My body is thin and athletic.

Athletic describes what a body does far more than what it looks like. Two people the same size, and one can run for a bus without dread while the other can't.

The things worth chasing are verbs.

Getting up off the floor without using your hands. Holding a plank while the timer becomes personally hostile. Carrying a heavy suitcase up a flight of stairs and not needing a minute at the top.

Those are trainable, they're the parts you actually live inside, and appearance has a habit of following capability around.