Milo of Croton, the ancient Greek athlete, strong man, and wrestler, may be credited as the first athlete to use the principle of progressive overload. Legend has it that Milo trained for the Olympics by carrying a newborn calf on his back every day for years prior to the Olympic start date, and by the time the Olympics arrived, the calf had grown to a full-size cow, and Milo was still carrying it on his back! In essence, Milo adapted to the growing weight of the animal by growing stronger himself. That's progressive overload. To follow this model for developing strength and tone, you lift weights that are heavy enough to create muscular fatigue at the 10th to 12th repetition and then when that gets easy, you increase the weight and lift that new weight until you can do it again for 10-12 reps. You can increase the weight every time you get to 10 or 12 reps. Typically every time you add new weight, you lift fewer reps because it's heavier, but then as your muscles grow stronger, you perform more reps.