tl;dr: Do something like professional chess, that:

1. Takes hours each day.

2. Creates a persistent stress response while you do it.

3. Distracts you from food.

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Using heart rate to estimate calories burned is mentioned. Has anyone here actually used their fitness tracker to discover an unexpected calorie sink?

e.g. I've had an action movie fight scene on the gym TV grab my attention for a couple minutes, and transition me into a sprint on the elliptical machine, without me realizing. Nifty, but I couldn't reproduce the effect.