For maximum muscle, this is when you should do your cardio workout

For maximum muscle, do your cardio directly after your lifting or the following day – never prior to. “Cardio fatigues muscles, leaving them too tired to do strength training to the best of your ability,” says certified strength and conditioning specialist and author of The New Rules of Lifting, Alwyn Cosgrove.

“Doing cardio with a fatigued body doesn’t matter because you’re going for heart-rate response, not speed,” he adds. If running harder is one of your goals, however, your body will be positioned to run further and faster if you wait at least a day after lifting weights. Yes, muscles undergo microscopic damage after a workout and need about 48 hours to repair themselves (becoming stronger and larger), but Cosgrove says the back-to-back days of stress won’t interfere with your strength gains. Reports to the contrary have been widely exaggerated, he says.