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Purpose: . It is not known if physical activity has a dose-response or a threshold relationship with function for persons with knee OA. Because physical activity is a key public health intervention, understanding this relationship has important implications for public health recommendations. A dose-response relationship would support advice to increase physical activity regardless of a person's current activity levels. A threshold relationship would support future research to identify what threshold target conveys functional benefits for persons with knee OA.
Methods: The Osteoarthritis (OAI) public data include n=2579 adults (aged 45-79) with radiographic knee OA (KL grade ≥2) at the baseline visit; n=2274 returned for the 1 year visit. Each person was assigned to a baseline physical activity quartile (Q1=low to Q4=high) from PASE (physical activity scores for elderly) scores. Function was assessed objectively by chair stand rate and walk rate over 20 meters. Multiple regression evaluated the relationship of PASE quartiles to functional outcomes controlling for demographics (age, gender, race, education, marital status), knee health (OA severity grade, knee symptoms, WOMAC knee pain, knee injury) and general health (BMI, comorbidity, depression, smoking, alcohol use, any hip, ankle, or foot pain).
Results: Average functional performance consistently increased with higher PASE quartiles for both 20m walk (Q1: 74, Q2: 77, Q3: 79, Q4: 82 meter/min) and chair stand performance(Q1: 25, Q2: 27, Q3: 28, Q4: 30 repetitions/min). To determine if higher physical activity levels consistently corresponds to better function among people with similar demographics and health, we examined functional differences controlling for these factors. These results (Table) showed a strong cross-sectional dose-response relationship and a statistically significant linear trend. The dose-response relationship was sustained over one year.
| Function differences between PASE baseline quartiles adjusted for demographic and health factors | |||
Baseline Function n=2579 | Q2-Q1 (95% CI) | Q3-Q1 (95% CI) | Q4-Q1 (95% CI) | Trend Test |
Walk rate | 1.5 (0.3, 2.7) | 3.00 (1.8, 4.2) | 4.22 (2.9, 5.5) | p<.001 |
Chair stand | 1.3 (0.2, 2.4) | 1.9 (0.8, 3.0) | 2.1 (0.9, 3.3) | p<.001 |
1 Year Function n=2274 |
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Walk rate | 1.0 (-0.3, 2.3) | 2.4 (1.1, 3.7) | 3.5 (2.1, 4.9) | p<.001 |
Chair stand | 0.8 (-0.4, 2.0) | 2.1 (0.8, 3.3) | 2.2 (0.9, 3.6) | p<.001 |
Conclusion: These findings demonstrate a strong dose-response relationship between physical activity and functional performance in persons with radiographic knee OA that is sustained over one year. This relationship persists controlling for demographic and health factors. These findings support efforts to increase physical activity at all levels to improve functional performance of persons with knee OA.