Single-leg vertical jumping in young adults with spastic cerebral palsy

Background: Maximum-strength tests are commonly used to detect muscle weakness in persons with cerebral palsy (CP). Tests of explosive strength (power) in the lower extremities, such as vertical jump tests, are more uncommon but might supplement maximum-strength testing by providing additional information about motor function. Research question: Is it feasible and useful to measure single-leg vertical jumping in young adults with CP? Methods: Eleven persons with spastic CP (18-30 years), able to walk without support, were compared with a reference group. Jump height and power generation in jumping were measured using a 3D motion-analysis system and force plates. Maximum strength in plantarflexors was measured on the same occasion. Data were analysed using non-parametric statistics. Results: Jump height was significantly greater in the reference group than in the group with CP, both relative to the less-involved leg of the participants with CP (p = .007) and relative to their more-involved leg (p < .001). In the group with CP, jump height was twice as great for the less-involved leg than for the more-involved leg (p = .008). Power generation at the hip joint was similar between the groups but differed for the knee and ankle joints (p = .001-.033). In the reference group, most of the power was generated at the ankle joint, while the hip was the dominant power generator for the more-involved leg in the group with CP. Muscle strength in the group with CP showed a high correlation with jump height (rho = .745, p < .001) and power generation at the ankle (rho = .780, p = .001). Significance: The single-leg vertical jump test proved capable of measuring jump height and power generation in participants with CP. It also identified explosive muscle weakness both relative to a reference group and between legs. Hence the jump test may provide information additional to common tests of maximal muscle strength in persons with CP.