“If you only have a small window to run, use it. I believe short training sessions under 30 minutes should either be very hard or very easy. Set a timer on your watch, app, or phone. For a fifteen-minute all-out run, I recommend you sprint for 30 seconds, then jog for 30 seconds. Stop at lights to do squats and at every bench to do push-ups. If you don’t have lights or benches, use a different visual marker, like every other house, tree, stop sign—you get the idea.”