How The Body Works

First, everyone's ability to make their body work, walk to their front door or run a marathon, is dependent upon these things: heart and lung function, blood vessel function, amount of muscle in the body and the strength of that muscle. One could compare the human body to a car. When cruising at 30 miles per hour on a country road the car needs some gas, some oil and the mechanical parts working properly to pump the fuel into the engine. However, when this car hits the interstate it may suddenly need to perform at maximum capacity to dodge an 18-wheeler coming into its path. So, at a time like this, it will maximize its abilities, burn more fuel, go as fast as it can, and force its mechanical parts to push harder.

Our bodies function the same way. We usually, almost always, perform (expend energy) way below what we could do in a recreational (swimming, jogging) or emergency situation (running for help). We hold a reserve for when we really need or want to hit that interstate at maximum speed. The fuel, which the body uses, is oxygen, not gas, and the ability to function above and beyond the usual is called the "reserve function". It's much like a savings account, there when you need or want to use it, but you can't take from it continuously or you will exhaust its supply.

Fueling The Pump

The body taps into "the cardiovascular reserve heart function "by first sending more blood back to your heart to be pumped. Your heart pumps the increased amount of blood faster than usual to your lungs. Your breathing gets deeper and faster. Essentially, the blood gets refueled (takes on oxygen) in the lungs. Then the heart pumps this newly oxygenated blood via your blood vessels (arteries) to your body's muscles. This provides the fuel (oxygen) to the muscles to do the "work" required.

The body taps into "the cardiovascular reserve heart function "by first sending more blood back to your heart to be pumped. Your heart pumps the increased amount of blood faster than usual to your lungs. Your breathing gets deeper and faster. Essentially, the blood gets refueled (takes on oxygen) in the lungs. Then the heart pumps this newly oxygenated blood via your blood vessels (arteries) to your body's muscles. This provides the fuel (oxygen) to the muscles to do the "work" required. Just as you can measure the amount of fuel used by your car during a trip by consulting your gas gauge, there is a way you can measure the fuel used by your body when it exercises. By determining your exercise capacity you can gauge the maximum rate of oxygen (or fuel) that can be delivered to your body during exercise. Your exercise capacity can be estimated easily by using a simple piece of equipment found in both doctors' offices, health clubs (and perhaps in your own home), a treadmill, and a standardized table. "Standardized" means that efforts have been made to assure that everyone taking the test does it the same way. That way, after you perform the test you can compare your exercise capacity with that of others your age and of other ages by using the table. You start the test by walking on the treadmill at a low speed and elevation. Gradually, about every 3 minutes, (called stages in exercise language) both the speed and elevation are increased. You do this until you cannot continue on the treadmill any longer because you are exhausted. This is the point at which you can no longer increase the amount of oxygen to your body. The total time you are able to do this exercise before you have to stop, due to exhaustion, gives an estimate of your exercise capacity.

Standards of Performance

Persons between the ages of 20-29, on the average, can stay on the treadmill during the standardized test for about 12 minutes. It has been estimated that at this point they are using 9 times the oxygen they would use if they were resting. This occurs because their hearts are pumping at four times the resting level and their muscles are taking in two and half times more oxygen than they do at rest. The young body is like a well-tuned 2000 Lamborghini coasting down the highway. But, what happens if the machine is a 1940 model (driven only on Sunday), but nevertheless, older model. It may still run great under most circumstances, but perhaps not quite as fast as the 2000 when the pedal is put to the floor. The body's ability to increase its oxygen consumption and performance has been shown to decrease with age, just like older cars. With less fuel and decreased ability to pump the fuel due to mechanical decline (aging), your exercise duration time (number of minutes you are able to walk and run) during the standardized exercise treadmill test, decreases as your body ages. The table below is based on standardized tests in over 10,000 people and shows the decline in time that one can stay on the treadmill with age. Essentially, this decrease in exercise capacity reflects the decline in your body's ability to get sufficient fuel (oxygen) during exercise.

You can see from this table that the average man between the age of 20 and 80 years loses 50% of his exercise ability. The number of minutes he can stay on the treadmill under the circumstances described goes from 13 to 7 minutes. Notice that the steepest decline in this ability occurs between the ages of 60 and 70 where it drops from 9 minutes to 7 minutes. Similar trends occur in women.

Testing the Engine

Are you in shape for your age? If you don't know and have never undergone a standardized treadmill test to determine how you compare to others your age and gender, maybe now is the time to do it. Ask your doctor to perform this test on your next check-up, or have one done at a supervised exercise facility. Then, compare your time on the treadmill to the chart for your age and gender.

In this first article, "Are You in Shape for Your Age", of our Series, "Aging of Your Heart and Blood Vessels is Risky," you have learned to what extent, on average, your exercise capacity is likely to decrease with aging, even if you remain healthy. And, we've given you a tool to compare your exercise capacity to others your age, the standardized table.
How much your exercise capacity should decrease with normal aging and how you can prevent this decline or slow it down is dependent on many factors, which will be discussed in future articles. In the next article of the Series we will talk about the mechanics of the heart and vascular system that occur with aging to cause your physical performance to decline.

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