Energy Dynamics During Exercise

The following is an exclusive excerpt from the book Developing Endurance, published by Human Kinetics. All text and images provided by Human Kinetics. 

As described previously, ATP (energy) can be produced via three energy systems. Although we looked at each of the energy systems separately, this does not mean that only one energy system can function at a time. To understand this concept better, we can use the analogy of a symphony orchestra: The orchestra includes several instrument groups, and each group plays softly, moderately, or loudly depending on the musical score.

At the beginning of the symphony, the string group may be loud, the woodwind group may be moderate, and the percussion group may be soft. These musical emphases may be reversed by the end of the symphony to reflect soft music by the string group and loud music by the percussion group. The same is true for energy production during exercise. Each of the three energy systems is in a state of dynamic flux. Like the instrument groups, each of the energy systems is operating constantly during exercise, but the systems operate at different levels of ATP production depending on the intensity and duration of the exercise.

An example of the “symphony orchestra” effect is shown in figure 1.8, which shows energy dynamics during a cycling road race, a sporting event that is classified as an endurance event. During pack riding, the exercise intensity is moderate, and the duration is relatively long. As discussed earlier, the dominant energy system during moderate-intensity, long-duration exercise is the long-term (oxidative phosphorylation) energy system. Although the long-term system is dominant, it is not the only energy system that is active during pack riding. The other two energy systems are active, but they are “playing softly.”

During a hill climb, the intensity picks up, but the duration is shorter compared with pack riding. This type of high-intensity, moderate-duration exercise requires the short-term (glycolysis) energy system to play the loudest, the immediate (ATP-CP) energy system to play louder, and the long-term system to play softer. Finally, the energy dynamics are reversed during the final sprint to the finish, which involves exercise at a very high intensity but for a short duration. In this phase, the immediate system is clearly the loudest, and the short-term and long-term systems are relatively quiet.

In endurance sport, the dominant energy system is the oxidative phosphorylation energy system. However, keeping in mind our symphony orchestra analogy, athletes must remember the role that the ATP-CP and glycolysis energy systems play in the performance of endurance activities. Knowing when to train and how much time to devote to training each of the three energy systems is an important ingredient of success in endurance sport. This knowledge is also reflected in a well-designed and scientifically based training plan. (Chapter 3 addresses this concept in more detail.)

The popularity of endurance sports continues to grow worldwide. Now, from the National Strength and Conditioning Association comes the definitive resource for developing the endurance training programs that maximize performance and minimize injuries. The book is available in bookstores everywhere, as well as online at the NSCA Store.