If you've never worked out before, lifting weights for 10 weeks can make your muscles stronger and bigger — especially in your legs and arms — while people who don’t train see almost no changes.

Whether you use machines that change resistance as you lift or keep the same weight all the way through, after 20 weeks of training, healthy men gain about the same strength and muscle size either way.

Older adults, even those over 85, can gain just as much leg strength as younger seniors from 12 weeks of regular weight training — and some even gain a bit more!

If you're a young adult who doesn't lift weights or do strength training for 8 weeks, your muscles won't get noticeably bigger or stronger on their own — you need to actually train to see changes.

If you're already strength training and you suddenly do more than 50% extra workouts per week, your biceps and triceps might grow a bit more—but if you only increase a little or even cut back, you won't see a big difference in muscle size compared to those who ramped it up a lot.

Lifting heavier weights is much better than lifting lighter weights for building muscle strength in healthy young adults, because it trains your muscles and nerves to work together more effectively for maximum power.