Primary outcome measure
The GMFM is a tool used to measure the child’s capacity for gross motor function. Capacity refers to a person’s underlying ability to perform in a standardized environment. It has been widely used to measure changes in gross motor function over time and the effectiveness of interventions. Items on the GMFM-88 are grouped into five dimensions: A: lying and rolling (17 items); B: sitting (20 items); C: crawling and kneeling (14 items); D: standing (13 items); and E: walking, running and jumping (24 items). The GMFM-66 was developed using Rasch analysis of the GMFM-88, whereby 22 of the original 88 items were deleted to improve reliability and validity. Of the 22 items deleted, 13 were from the lying and rolling dimension, 5 were from the sitting dimension and 4 were from the kneeling and crawling dimension. The GMFM-66 represents the unidimensional construct of gross motor ability according to task difficulty and thus is recommended for research purposes when comparing changes in gross motor function over time in children with CP. However, the GMFM-66 is much less useful when scoring children with a severe disability. Therefore, both the GMFM- 66 and GMFM-88 were used to assess gross motor function in this study.