When young men do heavy squat training with different numbers of reps, all rep ranges make their thigh muscles bigger, but higher rep ranges (like 13-15 or 23-25 reps) make their thigh size grow more than lower rep ranges.

Even if you’re already strong—squatting almost twice your body weight—adding more sets will make you stronger, but won’t make your muscles grow more than doing a moderate amount.

For men who already lift weights, doing either high-intensity or high-volume workouts for 8 weeks didn't make a big difference in leg strength or muscle size.

When young men did squat workouts with different numbers of reps, their body weight and hamstring muscle size changed about the same as each other and no different from guys who didn't train at all.

Lifting heavier weights for fewer reps makes your legs much stronger than lifting lighter weights for more reps, but both types of training help your upper body a little bit too, and this might work differently for different muscles.

When people who already lift weights do either mostly heavy lifts or mostly lighter lifts—but keep the total amount of work the same—both ways make them just as strong after 8 weeks.