Purpose: The primary purpose of this study was to determine the intrasession and intersession reliability of isometric force measurements using handheld dynamometry of the knee extensors and flexors and hip abductors in 15 children with cerebral palsy. A secondary purpose was to explore the relationships between muscle forces and standing and walking skills among these subjects.
Subjects: Fifteen children with spastic diplegic or quadriplegic cerebral palsy (mean age, 11.7 +/- 3.6 years) participated.
Methods: Two test sessions were separated by four to 14 days. Isometric force production was measured for three muscle groups bilaterally using a handheld dynamometer. Reliability was measured using the intraclass correlation coefficient (ICC 3,1) and the standard error of measurement. The relationship between muscle force values and standing and walking skills [measured with the Gross Motor Function Measure (GMFM), Dimensions D and E] was examined using Pearson's correlation coefficient.
Results: Except for left knee flexion, the intrasession and intersession ICCs were 0.84 or greater. The standard errors of measurement ranged from 6.72 to 25.26 N. GMFM Dimensions D and E were positively related to normalized hip abductor force. GMFM Dimension E and the sum of Dimensions D + E were positively related to normalized knee flexor force.
Conclusion: This group of children with cerebral palsy demonstrated primarily good to high reliability coefficients for isometric force measurements of three lower extremity muscle groups using handheld dynamometry. We suggest that physical therapists use the standard error of measurement for individual clients to help them distinguish measurement error from true changes in muscle force production.