Habitual Physical Activity Levels Are Associated with Biomechanical Walking Economy in Children with Cerebral Palsy

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Abstract
To evaluate in children and adolescents with cerebral palsy the relationship between habitual physical activity and biomechanical treadmill walking economy and whether treadmill belt speed or walking time affect economy. Physical activity was measured in 11 subjects (10.6–16.3 yrs) with mild cerebral palsy using a triaxial accelerometer. To determine biomechanical walking economy, subjects’ stride lengths and vertical sacral excursions were measured during each minute of three 3-min walks on a treadmill (at 60%, 75%, and 90% of individually determined fastest treadmill walking speed). Biomechanical walking economy at 60%, 75%, and 90% of (their) fastest speed each explained about half of the intersubject variance in daily physical activity (movement counts). A similar relationship was found between these biomechanical walking economy variables and movement counts at or above the 80th and 90th percentile (total minutes per day, number of 5-min bouts per day). Walking economy was 23.9% higher when subjects walked at 90% than when they walked at 60% of their fastest walking speed. No other speed-related effects on economy were found, nor did time affect economy. Within this population, those with high biomechanical treadmill walking economy are the more habitually physically active. Treadmill belt speed, but not walking time, affects biomechanical walking economy.