Capacity, Capability, and Performance: Different Constructs or Three of a Kind?

OBJECTIVES: The present study focused on motor activities of young children with cerebral palsy (CP) and examined the relation between motor capacity (what a person can do in a standardized, controlled environment), motor capability (what a person can do in his/her daily environment), and motor performance (what a person actually does do in his/her daily environment). DESIGN: The relations between motor capacity, motor capability, and motor performance were calculated by using Pearson correlations and visualized by scatterplots. SETTING: A cross-sectional study of a hospital-based population of children with CP. PARTICIPANTS: Subjects were children with CP (N=85) aged 30 months (Gross Motor Function Classification System levels I-V). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Motor capacity, motor capability, and motor performance were assessed with the Gross Motor Function Measure and 2 scales of the Pediatric Evaluation of Disability Inventory, respectively. RESULTS: Correlations between motor capacity, motor capability, and motor performance were high, between 0.84 and 0.92, and significant (P< .001). But when comparing children with the same level of motor capacity or motor capability, large ranges at the level of motor performance were found. CONCLUSIONS: Results imply that motor performance levels are only partly reflected by the motor capacity and motor capability levels in young children children with CP. Contextual factors (physical and social environment) and personal factors (such as motivation) influence the relations between capacity, capability, and performance. This information is essential in making decisions about the focus of therapy to maximize a child's independent functioning in daily life.