Aim: The purpose of this study was to determine if our previously developed muscle model could be used to predict forces of the quadriceps femoris and triceps surae muscles of children with spastic diplegic cerebral palsy (CP). Method: Twenty-two children with CP (12 males, 10 females; mean age 10y, SD 2y, range 7-13y; Gross Motor Function Classification System levels II and III) participated. A physiologically based mathematical model with four free parameters is presented. Results: For individuals with CP, the model predicted well the force profile throughout each contraction and both peak force and force-time integral responses to a wide range of stimulation frequencies (5-100Hz) and different stimulation patterns (constant-, variable-, and doublet-frequency trains) both for nonfatigued and fatigued muscles. Interpretation: The significance of this work is the insight the model can provide into the physiology of muscle in CP. Additionally, the model can potentially be applied clinically to design optimal electrical stimulation patterns for interventions to address impairments in strength and function in individuals with CP, such as functional electrical stimulation-assisted cycling.