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Table 2 Studies examining the effect of BMI on the relationship between physical activity and risk for developing knee OA

From: Factors that may mediate the relationship between physical activity and the risk for developing knee osteoarthritis

Author (year) Study design/participants Measure(s) of OA Measure(s) of physical activity Results: effect of BMI
Studies investigating self-reported symptomatic OA
   Felson et al. (2007) [11] 9-year longitudinal cohort study/1,279 participants from the Framingham Offspring cohort Self-reported, symptomatic Self-reported; frequency, type, intensity Overall results are presented in Table 1
     Among persons with BMI above the median, there was no relationship between the risk for knee OA and the following: walking (≥6 miles/week; OR 0.84, 95% CI 0.37 to 1.92); working up a sweat (≥3 times/week; OR 1.04, 95% CI 0.55 to 1.96); and activity level compared with peers (more active; OR 0.63, 95% CI 0.35 to 1.16)
Studies investigating self-reported physician diagnosed OA
   Hootman et al. (2003) [10] 12.8-year cohort study/5,284 participants from the Cooper Clinic Self-reported, physician diagnosed Self-reported; joint stress physical activity score (intensity, frequency, duration and type) Increasing levels of the joint stress physical activity score were not associated with an increased risk for hip/knee OA for both men (high level; OR 1.07, 95% CI 0.47 to 2.42) and women (high level: OR 1.31, 95% CI 0.92 to 1.87)
     BMI did not modify the relationship between moderate physical activity and risk for knee OA for both men (OR 1.07, 95% CI 1.03 to 1.11) and women (OR 1.12, 95% CI 1.06 to 1.19)
Radiographic studies investigating structural OA
   Felson et al. (2007) [11] 9-year longitudinal cohort study/1,279 participants from the Framingham Offspring cohort Radiographic, structural Self-reported; frequency, type, intensity Overall results presented in Table 1
     Among persons with BMI above the median, there was no relationship between the risk of radiographic knee OA and the following: walking (≥6 miles/week; OR 0.95, 95% CI 0.55 to 1.62); working up a sweat (≥3 times/week; OR 1.22, 95% CI 0.67 to 2.21); and activity level compared with peers (more active; OR 0.82, 95% CI 0.48 to 1.40)
   McAlindon et al. (1999) [14] 8-year longitudinal cohort study/473 participants from the Framingham Heart Study cohort Radiographic, structural Self-reported: Framingham physical activity index; activity type, duration The number of hours per day of heavy physical activity was associated with risk for knee OA (≥4 hours heavy activity/day compared with no heavy activity; OR 7.0, 95% CI 2.4 to 20 [P = 0.0002])
     Risk for OA was greatest among individuals in the upper tertile of BMI (≥3 hours/day of heavy physical activity; OR 13.0, 95% CI 3.3 to 51)
   Kujala et al. (1995) [15] Retrospective cohort study/117 male former top-level athletes Radiographic, structural Self-reported; parameters not-specified Risk for knee OA was increased in athletes with a higher BMI at age 20 years (OR 1.76/unit increase, 95% CI 1.26 to 2.45)
  1. BMI, body mass index; CI, confidence interval; OA, osteoarthritis; OR, odds ratio.