Runner's performance evaluation - Part 1: the VO2max.

The MET (Metabolic Equivalent of Task) is a physiological measure that expresses the energy cost of physical activities. It is defined as the ratio of metabolic rate during a specific physical activity to a reference metabolic rate (set by convention to 3.5 ml  O₂/kg/min):

The reference metabolic rate just mentioned, is the expression of an individual’s body capacity to transport and use oxygen during exercise and it is called VO₂ (milliliters of oxygen per kilogram of bodyweight per minute [ml/kg/min]). The maximum reachable value of VO₂ describes the maximum capacity to transport and use oxygen during an incremental exercise and it is called VO_2max. Various methods are available to predict the VO_2max value, but the most accurate values can only be obtained with a measurement.

The ergospirometer (it can be seen in Figure 1) is used to measure ventilation and oxygen and carbon dioxide concentration of the inhaled and exhaled air during a graded exercise test (in this case performed on a treadmill, but it can be done on a cycle ergometer or on a rowing ergometer, depending on the reference sport): the  VO_2max is reached when oxygen consumption remains at steady state despite an increase in workload (see Figure 2).

In Figure 3 is possible to see the plateau created by the VO₂ and the HR, when reaching the maximum values.

An average untrained man will have a VO_2max of around 45 ml/kg/min, while women's values are typically 10-15% lower. These values can improve with training (altitude training is a common way, for elite athletes, to improve the VO_2max values) and decrease with age, even if the degree of trainability is very variable: some individuals may double the initial values, while some others will never improve. Elite male runners can generate up to 85 ml/kg/min and female elite runners can generate up to 77 ml/kg/min, even if higher values are reported in literature.

The second part will be about the energy expenditure's splitting between fats and carbohydrates. Meanwhile...keep on training, people!