Background/Purpose:

Walking speed is a measure of performance, i.e., what people “can” do, and is a known predictor of future health, disability, and mortality in older adults.  Time in moderate-to-vigorous physical activity (MVPA), is a complementary measure of the frequency of behavior at given intensity, i.e., what people actually “do”, and is also associated with future health and mortality. However, it is unclear how both walking speed and MVPA are jointly associated with future health.  The purpose of this study was to examine the associations of combined walking speed (what people “can” do) and MVPA (what people “do”) categories with health-related quality of life (HR-QoL) and disability in adults with or at risk of knee osteoarthritis (OA).

Methods:

We used data from the Osteoarthritis Initiative, a large cohort study of people with or at risk for knee OA. Walking speed and MVPA were collected at the 48-month visit. Walking speed was calculated from a 20-m walk test. MVPA was measured with an accelerometer (Actigraph GT1M) worn at the hip for ≥10 hrs/day for ≥4 days, and defined as ≥2020 counts/min.  We classified people as Fast-Active (>1.2 m/s and MVPA >11 min/day, median value of the sample), Fast-Inactive (>1.2 m/s and MVPA <11 min/day), Slow-Active (<1.2 m/s and MVPA >11 min/day), and Slow-Inactive (>1.2 m/s and MVPA <11 min/day). Study outcomes were incident low HR-QoL measured with the Short-Form 12 Physical Component Score (SF-12 PCS, Score <40 indicating low HR-QoL) and incident disability measured with the Late Life Disability Instrument (Limitation Score [LLDI-L] <50 and Frequency Score [LLDI-F] <70 indicating disability) measured 4 years later. We calculated risk ratios and 95% confidence intervals adjusting for potential confounders at baseline.

Results:

Of 1876 people with baseline walking speed and MVPA data (55% women, age 65.1±9.1 years, BMI 28.4±4.8 kg/m²), 1419, 1250, and 1413 people were free of the outcome at baseline and had 4-year follow-up data for the PCS, LLDI-L, and LLDI-F, respectively. At the 4-year follow up, 11-15% of the analytic sample developed low HR-QoL and disability (Table 1). The Fast-Inactive and Slow-Inactive groups had greater risk of incident low HR-QoL compared to the Fast-Active group; the Slow-Active group had similar risk. The Slow-Inactive group had greater risk for incident disability (LLDI-F) compared to the Fast-Active group; otherwise the groups had similar risk.

Conclusion:

Compared to people who were fast and active, those who were slow and active were at similar risk, those who were fast and inactive had greater risk of HR-QoL, and those who were slow and inactive had greater risk of developing low HR-QoL and disability. Advising patients to “do”, i.e. spend more time in MVPA (e.g. a brisk walk), may be as or more important than ensuring that they “can” do, i.e. walk fast enough for community ambulation, to prevent the development of future low HR-QoL.