Depending on your goals and body type, different amounts of cardio may be required. A lean "hard-gainer" trying to add mass may benefit from only one or two cardiovascular sessions per week. On the other hand, someone like myself who is extremely prone to storing fat and sensitive to carbohydrates may require 3 or more sessions in order to maintain peak physique. Since you can only get better at a particular exercise by performing it, those interested in running marathons or participating in endurance events such as a triathlon must increase their frequency of cardio in order to prepare for the event.
MAXIM 1: Your body type and goal for training will dictate the type, frequency, and length of your cardio
When your goal for cardio is general health, you have a few decisions to make about what type of cardio you will perform. Many people enjoy taking long, slow runs. Enjoying cardio is important, so if you find an enjoyable method of cardio, there is no reason why you should discard it. The same decision should influence your choice for timing. Many people claim that you must perform cardio first thing in the morning and/or on an empty stomach to see maximal benefit. I disagree. If you have trouble waking up or putting a full effort into morning cardio, and will get a much more vigorous workout in the evening, then why not do it then? Perform cardio when you feel the best, when you are ready and know you will stick with it and give it 100%.
MAXIM 2: Find cardio that you enjoy, and do it when you feel you have the most energy
There are many styles of cardio. There is some debate about what cardio is best for you. People preach about training in the "zone" of a particular heart rate for maximum fat burning benefit. While it is true that your body will utilize more fat for energy during this period, this is not the entire picture. Moderate cardio means your body will recover quickly - your heart rate will return to normal within a short period. Intense cardio, which elevates your heart rate beyond the "zone", may not burn as much fat during the exercise, but your body will take longer to recover. Your body must process waste and your heart rate will remain elevated for hours after the bout of exercise. You will burn more calories throughout the day, and therefore you will receive a superior benefit.
To better understand this, let's consider a situation where you burn 200 calories during exercise. You have a choice: you might burn those calories walking at a brisk pace and reading a book, and it will take you 1 hour. Or, you might burn those calories performing short sprints followed by periods of moderate jogging, and you will burn those calories in 20 minutes. While the "hour" cardio kept you in the "zone" for fat burning, guess what? The 20-minute cardio elevated your heart rate and took you into an anaerobic zone where your body accumulated an "oxygen debt" - a need for oxygen and fat burning to help flush waste from your system and recover from the intense exercise. So during a 24-hour window, you will burn MORE than the 200 calories, and therefore be closer to your fat loss goal.
While there is no hard, scientific evidence to support this next maxim, I truly believe in it. I have witnessed this not only in my own transformation, but also with countless others as well.
MAXIM 3: The less time it takes to burn the same amount of calories, the more calories you will expend later that day
This maxim may seem confusing, but it's very simple. It means that if you are going to burn 200 calories, when you burn that 200 calories in 20 minutes instead of 1 hour, your metabolism will increase throughout the day and you'll end up burning MORE than 200 hours when that day is done. This is why high intensity interval cardio, like that recommended in David Greenwalt's book, The Leanness Lifestyle or the "20-Minute Aerobic Solution?" which is recommended by Bill Phillips in Body-for-LIFE? is so effective - it burns the most amount of fat in the shortest period of time
Just because high intensity cardio may burn more calories doesn't make it superior to moderate cardio except with respect to calories burned. There is some evidence that you may improve your cardiovascular health more quickly with high intensity cardio, but this is no reason to discard your long runs. If you have a busy schedule and wish you fit 3 short, 20-minute sessions, then intensity is the way to go. If, however, you truly enjoy your long bike ride or jog on the weekends, then go ahead and do it - you will still be improving your health and burning calories, and if it is something that you enjoy, you will stick with it! Remember, too, that if you are training for a marathon, all of the 20-minute high intensity cardio in the world will not prepare you fully to run 20+ miles. You must perform the moderate, long duration cardio to prepare your body for the event.
