Longitudinal assessment of muscle function and oxygen cost during isometric testing in children with cerebral palsy

The aim of the study was to document the longitudinal changes from one year to the next in knee extensor muscle strength and function and in cardiorespiratory demand during an isometric test in children with cerebral palsy (CP). Ten children with CP (GMFC I and II) and ten able-bodied children underwent a quadriceps strength and endurance assessment on an isokinetic dynamometer. Maximal voluntary isometric torque in the children with CP in the initial test was significantly lower than in controls (p = 0.0007) and did not change significantly over the year. No significant difference was found between the two groups for the initial static endurance measure (p = 0.93); it did not change significantly after one year in the children with CP (p = 0.74). Oxygen cost was significantly greater in the group with CP than in the control group (p < 0.01) and there was a further significant increase in the oxygen cost for the CP group 12 months later (p < 0.01). Ventilation and heart rate at exhaustion were also significantly lower in children with CP than controls in the initial test (p = 0.0001 and p = 0.009, respectively). The persisting muscle weakness and the increase in oxygen cost over time may in part have resulted from inactivity and misuse of muscle. Secondary adaptive soft tissue changes affecting the development of muscle may prevent the increases in strength and endurance normally associated with growth and development.