If you are in definition or in a lose weight plan and want to eliminate fat without losing muscle, to do cardio after weight training is the best for you because when you finish your workout you will have depleted your glycogen stores (carbohydrates) and your body will use fat as fuel instead of glycogen. A soft cardiovascular workout of about 30 to 40 minutes at a moderate pace will be sufficient to remove a good amount of fats.
What happens if I do cardio before doing weights?
If you make a cardio session before weights, let’s say running 20 minutes, spinning 20 minutes or stepping 20 minutes, you will have exhausted a large part of your glycogen reserves so your performance in anaerobic exercise (weights) will be affected and your performance will decrease when you lift weights. Also, your body will use your muscles as energy so instead of building your muscles they will be affected by the effort your body generates by consuming the last reserves of glycogen you have and consequently your muscles.
What do we recommend?
We recommend to warm up before the weights with a cardiovascular exercise not more than 5 minutes, then make your weights session hard as always and finally get on a machine like the treadmill and do cardio 30 minutes or a little more if you want to. This way you will warm up without depleting your glycogen stores, give your muscles a good session and finally burn fat with cardio.