Core Muscle Strengthening in Knee Osteoarthritis Rehabilitation
Core muscle strengthening is included in knee osteoarthritis rehabilitation because it provides statistically and clinically significant short-term pain reduction beyond conventional treatment alone, while also addressing the broader recommendation for progressive strengthening of major muscle groups to improve both pain and physical function. 1
Evidence-Based Rationale for Core Strengthening
Direct Evidence for Core Training Benefits
A randomized controlled trial demonstrated that adding core muscle activation exercises to conventional treatment produced statistically and clinically significant pain reduction at the end of 12 weeks of treatment compared to conventional exercises alone in knee OA patients. 1
Both pain reduction and improved physical function were observed throughout the intervention, with the combination therapy showing superior short-term outcomes without any reported adverse effects. 1
Integration with Guideline Recommendations
The inclusion of core strengthening aligns with EULAR (European League Against Rheumatism) guidelines that emphasize:
Progressive strength training involving the major muscle groups should be performed at least 2 days per week at moderate to vigorous intensity (60-80% of one repetition maximum) for 8-12 repetitions. 2
The core musculature constitutes a major muscle group that contributes to overall functional capacity and biomechanical stability, making it a logical target within comprehensive strengthening programs. 2
Biomechanical and Functional Considerations
Patients with knee OA demonstrate significant muscle impairments in the quadriceps, hamstrings, and hip muscles compared to age-matched controls, and these impairments are the primary underlying cause of functional limitations. 3
Muscle strength, especially quadriceps strength, is a major determinant of both performance-based and self-reported physical function in knee OA. 3
Core stability provides a foundation for lower extremity function and may enhance the effectiveness of lower limb strengthening by improving biomechanical alignment and load distribution during functional activities. 1
Evidence for Lower Limb Strengthening (Context for Core Addition)
Established Benefits of Strengthening Exercises
High-quality research evidence shows that quadriceps strengthening exercises reduce pain effectively (Effect Size 0.29,95% CI 0.06 to 0.51) and improve physical function (Effect Size 0.24,95% CI 0.06 to 0.42) in knee OA. 2, 4
Lower limb strength training produces even larger effects, with pain reduction (Effect Size 0.53,95% CI 0.27 to 0.79) and functional improvement (Effect Size 0.58,95% CI 0.27 to 0.88). 2, 4
All randomized controlled trials examining quadriceps strengthening exercises in knee OA showed significant improvements in pain compared to control groups (Effect Size 1.05). 4
Duration and Maintenance of Benefits
The beneficial effects of combined facility- and home-based muscle strengthening exercises on muscle strength begin to appear at 3 to 6 months after starting the exercise regimen, regardless of gender, age, body mass index, or baseline muscle strength. 5
These benefits can be maintained for up to 1-3 years with continued exercise, though they tend to diminish by 5 years, highlighting the need for long-term adherence. 5
Optimal Exercise Program Structure
Frequency and Intensity Parameters
Exercise programs should include strengthening exercises at least 2 days per week at moderate to vigorous intensity (60-80% of one repetition maximum) for 8-12 repetitions. 2, 4
Programs performed for 8-12 weeks, with 3-5 sessions per week, each lasting approximately 1 hour, appear to be effective. 6
Supervision and Progression
Twelve or more directly supervised sessions are more effective than fewer sessions for improving pain (Effect Size 0.46 vs 0.28) and physical function (Effect Size 0.45 vs 0.23). 4, 7
Progressive strengthening programs that increase intensity and/or duration over time are recommended, with most effective strength training in knee OA including dynamic exercises with progression. 2
Common Pitfalls and Clinical Considerations
Exercise Type Selection
Dynamic strengthening exercises are more commonly studied and recommended for knee OA, while research on isometric exercises remains sparse, though both should be included. 2, 4
The optimal exercise "dosage" and rate of progression remain somewhat uncertain, as one RCT showed reduced pain from progressive functional strengthening compared to non-progressive programs, but two other trials could not demonstrate differences from resistance-exercise programs. 2
Comprehensive Management Approach
Exercise should be combined with weight management for optimal outcomes, especially in overweight or obese patients, as weight loss interventions combined with exercise show improvements in pain, function, and weight loss. 2, 4
Education about self-management strategies should accompany exercise programs, as small but statistically significant effect sizes on pain (0.06,95% CI 0.02 to 0.10) and physical function (0.06,95% CI 0.02 to 0.10) have been reported from attending education or self-management programs. 2