Assume you can sprint and reach 40 km/h
Would it be possible to use almost no effort in your strides (feet touching the ground) to keep the momentum? Your legs, feets, hips, etc, would use the least amount of force possible to counteract friction forces and to keep you from falling

What would be required force from the runner body and the energy expenditure?

asking this because I tried sprinting once, and after getting upright somehow I couldn't hear my feet touching the ground anymore, and running was "effortless", it was almost as if I was floating