Creating optimal seat-to-floor height depends on many factors, including knowing which measurements are most important.
“Popliteal to heel is a crucial anatomical measurement for determining seat-to-floor height (to ensure adequate ground clearance) while considering how much knee flexion will be incorporated while seated,” said Jessica Presperin Pedersen, OTD, MBA, OTR/L, ATP/SMS, North American director of clinical education for Sunrise Medical. “A person’s height may require more knee flexion if trying to obtain a lower overall seat-to-floor height for rigid manual wheelchairs.
“Assess thigh-to-calf angle, as well as calf-to-foot angle, which will help determine foot placement and position on the footplate,” Pedersen added. “Some riders will choose to tuck their feet further under the frame, which will decrease the occupied frame length and may allow a lowered seat-to-floor height. If there is decreased range of motion at the thigh-to-calf angle, accommodation for foot placement through the front angle or foot support can help to support the foot in the desired position.”
Ultralightweight factors
For self-propellers, Pedersen said, “optimal seat-to-floor height should be determined based on optimal propulsion and reach to the rear wheels, taking into consideration environmental access. Cushion height and front frame angles can be modified to ensure both goals are met.”
“A seat-to-floor height that is too high may compromise stability, as this affects the rider’s center of mass and can result in posterior tippiness in the chair,” she added. “You can often have a more aggressive center of gravity if the person’s center of mass is lower in the wheelchair. Also consider the rider’s ability to reach the floor: If the seat-to-floor height is too high, this function may be compromised.
“Front frame angle affects the amount of knee flexion and foot position on the foot plate. The greater the front frame angle, the more knee flexion — allowing a lower seat-to-floor height with adequate ground clearance.”
Pedersen also considers the rider’s ability to maintain optimal positioning. Foot placement can be determined by several factors, not just front frame angle. Seat depth, frame length and footrest placement all contribute. “Seated stability is crucial,” she said. “If a person has great trunk control, less slope may be needed, while decreased trunk control might require greater stability at the pelvis, which can be achieved with a greater slope. This was demonstrated in research performed at Rancho Los Amigos National Rehabilitation Center [Downey, California].”
Power wheelchair factors
While their batteries and power seating systems mean that a certain amount of power chair seat-to-floor height is unavoidable, there are still multiple reasons to be mindful of how tall power chairs get.
If seat-to-floor height is too high, a power chair rider “may have reduced head clearance for vehicle access, and they may not be able to access tables/desks,” Pedersen said. “Seat-to-floor height can affect a rider’s visual field when driving from a power wheelchair — we need to be aware of floor-to-eye height.”
This story was originally published in Mobility Management’s December 2024 Seating & Positioning Handbook. To read more on seat-to-floor height, check out the Handbook’s digital edition.
