Ambulation in the adolescent with spina bifida. II. Oxygen cost of mobility.

This study was designed to determine the energy cost (measured as oxygen use) of walking and wheelchair propulsion in children aged 10 to 15 with myelomeningocele of thoracic to sacral levels, and to determine whether energy cost of mobility could be estimated from clinical measures. Oxygen consumption (measured with open circuit spirometry) and heart rate were measured during treadmill walking by 21 children, wheelchair use by eight children, and, for five children, in both modes. Speeds ranged from 27 to 134 m/min, with slopes up to 15%. Energy consumption for walking was linearly related to speed, slope, heart rate, and body weight (r = .90, p less than .001); for wheelchair propulsion, energy consumption was a linear function of speed, slope, and body weight (r = .90, p less than .001). The same linear function applied for all disabled children; maximum walk/run speed over a 30 m distance correlated highly with both maximal oxygen consumption (r = .87) and speed using 70% of VO2max (r = .82). For both wheelchair use and walking, the relative energy consumption (percentage of VO2max) was highly correlated with heart rate alone (r = .93), and the absolute level of energy consumption was highly correlated with heart rate and maximum walk/run speed (r = .89). Simple clinical measures of maximum ambulatory velocity and heart rate allow accurate prediction (r = .89) of energy consumption in all children with myelomeningocele, regardless of neurologic and functional level.