<p>Knee osteoarthritis (OA) is a common chronic disease that often occurs in older adults, affecting their quality of life. The purposes of this study were to examine 1) the relationship between physical activity and medial tibial cartilage volume and thickness in participants with clinical knee OA; and 2) the test-retest reliability of daily step counts produced by participants with knee OA.</p> <p>The study included 34 participants (age 60.6 ± 6.5 years; body mass index 28.5 ± 5.4 kg/m²). Dependent variables were medial tibial cartilage volume and thickness, measured from magnetic resonance images. Independent variables were average step counts and average time spent in light intensity activity, measured with an accelerometer. These data were then was analyzed using linear and second degree polynomial regression analyses to determine the relationship between dependent and independent variables along with age, sex and BMI as covariates. The test-retest reliability of step counts collected over 5 days was evaluated with an intraclass correlation coefficient (ICC).</p> <p>Average time engaged in light intensity activity, average daily step counts, sex and age accounted for 56.3% of the variance in medial tibial cartilage volume. Age and average time in light intensity activity explained 33.2% of the variance in medial tibial cartilage thickness. Results from the second degree polynomial analyses were not significant. The ICC for the daily step counts over first 5 days of 10 hours wear time was 0.929 (95% [CI] =0.883, 0.961).</p> <p>A weak linear relationship existed between physical activity and cartilage volume and thickness within the knee joint. The greatest medial tibial cartilage volume was found in men who were engaged in longer durations of low intensity physical activity. The test-retest of step counts data by participants with knee OA was very reliable over the 5 days. Findings from this study augment current knowledge of knee OA.</p> / Master of Science (MSc)