Performance of stair negotiation in patients with cerebral palsy and stiff knee gait.

•Patients with BSCP and stiff knee gait are able to walk stairs.•In walking stairs these patients increase their step time and knee flexion.•Increasing knee flexion is an important factor to maintain foot clearance on stairs.•Knee flexion on stairs is even higher than required for normal level walking.•The muscle activity of rectus femoris can be adapted on stairs.