Female subjects over the age of 40 will be recruited and randomised into a progressive resistance training (PRT) or sham-exercise group. The PRT group will train at 80% of their peak strength, using Keiser pneumatic resistance machines, and progress approximately 3% per session. Strength will be re-assessed fortnightly. Exercises will target muscles around the hip and knee. The sham-exercise group will train on the same equipment as the PRT group except hip adduction, but without added resistance or progression. Both groups will train 3 days per week for roughly 45 minutes for 6 months.

It is hypothesised that high intensity PRT will decelerate the tibial and femoral cartilage degeneration in the knee affected most by OA.

Primary Outcome:

Articular cartilage morphology following 6 months high intensity progressive resistance training

Secondary Outcomes:

Muscle and fat cross-sectional area (CSA) (pre and post) Muscle strength, power, endurance, and contraction velocity (pre, 3 months, & post) Medications (pre, 3 months, & post) Body composition (pre, 3 months, & post) Balance; Physical function (pre, 3 months, & post) Questionnaires (pre, 3 months, & post)

• Habitual exercise (PASE) -WOMAC index (pain, stiffness and functional ability)
• Depressive symptoms (Depression Scale) -Quality of life (SF36)
• Confidence performing physical activity (Ewart) -Demographics

Inclusion Criteria:

• Female
• Aged over 40 years old
• Primary Osteoarthritis in at least one knee using standard criteria of the American College of Rheumatology (ACR) criteria for classification of clinical osteoarthritis
• Ambulatory without human assistance
• Willingness to be randomised to experiential or control group
• Ability to attend scheduled exercise and testing sessions

Exclusion Criteria:

• Regular exercise of any kind over the past 3 months (>1dpw).
• Secondary osteoarthritis (traumatic or post-surgical), rheumatic disease, gouty or septic arthritis, Paget's disease, pseudogout, major congenital abnormalities, hemochromatosis, Wilson's disease and other rare forms of arthritis
• Joint injury, injection or surgery within the past 6 months or knee joint replacement
• Contraindications to MRI/Exercise