Should I do cardio before or after I lift weights for muscle gain / fat loss? To answer this question we must ask ourselves what is our goal and what are we trying to achieve?
In the perfect world we would do cardio and weights on different days to gain the maximum benefit from each. Any time you do one followed by the other the second one will suffer at least a little. (Studies have shown however you may improve your overall endurance this way)
The question normally comes down to priorities. If you’re trying to build muscle mass doing cardio straight after weight training may not be the smartest idea because the more depleted your muscle fuel becomes (Glycogen) the more protein your body can use as fuel. Protein is the body’s building blocks for muscle growth and repair so it’s critical we optimize our protein stores. After an hour of intense weight training (exercise) protein may provide up to 10% of the fuel your body requires compared to 1-2% it normally provides. That’s the opposite of what you want for building muscle and strength. If building muscle is your goal as soon as possible after your strength training you want your body to shift into repair and rebuild mode. The best way for this to happen is to eat instead of doing cardio.
If you’re trying to lose fat and maintain the muscle you’ve built then doing cardio after your strength training is considered the best strategy. This will allow the physical and mental focus it requires at the start of your workout weight training to build and add the strength to your body. You require every last ounce of energy to move your weights required in heavy compound movements safely and with your greatest force possible which is so important for gaining overall strength and muscle building. The percentage of energy contributed by fat goes up considerably after an hour of exercise. Since strength training uses mostly glucose for energy doing weight training first will also increase the amount of fat your body uses for the cardio post workout. If you chose to do your cardio after weight training then I strongly suggest having a serve of ECAA or BCAA to feed your body the food it requires to help maintain your hard earned muscle but also allowing you to turn your body into a fat burning machine during post weight training cardio.