adie syndrome anatomy animal locomotion balance disorder bone bone density bone remodeling bone resorption cardiac muscle cartilage chondrogenesis dementia exertion extensor muscle eye movement eye surgery flexor muscle gait hand strength human physiology hypertonia hypotonia isometric exercise medicine movement muscle muscle contraction musculoskeletal physiology nerve neutral spine ophthalmology osseointegration osteogenesis osteolysis paratonia physical exercise physiology smooth muscle strabismus toning exercises