Physical Strain: A New Perspective on Walking in Cerebral Palsy.

Abstract

To describe (1) physical strain of walking, (2) the proportion of participants walking above the anaerobic threshold, and (3) 4 phenotypes of physical strain of walking on the basis of deviations in aerobic capacity and walking energy cost (EC) in children and adolescents with cerebral palsy (CP). Cohort study. Academic medical center. A sample (N=57) of participants (n=37; mean age, 13.5±4.0y) with CP (Gross Motor Function Classification System [GMFCS] levels I [n=13], II [n=17], and III [n=7]) and typically developing (TD) participants (n=20; mean age, 11.8±3.5y). Not applicable. Oxygen consumption (Vo₂walk), speed, and EC were determined during walking at a comfortable speed. Peak oxygen consumption (Vo₂peak) and anaerobic threshold were measured during a maximal cycling exercise test. Aerobic capacity was reduced if lower than the 10th percentile, and EC was increased if higher than 3SD. Physical strain was defined as follows: (Vo₂walk/Vo₂peak)×100. Participants with CP had a higher physical strain (GMFCS level I, 55%±12% GMFCS level II, 62%±17%; GMFCS level III, 78%±14%) than did TD participants (40%±11%) (P<.001). Forty-three percent of participants with CP showed a Vo₂walk at or above their anaerobic threshold as compared with 10% of TD participants (P=.007). Phenotypes showed that a reduced Vo₂peak (n=9) or an increased EC (n=9) lead to an 18% to 20% higher physical strain, whereas a combination (n=12) leads to a 40% increase. Children and adolescents with CP walk at a high physical strain, approximating intense exercise and a considerable proportion walks close to or above their anaerobic threshold, probably explaining fatigue and reduced walking distance. Both an increased EC and a reduced Vo₂peak contribute to high physical strain in children or adolescents with CP. The different causes of high physical strain in individuals with CP require different intervention strategies.