The blows rain down upon me: first a solid right to the gut that weakens my knees and loosens my bowels, then several hooks to the head. I taste metal fillings and smell the mothballed aroma of boxing-glove stuffing. I’m stumbling around, trying not to fall, when finally a voice yells "Break!" and my assailant steps back, revealing herself as a five-foot-tall woman in her early seventies.

That’s when humiliation settles in. I’m a middle-aged suburban dad, pudgy and pulsing with the bad kind of cholesterol, and I just got my ass whooped by a little old lady with white hair and matronly blue eyes. How did I end up here?

I’d wanted to learn martial arts since I was a kid reenacting Kung Fu Theatre on my parents’ couch cushions, but I never had the courage to try it, not even after my own son signed up. At a certain point, it just seemed too late. Then, one year, my wife bought me lessons as a Christmas gift, her gentle way of saying it was time for me—after a decade of babies and career and commuting and cronuts—to find a hobby, spend some quality time with the boy, and get in shape.

Three More Ways to Uppercut Your Metabolism

Whether you’re ercising the same way every time out or not ercising at all, it’s dangerously easy to sink into a rut. Your body needs new forms of stimulation. Not into the martial arts? You’ve got options.

1)** If you play basketball, try > rock climbing**.

It’s still about timing and accuracy and explosive strength, and you don’t need nine other dudes to get a pickup game.