This study is the first well-designed randomized controlled trial to assess the effects of a novel home-based virtual cycling training (hVCT) program for improving muscle strength in children with spastic cerebral palsy (CP). Twenty-eight ambulatory children with spastic CP aged 6-12 years were randomly assigned to an hVCT group (n = 13) or a control group (n = 15). Outcome measures, including gross motor function of the Bruininks-Oseretsky Test of Motor Proficiency (BOTMP) and muscle strength (isokinetic torque of knee extensor and flexor muscle), were administered before and immediately after the 12-week intervention. Analysis of covariance (ANCOVA) at post-treatment showed that, compared to the control group, the hVCT group had significantly higher isokinetic torque in the knee extensor and flexor muscles at 60 degrees/s and 120 degrees/s angular velocities (p less than 0.05). At post-treatment, the hVCT group also showed greater isokinetic strength improvement in the knee flexor than in the knee extensor at 60 degrees/s (knee flexor: 41%; knee extensor: 19%) and at 120 degrees/s (knee flexor: 36%; knee extensor: 30%). However, the BOTMP scores at post-treatment did not differ between the two groups. Although the proposed 12-week hVCT protocol does not improve gross motor function, it enhances knee muscle strength in children with CP. The protocol obtains larger gains in the knee flexor than in the knee extensor at different angular velocities. The study findings will help clinicians to provide more effective and efficient strategies for muscle strength training in children with CP. (Contains 2 figures and 2 tables.)