Feeling a muscle cramp or intense contraction during an exercise, such as in the bicep or calf, indicates that the muscle is being adequately stimulated for growth and performance.

“If you can flex your bicep to the point where it hurts a little bit, like it almost feels like a cramp or a cramp, or you can flex your calf to the point where it really cramps up a little bit, almost feels like it's nodding up, that's a pretty good indication that you're going to be able to stimulate that muscle well under load if you're doing the movement properly.”