An exercise-tolerance test used in chronic respiratory disease and heart failure. It measures the distance a person is able to walk in six minutes on a hard, flat surface. The person walks as far as possible in six minutes and is allowed to self-pace and rest as needed as he or she goes back and forth along a marked walkway. The test is also used as a performance-based measure of functional exercise capacity in other populations, e.g., healthy older adults, people undergoing knee or hip arthroplasty, fibromyalgia, and scleroderma, and children.