The effects of physical therapy on individual muscle force production and function in children with Cerebral Palsy

Cerebral Palsy (CP) is a chronic neurological disorder that affects the ability to perform basic motor tasks, posture, and muscle coordination. Current intervention techniques, including physical therapy, can produce vast improvements in some children, while other children do not respond. The underlying muscular improvements that are associated with physical therapy are unclear, and may be important to understanding why only some children benefit from therapeutic interventions. Musculoskeletal modeling and simulation can be used to determine changes in dynamic muscle force production and muscle contributions to body center of mass accelerations at the individual muscle level as a result of physical therapy. Changes in muscle force and function were characterized for children with CP who participated in both gait and strength training. Gait training significantly affected contributions to body support from the vasti and rectus femoris muscles, and contributions to body propulsion from the soleus, resulting in muscle functional roles more similar to able-bodied gait. Strength training significantly affected gastrocnemius contributions to support, again resulting in muscle function more consistent with able-bodied gait. Changes in muscle function as a result of gait training metrics were significantly correlated to the 6-minute walk test, which is a clinical assessment of muscle endurance. Changes in muscle force and function as a result of strength training were not consistent with measured isometric strength at the joint level, suggesting that dynamic muscle behavior during movement tasks cannot strictly be predicted by static measures. Musculoskeletal modeling and simulation are therefore needed to assess how muscles coordinate to improve mobility. Both types of therapy produced highly variable changes in muscle dynamic metrics across children, which corresponded to the highly variable neuromusculoskeletal impairments of children with CP. The use of musculoskeletal modeling and simulation can identify the muscular deficits of individual children, and have the potential to be instrumental in developing targeted physical therapy protocols that are tailored to a specific patient.