“Cardio” is short for “cardiovascular exercise.” Basically, this is usually a form of long-duration, low-to-moderate-intensity exercise that involves continuous effort. Cardio includes things like running, biking, swimming, and using the “cardio equipment” in the gym, like the elliptical or rowing machine.
The point of cardio is to train the cardiovascular system and to burn a lot of energy. Because effort involved is continuous, you have the highest capacity for burning calories by doing cardio (as opposed to lifting weights or doing HIIT). Running is usually clocked as the highest calorie-burning exercise, and the most calories burned ever recorded in a day was in elite cyclists.
It’s important to know that this doesn’t mean cardio is the best option for achieving fat loss. While cardio can help you burn more calories, it’s not likely to change your energy balance as much as your diet. That’s why nutrition is the most important part of attempting to lose weight.
And cardio might be as useful a tool for fat loss as lifting weights. Cardio burns calories, but resistance training offers a bigger benefit: it burns calories and preserves muscle while dieting. Certainly, everyone can benefit from a little cardio while they diet, but it shouldn’t be a heavy focus, especially not early in the weight loss phase. During reverse diet and muscle gain phases, cardio should be kept to a minimum as well, since it can undercut the goals of increasing metabolism and building muscle.
Cardio has important health benefits besides being a tool for changing body composition. It can improve heart health, mood, and general disease risk. For that reason, it can be good to incorporate a little cardio into your routine. But don’t lean on cardio as a driver of fat loss unless you’re deep in a weight loss phase and would rather increase energy burn than decrease food.
If you’re reverse dieting, we recommend limiting cardio as much as possible (unless you’re doing cardio for enjoyment or heart health only--in this case, stay consistent from week to week). If you were doing a lot of cardio to control your bodyweight prior to starting your reverse diet, slowly taper it down until you aren’t doing cardio or until you’re doing very little. That way, the extra energy burn won’t get in the way of your reverse diet.