Is it better to run outside or on a treadmill?

1. Exercise effect, road running wins. During treadmill running, the biceps and rectus femoris muscles were more active, while the vastus lateralis muscle was less contractible. Road running works more of your leg muscles. And the treadmill is simulated exercise, not as good for the heart and lungs as road running. 

2. Treadmill wins in terms of energy saving. Running indoors does not have to overcome air resistance, and the elastic running belt also reduces physical exertion, so running on the treadmill is easier. 

3. No difference in knee protection. Where do you like to run?