Aerobic Fitness for Geeks

The information in this page gives a detailed explanation of ways to monitor and ensure that one is getting the proper intensity and duration for aerobic fitness. It's intended for those geeky types who like numbers and want to know a more exact explanation of heart rate zones and other interesting terminology that gets thrown around in the fitness world. Remember, this is only intended for fitness and not performance. Performance is an even lengthier, more debated subject. Also, always check with your physician before beginning an exercise program.

Duration
The American College of Sports Medicine (ACSM) recommends 20 to 60 minutes of continuous or intermittent exercise. However, when doing intermittent exercise, the intervals must be at least 10 minutes long.

Duration and intensity are inversely related. Thus, when the intensity (how hard) is increased, the duration (how long) must be decreased. When the intensity is decreased, the duration can be increased.

Intensity
The ACSM recommends exercising at an intensity of 65 percent to 90 percent of maximum heart rate or 50 percent to 85 percent of maximum oxygen uptake reserve (for most people). Unless you always exercise in a lab with a gas analyzer hooked up, then percentile of maximum heart rate is going to be more useful. There are two ways to measure your heart rate while exercising: one way is to stop and count your pulse for 15 seconds and multiply by four, and the second is through the use of a heart rate monitor.

Stopping to count your pulse is not particularly accurate since your heart rate will be going down while you take your pulse. Also, it is rather inconvenient. The best way is to use a heart rate monitor. Heart rate monitors can be purchased for around $60 at a minimum. They are a very handy tool when used properly.

A very rough estimate of maximum heart rate is 220 minus your age. Thus if you are 40 years old, your maximum heart rate would theoretically be 180 beats per minute (bpm). The best way to determine maximum heart rate is through an exercise test, but this is not suggested unless done under the supervision of your physician.

Using the example of a maximum heart rate of 180 bpm, you would multiply 180 by 0.65 and 0.9 to know your heart rate range for exercise. The range in this example would be 117-162 bpm. You can use your heart rate monitor to adjust the intensity so that you stay in this range while exercising.

Heart Rate Zones
As you may have noticed, the above heart rate range is 45 bpm. That is a very broad range, and exercising at a heart rate of 117 bpm and a heart rate of 162 bpm are certainly not the same! This is why athletes, coaches, physicians, and exercise physiologists have attempted to create heart rate zones that one would use to make sure he or she is exercising at the exact heart rate for maximum gain. The topic of heart rate 'zones' and aerobic and anaerobic thresholds is much debated and disagreed on. It is important to remember that the ACSM's recommendations are for fitness, not performance gains, and are meant for a wide range of ability.

The ACSM's recommended range seems to have been placed so that it is between the two oft-debated first and second aerobic thresholds. For most people, exercising at a heart rate less than 65 percent of maximum heart rate is quite easy and produces only a small increase in ventilation. Depending upon how fit you are, exercising somewhere just above 65 percent of maximum heart rate produces a noticeable but not dramatic increase in ventilation. However, 90 percent of maximum heart rate represents a threshold that even the world's elite athletes cross at no greater than around 90 percent of maximum heart rate. After crossing this threshold, ventilation is substantially increased and the exercise becomes very hard. Most people other than elite athletes cross this threshold somewhere below 90 percent and above 65 percent of maximum heart rate. However, these thresholds vary from individual to individual and also depend upon how fit one is. This is one reason that the ACSM's range is so large. More often than not, you can't simply look at the numbers on your monitor unless you have a bit of experience exercising with it.

Using Your Heart Rate Monitor
Now that you know your ACSM recommended heart rate range, you can use your heart rate monitor to help you stay in that range while exercising. However, you must pay attention to how you feel in the range. For example, it is entirely possible that you feel like you are crossing the second threshold well before you reach 90 percent of your maximum heart rate. That is normal. You may even feel that the threshold occurs around 80 percent of maximum heart rate instead of 90 percent. In fact, that is more than likely true (unless you are an elite runner, cycler, etc.). In this case, you would restrict the upper limit of your range to 80 percent.

Now that you have a feel for your range, you can use your monitor to keep you from going too hard or too easy. You can even adjust the intensity from day to day. Remember that intensity and duration are inversely related. So, if you are short on time, you can take a run for 20 minutes closer to that upper heart rate limit. If you have a lot of time on your hands or want to do something slower, you can do a 60 minute run at 65 precent of heart rate maximum (the lower limit). Remember though, not every run has to be on the extreme end. You could just do 30 minutes at 70 percent of heart rate maximum. It's up to you.

The Trouble with Heart Rate
The trouble with using your heart rate as a training tool is that it is influenced by your environment. For example, heat, dehydration and caffeine can all make your heart rate higher than normal. Heat and dehydration are the main causes of an increase in heart rate while working out. As your body sweats and loses water, your blood volume slowly drops. The heart must compensate for this loss in blood volume by increasing its rate. Thus, heart rate increases even though you are running the same speed. This phenomenon is known as cardiac drift. You may notice it even under normal conditions on a longer run. Part of this is due to muscle fatigue and part is due to water loss. Watching your heart rate is a good way to remind yourself to start drinking more fluids.

It is important to monitor how you feel as well as your heart rate. Sometimes, heart rate does not tell the whole tale. Listen to your body.

Indicators to Take it Easy
Monitoring your heart rate is a useful way to prevent overtraining. There are several scenarios to watch for:

1. If you see a heart rate that is especially high for the effort and you feel tired or worn, this is usually a sign that you are either ill or overtraining. You should stop immediately and go home.
2. If your heart rate is higher than normal for the effort and you don't feel too tired, you should still take it easy.
3. If your heart rate just doesn't seem to want to get up to normal and you feel tired, this too can be a sign of overtraining. You should take it easy.
4. If your heart rate is lower for the same running pace and you feel good, maybe you're getting in better shape!
5. Remember, heat, dehydration and caffeine can also cause higher heart rates.

Hopefully all this information has been interesting and helpful. Just remember, when it comes to fitness, doing something is better than nothing.

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