Background: Quantifying leg muscle strength in young children with cerebral palsy (CP) is essential for identifying muscle groups for treatment and for monitoring progress.
Aim: To study the feasibility, intratester reliability and the optimal test design (number of test occasions and repetitions) of measuring lower-limb strength with handheld dynamometry (HHD) and dynamic ankle plantar flexor strength with the standing heel-rise (SH) test in 3-10 year aged children with CP.
Design: Test-retest design.
Setting: Rehabilitation centre, special needs school for children with disabilities, and university medical centre.
Methods: Knee extensor, hip abductor and calf muscle strength was assessed in 20 ambulatory children with spastic CP (3-5 years [N.=10] and 6-10 years [N.=10]) on two test occasions. Intraclass correlation coefficients (ICC) and Smallest Detectable Differences (SDD) were calculated to determine the optimal test design for detecting changes in strength.
Results: All isometric strength tests had acceptable SDDs (9-30%), when taking the mean values of 2-3 test occasions (separate days) and 2-3 repetitions. The one-leg SH test had large SDDs (40-128% for younger group, 23-48% for older group).
Conclusion: Isometric strength (improvements) can only be measured reliably with HHD in young children with CP when the average values over at least 2 test occasions are taken. Reliability of the SH test is not sufficient for measuring individual changes in dynamic muscle strength in the younger children.
Clinical rehabilitation impact: Results of this study can be used to determine the optimal number of test occasions and repetitions for reliable HHD measurements depending on expected changes, muscle group and age in 3-10 year old children with CP.