If you're new to working out, doing leg exercises for 10 weeks can make one of your big thigh muscles grow bigger, even if the individual muscle fibers don't get thicker.

When healthy young men perform knee extension exercises as part of resistance training, the thickening of the vastus lateralis muscle is greater in the lower part of the muscle than in the upper part.

When untrained men get stronger in a static leg press, the main reason is that their thigh muscle near the hip gets bigger and its fibers angle more, which helps push harder.

If you're someone who's been lifting weights for a while, doing the same amount of heavy training over 9 weeks will make your thigh muscles grow by about half a centimeter — whether you spread your workouts over 2 or 4 days a week.

Even if you do a lot of leg workouts, your thigh muscles grow about the same amount whether you do 20 or 50 sets a week—just doing any consistent training makes them bigger.

If you're new to strength training, having more tiny blood vessels around your fast-twitch muscle fibers might help those muscles grow more when you start working out.