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Table 1 Studies examining the effect of age and sex 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 age/sex
Studies investigating self-reported symptomatic OA
   Felson et al. (2007) [11] 9-year cohort study/1,279 participants from the Framingham Offspring cohort Self-reported, symptomatic Self-reported; frequency, type, intensity No association between OA risk and the following in middle-aged and elderly individuals: walking (≥6 miles/week; OR 0.78, 95% CI 0.49 to 1.24); working up a sweat (≥3 times/week; OR 1.23, 95% CI 0.72 to 2.10); and activity level compared with peers (more active; OR 0.94, 95% CI 0.60 to 1.47)
     Sex analyses did not alter the results
   Sutton et al. (2001) [20] Retrospective case-control study/1,080 healthy participants Self-reported, symptomatic Self-reported; parameters not specified Individuals who retrospectively reported being active in early life had no increased risk for knee OA compared with age-matched control individuals who reported a sedentary lifestyle (14 to 19 years: OR 1.2, 95% CI 0.8 to 1.9 [P = 0.39]; 20 to 24 years: OR 1.0, 95% CI 0.6 to 1.6 [P = 1.0])
     Individuals who reported being highly active in early life (age 20 to 24 years) had an increased risk for knee OA (OR 1.60, 95% CI 0.94 to 2.73 [P = 0.085])
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 physical activity 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)
   Rogers et al. (2002) [13] 2-year nested case-control study/415 cases and 1,995 control individuals from the Cooper Clinic Self-reported, physician diagnosed Self-reported; joint stress (based on activity type) Physical activity involving low or moderate/high joint stress was associated with reduced risk for hip/knee OA in women (low: OR 0.58, 95% CI 0.34 to 0.99; moderate/high: OR 0.24, 95% CI 0.11 to 0.52)
     In contrast to low joint stress activity, moderate/high joint stress activity was associated with reduced risk for hip/knee OA in men (OR 0.62, 95% CI 0.43 to 0.89)
   Cheng et al. (2000) [8] 10-year prospective, cohort study/16,961 patients from the Cooper Clinic Self-reported, physician diagnosed Self-reported; activity type, duration High-level physical activity (running ≥20 miles per week) was significantly associated with hip/knee OA among younger men (OR 2.4, 95% CI 1.5 to 3.9) but not older men (OR 1.2, 95% CI 0.6 to 2.3)
     Nonsignificant findings were reported for younger women (HR 1.5, 95% CI 0.4 to 5.1) and older women (HR 1.4, 95% CI 0.4 to 4.6)
Radiographic studies investigating structural OA
   Felson et al. (2007) [11] 9-year cohort study/1,279 participants from the Framingham Offspring cohort Radiographic, structural Self-reported; frequency, type, intensity No association between OA risk and the following in middle-aged and elderly individuals: walking (≥6 miles/week; OR 1.10, 95% CI 0.73 to 1.66); working up a sweat (≥3 times/week; OR 1.24, 95% CI 0.77 to 2.00); and activity level compared with peers (more active; OR 0.94, 95% CI 0.63 to 1.40)
     Sex analyses did not alter the results
   McAlindon et al. (1999) [14] 8-year longitudinal cohort study/473 participants from the Framingham study cohort Radiographic, structural Self-reported: Framingham physical activity index; activity type, duration The number of hours/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])
     Heavy physical activity (≥4 hours/day) was associated with increased risk for OA in elderly men (OR 7.0, 95% CI 1.7 to 29) and women (OR 9.0, 95% CI 1.7 to 48)
Radiographic studies investigating structural OA
   Felson et al. (1997) [17] 8-year longitudinal study/598 participants from the Framingham Study cohort Radiographic, structural Framingham physical activity index; activity type Habitual physical activity increased the risk for knee OA for participants in the highest quartile of physical activity compared with those in the lowest quartile (OR 3.3, 95% CI 1.4 to 7.5)
     A sex-specific effect was observed in an elderly cohort (men: OR 3.8, 95% CI 0.9 to 17.3; women: OR 3.1, 95% CI 1.1 to 8.6)
   Hannan et al. (1993) [18] Longitudinal cohort study (conducted over 19 years)/1,415 individuals from the Framingham study cohort Radiographic, structural, Self-reported: duration, frequency, type; physical capacity measures: FEV, pulse rate Habitual physical activity did not increase the risk for knee OA in elderly men or women (highest quartile; men: OR 1.34, 95% CI 0.66 to 2.74; women: OR 1.09, 95% CI 0.63 to 1.90)
     In contrast to women, men in the highest quartile of habitual physical activity had significantly elevated rates of asymptomatic osteophytes (OR 2.14, 95% CI 1.01 to 4.54)
   White et al. (1993) [12] Case-control study/305 physical education teachers and age-matched control individuals Radiographic, structural Self-reported; frequency, duration There was a significantly lower prevalence of knee OA in middle-aged physical education teachers compared with the control individuals in both 'younger' (48 to 54 years [P < 0.001]) and 'older' (55 to 60 years [P < 0.001]) age categories
  1. CI, confidence interval; FEV, forced expiratory volume; HR, hazard ratio; OA, osteoarthritis; OR, odds ratio.