In my daily bicycle trips to work, I discovered a fun new game: when you're biking and stopping at a red light, notice how you usually put your right foot down to stabilize yourself. Now, here's the game:
instead of the right foot, put the left foot down every time you stop on your bike.
And be careful the first time you try it, as you're likely to... fall over! If you've never done it before, you will be surprised to see how an apparently simple mirroring of movement is difficult. And then if you try to do it repeatedly over, say, a week, you will quickly find the source of the difference: that small muscle on the outside of your left calf that is now throbbing in pain is the culprit, and clearly is not really used all that much even when you do something as varied as Parkour training.