Osteoarthritis is a prevalent and disabling condition. Exercise is recommended to maintain strength and mobility, and to decrease pain. However, acute bouts of exercise have conflicting outcomes: they are fatiguing and they also can increase coordination and balance. The purpose of this study is to assess the effects of a single bout of exercise (30 minutes) on balance performance of individuals with self-identified unilateral knee osteoarthritis. Balance will be assessed using the star excursion balance test before and after the exercise session. Differences in performance between the two star excursion balance tests will reflect the changes due to exercise. The changes between their balance performance on each limb will reflect the changes due to osteoarthritis.

Knee OA affects over 241 million people worldwide, and poses a significant burden to the healthcare system (Cross et al., 2014). Knee OA leads to decreased quadriceps muscle strength, and impaired postural control and joint proprioception (Hurley et al., 1997). These factors lead to balance impairments in individuals with osteoarthritis compared to controls (Wegener et al., 1997). It has been reported that the completion of a warm-up program improves the dynamic and static balance of healthy individuals (Daneshjoo et al., 2012). Therefore, exercise may acutely facilitate neuromuscular control, reduce stiffness and significantly improve dynamic balance in individuals with knee OA. Alternatively, muscular fatigue that may negate these benefits (Nardone et al., 1997). Given that falls are a devastating injury in the elderly (Sri-On et al, 2017), and that exercise programs improve balance (Carter et al, 2001; Tse et al, 2015) it is important to evaluate the acute effects of a single bout of exercise on balance performance in individuals with osteoarthritis. The Star Excursion Balance Test (SEBT) has been validated for quantifying dynamic balance in healthy individuals (Kinzey & Armstrong, 1998) and individuals with knee OA (Kanko, 2017). It is important to evaluate the effects of exercise on balance in individuals with OA as changes in balance following exercise may lead to either impairments or improvements, and have direct implications for the safety of exercise as a recommended approach in OA.

This study will recruit 35 individuals with self-identified unilateral knee osteoarthritis, according to clinical criteria for classification of idiopathic knee OA (Altman et al., 1986). They will complete a Physical Activity Readiness Questionnaire for Everyone (PAR-Q+) to clear them for participation in physical activity (Warburton et al, 2011). They will complete a standard questionnaire assessing knee function: the Knee injury and Osteoarthritis Outcome Score (KOOS) (Roos et al, 2003). They will complete the star excursion balance test, on each of their affected and unaffected limbs, before and after completing a 30 minute bout of exercise. This exercise session will be supervised, and emphasizes optimal alignment of the trunk and lower limb joints relative to one another, as well as quality of movement performance, while dynamically and functionally strengthening the lower limb muscles (Bennell et al, 2011). The research participants will dictate the intensity and duration of the program.

Differences in performance between the two star excursion balance tests will reflect the changes due to exercise. The changes between their balance performance on each limb will reflect the changes due to osteoarthritis.

Inclusion Criteria:

• unilateral knee osteoarthritis according to clinical criteria for classification of idiopathic osteoarthritis (OA) of the knee (Altman et al., 1986)
• routinely engaging in mild exercise, such as walking or gardening.
• a completed PAR-Q+ indicating no contraindications

Exclusion Criteria:

• lower extremity joint replacement
• Inflammatory or Infectious Arthritis
• Major neurological disorder (ex. Parkinson's disease, Huntington's disease, Multiple Sclerosis, peripheral neuropathy)
• Major medical illness that would interfere with participating in a 30 minute bout of exercise
• Inability to engage in moderate physical activity for 30-40 minutes
• Inability to read English
• Psychiatric illness that limits informed consent
• Inability to stand on limb for more than 5 seconds

Each participant will be identified with a code (eg. STAR001) that correlates to his or her addition to the study. The master sheet will be the only document that contains the decoding system, and will be stored in a locked filing cabinet. All other data will be labeled using the participant's identification code.