Obesity is a major risk factor for the onset of musculoskeletal injuries such as knee osteoarthritis and increased falls risk. With increasing prevalence of obesity worldwide, medical costs, morbidity, and disability associated with obesity-related injuries are likely to increase in the upcoming years. A drawback of many studies evaluating biomechanical gait patterns in obese subjects is the methodology. All included studies in the recent systematic review on gait biomechanics in obese subjects used surface markers for the measurement of skeletal movement which suffer from relatively large measurement errors due to movement of the skin relative to the underlying bone, especially with large subcutaneous fat mass, as in obese. The magnitude of the measurement errors when using surface markers makes evaluation of knee joint kinematics, especially in the frontal and transverse planes among obese, highly questionable. Recently, new measurement techniques have been developed to overcome these drawbacks. Knee kinematics of obese have never been compared to normal-weight controls using high sensitive methods, such as high-speed biplane radiography. In collaboration with Scott Tashman (Co-Investigator), this study compared knee kinematics during unperturbed gait (normal walking) and knee kinematics/associated falls risk during perturbed (simulated slips/trips) gait between otherwise healthy obese and normal-weight subjects. The purpose of this study was to explore the knee biomechanical mechanisms during normal walking and a simulated slip/trip in obese and non-obese adults.