By measuring the actual oxygen uptake and estimating the required oxygen uptake for the high-intensity effort it is possible to quantify the accumulated oxygen deficit. During a maximal high-intensity effort this measurement can become a useful index of anaerobic fitness. Figure 14.1 presents an example of an exercise task that is performed for 2 minutes at an exercise intensity that equals the power output that elicits the maximal oxygen consumption. The lower, shaded area reflects the aerobic contribution to the effort, and the upper area reflects the anaerobic contribution to the effort. In this example it appears that anaerobic energy-yielding systems contribute approximately one-third of the total energy required for the effort.