I hear all rumors about that only with cardio you will burn fat properly. But why should I do cardio, instead of weightlifting? isn't it all about the caloric deficit? I don't see why I should replace 30 minutes of weightlifting with 30 minutes of cardio, when I try to lose bodyfat.
Althought previous 2 answers are not wrong, I think it's more complex than that.
1 - Cardio is great at fat burning 2 - Muscles are great at fat burning.
It mostly depends what approach you want to take and, more importantly, implement it correctly for your own metabolism.
So, cardio. The lower the exercise level (in terms of your maximum heart rate, max HR) the more fat you burn. But, the lower the HR, the fewer calories per minute you burn. So there's a bit of a balance to maintain there. But as you crank up the HR during exercise, your body starts to need to use faster fuels (e.g. carbs/glucose stored in your body) to allow you to maintain the higher exercise level. So it "switches" from fat burning to other energy sources.
Generally speaking you would want an exercise that allows you to maintain your HR at ~60% of your max HR. Truly knowing your max HR isn't that easy - there's the famous "220 minus your age" and variants of it, but it's a very generic approximation. However for your purpose, your could be satisfied with that as an approximation, completed with the following observations:
- If you're doing it right, you should be able to speak in complete sentences while performing the exercise. Your may have to stop in between sentences to catch a breath, but a normal conversation would still be doable without cutting every few words for air.
- You should still feel an increased need to breath deeper and more rapidly than usual (otherwise you're not really maximizing the exercise).
- If you find yourself having to cut mid-sentence frequently, you're going too hard. (hold an imaginary conversation if you're going it alone).
Depending on your fitness level, this may correspond to fast walking, or very light running (5-6 mph). The mentioned 7 mph isn't wrong but doesn't really show the whole picture. For me, that level of exertion is about the top-end of my so-called fat-burning. However I run ~40 miles per week with good running form, so someone relatively untrained would be way past the beneficial for fat burning. On my watch (I do have a cardio watch), I would be at around 130-140 beat per minute at that running speed. If you're not that used to walking/running/cycling, I would suggest to not rely too heavily on specific speed figures. What's accurate for others may not be for you. They will also change overtime, assuming you stick to it. Using a cardio watch and getting to know how your body reacts is a much better way to do it imo. It will also change from day to day - for example, on days where I'm well rested, the 7 mph feels easy and slow and I can see that my HR is lower than usual at that speed. Things like temperature, how much sleep you got, wind, hills, etc... will also factor big time into that.
Ideally, you need at least 30 minutes of continuous exercise to really get fat burning effects. Also, you would get more out of your bucks if you do it first thing in the morning (before breakfast) than after a full meal. It may sound brutal, but it's actually not - a moderate exercise will tend to lower your (immediate) appetite after 10-15 min because your body is getting busy increase your HR and not all that interested anymore in using its abilities to process food just now.
For a complete and critical perspective on the relation between cardio & fat-burning:
I'm not that much of a metal-pusher, so I know less about that. Eric is right when saying that strength training will increase your muscle mass, and that muscle (even at rest) consumes more calories than other stuff. Your can see it as money in some investment paying interests. However it's not that easy because:
- Training to increase muscle mass is overall an harder exercise than the one you would need using cardio. This is somewhat debatable (how hard things are is subjective). However if you really want to gain muscle mass, doing 20 reps of some exercise at a charge that is pretty easy for you won't do that much. Increasing the charge and lowering the number of reps will be better - but then it'll feel harder as well. While fast walking/running or cycling, by definition, is supposed to be done at low intensity and thus not be that hard.
- It depends how you want to measure progress. You may very not loose weight, or even GAIN weight with strength training. This is because muscle is much denser than body fat. You would be leaner, but just don't obsess on weight as your metric to measure success.
- If you do cardio, you may just have one activity to "master", like cycling or running, and if you stick to low intensity your lack of proper tech may not matter that much. However strength training can get you injured if not done properly, and each exercise you do may be done wrong in different ways, leading to injuries. Of course you can get injured doing any exercise - my point being that "getting it right" for cardio fat burning is also going to be easier than strength training, and thus the risks of getting injured at less imo.
Diet & other remarks
As Eric mentioned, diet is an important part of that. I'm not a nutritionist so will refrain from commenting, but it's a safe bet to say that if the bulk of your nutrition is vedgetables, fruits and whole food you'll be better off than getting lots of process/prepared meals, white flour bread etc. Trying to restrict your eating window (e.g. meals are to be between say 8am up to 7 pm, but not late-night snaking etc.) can also help.
