Knee osteoarthritis (OA) commonly reduces function because of cartilage loss, joint inflammation, and muscle weakness around the knee. Evidence from randomized trials and guideline work led by Kim L. Bennell University of Melbourne supports progressive strengthening of the thigh muscles as a core strategy to reduce pain and improve function. Research summarized by Jeffrey N. Katz Brigham and Women's Hospital and Harvard Medical School also emphasizes that exercise delivered with appropriate modifications is safer and more effective than no exercise for most people with knee OA.
Principles of modification
Modify resistance exercise around three core principles: load management, pain-guided progression, and individualized selection. Load management means reducing external weight, decreasing repetitions to control fatigue, or shortening lever arms to lower joint stress. Use pain as a guide so that activity causes no more than mild to moderate transient discomfort and does not produce sustained worsening over 24 to 48 hours. Individualization accounts for comorbidities, body habitus, and cultural or environmental constraints such as access to gyms or pools.
Practical exercise adjustments
Emphasize quadriceps strengthening with exercises that minimize compressive forces. Examples include short-arc knee extensions, isometric quadriceps contractions, and controlled sit-to-stand from varying chair heights. Prefer exercises with slower controlled movements and avoid deep knee flexion under heavy load when pain or joint deformity is present. Closed kinetic chain activities are often better tolerated than open chain when loads are similar, and aquatic resistance training provides buoyancy that reduces joint load for people with higher pain or body weight. For frail or deconditioned individuals, begin with bodyweight or elastic band resistance and progress frequency to two to three sessions per week as tolerated.
Cultural norms, work demands, and environmental access shape what modifications are feasible; for example, urban residents may lack private space for exercise while rural communities may have stronger traditions of manual activity that influence program tailoring. Consequences of inadequate modification include exercise avoidance, symptom flare, or injury, whereas appropriate adjustments support adherence, slow functional decline, and reduce reliance on analgesics or invasive procedures. Clinicians should collaborate with trained physiotherapists and local community programs to adapt exercises to individual needs, monitor response, and progressively load the muscle system while protecting the joint. When guided and individualized, resistance exercise is a cornerstone of conservative care for knee osteoarthritis.