Purpose: This dissertation has two primary aims; 1) to better understand how various physical, psychological, and general health factors influence physical activity (PA) and 2) to better understand different clinical phenotypes in people with knee osteoarthritis (OA) and functional outcomes, including PA. Methods: This dissertation utilizes data from the 48-month follow up of the Osteoarthritis Initiative, an observational longitudinal study of 4,796 participants examining onset and progression of knee OA in community dwelling adults between the age of 45-79. For the first study: 403 participants in a subset of participants using accelerometer- derived PA data, were analyzed for significant correlates of total PA time to estimate total PA using a linear regression model with bootstrapped standard errors. The second study includes data from 1,057 participants to perform a K-Mean Cluster analysis using body mass index, depressive symptoms, strength and radiographic evidence. One Way Analysis of Variance analysis and a Tukey’s post-hoc test was utilized to compare clinical outcomes between clusters including PA, function and pain. Results: In our first study: Over three-quarters of our sample did not meet the recommended volumes of PA. Negative associations were noted between higher BMI and total PA, comorbid conditions and total PA, and increasing age and total PA. A positive association was noted between diverting attention as a coping strategy and higher volumes of PA. In our second study: The cluster analysis identified 5 clinical phenotypes. Significant differences were noted between phenotypic groups in all clinical outcomes measured. Conclusion: Older adults with knee OA are not meeting recommendations for total PA, which can improve function and attenuate the effects of functional decline and disability. Four major factors were associated with total PA levels in a population with mild to moderate knee OA: co-morbidities, age, BMI, and the diverting attention coping strategy. In our second study, we identified five phenotypes of individuals with knee osteoarthritis and revealed differential clinical outcomes based on phenotypes. Understanding clinical differences between phenotypes may enable us to efficiently and effectively target our interventions to optimize PA and functional outcomes in people with knee osteoarthritis.

[Truncated abstract] Knee osteoarthritis (OA) patients have high levels of pain, functional and strength deficits of the quadriceps, decreased proprioceptive acuity, and increased co-contraction and knee joint loading in gait, compared to age matched controls. The increased knee joint loading in this population occurs most commonly in the medial tibio-femoral compartment, due to increased external adduction moments, and with increasing disease severity there is a concomitant increase in the knee adduction moments. A key finding within the knee OA literature is that dynamic loading in gait, due to increased external adduction moments, strongly predicts pain and radiographic disease progression. Current research has shown that exercise interventions reduce pain and time to complete functional activities; however, the effect of these interventions on knee joint loading and muscular activation in gait is still unclear. In addition, the need for specific knee joint strengthening to cause these alterations has not been investigated and it remains unknown if improvements occur due to specific muscle strengthening or due to some general effect of exercise. Therefore, the primary aim of this research study was to examine the effects of general (upper body) and specific (lower body) resistance training interventions on self-perceived outcomes, neuromuscular function and kinematic, kinetic and muscle activation during gait of OA patients compared with asymptomatic controls. ... The examination of gait data following exercise (Study 4) showed trends for changes in the muscle co-contraction ratios. Specifically, the medial/lateral co-contraction ratio (MLCCR) displayed a trend in early stance where the upper body exercise group increased their lateral muscle activity and the lower body group reduced their lateral muscle activity, and the medial/lateral hamstring co-contraction ratio (HAMCCR) displayed this same trend during loading. The trend toward reduced lateral muscle activation, following lower body resistance training, suggests that specific muscle strengthening may have the ability to alter the load distribution. The kinematic and kinetic variables of gait were unchanged by the exercise interventions, highlighting the sensitivity of muscle activation pattern changes due to muscle strengthening. This thesis provides new insights into the co-contraction strategies utilised by knee OA patients. The directed co-contraction strategy employed by knee OA patients and its relationship to the external adduction moment in gait suggest an attempt to redistribute the loading within the knee joint, most likely in response to pain. Further, we have separated the effects of exercise and found differences in self-perceived outcomes based on exercise specificity. This first examination into muscle co-contraction following resistance training of knee OA patients has highlighted the possibility of alterations to the co-contraction patterns following lower body exercise. However, the implications of altering this muscle activation strategy and the consequent effect on distribution of load within the knee joint requires further consideration.