Muscle weakness and atrophy are common and disabling manifestations of rheumatoid arthritis for which various types of active exercises are usually prescribed. It is well known that active exercises result in substantial increases in muscle mass and power only when performed repeatedly against resistance with considerable physical effort (1). Although physical activity has been reported to have a protein-anabolic effect and cause calcium retention in normal subjects (2, 3), the metabolic responses to exhaustive physical exertion during active rheumatoid arthritis have not been investigated. These studies were undertaken to determine the effects of heavy resistance exercises on nitrogen, phosphorus, and calcium metabolism in patients experiencing exacerbations of this disease. Laboratory studies revealed a normal urine, a corrected sedimentation rate of 1.38 mm. per minute, and a hemoglobin of 12.5 grams per cent. Urinary 17-ketosteroids were 10.8 mg. in twenty-four hours.X-ray studies revealed minimal osteoporosis of the carpal bones and slight spur formation at the margins of the coronoid processes and olecranons. There was marked osteoporosis of the tarsals and metatarsals.2. J. W., a 47-year-old white male, developed rheumatoid arthritis three years before admission with swelling, aching, redness, and heat in the second and third metacarpophalangeal and mid-phalangeal joints of both hands, subsiding in three weeks. Nine months before admission, he developed pain and swelling in the left wrist. This pain subsided within three months but slight swelling remained. Two months before admission he developed pain and swelling in both ankles, the right large toe, right elbow, and left knee. During the two months before admission, he experienced marked fatigue and anorexia and lost twenty-seven pounds.His height was 178.7 cm., weight, 80 Kg., blood pressure, 125/70, and temperature 98.6°F. There was soft tissue swelling of the midphalangeal joints, wrists, left knee, and both ankles. A small effusion was present in the left knee. Motion was limited in the right hand, both wrists, right elbow, and both ankles.Laboratory studies revealed a normal urine, a corrected erythrocyte sedimentation rate of 1.55 mm. per minute, and a hemoglobin of 12.5 grams.X-ray studies revealed considerable osteoporosis of the ends of the long bones of both hands and narrowing of the joint spaces of the right fourth metacarpophalangeal joint and several interphalangeal joints. PROCEDUREThree balance studies were performed in accordance with methods described by Reifenstein, Albright, and Wells (4). Stools were collected in six-day periods and urines in three and six-day periods. Diets, urines, and stools 505