A lighter workout style called LST can make your muscles produce as much lactic acid as a harder workout called HN, which might help build muscle size just as well, even though it's less intense.

When doing slow, gentle weight training for your whole body, your muscles get just as tired and produce the same chemical buildup as fast, hard training—even though you're not lifting as heavy. This means your body is working hard in a different way to make the exercise effective.

When trained men do certain types of weightlifting workouts, their bodies produce more lactic acid compared to other workout styles, which means their muscles are working harder and under more stress.

When you lift weights until your muscles burn, the buildup of waste products might help your muscles grow bigger, but scientists aren't sure yet if it's actually causing the growth or just happening at the same time.

A certain type of weight training keeps your muscles working non-stop, making them use more oxygen and possibly grow bigger because of changes inside your body.

When lifting weights at 30% or more of your maximum strength, your blood lactate levels and heart rate rise more than when lifting at 10% of your maximum, showing greater metabolic demand.