What's the first thing you think of when trying to lose weight? For most people, they start eyeing the treadmill or going for runs. What people don't understand is that during that one session, you will probably burn more calories than you would with resistance training... BUT resistance training builds muscle. When you build muscle, you body uses energy to maintain that muscle. The calorie burning effects of cardio stop as soon as you are done with the activity. When you build muscle, you burn calories all day long because your body is working to maintain that muscle mass. Therefore, studies show that the best way to lean out is actually resistance training.
So, is cardio useless? Not at all. I like to think of it in three different buckets.
1) Athletic - If you practice cardio for a specific purpose i.e. marathon runners, college/pro athletes, long-distance biking, etc. If you are training for a specific event or game that REQUIRES a large amount of cardiovascular endurance.
2) As a tool - Gaining and losing weight is an energy balance. If energy in is equal to energy out, you don't gain or lose weight. We can tip the balance of that scale by increasing your energy output. This can be a lot of things like adding in another gym session, staying more active, moving around more. It can also be prescribed cardio. This typically comes into play with bodybuilding or sports where you need to do a weight cut.
3) General Health - This is where most people sit. Your heart is a muscle and it needs to be trained like a muscle. We obviously can't give it a barbell to squat with but we can increase its workload. Studies show that doing some sort of cardio or aerobic activity 20-30min, 3x/week is sufficient in keeping that heart and body healthy.
Unless your a marathon runner, bodybuilder, college or pro athlete, doing excessive amounts of cardio won't benefit you a whole lot. What tends to happen is people who do lots of cardio with little to no experience in resistance training will lose weight but they will also lose muscle mass. This causes the body to look flat and "pancake-y." To get shape you need muscle and to get muscle you need to resistance train. There are also studies that show that people who engage in LONG distance (ultra-marathon runners) aerobic activity for extended periods of time (years) have severe heart and lung issues similar to smokers. It is a byproduct of all of the oxidative stress on the body, and the constant pounding of joints in the same repetitive pattern leads to issues later in life.
What's the best course of action? Get to the gym and weight train. Learn the big compound movements and get comfortable moving some weight. Then, add in 20-30min 3/week of cardio to keep that heart healthy. That can be anything from a leisurely walk with the dogs or it could be the stairmaster - choice is up to you.
But, do you ever notice how high your heart rate gets when you get a good weight session in?