Assessment of postural muscle strength in sitting: reliability of measures obtained with hand-held dynamometry in individuals with spinal cord injury.

BACKGROUND AND PURPOSE Muscle weakness frequently impairs the ability to maintain upright sitting in individuals with spinal cord injury (SCI). The primary purpose of this study was to examine the intrarater and interrater reliability of hand-held dynamometry to assess postural muscle strength for maintaining upright sitting in individuals with SCI. We also assessed reliability of forces measured in four directions of force application and of measures obtained by experienced versus student physical therapist examiners. METHODS Twenty-nine individuals with SCI (mean age, 32.4 +/- 11.0 years; injury level C4-L1; American Spinal Injury Association Impairment Scale (AIS) classification A-D) participated in this study. The raters were two experienced physical therapists and two student physical therapists. Force was applied to the anterior, posterior, and right and left lateral trunk. Values were acquired in a group of participants who did not require upper extremity support for sitting (n = 22) and a group who did require upper extremity support (n = 7). RESULTS Intrarater reliability was good to excellent (intraclass correlation coefficients, 0.80-0.98 [unsupported]; 0.79-0.99 [supported]) for all raters in the four directions of force application. Interrater reliability was excellent (intraclass correlation coefficients, 0.97-0.99 [unsupported]; 0.96-0.98 [supported]) for all directions. There were no significant differences among peak forces obtained among the four directions of force application or by experienced raters compared with student raters. DISCUSSION AND CONCLUSION The use of hand-held dynamometry to assess postural muscle strength for maintaining upright sitting in individuals with SCI has high intrarater and interrater reliability. The direction of force application and experience of the rater did not influence the level of reliability. Future research is needed to identify the minimum muscle strength required to maintain the seated posture and to understand how this measure relates to seated postural control and balance.