The theories of fatigue, we discussed in the previous lesson, open up alternative ways to view fatigue and provide possible training insights. In this lesson, we examined how fuel supply can cause fatigue. Short bouts of exercise are most effected by energy supply because the phosphocreatine and glycogen have limited ATP production capabilities. In essence, we will look at fatigue from the point of view of the energy supply and energy depletion theory. Now, muscle trauma is also involved in limiting short burst of activity. But this is not going to be the focus in this particular lecture. Most sports involved short bouts of sprinting. So, insights into what causes fatigue during sprinting has a really, really wide application. The mean distance and duration for sprinting in team sports is between ten to 20 meters, lasting between two to three seconds. Recovery is an important consideration. So the athlete is ready for the next bout of sprinting within minutes. In track sprint events, a running performs a single bout of sprinting with very little consideration about the rate of recovery from this effort. However, training for these sprint race involves repeated bouts of sprinting on various duration and distances that is close to the athlete's maximum velocity. And the questions that are of interest to us include how does repeated bouts of sprinting cause muscle fatigue? And the second question is how are the three energy systems each affected. Now we know that maximum speed cannot be maintained for very long. Power output declines with increasing distance and duration, as you see here. Power is lowest at 30 seconds and it's highest at six seconds. The insights we have for why this happens comes from research using needle biopsy techniques. A sample of the athletes muscle is snipped out by using a specially designed needle and frozen within four to six seconds. And in this way the samples closely reflect the state of the muscle during exercise. In this lesson, we examine how the prostate create in the PCr, the glycolytic and the aerobic energy systems interact to supply ATP during sprinting. We discuss the recovery time necessary to replenish the fuel sources for the Phosphate Creatin and Glycolytic Energy System during sprinting. We will examine how you decide when the athletes Phosperic Creatin Energy System has run low on its fuel supply. So let's get started.