for some medical purposes, such as reducing the risk of pressure sores, providing passive movement of hip and knee joints, and making it easier to perform some nursing procedures, such as intermittent catheterization to empty the bladder and transfers to beds, and also for personal reasons, such as people who like using an attached tray. The use of reclining wheelchairs is particularly common among people with spinal cord injuries such as quadriplegia. In the case of tilting wheelchairs, the seat-back, seat base, and leg rests tilt back as one unit, somewhat similar to the way a person might tip a four-legged chair backward to balance it on the back legs. While fully reclining spreads the person's weight over the entire back side of the body, tilting wheelchairs transfer it from only the buttocks and thighs (in the seated position) to partially on the back and head (in the tilted position). Tilting wheelchairs are preferred for people who use molded or contoured seats, who need to maintain a particular posture, who adversely affected by sheer forces (reclining causes the body to slide slightly every time), or who need to keep a communication device, powered wheelchair controls, or other attached device in the same relative position throughout the day. Tilting wheelchairs are commonly used by people with cerebral palsy, people with some muscle diseases, and people with limited range of motion in the hip or knee joints. Tilting options are more common than reclining options in wheelchairs designed for use by children. Standing wheelchairs A standing wheelchair is one that supports the user in a nearly standing position. They can be used as both a wheelchair and a standing frame, allowing the user to sit or stand in the wheelchair as they wish. Some versions are entirely manual, others have a powered stand on an otherwise manual chair, while others have full power, tilt, recline and variations of powered stand functions available. The benefits of such a device include, but are not limited to: aiding independence and productivity, raising self-esteem and psychological well-being, heightening social status, extending access, relief of pressure, reduction of pressure sores, improved functional reach, improved respiration, reduced occurrence of UTI, improved flexibility, help in maintaining bone mineral density, improved passive range motion, reduction in abnormal muscle tone and spasticity, and skeletal deformities. Other wheelchairs provide some of the same benefits by raising the entire seat to lift the