Using incline on a treadmill can sometimes lead to a sharp pain in the knees, sometimes known as ‘runner’s knee.’ This is because the incline shifts pressure from the ankles to the knee joints, as they are loaded up with the weight of the body.
However, using a less steep incline of 3% or below can actually be easier on the knees than a completely flat treadmill. The slight incline reduces some of the pressures acting on the knee. There’s also the fact that using an incline means you won’t have to accelerate to as high a speed to get a solid workout, which reduces a lot of the impact on your joints.
As with all things in exercise, it’s important to pay attention to your body and whether an exercise is causing pain. Work your way up the incline levels and only progress as you feel comfortable.
This will also be influenced by how much you warm up and cool down for your workout, which will give your muscles the best chance to handle the incline and recover from any irritation afterwards.