This group will do a 12-week high intensity exercise program. The subjects will exercise by increasing how much they lift their knees while walking on treadmill. The exercise will also involve controlling the impact of the feet on the treadmill. A TV placed in front of the treadmill shows how high individuals need to lift their knees. How much participants need to lift their knees is calculated based on real-time heart rate readings.

This group will do initially a 12-week period of no intervention. After these 12 weeks, participants will do a 12-week high intensity exercise program. The subjects will exercise by increasing how much they lift their knees while walking on treadmill. The exercise will also involve controlling the impact of the feet on the treadmill. A TV placed in front of the treadmill shows how high individuals need to lift their knees. How much participants need to lift their knees is calculated based on real-time heart rate readings.

This study introduces a new way to exercise using a hip flexion feedback system (HFFS). The subjects will exercise by increasing how much they lift their knees while walking on treadmill. The exercise will also involve controlling the impact of the feet on the treadmill. The HFFS monitors the subject's heart rate during the exercise using a standard heart rate monitor. A TV placed in front of the treadmill shows how high individuals need to lift their knees. How much participants need to lift their knees is calculated by the HFFS based on real-time heart rate readings. Therefore, the HFFS can help people stay at a specific exercise intensity by controlling how high it tells them lift their knees during the exercise.

Cardiorespiratory fitness will be quantified as peak oxygen consumption (VO2max) and walking efficiency. VO2max will be evaluated using a Balke treadmill exercise testing protocol [35]. This protocol maintains a constant speed during the test and progressively increases treadmill inclination (grade) until exhaustion. In contrast, walking efficiency will be evaluated using a submaximal exercise test (performed prior to the VO2max test). This submaximal exercise test will require participants to walk on a treadmill at a self-selected pace, during which time VO2 will be recorded.

Cardiovascular function will be quantified by resting blood pressure, heart rate, heart rate variability (HRV) and carotid-femoral pulse wave velocity (cfPWV). Blood pressure and heart rate will first be collected in the seated position using a manual sphygmomanometer according to the World Health Organization (WHO) recommendations. Next, heart rate will be recorded for approximately 10 minutes in the supine position, which will be used for assessment of HRV. During this collection period, participants will breathe at a rate of approximately 7 breaths per minute, which will be maintained using a metronome. The ECG data collected during this ten-minute period will then be analyzed using time domain HRV analysis and spectral HRV analysis. Lastly, cfPWV will be collected using applanation tonometry.

Subscales for pain, stiffness and physical function will be used to assess knee osteoarthritis symptomatic burden. The WOMAC includes a total of 24 items with subscales of pain (five items), stiffness (two items), and function (17 items), which are all rated on a Likert scale of 0 (no symptoms) to 4 (extreme symptoms). The total WOMAC score will be calculated (score range of 0- 96 [no to extreme problems]), as well as the pain (score 0- 20), stiffness (score 0- 8), and function (score 0- 68) subscales.