Working your muscles when they’re stretched out—either fully or at the start of the movement—helps them grow best in your thighs, biceps, and triceps.

To grow your quads, biceps, and triceps best, it helps to stretch the muscle more during exercise—either by going all the way down or starting the movement early.

When guys who work out a little bit lift heavy weights (85% of their max), their triceps muscles grow faster and more reliably than when they lift light weights (30% of their max)—so how heavy you lift might change when your muscles start getting bigger.

If you're someone who regularly lifts weights, doing more triceps exercises each week might help your triceps muscles get a little bigger—but only a little, and not as much as it helps your biceps.

All three types of muscle movements—squeezing, lengthening, and holding—can help build muscle in your thighs and arms just as well, as long as you train hard and often enough.

If you're a young woman just starting weight training, slowly lifting heavier weights over time will make your triceps (the back of your arms) grow about twice as much as just doing the same workout over and over.