by Al Sears, MD (http://www.alsearsmd.com/content/)
Look at any rack of fitness magazines and you'll see dozens of covers telling you that you need "cardio." Go to any gym and the trainer will insist on devoting some of your time to "cardio." You probably don't like doing it, yet you feel compelled to comply. After all, who doesn't want a healthy heart?
Common parlance has even accepted the term "cardio" (short for cardiovascular endurance training) as synonymous with exercise for your heart. But shouldn't exercise make the targeted body part stronger?
When you study the heart's changes as a result of cardiovascular endurance training, you find it getting weaker in some critical capacities that simulate the changes caused by stress and aging.
Routinely forcing your body to perform the same continuous cardiovascular challenge by repeating the same movement, at the same rate, thousands of times - without variation, without rest - is unnatural. By that, I mean our ancestors didn't regularly stress their cardiovascular systems in this manner. They may have put this type of demand on their hearts - but rarely, and not in the context of the daily environment of a native society in balance with its surroundings.
Yet nature designed your body to adapt to whatever environment it encounters. If you ask it to perform an activity repeatedly and routinely, it will gradually change the systems involved to meet the challenge more effectively.
But what adaptive changes does continuous cardiovascular activity cause?
Continuous-duration exercise that taxes your endurance produces some unique challenges your body must overcome. It must not run out of fuel, overheat, or be overwhelmed by metabolic wastes. Its primary adaptation will be to become more efficient at light, long, continuous, low-energy output. One of the ways your body does that is by gradually rebuilding your heart, lungs, blood vessels, and muscles to be as small as possible, while maintaining the minimum "horsepower" required to perform the activity.
You waste fuel and raw material with a Ferrari-sized engine going 20 miles per hour. Forced, continuous-endurance exercise induces your heart and lungs to "downsize," because smaller allows you to go further ... more efficiently ... with less rest ... and less fuel.
The Danger of "Downsizing" Your Heart's Capacity
So what's wrong with increasing durational capacity through downsizing? Instead of building heart strength, it robs your heart of its vital reserve capacity. Your heart's reserve capacity is that portion of its maximal output that you don't use during ordinary activity.
Let's go back to the car analogy. Say you normally drive at a speed of 40 miles per hour, but your car has the ability to reach a top speed of 140 miles per hour. If you think of your heart as the engine, your reserve capacity is the difference between your normal cruising speed and that top speed.
So if you downsize your heart and lungs, you have traded reserve capacity for efficiency at continuous duration. That forces those organs to operate dangerously close to their maximal output when circumstances challenge them. This is a problem you don't need ... especially for your heart.
Heart attacks don't occur because of a lack of endurance. They occur when there is a sudden increase in cardiac demand that exceeds the heart's capacity. Giving up your heart's reserve capacity to adapt to unnatural bouts of continuous prolonged-duration output only increases your risk of sudden cardiac death.
A ground-breaking study of long-distance runners showed that, after a workout, their blood levels and the oxidation of LDL (bad) cholesterol and triglycerides increased. (High triglycerides dramatically increase your risk of heart disease.) The researchers also found thatprolonged running disrupted the balance of blood thinners and thickeners, elevating inflammatory factors and clotting levels - both signs of heart distress.
These changes do not indicate a heart that's becoming stronger with long-duration exercise.
Exercising for long periods makes your heart adept at handling a 60-minute jog, but it accomplishes this feat by trading in its ability to provide you with big bursts when circumstances might demand. The real key to preventing heart disease and protecting and strengthening your heart is to induce the opposite adaptive response produced by continuous cardio and increase your heart's reserve capacity. Bigger, fastercardiac output that's readily available is what you really need.
Recent clinical studies show us the benefit of avoiding long-duration routines and exercising in shorter bursts. Researchers from the University of Missouri found that short bouts of exercise were more effective for lowering fat and triglyceride levels in the blood. Another study revealed that the duration of exercise routines predicts the risk of heart disease in men. They found that several shorter sessions of physical activity were more effective for lowering the risk of coronary heart disease.
The Secret to a "100-Year Heart" Is Millions of Years Old
Our ancestors lived in a world where their food fought back. Predators attacked without notice. Humans had to run or fight - fast and hard. These short bursts of high-output activity fine-tuned their bodies and kept them fit.
We still have the same physiology.
How do you recreate that kind of physical challenge? The key is to create an "oxygen debt." Simply exercise at a pace you can't sustain for more than a short period. Ask your lungs for more oxygen than they can provide. The difference between the oxygen you need and the oxygen you get is your oxygen debt. This will cause you to pant and continue to breathe hard even after you've stopped the exertion. (Until you replace the oxygen you're lacking.)
Here's an example: Pedal a bike as fast as you can for 15 seconds. When you stop, you'll continue to pant. This is the kind of high-output challenge you can't sustain for very long. You will have reached a supra-aerobic zone. This is very different from doing an aerobic workout for 45 minutes.
Another example: Do one-minute intervals - either running or riding a bike. Work yourself up to a speed that you cannot sustain for very long. After one minute, rest. You can rest by slowing down to a very slow speed or (if you need to) you can stop altogether. Do this 3 or 4 times.
With these types of interval exercises, you'll quickly start to build up reserve capacity in your heart. This is exactly what you need to prevent heart attacks and heart disease.