^^^ This. I rode a soft 20 miles with my wife last Saturday, then turned around and rode the exact route in reverse... only faster.
Or make a mental game of it. If I'm not feeling motivated to do a route, I play a game of "red light, turn right!" in which I make an effort to not stop at all-- moving time and elapsed time should be equal. Left turns can be tricky to time, and a 20 mile morning can quickly turn into 35, because I can't time a damn left!
Another is I pick an arbitrary HR number, and don't let myself either go below or above that number. Same with power, speed on climbs, etc. This morning I tried to keep my HR at 138 for as long as possible. Staying on one number is tough.
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