Background/Purpose:

Physical activity conveys health benefits for people with osteoarthritis (OA).  Public health activity guidelines are tied to time spent in bouts of moderate/vigorous physical activity (MVPA) lasting 10 minutes or more.  This study compares objective accelerometer measures of MVPA with self-reported Physical Activity Scale in the Elderly (PASE) scores and their association with function in adults with and without radiographic knee OA.

Methods:

The Osteoarthritis Initiative accelerometer ancillary study includes 586 adults without and 969 with radiographic knee OA (Kellgren-Lawrence score ≥2 in one or both knees), aged 55 and above.  Participants’ response to the PASE questionnaire was followed by 7 days of accelerometer monitoring.  Accelerometer measures included average daily MVPA minutes and MVPA minutes acquired in bouts.  Function measures included gait speed averaged from two 20 meter walks, WOMAC (Western Ontario MacMaster) function, and SF12 (12-Item Short Form Health Survey) physical function. Nonparametric Spearman correlations were used to assess associations.

Results:

Adults with and without knee OA had mean (SD) PASE scores: 149.82 (78.5), 154.5 (79.0); mean accelerometer MVPA minutes/day: 15.6 (17.2), 19.2 (20.5) and mean MVPA bouted minutes/day: 7.2 (12.4), 9.3 (15.8), respectively.  PASE score correlations with accelerometer measures are shown below.  In this sample, PASE was correlated most strongly with total activity counts followed by MVPA minutes and had weakest association with MVPA minutes accumulated in bouts. Further analysis shows all objective accelerometer measures had stronger associations with function than PASE (e.g., correlations from overall sample of gait speed function with self-reported PASE: r=0.16, accelerometer counts: r=0.29, MVPA: r=0.34, MVPA bouts: r=0.28).  These findings were true of both adults with and without radiographic OA.

Conclusion:

In this sample with and without radiographic knee OA, the self-reported PASE score had stronger although modest correlations with objective measures of total activity than with MVPA minutes or MVPA bouted minutes.  Objective physical activity measures compared to self report had stronger relationships with function. The choice of PASE, a recall measure of various activity types, and/or objective measurement for future epidemiologic studies must take into account the purpose for which physical activity is being measured.