Test-Retest Reliability of a Static and Dynamic Motor Fatigability Protocol Using Grip and Pinch Strength in Children with Cerebral Palsy

Abstract

Objective: The purpose of this study was to investigate the test-retest reliability, measurement error, and interpretability of new motor fatigability outcomes of grip and pinch strength for children with unilateral cerebral palsy (UCP). Methods: Motor fatigability during grip and pinch strength was measured twice (within 48 hours) in both hands of 50 children (mean age = 11 years 2 months; 14, 31, and 5 children with Manual Ability Classification System levels I, II, and III, respectively) using a 30-second static and dynamic maximum exertion protocol. For static motor fatigability, the Static Fatigue Index (SFI) and mean force (Fmean) in the first (Fmean1) and last (Fmean3) 10 seconds were calculated. For dynamic motor fatigability, Fmean1, Fmean3, and the number of peaks in the first and last 10 seconds were calculated. Results: For static motor fatigability, the intraclass correlation coefficients (ICCs) were moderate to high for Fmean1 and Fmean3 (0.56-0.88), and the SFI showed low to moderate reliability (ICC = 0.32-0.72). For dynamic motor fatigability, the ICCs were moderate to high for all outcomes (0.54-0.91). The standard error of measurement agreement and the smallest detectable difference agreement were large in all outcomes, except for the SFI in static motor fatigability. Details per age group are provided. In general, younger children (6-11 years old) showed lower reliability than older children (12-18 years old). Conclusion: Most outcome measures for static and dynamic motor fatigability of grip and pinch strength show moderate to high reliability in children with UCP, indicating that these tests can be used reliably to investigate the presence of motor fatigability in UCP, especially in older children. Standard error of measurement agreement and smallest detectable difference agreement indicated that these outcome measures should be interpreted with caution when evaluating change. Impact: Most of the proposed outcome measures for static and dynamic motor fatigability of grip and pinch are reliable in children with UCP and can be used for discriminative purposes.