Knee Extension and Sustained Forces indicate need for Dynamic Footrests 0 With both feet unstrapped from her wheelchair, Alex quickly extends both knees with sustained force. Her movement, which is strong enough to damage her wheelchair and cause frequent bruising, indicates that Dynamic Footrests could help. Learn more about Alex and how Dynamic Seating components have helped her. Posted in Assessment of Dynamic-Seating, Clients Using Dynamic Seating, Videos and tagged diffuse force, Dynamic Footrests, equipment breakage, extension, wheelchair breakage