The plank is a body-weight exercise that works the abs and hip flexors, the glutes and lats. To do it, get into a pushup position, but with your hands together
and your weight resting on your forearms, not your palms. Keeping your back straight, tighten your abs as though you are about to be punched in the belly. Hold this position for 1 minute.
Run outdoors. Running on land is more challenging than on an indoor treadmill, and it trains you better.