Mad Jee wrote:
"A treadmill actually assists your running" No.
Yes. Treadmill belt moves underneath you and we only use predominantly anterior muscles to lift our legs in that situation. Outside we actually need glutes and hamstrings to contract and help propel us forward as well as slow down the leg. On a treadmill, hip flexors doing a lot more work to lift the leg to meet the speed that the belt is moving underneath.
So while HR is HR and that's good for training effect, I think most people agree that treadmill used sparingly is good for interval work and occasional workouts. But you can't train on a mill for long and expect to keep the same pace at equal effort. So while HR on a treadmill at 7 min pace might be XX, HR outside at that same 7 min pace is going to be XX+ and youre going to fatigue a lot quicker in your posterior chain muscles.