Lifting light or heavy weights to exhaustion for 12 weeks didn’t change body fat or muscle mass in women who had never lifted before.

In simple terms, this means that doing resistance training with either medium or heavy weights leads to about the same amount of fat loss in young women who are new to exercise over 8 weeks. Both types of workouts can help you lose fat.

When young women lift weights until they can't anymore, their arm and leg muscles get thicker by about 6-9% after 6 weeks. It doesn't matter if they lift heavy or light weights—both work the same for muscle growth.

For guys who don't usually work out, doing regular weightlifting cuts more overall body fat and thigh fat than a special pre-exhaustion method over 9 weeks, probably because you lift more total weight with the regular way.

For young women new to weight training, lifting weights until you can't do more reps (either 5-7 reps per set or 10-14 reps per set) three times a week for two months gives about the same muscle growth and strength gains, no matter which rep range you use.

Doing light weight exercises until you can't do any more for 8 weeks won't make your arms stronger or more powerful if you're new to lifting — you probably need to lift heavier or move faster to see real gains.