People who didn't work out at all for 20 weeks didn't get stronger, more tired-resistant, or more muscular — so if others who did work out did get better, it's because of the exercise, not just because time passed.

If you're already strength-trained and do upper-body workouts for 8 weeks, it doesn't matter much if you lift all the way up and down or just do part of the motion—your muscles grow and get stronger about the same either way.

Whether you lift heavy weights for fewer reps or light weights for more reps—as long as you push until you can’t do another rep—your muscles grow about the same amount.

Using machines or bands that change how hard they feel as you move might make your muscles work more evenly during an exercise, but that doesn’t always mean you’ll grow bigger muscles faster than with regular weights—especially if you’re just starting out.

Whether you lift heavy weights with fewer reps or light weights with more reps—as long as you push until you can’t do another rep—your muscles grow about the same amount.

Lifting weights until you're tired, whether with light or heavy weights, makes your muscles bigger and stronger in the same way for beginners.