If young guys switch up their weightlifting exercises for the same muscles, they’ll get just as strong as if they stuck to the same routine for 9 weeks.

If young guys lift weights all over their body 3 times a week for 9 weeks, they'll get stronger — no matter if they switch up their exercises or stick to the same ones.

Even though lifting weights makes your muscles bigger and more active, those changes don’t explain why you get stronger—meaning something else, like how your nerves coordinate movement, might be more important.

Even though lifting weights makes your muscles bigger and more active, those changes don’t explain why you get stronger at dynamic movements but not at holding static positions — something else, like how your brain coordinates movement, might be more important.

Beginners get way stronger from weight training than experienced lifters, and even among beginners, they get much stronger at moving weights than at holding them still.

Lifting weights with movement (like squats or bench presses) makes you much stronger at those exact movements, but doesn’t make you much stronger at holding a static position—even if you’re using the same muscles.