Background/Purpose: Knee osteoarthritis (OA) is the leading cause of functional limitation in older adults, e.g., slow walking. Physical activity (PA) is beneficial for those with knee OA, as those who walk more or engage in more moderate-to-vigorous PA (MVPA) have better physical function than their less-active counterparts. However, it is unclear to what extent work may modify this association.  Over half of all PA occurs in a work context, i.e. preparing for work, commuting, and engaging in employment-based tasks. Therefore, the purpose of this study was to determine to what extent employment status may modify the association of physical activity with incident slow walking in adults with or at risk for knee OA.

Methods: We used data from the Osteoarthritis Initiative (OAI), a large cohort study of individuals with or at risk for knee OA. Objectively-measured PA (steps/day and MVPA) and employment status (yes or no) were collected at the 48-month visit (baseline). PA was measured with an Actigraph GT1M accelerometer worn at the hip for at least 4 days, 10 hours/day and MVPA was defined as ≥ 2020 counts/min. Employment status was obtained from the Physical Activity Scale for the Elderly (PASE) when asked whether they worked for pay or as a volunteer in the past 7 days. Gait speed from a 20m walk test was collected at the 48-month and 96-month visits. PA metrics were separately dichotomized into Active and Inactive using 6000 steps/day and 45 min/week of MVPA. Gait speed was dichotomized using 1.22 m/s as the cutoff to identify slow gait speed as walking less than that represents the inability to safely cross a timed street intersection. To determine to what extent employment status modifies the association between PA and incident slow gait speed at the 96-month visit, we first used binary logistic regression to calculate risk ratios and 95% confidence intervals (95% CI), adjusting for potential confounders at baseline. Next, we evaluated the interaction effect of PA and employment status on FL in a separate binary logistic regression model.

Results: Of the 1305 individuals with valid accelerometry data who were free of FL at the 48-month visit (age: 63.4 ± 8.6 years old, sex: 51.6% female, BMI: 28.0 ± 4.5 kg/m²), 1133 had gait speed data at the 96-month visit. For both steps/day and MVPA, inactive individuals had greater risk of incident slow gait speed relative to active individuals. Risk for incident slow gait speed was similar based on employment status in both models. In a separate model, the interaction effect of PA and employment status on FL was not significant (p = 0.11).

Conclusion: Regardless of employment, those who were inactive throughout the day, either in terms of daily walking or MVPA, had greater risk for incident slow walking relative to those who were active. This suggests that PA is a driving factor in the development of slow walking habits and that simply whether an individual was previously employed does not impact future slow walking.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/activity-in-work-and-life-the-association-between-physical-activity-and-employment-status-with-future-slow-walking-in-knee-osteoarthritis/