Objective: To investigate the short- and long-term reliability of isometric trunk strength measurements in patients with chronic low back pain in different age groups.
Design: Test-retest reliability study.
Patients: A total of 210 patients (age groups 18-39, 40-59 and 60-90 years).
Methods: Patients performed testing at baseline, 1-2 days (day 2) and 6 weeks.
Results: Only the oldest age group showed similar extension strength on all three test days All age groups showed significant changes in rotation and flexion scores from baseline to 6 weeks. Younger age groups (18-39 and 40-59 years) showed significant increases in extension, flexion, and rotation strength at both short-term (baseline to day 2) and long-term (baseline to 6 weeks) retests, but not from day 2 to 6 weeks. In patients over 60 years of age the smallest real differences normalized to baseline (%) were smaller from day 2 to 6 weeks than from baseline to 6 weeks. Long-term intraclass correlation coefficients were lowest between baseline and 6 weeks. No relevant impacts of feelings, motivation, or pain on reliability were detected.
Conclusion: Reliability of isometric trunk strength measurements in patients with chronic low back pain is similar in older and younger patients. Short-term test repetition a few days after baseline is recommended, if clinically feasible, and especially in research evaluating the effects of exercise on strength.