First off, why should you even bother with cardio? Well, it has numerous benefits:
- Reduced body fat and improved weight control
- Lower resting systolic and diastolic blood pressure
- Increased HDL cholesterol (the good cholesterol)
- Decreased total cholesterol
- Improved glucose tolerance and reduced insulin resistance
- Decreased clinical symptoms of anxiety, tension and depression
- Increases maximal oxygen consumption (VO 2max)
- The more oxygen you are able to consume, the more you are able to exercise at higher intensities.
- Improvement in heart and lung function
- Increased blood supply to muscles and ability of them to use oxygen
- Lower heart rate and blood pressure (including resting heart rate)
- Increased threshold for muscle fatigue (lactic acid accumulation)
Sound good? I think so, too. However, it is important to note that weight training also offers many of the same benefits, and has the added benefit of building muscle. This isn't to say that weights are a substitute for cardio, just that cardio is often largely overrated. Cardio is a tool in your toolbox that gives you a little extra wiggle room in your diet, boosts your health, burns calories, and allows you to walk the dogs without getting winded.
However, the mere act of standing on a treadmill does not bestow you with these benefits. Time and time again I will see someone dreamily coasting on the elliptical while reading a magazine, chatting on her cellphone, and doing her taxes. I'm sorry to say, but "work out" has the word "work" in it for a reason.
There are some folks, primarily bodybuilders, who eschew cardio claiming that it's "catabolic". It is true you run this risk with cardio that lasts over 30 minutes. However, if you're very concerned about muscle loss, eat beforehand, eat after, and suck down an energy gel midway through. The catabolic effects of cardio are largely overstated, especially if you eat sufficient calories and also do weight training. I wouldn't worry unless you are a professional competitive physique athlete, or if you're training for a marathon where you're doing crazy amounts of cardio. Similarly, cardio is not a substitute for lower-body weight training. So keep doing your squats and deadlifts! Either do cardio on a seperate day, or do it after weight training; do your weights when your muscles are fresh, to prevent injury.
Speaking of food, I have done a TON of research in peer-reviewed scholarly journals as to whether or not you should eat before cardio, and if so, what you should eat. The more research I do, the more confused I become. Studies vary so wildly in their results that I've come to the conclusion that it just doesn't matter. If it did, studies would point to the same answer rather than exhibiting so much stochasticity. So I say, do what allows you to push yourself best. If your stomach growls and you feel faint on an empty stomach, eat. If cardio after breakfast makes you feel like you're going to hurl, skip it.
Now that my cardio mini-FAQ is out of the way, I can get to the meat of the article: what type of cardio should you do? I've divided it into three subtypes: low, medium, and high intensity.
This refers to exercise that doesn't really raise your heart rate, but gets you active. Specifically, walking or coasting slowly on a bike or similar. This is often preferred by people who are particularly paranoid about muscle catabolism, or have a medical condition that prohibits higher intensity. Unfortunately, a lot of people stay at a slow pace so that they can be in the "fat burning zone". Many exercise machines boast a little chart that shows the fat burning zone at the low end. However, this is largely misinterpreted. You burn a larger percentage of your calories from fat, but fewer calories overall, and thus less net calories from fat. For example you may burn 100 calories at a low-intensity with 80% from fat, but then burn 250 at a higher insensity with 50% from fat. Anyway, low intensity cardio is better than nothing, but I wouldn't expect great results from it. I like it in addition to a regular exercise regime, for example talking a recreational walk after dinner, but I don't consider it training. For more information, check out SparkPeople's walking center.
Medium-intensity cardio is usually done at a fairly steady state, where you can maintain your pace for 45-60 minutes but are still keeping your heart rate up. This is the pace set in most cardio group fitness classes such as spinning and step aerobics, though you can also do it on your own. On machines, intensity can be increased by picking up speed or adjusting incline and/or resistance. For machines like the elliptical or recumbant bike, it's a good idea to keep some resistance on, because otherwise the machine essentially helps you along at higher speeds. You can also get a pretty good cardio workout doing circuit training.
This is the type of cardio that has the worst reputation for eating muscle. However, I still do it regularly -- I'm addicted to my spinning classes. Why? Because since I started, I've been able to go on long hikes, mountain-biking trips, or spend an entire day exploring a city on foot. I can dance for hours at a club without whining to go home early. And it's also a great stress release. The increased stamina and better moods are worth sacrificing a little bit of muscle tissue.
Keep in mind, however, that just plodding on the stairmaster does not constitute medium intensity. You should be breathing heavy and sweating with your heart rate increased. If you can read a magazine, you're doing low intensity. For more information, check out SparkPeople's wonderfully comprehensive page on aerobic exercise. For a sample routine, take a look at Couch to 5k.
This is most often referred to as high intensity interval training, or HIIT. Why? Because for truly high intensity, you HAVE to do it in intervals, intersparsed with light jogging or brisk walking. It's physically impossibly to keep it up for long periods of time! HIIT is favored by people who want to maintain muscle and still burn fat. Since you push your body into the anaerobic zone, you train the same type of muscle fiber trained with weights. Again, this is not a substitute for weight training but it is a good way of preserving muscle. I personally hate the treadmill for HIIT because I don't like having to mess with the buttons every couple of minutes. Instead I like the recumbant bike where I can just pedal harder for the work intervals. I'm personally not crazy about the elliptical for this because I can't really reach the anaerobic zone. If you must use it, crank up the resistance all the way. SparkPeople has a very complete page on HIIT which includes a sample training program at the end. Definitely read through it because it goes over some very important points which I don't make here. This is my favorite type of cardio to do outside of a classroom setting.
A final word
People ask so many questions about cardio. Should I use the elliptical or the treadmill? Does it burn more calories to run for 20 minutes or jog for 40 minutes? I truly believe that there's no reason to get so analytical with it. The most important factor for fat loss is your diet. Keep your diet in check, and do the form of cardio that you most enjoy and can stick to. Ultimately, that will serve you best. Fitness is not about individual spurts of activities. It's about setting consistant trends. So find a form of cardio that you like and can look forward to. Most importantly, learn to love being active. Because even if you spend an hour per day in the gym, you might be sedentary for the other 23. An active lifestyle is of the utmost importance.