This leads us to another maxim. Your heart rate can provide you a lot of information about your training. Over time, your resting heart rate should decrease. Mine went from the high 60's to a current value of 48 due to my cardiovascular conditioning. When you train with weights, you can use a heart rate monitor to see what your target heart rate is (weight training will take it to the anaerobic levels, or about the maximum heart rate you would want to train at) - this will provide much better feedback than a generic formula. By tracking your heart rate, you can monitor your effort. If you train today at 160bpm then have a lousy day and don't feel like you're receiving any benefit, use your heart rate as a guide. As long as you are pushing hard enough to hit that 160bmp mark again, you know you are getting at least the same intensity from your training as the time before.
MAXIM 4: Use your heart rate as a tool for feedback about your progress, not as a "RULE" for fat loss (i. e. the "zone", etc)
Many people are very intrigued by the readouts on machines when they perform cardio. Unfortunately, those numbers are based on generic equations that fit the "general population" rather than you as an individual. For example, calories burned are based on your weight. A 200-pound person at 8% body fat will have the same formula applied as a 200-pound person at 30% body fat. However, the more that you train and the leaner you are, the less calories you will burn during the same activity. In this example, the 8% person will actually burn fewer calories than the 30% person, due to their level of health and amount of lean mass. There are also issues with metabolism, activity throughout the day, nutrition, and many other factors that are not taken into account.
Does this mean that the readouts are worthless? Not at all. In fact, they are very useful. When I did my morning run this morning, the readout said that I burned 610 calories in 30 minutes. While I may not have truly expended that amount of energy, it is a great reference for me. Why? Because the next time that I perform cardio on that machine, I'm going to push myself harder and try to burn 650 calories. Again, I may not actually be burning 650 calories, but you can be certain that if the readout gives me that number, I will be working harder next week than I did today. So it is a great tool to gauge your own progress. It is also a great tool to mix up your style of training. If I do a high intensity workout and burn "400" calories, then I know if I come back and perform moderate training, I can shoot for "400" calories and expend about the same amount of energy during the activity.
MAXIM 5: Do not take the readouts on cardio machines literally - use them as a scale to gauge your own progress
It is interesting to learn the various ways that different styles of cardio expend energy. A slow, moderate run may take 45 minutes to burn 400 calories. However, the same amount of calories might be expended in a 15 minute, high intensity run. This is due to the fact that your heart rate becomes extremely elevated, and your muscles begin performing extreme work in order to help you accelerate through the intense periods. On the same token, a "slow" jog on a steep incline may burn the same amount of calories. In this situation, your body is fighting against gravity, so again you are still performing "high intensity" effort despite the slower pace.
As a final ingredient, consider variety. I can guarantee that if you always use the treadmill, your body will become so efficient at using the treadmill that you will begin to burn fewer calories doing the same workout. On the other hand, if you perform treadmill work one session, stair climber work another session, then go for a jog, you will continue to see the benefit of increased calorie expenditure. If your training permits, try to build in as much variety as possible. This will keep the fat melting off and continuously improve your cardiovascular condition.
MAXIM 6: Variety is key - whenever possible, vary not only your style of training (i. e. moderate, high intensity, etc) but also the terrain or equipment that you train on
I often have clients complain that they don't have access to the right equipment to perform much variety with cardio. If you simply purchase an inexpensive jump rope, you can easily train two different exercises: jogging, and jump roping. Now consider different styles of training: moderate (low intensity), high intensity interval training, and just high intensity training (where you try to elevate your heart rate and maintain that throughout the duration of the exercise). This alone provides 6 different possibilities for a cardio session, which is more than enough variety to change things throughout your training cycles.
Cardiovascular exercise is an important component of general health. While certain people may require different amounts and types of cardio, everyone should engage in at least a little cardiovascular activity each week. There are many methods for training which all have their advantages. You should learn what works for you and what you truly enjoy so that you will continue to perform cardio and reap benefits of good health.
Don't let someone fool you into thinking cardio isn't necessary. Even if you are in top shape, a little cardiovascular exercise can still benefit your general health. The key is to change the style and frequency of cardio to suite your lifestyle and fitness goals. Consider various styles of training, different terrains, and new types of equipment to train on. As always, learn your body and don't use any one else's rules to dictate your training. Keep a good journal, and find out what works for you. Peak cardio is a sure way to move closer to your peak, natural physique.