I'm not sure how it detects how hard a punch is, but I suspect form (or the closest approximation it can detect) is a significant factor.

But honestly, it's not real boxing it's a boxing themed cardio exercise. At a purported 10-15 calories a minute it seems like a pretty good cardio workout as well.

My form is fine, it’s just that swinging as hard as you can i to air many times is going to take its toll.