Experts agree that cardiovascular endurance is the most important component of health-related fitness.¹⁸ Good to high levels of cardiovascular fitness in adults has been linked to a lower risk of disease and death.¹⁹ Maintaining and improving cardiovascular fitness assures that children and adolescents will enter adulthood with a sound investment toward their future health. Cardiovascular fitness is no less important for children and adolescents with disabilities.⁷ Many youth with disabilities have very low levels of cardiovascular fitness as a result of a sedentary lifestyle.²⁰ This makes it difficult for them to perform activities of daily living or keep up their peers in recess or physical education class.¹⁷

Without adequate cardiovascular fitness, sustaining activities for longer than a few minutes, especially when the intensity level reaches a high percentage of the child's functional capacity, is difficult or impossible. For example, participating in a game of wheelchair basketball where a player has to wheel up and down the court for several continuous minutes without stopping requires good cardiovascular fitness. A child in a wheelchair who is on a school outing will also need an adequate level of cardiovascular fitness to keep up with his or her schoolmates.

One of the first investigators to assess the cardiorespiratory fitness levels of persons with cerebral palsy was the Swedish physiologist, Ake Lundberg.²¹ The aim of Lundberg's earlier research was to determine the maximal aerobic power of persons with spastic cerebral palsy. Lundberg measured the aerobic power of nine children and five young men with spastic diplegia. Nine nondisabled children and five nondisabled men served as the control group. The degree of disability ranged from slight (no aids to ambulate) to severe (six of the 14 subjects used a wheelchair). All tests were performed on a mechanically braked bicycle ergometer. Results showed that the subjects with cerebral palsy had lower values for heart rate, oxygen uptake, ventilation and blood lactate concentrations compared to the control group. Physical work capacity at 170 beats per minute (bpm) was only 50 percent of nondisabled controls.

In a later study, Lundberg examined longitudinally the physical work capacity and aerobic power in 19 children with spastic diplegia, and compared them to a control group of 12 nondisabled children of the same age and sex.²² The degree of impairment ranged from slight (no aids required to ambulate, 6 boys, 3 girls) to fairly severe (6 boys, 4 girls, 8 of whom used a wheelchair). Heart rate, oxygen consumption (VO2), physical work capacity at heart rate 170, pulmonary ventilation, and blood lactate concentrations were measured during submaximal and maximal work on a bicycle ergometer two or three times a year over a six year period. Levels of fitness (VO2 and physical work capacity) were higher for the control group compared to the children with cerebral palsy.

Several other studies have confirmed low cardiovascular fitness among children with disabilities. Agre and colleagues studied 33 children with spina bifida and concluded that they had lower levels of aerobic capacity compared to nondisabled children.²³ Dresen and coworkers reported lower physical work capacities in 24 children with cerebral palsy compared to nondisabled controls.¹³ And Sockolov and coworkers reported lower cardiovascular fitness in boys 6 to 11 years of age who had Duchenne muscular dystrophy compared to nondisabled controls.²⁴