Estimating the Difficulty Level of Motor Practice During Physical Therapy in Young Children with Cerebral Palsy

Purpose/Hypothesis: Infants with typical development continually challenge their motor skills by practicing more difficult movements and postures as their skills develop. Practicing challenging skills is presumably important for motor skill acquisition, but this has not been studied in children with cerebral palsy (CP). Our objective was to quantify the difficulty level of motor practice during physical therapy (PT) in young children with CP.

Number of Subjects: Twenty toddlers with CP (12 boys, mean age 26.9 months, GMFCS level I-IV) were included. Children were enrolled in a clinical trial (NCT#02340026) and could not take independent steps.

Materials/Methods: Children were randomly assigned to conventional PT (dose-matched control group) or to an intervention designed to facilitate practice of skills beyond the participant’s current level of function using dynamic weight support (experimental group). Participants were stratified by age and motor function to ensure equivalence at baseline. The Gross Motor Function Measure (GMFM-66) was scored by a blinded assessor at baseline and after 12 weeks. Difficulty level of motor practice during therapy was determined by estimating a GMFM score from manually coded videos of randomly selected PT sessions (116 videos total). Two coders simultaneously viewed each video to identify and score each gross motor activity that corresponded with a GMFM test item. All videos were 20% double coded for reliability by a third coder, and disagreements were reconciled for any that did not reach 85% reliability. An individualized difficulty level was measured as the difference between the estimated GMFM score and the actual GMFM score, essentially normalizing the raw difficulty level to the child’s individual level of function. Positive values meant greater difficulty in therapy compared to current function. Difference between groups was assessed with an unpaired t-test and the relationship to baseline gross motor function was quantified by Pearson correlations.

Results: Estimated difficulty level during PT exceeded participants’ current level of function in both groups (experimental group mean 9.6; conventional group mean 3.4) and was significantly greater in the experimental group compared to the conventional group (p=0.0014). These observations suggest that the dynamic weight support harness allowed practice of harder motor skills and, more importantly, indicate that difficulty level can be manipulated during PT in young children with CP. Lower baseline motor function was significantly related to greater difficulty levels in both groups (experimental group -0.74, p=0.021; conventional group -0.61, p=0.046), meaning that children with more significant impairment practiced skills at a greater relative level of challenge.

Conclusions: PT can encourage motor practice at levels that are challenging for young children with CP, even those with significant functional impairment.

Clinical Relevance: The degree of difficulty of motor practice can be manipulated in PT and may be important in the acquisition of motor skill. Future work should investigate the relationship between difficulty of motor practice and rehabilitation outcomes in children with CP.