If young guys who used to work out take a break and then do the same strength exercises over and over for about two months, some parts of their muscles might not grow much — especially on the side of the thigh and upper arm — which means doing the same routine might not help all muscles grow equally.

Young guys who took a break from working out didn’t see much muscle growth in certain areas—like the middle of the outer thigh and upper arm—after nine weeks of doing the same strength exercises.

If young guys who haven’t worked out in a while switch up their strength exercises for the same muscles, they’ll likely build muscle more evenly across their thighs and arms over nine weeks compared to doing the same moves every time.

If you mix up your strength workouts for the same muscle, it might help it grow more evenly from top to bottom, especially if you haven’t been training for a while.

If young guys who haven't worked out in a while do different leg exercises for 9 weeks, their upper outer thigh muscles grow more than the middle part — even with exercise variety, growth isn't even.

If you switch up your leg exercises during a workout routine, you might build more muscle in certain parts of your thigh—like the upper side—compared to sticking with the same moves.