What is the most frequent form of exercise? It’s CARDIO, short for cardiovascular endurance training. Most people I know who “workout” describes their routine as running a certain number of miles (usually 3 or more), walking on the treadmill for a particular period of time (usually 30-60 minutes), or spending a long segment on another cardio machine such as the elliptical (again, usually for periods of 30-60 minutes). We do this because we have been told for many years that cardio saves our heart and burns fat. But what if it can actually weaken your heart? What if it is an inefficient method of burning fat? Intrigued? Keep reading...
If our only form of cardio is long endurance training where we are going at relatively the same pace for the entire time, we are teaching our hearts to endure that exercise. In order to endure the task, the heart essentially sets up on reserve; it works at just a high enough capacity to get the job done, reserving itself so that it can work effectively for the duration of our regular workout.
The result is that our hearts get weaker in some critical capacities, simulating the destructive effects caused by stress and aging. Unfortunately, this means that our hearts are not prepared if the time comes when they need to work extremely hard for a short, sudden period. This research got underway when the fitness world was bewildered when well-known endurance athletes, such as marathon runners, were dying of heart attacks.
Allow me to share an analogy written by Dr. Al Sears:
Think of your body as an engine with the nifty additional feature of being able to gradually redesign itself. If you require this engine to repeatedly go non-stop for long distances against low resistance, at a relatively slow speed, its primary adaptation will be to become more efficient at light, long, continuous, low output. Continuous duration taxing your endurance produces some unique challenges your body must overcome. It must not run out of fuel, overheat, or be overwhelmed with metabolic wastes. One of the ways that your body adapts is by gradually rebuilding your heart, lungs, blood vessels and muscles as small as possible and still have the minimum “horsepower” required.
In addition, this form of medium intensity exercise is not the most effective way to burn fat. On the contrary, it can actually promote fat storage. The chart below (Adapted from: McArdle W.D. 1999. Sports & Exercise Nutrition. NY: Lippincott Williams & Wilkins) outlines from what source our bodies retrieve energy during low, medium, and high intensity workouts.
| Low Intensity | Medium Intensity | High Intensity |
Protein | 5-8% | 2-5% | 2% |
Carbohydrates | 70% | 40% | 95% |
Fat | 15% | 55% | 3% |
At first glance, it would appear we should all be doing moderate intensity so that our bodies can burn 55% of our energy from fat. However, the opposite is actually true. If our bodies constantly burn fat, our bodies are conditioned to constantly produce and reserve fat (simply supply and demand). Whereas, if we are burning a high level of calories but deriving our energy from stored carbohydrates (high intensity), the body burns whatever fat it consumes because it has no programmed reason for storing it. This, then, is our most effective form of fat-burning exercise.
Also, keep in mind that the most important changes from exercise occur after, not during, the exercise period. The way we exercise affects our metabolism for several days. Short bursts of exercise tell our bodies that storing energy as fat is inefficient, since we never exercise long enough to utilize the fat during each session. Carbohydrates, which are stored in muscle rather than fat, burn energy at high rates. Exercising for short periods will use these carbs and burn much more fat after exercising while you replenish the carbs. Short interval exercise maximizes fat “after burn.” (PACE®: Rediscover Your Native Fitness).
So what is the solution? There is no need to give up that long run. I went on one this morning! Endurance activities certainly help us strengthen muscle, make the heart work harder than it normally does, and provide a great deal of stress relief. However, we cannot let that alone be our workout. Several times a week, we should engage in workouts where we are running as hard as we possibly can for 1-2 minutes, walking for 30 seconds, and then repeating the process for about 10 minutes (this is following a 2-3 minute walk for warm-up). This hard run followed by a short recovery will condition the heart to respond to a multitude of scenarios, burn calories, and help set up our bodies to continue to burn fat even long after the workout had ended. If ultimate fitness is our goal, endurance cardio is not the answer.
