Improving Cardiovascular Endurance

Use FITT principles for safer, more enjoyable diving.

In the last three "Dive Fitness" columns, we've covered exercises to build strength and endurance in the muscle groups used most by divers. In this issue, we tackle an even more important topic for overall fitness: cardiovascular endurance.

NOTE: Strenuous exercise following a dive may increase the risk of decompression sickness. DAN recommends divers avoid exercise for 24 hours after surfacing.

What is Cardiovascular Endurance?
Cardiovascular endurance is the ability of the heart, lungs and blood vessels to deliver oxygen to your body tissues. The more efficiently your body delivers oxygen to its tissues, the lower your breathing rate is. While this may help you get a little more bottom time from each tank of air, the real benefits are being more relaxed during each dive, experiencing less fatigue and being better able to respond to challenging currents, long swims and any emergencies that may arise. Essentially, a stronger, more efficient oxygen delivery system allows you to dive with greater ease in any situation.

The good news is that you can improve your cardiovascular endurance through a sensible program of regular aerobic exercise performed within a target range of 60 to 85 percent of your maximum heart rate (MHR). Most people see significant improvement in about three months as the heart muscle grows stronger and pumps more blood with each beat. Blood vessels become more elastic, reducing blood pressure, and capillaries — the tiny vessels that actually deliver oxygen to your tissues — create more branches. Oxygen is taken up by the tissues more effectively as the density of oxygen receptors (called mitochondria) increases. The net result is a positive effect on overall health and wellness.
Resting Heart Rate: An Indicator of Cardiovascular Endurance
Your resting heart rate (RHR) is both a reliable indicator of cardiovascular endurance and the baseline measurement for monitoring your aerobic workouts. An untrained individual has an RHR of approximately 70 beats per minute (bpm), while an elite athlete like Lance Armstrong may have an RHR of approximately 35 bpm. A healthy goal is around 65 bpm. Try measuring your RHR on three separate occasions; multiple attempts minimize any impact of nervousness or technique. If you discover an RHR above 80 bpm, see a physician before beginning a cardiovascular training program.

Your RHR can be determined by taking your pulse (radial or carotid) first thing in the morning before you get out of bed, ideally after a good night's sleep. Count beats for 30 seconds and multiply by two to determine beats per minute. Repeat the process over several days, and take the average as your true RHR. Check for accuracy by comparing your count to a heart rate monitor or by having a partner count, too; have him or her count your radial while you count your carotid pulse, and see if you get the same result.
The FITT Principles
Once you know your RHR, it's time to build an aerobic exercise regimen. An effective workout is a balance between frequency, intensity, type and time (FITT). FITT principles will help you manage your fitness plan, but always listen to your body to achieve an appropriate balance. An aerobic training program is supposed to decrease stress levels, not increase them.

The American College of Sports Medicine currently recommends that healthy adults participate in moderate aerobic exercise 30 minutes a day, five days a week, or vigorous cardio exercise 20 minutes a day, three days per week. Follow these guidelines, and you should start feeling the results within the first few days. Unfortunately, detraining also occurs quickly, so it is important to make sure there are no more than two days of rest between cardio workouts. Although these guidelines are ideal, remember that any exercise is better than no exercise. If you can squeeze in even 5-10 minutes, it will help to maintain your current fitness level.
Cardiovascular endurance improves when you exercise in an aerobic training zone that elevates your heart rate to somewhere between 60 and 80 percent of your maximum heart rate. To find your MHR, subtract your age from 220. Your true MHR should fall within 12 beats above or below this number.

Then use these formulas to find the upper and lower range:
Aerobic Training Zone
((MHR - RHR) × .60) + RHR = Lower Limit of Range
((MHR - RHR) × .85)+ RHR = Upper Limit of Range
Shorter workouts will be closer to the upper limit, while longer workouts will be closer to the lower limit.

Interval training, which alternates bursts of vigorous and moderate intensity, has a greater impact in a shorter time. Use the low-intensity range for a warm-up, then begin with a 1:1 work/rest ratio. For example: Follow 30 seconds of activity with 30 seconds of recovery. There are countless variations of intensity levels depending on the duration of your workout, work/rest ratios and where you want to be within the lower or upper limits of each training zone.

The Borg Rate of Perceived Exertion (RPE) is one way to measure intensity. It is a 15-point scale based on heart rate; add a 0 to the right of the rating to find your own heart rate. A rating of 6 should correspond to 60 bpm, while a rating of 20 should correspond to 200 bpm. You can also monitor your heart rate during exercise by using a basic heart rate monitor or by taking your pulse for 15 seconds and multiplying it by four to get beats per minute.
Common aerobic activities include walking, jogging, swimming, cycling and stair climbing, but it doesn't matter what type of exercise you choose as long as you stay in your training zone. Choose aerobic activities that you enjoy and can realistically fit into your daily routine. Consider mixing activities to alleviate boredom, work different muscle groups and avoid overuse injuries. Strength training can also meet cardiovascular needs if you minimize or eliminate the waiting time between exercises and keep your heart rate elevated. The push-pull structure of the strength training workouts in the last three "Dive Fitness" columns allow you to improve cardiovascular endurance while improving muscle strength.
Time is the duration of a given workout. Your goal should be a minimum of 30 minutes in your target range (20 minutes for interval training) per workout. If you're having trouble reaching that at first, take baby steps. Start with accumulating 30 minutes in your target range over the course of a day; try 10 minutes before breakfast, 10 minutes before lunch and 10 minutes before dinner. Keep your heart rate up for a little while today and a little longer tomorrow.

Once you've established an aerobic workout routine, stick with it. If time is tight, shorten your workout but increase the intensity. If you are tired before you start, plan for a less intense workout, but extend the time.

Above all, be realistic with your goals, and remember this is a program for life.