This study examined the effects of immobilization and low-intensity isotonic muscle contraction exercise on swelling and pain threshold during the early stages of arthritis in rats.Twenty-one male Wistar rats (8 weeks old) were randomly divided into 4 groups : (1) arthritis group (n=5); (2) arthritis and immobilization group (immobilization group, n=5); (3) arthritis and exercise group (exercise group, n=6); and (4) sham arthritis control group (control group, n=5). Arthritis was induced by injecting a mixture of 3% kaolin and 3% carrageenan into the right knee joint. Plaster casts were used to immobilize the right knee joint of rats in the immobilization group. Low-intensity isotonic muscle contraction of the quadriceps was initiated the day after injection and induced by electric stimulation (frequency, 50 Hz ; intensity, 2 -3 mA) for 20 min/day, 6 days/week, over 4 weeks. Joint swelling was determined by measuring the width of the knee joint. The pressure withdrawal threshold (PWT) was measured in the area of the lateral knee joint using a strain gauge algometer. Mechanical hypersensitivity in the hind paw was evaluated using von Frey filaments.Joint swelling was significantly increased for 2 weeks after injection in the arthritis and exercise groups compared with that in the control group. In the immobilization group, joint swelling remained significantly increased for 4 weeks compared with that in the control group. The PWT was decreased from the first day after injection in the arthritis, immobilization, and exercise groups. In the exercise group, the PWT was significantly increased at 1 week