149-b : VO2 max and FTP

The FTP is the power, in watts/kg, a cyclist can sustain for one hour.

The VO2 max is the maximum volume of oxygen which the body  can  handle per unit of time in ml / kg / minute.

In practice, you reach VO2 max in an effort that can be sustained for up to 10 minutes. Since oxygen in the body is used to produce energy from the combustion of glycogen and fats, the VO2 uptake indicates, in fact, also the amount of power that is delivered. The power delivered is the amount of energy per unit of time. What is the relationship between VO2 max and FTP?

THE ENERGY PRODUCTION OF THE FOUR HUMAN  ENGINES

The table shows how much the four engines on human energy produce. With the help of this table, we can calculate that the production of energy for the complete aerobic conversion of glycogen and fats, corresponds to 4 and 9 kcal/g.

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THE ENERGY  PRODUCTION PER LITER OXYGEN O2

In order to calculate how much power corresponding to the VO2 one must in the first place determine the energy production per liter of O2. Which is calculated for both aerobic processes. So for the conversion of glycogen and the conversion of fats. Then it can be divided by the amounts shown in the table by the number of moles of O2. There are six in the conversion of glycogen and 23 in the conversion of fats and then by the molar volume of O2, 24.3 L / mol at 25 degrees Celsius. The result is shown in the table.

Glycogen: 2880/6 = 480/24.3 = 19.76 KJ    

Fatty acids: 9853/23 = 428/24.3 = 17.64 KJ

The conversion of fats delivers less energy than the conversion of glycogen. Incidentally, this does not explain the phenomenon of “hitting the wall”, which occurs when the glycogen in the muscle is exhausted and the muscles have to pass on fat burning. The explanation for ‘ hitting the wall’ is that the power, so the speed of the combustion process of fats, is much slower than with glycogen.

THE ENERGY PRODUCTION AT THE VO2max

At the VO2max 90% of the energy is provided by glycogen and 10% by the fatty acids. Using the values from the table we can calculate the energy of the VO2 max is equal to:

0.9 x + 0.1 x 17.64 = 19.76 19.55 kJ / L O2

In order to calculate the power at the VO2max, in watt / kg, the VO2 max, in watt / kg / min, so only multiplying by 19.55 kJ / L, divided by 60, the ratio of seconds to minutes, and multiplying it by the muscle efficiency of 25%.

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The example applies to a rider with a VO2max of 55.4 ml / kg / min. Please note that specific power, 4.54 Watt / kg of the VO2 max is higher than the power at his FTP, as the latter applies to an effort of 1 hour.

POWER AT THE VO2 max:
Watts / kg = 0.25 x VO2 max x 19.55 / 60
Example:
VO2 max = 55.4 ml / kg / min
Power = 0.082 x 4.54 = 55.4 Watt / kg

THE RELATIONSHIP BETWEEN FTP AND VO2max
The power at the FTP, exercise duration 1 hour, is equal to 0.88 times the power at the VO2 max, with an exercise time of 10 minutes. This is the relationship between FTP and the VO2 max.

RELATIONSHIP FTP – VO2max
FTP = 0.88 x 0.25 x VO2 max x 19.55 / 60
FTP = 0.072 x VO2 max
Example:
VO2 max = 55.4 ml / kg / min
FTP = 0.072 x 55.4 = 4.0 watts / kg

149b-3
The figure is a graphic representation of the relationship between the FTP and VO2 max for all relevant values of the FTP, is between 33 and 89 ml / kg / min. Earlier we saw that 6.4 watts / kg and 88 ml / kg / min are the current limits of human performance.