title: Association between quadriceps strength and self-reported physical activity in people with knee osteoarthritis.
abstract: OBJECTIVE
  Physical inactivity is common in patients with knee osteoarthritis (OA) and has been linked to serious comorbidities such as cardiovascular disease, obesity, and diabetes. The purpose of this study was to examine the association between quadriceps strength and self-reported physical activity in patients with radiographically confirmed knee OA. Secondarily, the authors' sought to determine if there were differences in quadriceps strength between knee OA patients with low physical activity (LPA) and knee OA patients with higher physical activity (HPA). A tertiary aim of this study was to examine the effect of gender on physical activity and quadriceps strength in patients with knee OA.
  
  
  METHODS
  Thirty-six patients with radiographically diagnosed tibiofemoral knee OA participated (15 males, 21 females; age = 59.9±11.6 yrs; height = 171.2±9.2 cm; mass = 84.3±18.9 kg; body mass index (BMI)= 28.9±6.9;Godin Leisure-Time questionnaire =32.5±25.01). Maximal isometric knee extensor strength was assessed with a Isokinetic dynamometer in 70° of knee flexion. Knee extension torque values were normalized to body mass (Nm(*)kg(-1)). Physical activity was evaluated using the Godin Leisure-Time questionnaire. A Godin-Leisure time score of 32.5, which was the mean score in the current dataset, was what was used to categorize subjects into LPA and HPA subgroups. Independent t-tests were used to determine differences in strength between HPA and LPA subgroups, as well as differences in strength and physical activity between genders. Pearson Product Moment and Spearman rank correlations were used to analyze associations between normally and non-normally distributed variables.
  
  
  RESULTS
  Quadriceps strength was positively correlated with physical activity (r=0.44, r(2)=0.18, p=0.01). The HPA subgroup had significantly greater quadriceps strength (n=15, 2.01±0.84) compared to the LPA subgroup (n=21, 1.5±0.59, p=0.04). Strength was significantly correlated with physical activity in the HPA subgroup (ρ=0.53, p=0.04), but not in the LPA subgroup (ρ=-0.21,p=0.35). Males reported significantly more physical activity (43.0±28.5 vs 25.1±19.64; p=0.03) and greater strength than females in the entire cohort (2.15±0.73 Nm(*)kg(-1) vs 1.40±0.57 Nm(*)kg(-1); p= 0.002), and the HPA subgroup (2.4±0.65 Nm(*)kg(-1) vs 1.4± 0.68 Nm(*)kg(-1); P=0.02). There were no gender differences for strength in the LPA subgroup.
  
  
  CONCLUSIONS
  Higher levels of quadriceps strength correlate with higher physical activity in knee OA patients. The association between higher strength and increased physical activity is stronger in the HPA subgroup compared to the entire sample. Additionally, the HPA subgroup demonstrated greater quadriceps strength compared to the LPA subgroup.
  
  
  METHODS
  3.
authors.affiliation: Department of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Pietrosimone
authors.affiliation: Department of Kinesiology, University of Toledo, Toledo, Ohio, USA.
authors.forename: Abbey C
authors.initials: AC
authors.lastname: Thomas
authors.affiliation: Department of Human Services, University of Virginia, Charlottesville, Virginia, USA.
authors.forename: Susan A
authors.initials: SA
authors.lastname: Saliba
authors.affiliation: Herbert H. and Grace A. Dow College of Health Professions, Central Michigan University, Mount Pleasant, Michigan, USA.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Ingersoll
keywords: Inactivity; maximum voluntary isometric contraction; physical function; quadriceps