I would say the "ideal" approach would be a combination for all that - cardio, strength/muscles & diet. You will get great benefits from cardio activites (https://www.youtube.com/watch?v=Y6U728AZnV0&list=LLf4GzXneGCWaWqF3kKOcDZA&index=86&t=0s), and also from strength training, and also from a better diet.
The crux of the matter however is staying motivated. If you can find a way to include the activities in your life (cycle/run commute for example, be it for work or for going to town or whatever) it would be ideal. Or finding an activity you actually like to practice and want to practice for its own sake, not just for the benefits you get. I find that most people are motivated by activity for health's sake during a time, but if there isn't more than that attaching them to it, they tend to let it slide after a time. Or finding a group of people doing that activity - it's easier to stay on the couch if it's just you you're letting down than if it's a friend/acquintance you've told you would be there, and then have to call to say "yeah I'm not gonna go today because insert here some bs for not going.
There are charts that show how much calories you burn during a certain physical activity, for example, this one from Wisconsin Department of Health And Family Services:
A 155 lbs or 70 kg person (the middle column in the chart), Calories burnt per hour:
- Weight lifting, light or moderate effort: 211 Cal; vigorous effort: 422 Cal
- Running 7 mph (11.2 km/h): 809 Cal
Running is a sustained effort, but weightlifting is exercise, rest, exercise..., so you do much more actual work during running.
It is true that with increased muscle mass, the baseline calorie usage rises, but a muscular guy would still likely burn less calories during weightlifting than a skinny guy during runnig (assuming about the same intensity of both activities).
Muscle growth and reparation after exercise are relatively slow processes and do not burn much more calories per hour than other processes in the body (digestion, heart pumping, etc.).
It seems counterintuitive but strength training is (almost always) a more effective way of controlling body fat than cardio exercises. Diet trumps both of them, by far.
A person with a basal metabolism of 1800 will burn an extra 144 calories (8%) per day just sitting on the couch, if they are strength training properly. This does not include the actual calories consumed while training, which would be additive to that.
Anecdotally, I find that most distance runners and cyclists have terrible diets. Their caloric needs are so high that they can nearly eat pizzas every day and be okay. But eventually (during injuries, during the off season, etc) those terrible habits catch up with them. And as where a person with sufficient muscle mass will continue to burn extra calories if injured for a week, a runner not running for a week is just someone eating too much food.
Less to do with calorie burning and more to do with how often it can be done.
Calorie deficit is king, but that doesn't mean that certain types of physical activity don't offer certain other benefits.
For instance, 'aerobic training' (which contrary to popular opinion, doesn't need to be slow and steady) oxidizes fatty acids better than resistance training does. Doing some even if resistance training is your focus for fat loss, doing some aerobic training is likely a good idea taking advantage of this metabolic pathway.
Having a 'decent' aerobic system (Resting Heart Rate ~60 BPM) improves recoverability. Done in the appropriate dosage (2-3x a week for 20-30 minutes on a non-weight bearing tool like a bike) it still leaves plenty of time available for resistance training, while improving your ability to do resistance training regularly. The aerobic energy system is what helps you recover between sets of resistance training, AND between days of resistance training.
But ultimately it still comes down to frequencies and durations you can do cardio. If you're smart and you're chasing fat loss you're likely either resistance training every other day full body or you're using a 4x a week split (for instance upper/lower). Likely that's no more than an hour per training session.
So yes, still a fair bit of time relatively speaking but if you can free up 3-4 hours a week, you can likely free up 3-4 more (or at least 1-2). You can't fill those with more resistance training and you'd be unwise to fill them in HIIT or SIT too. You just can't recover from that much resistance training or high intensity exercise effectively in a given week.
The main goal of resistance training during a fat loss phase of programming is to preserve muscle mass, not burn calories. So you can actually get away with even less than you think, it's maintenance programming. 2-3 sets of a few key lifts, then switch gears.
Enter cardio. It's what you can use to fill in the gaps and add a boost to any 'fat loss phase' of programming you happen to be doing. If you have the time available.
It's not about replacing resistance training with cardio, it's about adding a little bit (that 'edge') to your routine. There is a limit to how much resistance training you can really do in any given week (and other higher intensity forms of exercise).
It's like the brain exercise about filling a jar with big rocks (resistance training in this case). Is it full? No, of course not, you can still fill in the gaps with gravel or sand (the 'cardio' and/or the mobility training).
Lastly of course, there is the issue of health. Specifically heart health. Do you want to get lean at the expense of that? Resistance training doesn't train the heart as well as aerobic activities do and aerobic activities maintain ventricle elasticity far better than high intensity exercise (which tends to thicken the heart more).