Reproducibility and validity of a new test protocol for measuring isokinetic trunk extension strength

Objective. To investigate the reproducibility and validity of isokinetic trunk extension strength scores obtained using a range of motion of 20 degrees and velocities of 10 and 40 degrees /s. Background. Common protocols for testing trunk extension strength incorporate a range of motion of 40 degrees or more and test velocities of between 30 and 180 degrees /s. These test parameters may be neither necessary for portraying the strength profile of the muscles involved nor suitable for patients impaired with low back dysfunction. Design. Test-retest of maximal concentric and eccentric isokinetic trunk extension strength in healthy subjects. Methods. 17 women and 18 men were tested twice within 1-2 weeks. Tests were performed with subjects positioned in sitting. Results. The trunk extension strength scores revealed excellent agreement with the expected physiological moment-velocity curve. On average women's trunk extension strength was 62% that of men (range: 59.3-64.4%). The test-retest correlation coefficients were generally higher in women (0.70-0.87) than in men (0.52-0.78) and significant at P = 0.01. The standard error of measurement ranged between 13 and 21 N m for women and between 35 and 50 N in for men, which were equivalent to 9% and 15% of the mean strength in women and men, respectively. Conclusion. This study indicates that the present protocol may be validly applied in assessing trunk extension strength in normal women.