Running on a treadmill without taking proper precautions could cause some injuries on your knees. For example, running on a treadmill at a 0% incline can cause minor wear to your knee and patella tendon over time. By setting it to a moderate slope at 3%, it can assist alleviate these issues. A 3% incline reduces the force impact on the legs and knees by 24%, but getting it steeper at a more than a 3% incline (utilize for runners straining for uphill terrain) should be use in caution as it can also put your knee joint under stress. Always remember to do proper stretching before and after running.