Cardio and Muscle Mass

[EyeBRollin]

Also instead of overdoing cardio you can under-eat instead, on under-eat days just make sure you have enough protein and cut carbs and some fat.

It's really this right here.

Cardio doesn't negate muscle gains. Muscle gains are had with a combination of strength gains and caloric surplus. (Though I'm skeptical a surplus is needed for strength gains. Surplus is required for size and the assumption is that size = strength).