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.
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.
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%.
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.
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[tm]" which is recommended by Bill Phillips in Body-for-LIFETM 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.
We will cover this next maxim and more in Part II.