When eight trained bodybuilders did arm curls with heavy weights, their muscles made more lactic acid the more sets they did — which means their bodies were working so hard they had to rely on a...

When eight trained bodybuilders did arm curls with heavy weights, their muscles used up a bit of stored sugar—12% after one round and 24% after three rounds—showing that even short, intense weightlifting burns some muscle fuel.

When you push your muscles super hard until you can't do another rep, your muscles build up a lot of lactic acid—this means your body is burning energy without oxygen and getting more acidic inside.

Pro bodybuilders might keep building muscle with a special type of workout called lacto-resistance training, even when regular workouts stop giving them results.

Doing a special kind of weight training that builds up lactic acid gives pro bodybuilders a bigger metabolic boost than regular weightlifting — their muscles show more stress signs like lactic acid and ammonia after just one workout.