This study was designed to investigate the effect of six weeks of accommodating variable-resistance training on muscle architecture, muscle strength, and functional performance in patients with juvenile idiopathic arthritis. Fifty-eight children with juvenile idiopathic arthritis were randomly allocated to the experimental group (n = 29, received the accommodating variable-resistance training) or the Control group (n = 29, received usual physical rehabilitation alone). Both groups were assessed for muscle architecture, muscle strength, and functional performance before and after treatment.

Fifty-eight patients with juvenile idiopathic arthritis participated in the study. They were recruited from King Khalid Hospital and two other referral hospitals, in Riyadh, Saudi Arabia. They were between 12 and 18 years old, had poly-articular onset and bilateral knee involvement, were on stable doses of medications, and were not engaging in regular exercise regimens. Patients were excluded if they had fixed deformities, a history of joint surgery, or whose radiological investigations revealed erosive changes of bone, ankylosing, or fractures.

Outcome measures

1. Muscle architecture: the fascicle length, pennation angle, and thickness of the vastus lateralis muscle were assessed using a standard high-resolution ultrasound imaging system.
2. Muscle strength: The peak concentric torque of the right and left knee extensors was measured through an isokinetic dynamometer.
3. Functional capacity: Three tests were used; the 6-minute walk test, the timed up and down stairs test, and the 4x10 meter Shuttle Run test.

The experimental group received a 6-week accommodating variable-resistance training, two times a week for six consecutive weeks, in conformity with the National Strength and Conditioning Association guidelines and American Academy of Pediatrics safety standards. The training protocol included maximum voluntary concentric knee flexor/extensor actions through a motion range between 10 and 90 degrees. Three sets of five to 10 repetitions at angular speeds of 240, 180, and 120 degrees/second were performed. The training started with a warm-up for 10 minutes and ended with a cool-down for 5 minutes.

The control group received the standard exercise program, 45 minutes per session, two times a week for six consecutive weeks. The program consisted of flexibility exercise, strength training, weight-bearing, proprioceptive training, and free treadmill walking or cycle ergometry.

Inclusion Criteria:

• Confirmed diagnosis of JIA
• Polyarticular onset of JIA with bilateral involvement of the knee joint
• Age between 12 and 18 years
• Stable conditions (i.e., receive stable doses of medications in the past three months)
• Not participating in a regular exercise program in the past six months

Exclusion Criteria:

• Fixed deformities
• History of joint surgery
• Ankylosing or fractures
• Bone destruction (erosive changes of the knee joint)
• Cardiopulmonary comorbidities
• Recommendation against engaging in potentially explosive physical activities by the attending Rheumatologist.

This was a single-blind protocol. The researcher who collected the data was blind to the allocation of treatment