with time

You would think in time it won't take that much effort. You run more often, you work harder, you are in better shape. You expect there will be a point when it will get easier.

But it doesn't. You still get sore, it's still hard on your lungs, you still hate getting up while it's still night.

Okay, so the casual 5K, that you would do just to loosen up the muscles, seems less daunting. Okay, so sometimes you manage a good run that doesn't take it all out of you.

Aside from that, on the whole, it doesn't take less effort.

You just get more used to it.