Nutrition & Health OnLine Magazine

ENERGY SYSTEMS: Part 2

Davey Dunn

Part 1 of Energy Systems appeared in the last issue of Nutrition & Health OnLine Magazine. If you have not read Part 1 please Click Here

As we saw, the ATP-CP system is involved at the beginning of all activities but is most heavily involved in activities that last less than ten seconds and require short bursts of energy. Weightlifting, throwing the shot, and forty-yard sprints are all activities that are fueled by the ATP-CP system. Since the amount of ATP available for such activities is completely dependent upon the amount of Creatine Phosphate stored in the muscle a diet that includes high levels of Creatine has been shown to boost performance in such activities.

You can obtain small amounts of Creatine from your diet by eating meat and fish however the most practical way of increasing Creatine Phosphate stores in your body is through supplementation. Research has shown that short term supplementation of fifteen to twenty-five grams a day of Creatine can increase the Creatine Phosphate stores by as much as forty percent.¹ Research has also demonstrated that the increased stores of Creatine Phosphate will translate into increases in performance.¹ If you participate in a sport that requires short intense bursts of power then you can improve your performance by boosting your Creatine intake.

For activities that last longer than ten seconds and up to two minutes we saw that the ATP-CP system is involved at the beginning of the exercise but the primary energy system is Anaerobic Glycolysis. This energy system relies on glucose in the blood or glycogen stored in the muscle and is therefore dependent upon a diet that includes plenty of carbohydrates.

The Oxidative system was the third energy system we examined and we saw that it becomes involved in producing energy only after an activity has lasted at least two minutes. The Oxidative system is also heavily dependent upon glucose in the blood or glycogen stored in the muscle even though it can also use fat or protein when neither of the former fuel sources is available. As with activities that utilize the Anaerobic Glycolysis system, the Oxidative system is heavily dependent upon a diet that includes plenty of carbohydrates.

The most important concept to understand from examining the body's energy systems is that the primary source of fuel comes from glucose in the blood or stored glycogen, which can only be derived by eating carbohydrates. Yes, the body can use fat or protein for energy through the Oxidative system but the process of producing ATP is much less efficient.

The effect of not eating enough carbohydrates has been thoroughly studied and the results have clearly shown that low carbohydrate diets lead to fatigue and decreased performance. A classic study was performed by Dr. David Costill way back in 1980 that showed how muscle glycogen decreased rapidly following intense bouts of training when an inadequate amount of carbohydrates were consumed. Figure 1 shows the effect of intense training on muscle glycogen levels with a diet that is low in carbohydrates compared to one that provides adequate carbohydrate consumption. ²

The reason that maintaining muscle glycogen levels is so important is because training intensity is so closely related to energy production. When you run out of energy your body quickly ceases to function. Most long distance runners have experience with the body running out of energy. They call it "hitting the wall" which usually happens late in the race when their glycogen stores have been completely depleted.

Many athletes have been duped into believing that they can maintain their performance levels while using a high protein/low carbohydrate diet like those advocated by self proclaimed weight loss gurus who clearly know very little about the energy systems of the body. As we have seen, the only energy system that can even use fat or protein for fuel is the Oxidative system which does not even come into play until an activity lasts at least two minutes. This means that if you spend most of your time lifting weights you will have to rely on the ATP-CP system, which is only good for about ten seconds and will not be enough for more than one or two repetitions. Even if you are engaging in an activity that lasts long enough to involve the Oxidative system, research has shown that performance decreases drastically when the body burns predominately fat.² The Science is clear, eat enough carbohydrates or your performance will suffer.

The purpose of studying the body's energy systems is to understand how the body generates energy so that you can eat the right kind of diet. It should be clear by now that eating a diet that is rich in complex carbohydrates is crucial to success in your training program. It is also pretty clear that you can boost your performance in brief powerful movements by supplementing your diet with Creatine. Lack of energy is the limiting factor in most activities so utilize what you have learned here about the body's energy systems to optimize your diet so that you will maximize your performance in your chosen activity.

¹Kreider, R.B. "Creatine Supplementation: analysis of ergogenic value, medical safety and concerns" JEPonline, v 1, n 1, 1998
²Costill, D.L., et al, Int. J. Sports Medicine, 1980, p. 2-14.

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