Fractional Utilization, Low Carbohydrate Diets and Running Performance
Fractional utilization refers to the fraction of VO2max that an athlete sustains during an event. It varies between events and between athletes. An athlete can sustain a greater percentage of VO2max for a shorter duration (5000m vs. 10,000m). Fractional utilization is sometimes referred to as lactate threshold. While the concepts are related, they are not the same. Consider an athlete with a VO2max of 70 ml/kg/min: If we find that he can average 90% of VO2max over the course of a 5000m run, he averages 63.0 ml/kg/min for the race. If he averages 86% of VO2max during a 10,000m run, he averages 60.2 ml/kg/min. Athletes may train for years, increasing fractional utilization. By increasing fractional utilization, an athlete will be able to complete a distance at a greater percentage of VO2max. For example, if that same athlete increases his fractional utilization during the 5000m to 93%, he can now average 65.1 ml/kg/min. That 2.1 ml/kg/min increase in utilization means more O2 is cons