Since the individual is able to move in a controlled manner during active sitting, the body will strengthen postural muscles to maintain balance. This conditioning of the core muscles of the spine and trunk may significantly aid in preventing back pain. In turn, it is understood that movement lubricates and nourishes the spinal joints and intervertebral discs, keeping skeletal joints flexible and healthy. Many age-related changes in spinal joints are likely due to a lack of proper nourishment and motion. With postural stabilization in sitting and reaching, the leg and calf muscles are activated. When the muscles of the lower extremities work lightly, as during active sitting, the resulting regular pumping action stimulates the return of lymphatic fluid, and minimizes lower leg edema and swollen ankles. Since movement allows blood to flow freely from the lower extremities, this improved circulation can reduce the risk of the development of deep vein thrombosis (DVT) while seated. Meanwhile, overall bodily movement may "shake out" muscle tension and stress that can build up in the neck, shoulders, or jaw during prolonged sitting postures. It is even thought that movement while sitting might improve focus and alertness because of the sensory and vestibular input. The concept of active and dynamic sitting has further relevance beyond those in the able-bodied population whose daily activity involves extended periods of sitting. For the population of wheelchair users, both children and adults, the topic of active, dynamic sitting is increasingly a subject of focused discussion, research, and product development. For wheelchair users, prolonged sitting can have similar adverse effects and health issues as for the able-bodied. Wheelchair users are perhaps at even greater risk since their bodies are already limited due to their health condition. Thus, for wheelchair users, a less than optimal, prolonged static seated posture could be likely to lead to physical discomfort or to deterioration of health status. The concept of dynamic or active sitting can apply to both the adult and pediatric populations in the field of rehabilitation. For the pediatric population, childhood is a time of significant physical and cognitive development, and appropriate intervention can impact long-term outcome. So particularly for young wheelchair users, it is crucial to also provide adaptive seating that accommodates their unique needs and enables active seated postural control and function. However, this need for appropriate adaptive seating is equally true for adult clients with diagnoses such as spinal injuries, stroke, cerebral palsy, multiple sclerosis, or brain injury. Wheelchair users can have unique physical characteristics that pose specific challenges to both sitting posture and to upper extremity function.