Reduced Pulmonary Function Association with Abnormal Muscle Activation with Knee Osteoarthritis and Increased Cardiovascular Disease Risk

This study aimed to explore the cardiopulmonary function, physical activity, and activation of major lower-limb muscles in individuals with knee osteoarthritis (OA) with increased cardiovascular disease (CVD) risk. A total of 21 individuals with knee OA and increased CVD risk and 29 individuals with isolated knee OA completed the long-form International Physical Activity Questionnaire (IPAQ) in an interview format. Pulmonary function was assessed by measuring Forced Vital Capacity (FVC) and Maximum Voluntary Ventilation (MVV). Cardiorespiratory fitness was evaluated using a treadmill-based cardiopulmonary exercise test (CPET) with a modified Bruce protocol. Furthermore, surface electromyography (sEMG) data were collected from the major lower-limb muscles of the symptomatic limb during stair-climbing tasks performed at a self-selected, habitual speed. Compared with the knee OA group, the knee OA with CVD risk group demonstrated significant reductions in vigorous physical activity, maximal voluntary ventilation (MVV), and a lesser decrease in peak oxygen uptake. Additionally, the knee OA with increased CVD group showed greater muscle activation of the biceps femoris (BF) during stair ascent and descent. Furthermore, there was a negative relationship observed between lower MVV and greater BF activation in the knee OA with the CVD risk group. These findings suggest two main conclusions. First, sEMG serves as a valuable non-invasive tool for identifying clinical hallmarks in knee OA patients at risk of CVD by detecting aberrant muscle activation during stair climbing. Second, among these at-risk individuals, superior cardiovascular function is linked to a more balanced knee muscle coordination pattern, as reflected by the inverse relationship between MVV and biceps femoris activation.