Measuring your arm or leg size with a tape measure isn't a great way to tell if you're actually building muscle. Since the tape can't tell the difference between muscle, fat, and water, changes in size might just be from gaining fat or holding water instead of real muscle growth.

When people lift weights to build muscle, how much muscle they seem to gain depends on how you measure it—different ways of measuring show different results.

Scientists use tape measures and skin pinches to guess how much muscle people gain from weight training, but these methods aren’t precise enough to notice small muscle gains.

Most studies measure muscle growth by weighing your whole body and subtracting fat — but that includes water and fuel, not just muscle. That’s like measuring your car’s weight to see if the engine got bigger.

If you do the same total amount of weightlifting each week, it doesn't matter if you split it up over several days or do it all at once—your muscles will grow the same amount. Objective measurements show that how often you train doesn't change the results as long as the total work stays the same.

If you're a guy who already lifts weights, doing lower-body workouts for 8 weeks will build leg muscle — and it doesn't matter if you do your usual number of sets or increase them by 30% or even 60%.