In my movement classes, I often say, “Toes are the gas; heels are the brakes!”
Whatever angle you use to apply force to the ground is equal and opposite to the angle that the ground applies that force back. If you are digging in your toes and running with your legs behind you to accelerate, the ground is pushing you forward as that energy travels back up your legs in a forward direction.
A mistake people often make when running is allowing their heel to strike the ground first. When this happens, yes, there is a short burst of forward energy from the heel strike that travels forward to your toes, but much of that energy travels in a backward direction up your leg. This is an energy leak.
An energy leak is wasted energy that is not contributing to moving our body in the desired direction. Our bodies are full of these energy leaks that waste time and movement during stages. They can also contribute to injuries over time.
Think of running more like a series of falling and catching yourself. Use gravity to your advantage. And remember to use your toes as the gas and heels as the brakes!