Reliability of Hand-Held Dynamometry for Measuring Force Production in People with Parkinson's Disease

Purpose: People with Parkinson's disease (PD) have impaired force production, which is associated with decreased mobility and falls risk. Reliable measurement of force production is important. Design: A repeated-measures, intra-and inter-rater reliability study was undertaken. Participants: 24 people with mild PD were measured by one or two raters. Outcome measures: Isometric force of the major upper and lower limb muscle groups was measured using hand-held dynamometry. Results: Fourteen participants were measured by the same rater on two occasions to determine intra-rater reliability. Ten participants were measured on two occasions by two different raters to determine inter-rater reliability. The intra-rater reliability of hand-held dynamometry was excellent in every muscle group, except the dorsiflexors. Intra-rater reliability was highest when measuring wrist extensors (ICC(2,1) = 0.98, 95% CI: 0.94 to 0.99) and lowest when measuring ankle dorsiflexors (ICC(2,1) = 0.87, 95% CI: 0.43 to 0.97). Inter-rater reliability was variable ranging from poor (wrist flexors: ICC(2,2) =-0.15, 95% CI:-1.14 to 0.60) to excellent (grip strength: ICC(2,2) = 0.97, 95% CI: 0.88 to 0.99). Conclusion: Hand-held dynamometry has good to excellent intra-rater reliability, but poor inter-rater reliability, for measuring force in the upper and lower limb in people with mild PD.