What do you think about incline on a treadmill? Without the incline you can move your legs faster without a raise in HR.
And when you run on a treadmill, is it like running on like concrete or soft as dirt? How good for your legs is the surface which u run on?
Any treadmill I used has a very cushioning surface. I used to own a treadmill and it had some much cushion that I wore racing flats when I ran on it.
1.0-1.5%
Some decks are springy, some are like running on a mattress or sand. They all are more forgiving than pavement.
The incline is important because the ground is moving under you and your foot strikes too far under you center of gravity. A slight incline 1-1.5% mimiks running better than no incline. Jack Daniels covers this in his book as well.
8% incline at 8mph...try it for a bit....then try 10% at 10mph...it's fun.
Then set it to 15% incline and find a pace you can actually maintain for a good hard 2-3 minutes. It will humble you.
Alan