We are a commune of inquiring, skeptical, politically centrist, capitalist, anglophile, traditionalist New England Yankee humans, humanoids, and animals with many interests beyond and above politics. Each of us has had a high-school education (or GED), but all had ADD so didn't pay attention very well, especially the dogs. Each one of us does "try my best to be just like I am," and none of us enjoys working for others, including for Maggie, from whom we receive neither a nickel nor a dime. Freedom from nags, cranks, government, do-gooders, control-freaks and idiots is all that we ask for.
Aerobic exercise (often aka Aerobic Cardio) is much disparaged these days, but it is not entirely useless as one component of fitness. It's roughly defined as exercises that keep one's heart rate elevated significantly for extended lengths of time (ie 20 minutes plus, but around 20 is enough for the benefits), and physiologically defined as exercises in which oxygen supply can keep up with metabolic demand. Thus jogging, running, swimming, rowing, biking etc. Eventual fatigue in these exertions has to do with depletion of muscle glycogen supplies or plain muscular inadequacy.
Heart rates for a beneficial cardio workout vary by age and fitness, but a rule of thumb is that if you can converse, you aren't doing anything; if you can get a few sentences out you're about right; and if you can barely speak you are probably over your limit or in a sprint.
Cardio is not very useful for fat loss or strength-building but it's good for maintaining or building endurance, bone fitness, and cardiac fitness. Better than sitting or walking, for sure. If you can bike 50 miles at any speed, that is great because most people can't.
As an aside, reader Mike reminds us that excess cardio can lead to muscle loss. True, but really only if you are in good shape with little fat.
Anaerobic cardio exercises are those which exceed the ability of oxygen metabolic pathways to keep up with the muscular demands, eg sprinting, weight-lifting (yes, resistance exercises do stress the heart), and other high-intensity exercises like calisthenics. Anaerobic exertions build up lactic acid in muscle, hence the burn - but burn has nothing directly to do with any benefit other than maybe encouraging muscles to increase their glycogen storage. Almost any aerobic exercise can be made anaerobic by increasing intensity. This can not be sustained for very long, at most a couple or a few minutes. Cellular machinery cannot keep up with the demand.
Any exercise that leaves you limp, gasping, or burning pain after a brief time has probably become anaerobic. Good stuff, and more likely to be building rather than maintaining. This is why, for the Cardio piece of the Conditioning Triad, we recommend interval cardio (HIIT) for efficiency instead of endless aerobic cardio. The sprints will get your heart rate way up but only for a brief (30-60 seconds) while.
Men seem to have an innate preference for anaerobic exercise, women for aerobic. That's statistical only and I have no idea what relevance it has to anything.
The physiology of aerobic and anaerobic cellular metabolism is interesting, and miraculous. Minimal Bio education needed to understand it.
Not necessarily a recommendation, but for "cardio" I do two approx 20 min sets of HIIT per week and about a total of 80 mins of calisthenics each week. (Plus my 2 hrs of weights.) Feels like a good balance.
Hey BD - I'm guessing you knew I would throw in my 1 cent (that's my two cents that probably worth only half of what I think it is).
Well, first, cardio IS good for fat loss. When HIIT first gained popularity, the claim was that EPOC following HIIT would "burn" more calories than conventional aerobic training. While it is true that EPOC for HIIT is greater than EPOC for "aerobics", most of the caloric expenditure happened during the exercise interval.
Here's the problem: While aerobic exercise does lead to fat loss, it also leads to muscle loss (see my previous comments). I'm sure you understand the problems here: (1) less muscle to do functional activities, and (2) less muscle to act as a fat burning engine, i.e. lower BMR.
Second - and you probably realize this, but your post can leave one with some ambiguity - 20 minutes of HIIT (as you describe for what you are doing) is not the same as 20 minutes of aerobic cardio.
In my own HIIT training, I aim for at least 6 intervals of 1 minute each at an intensity of 10 METS or greater (yeah, it sucks) and I do these twice a week (rarely three times) using a variety of methods (bike, treadmill w/o hand bars, StepMill w/o hand bar, Concept rower s min or 500 meter intervals). When I find something is getting "easy" (defined as "sucks less"), I figure I'm getting efficient and I switch to something more inefficient.
The reason I opt for inefficient exercise is that it burns more calories and I like to eat. Yeah, I know, you can't outwork a crappy diet (but I try).
Mountain biking on rugged terrain does it all. You are forced to sprint repeatedly to clear steep sections and obstacles. Plenty of upper body work handling the bike over the rough stuff. But most importantly it is FUN. And a bit dangerous and scary, which is FUN too. Climbing relentless grades on a mountain bike will be the hardest thing you ever do and will make you fit and tough. Descending on technical single track will be one of the funnest things you'll ever do once you have the skills. And does require a high degree of skill, making it a real challenging, satisfying sport as opposed to running, lifting, etc. I lift too, but it isn't much fun.