The usability of six physical performance tasks in a rehabilitation population with chronic low back pain.

Objective: To examine the influence of task experience on the difference between test and retest and to assess test-retest reliability and limits of agreement of six performance tasks in chronic low back pain patients. These measures will be used to define the clinical usability.

Design: Test-retest of six performance tasks in a group of patients with no experience and a group of patients after previous experience with these tasks.

Setting: Three rehabilitation centres.

Subjects: Fifty-three patients with non-specific chronic low back pain.

Main Measures: Five-minute walking, 50-ft (15 m) fast walking, sit-to-stand, loaded forward reach, 1-min stair-climbing and Progressive Isoinertial Lifting Evaluation (PILE). To assess the influence of task experience, differences between test and retest between both groups were tested using Mann-Whitney test. For both groups together, intraclass correlation coefficients (ICCs) and the limits of agreement using Bland and Altman plots were calculated.

Results: Thirty patients with no task experience and 23 patients who had already undertaken the tasks on at least two occasions participated. Both groups showed similar differences between test and retest. The test-retest reliability for the total study population was good to very high: ICC varied from 0.74 to 0.99. For the total study population, the limits of agreement expressed as percentage of the mean score of each task was low to moderate for 5-min walking and 1-min stair-climbing (21% and 20% respectively), moderate for 50-ft (15 m) fast walking, sit-to-stand and forward reach (33%, 29% and 36% respectively) and high for the PILE (48%).

Conclusions: Task experience did not significantly influence test-retest differences. All tasks showed sufficient test-retest reliability. Based on the natural variability of the tasks, the 5-min walking and stair-climbing task, and to a lesser degree the 50-ft (15 m) walking, sit-to-stand and loaded forward reach, seem clinically useful. There are major concerns about the usability of the PILE.