Reliability, Validity and Minimal Detectable Change of a Power Leg Press Test in Individuals with Cerebral Palsy

Background: Lower extremity muscle power influences walking ability in individuals with Cerebral Palsy (CP). Aim: Determine the reliability, validity, and minimal detectable change (MDC) of a novel power leg press (PLP) test to measure muscle power in individuals with CP. Methods: Individuals with spastic CP (n = 26 (10 adults, 16 children); mean (SD) age = 19.3 (7.8) years(all); 27.9 (4.89) years (adults); 13.85(2.68) years (children)) performed 2 sessions of the PLP test, 2–10 days apart. A linear position transducer and custom computer code were used to calculate mean and peak power in watts (W). Intraclass correlation coefficients (ICC), standard error of measurement, MDC, and percent change of MDC (MDC%) were calculated for 4 power measures (average and maximum of mean and peak powers) for all participants (AP) and separately for adults (A) and children (C). Validity was evaluated against isokinetic knee extensor power. Results: Test-retest reliability was excellent for all measures of power (ICC = 0.94–0.99). Ranges for MDC/MDC% by the group for power measures were between 33.7–80.7W/15.5–29.4% (AP), 41.1–65.3W/10.7–22.3% (A), and 27.6–79.8W/19–34.3% (C). Correlations were good to excellent between PLP and isokinetic power at all speeds (r = 0.75–0.88, p <.001). Conclusions: The PLP test demonstrates excellent validity, reliability, and precision for measuring muscle power in those with CP.