Running and flying have an odd similarity. The power curve.
Straight and level flight is an easy to understand flight condition. You are maintaining a given altitude and proceeding in a straight line. This is where you spend the majority of your time flying.
Descending isn’t a whole lot harder. You point the airplane down a bit and lose altitude. Unless you make other adjustments, you will also gain some airspeed.
Climbing is a bit different. In most instances you use your excess of power — the power available that you don’t need simply to maintain altitude — to add some feet of safety between yourself and the ground.
What can get weird is when you are at a high angle of attack (your nose pointed nicely skyward) at slow speed and your drag increases so much that a shocking amount of power is needed just to maintain altitude. This is referred to as “getting behind the power curve”. You are so out of sorts that you have to work really hard just to do what should have been pretty easy.
Running can be the same kind of thing. You can go out hard and fast, but can easily get yourself worn out to a point where maintaining your normal pace is impossible without extraordinary effort and you end up screwing up your whole race.
So, in flying and running, don’t get behind the power curve. Stay within your capabilities and you’ll be much more successful in the long run.