Monday, April 9, 2007

Two Kinds of Endurance

Most of the time on this blog I talk about strength and power. That's because I believe that the first element of truly functional fitness is strength and power. Strong, powerful muscles stabilize your skeletal structure, correct muscle imbalances and posture, and decrease the risk of injury in your daily activities and recreation.

The second element of functional fitness is endurance. In my book there are two kinds of endurance:

  1. High-intensity endurance
  2. Low-intensity endurance

I differentiate them based on the kind of nutrient utilized as feul and the purpose which they serve. I'm sure exercise physiologists have different, more-scientiffic names these two kinds of endurance, but these labels make sense to me. Today I'm just going to hit on the primary differences and why they're important. In upcoming posts, I'll tell you how to train to increase both kinds of endurance.

High-intensity endurance is a matter of how long can you engage in vigorous activity like swinging lifting weights or sprinting. This kind of high-intensity activity primarily utilizes the anaerobic energy system, which is feuled strictly by carbohydrates. All muscular contractions depend on a chemical known as ATP. In high-intensity exercise the muscles first consume ATP already available in the muscle fibers. Then the mitochondria in the fibers turn on its energy systems to make more ATP. The Anaerobic systems are the first to be utilized because ATP is produced more quickly and doesn't require the high quantity of oxygen that the aerobic energy system requires. However, the anaerobic systems do not create ATP in as much abundance as the aerobic system and the byproduct is lactic acid, the build up of which leads to muscle failure.

Increasing your high-intensity endurance increases the amount of time you can engage in high-intensity activity before muscle failure due to decreased availability of ATP and build-up of lactic acid. A real-world appliction might be a self-defense situtation in which you either need to fight off an attacker or sprint to escape one. High-intensity endurance keeps your fighting stronger and more accurately long enough to finish the job and enables you to sprint far enough to outrun the attacker. High-intensity endurance will also help you catch that bus when you're running late to work.

Low-intensity endurance is about how long you can engage in a less-intense activity before exhausting your energy systems. It doesn't matter whether we're talking about a marathon run or playing outside with your kids. Low-intensity endurance lets you engage in activity for longer. It also determines how long before you can engage in the next bout of high-intensity activity, because the ATP produced can be used for any sort of activity. That's why you rest between sets of weightlifting; the aerobic energy systems supplement the anaerobic systems to provide enough energy for that next set.

Low-intensity endurance is primarily feuled by the aerobic energy systems, which consume fat, carbohydrates and protein to manufacture ATP. The less intense the activity, the higher the ratio of fat is being burned. That's why jogging, aerobics and similar activities are so popular for weight loss--they increase the number of calories being burned and, because of the low intensity, burn more fat calories than anything else. However, the aerobic systems are also utilized to replace the ATP consumed during high-intensity of exercise and the highest ratio of fat is burned during periods of rest. Since high-intensity exercise burns more ATP and calories in less time, it may be more efficient to burn calories with high-intensity exercise and let the aerobic system burn fat to replace that energy during recovery.

Anyway, in my estimation, the greatest reason for increasing low-intensity endurance is that it increases your energy levels and endurance for ALL activities--even sitting in your office typing on the computer. By training your low-intensity endurance capacity, you increase your energy levels for daily actitivities and increase your overall metabolism, which results in more energy, more fat burn, yada yada yada.

Next time we'll discuss how to increase your endurance capacity.

Live strong, live well

John Fike


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