We evaluated the effect of strenuous aerobic exercise on joint symptoms and compared the functional capacity and muscle strength among patients with rheumatoid arthritis (RA) and osteoarthritis (OA), and very sedentary matched controls. Strenuous ergometer exercise did not exacerbate joint symptoms in these patients. Isotonic leg extension and flexion as well as grip strength were diminished in the RA and OA subjects compared to controls (p less than 0.05). All subjects displayed low maximum oxygen consumption indicating reduced functional capacity. Acute bouts of strenuous exercise performed on bicycle ergometer do not appear harmful to the nonacute arthritis patient.