coefficient of variations (CV) and limits of agreement (LOA) related to the intra-session and inter-session reproducibility.

Conclusions:
Reproducibility appeared satisfactory for the strength test, moderate for the Sorensen test and low for the dynamometric endurance test in patients with moderate CLBP.