Glossary of terms


Anaerobic threshold - AT.

The intensity at which the lactate production rate equals lactate combustion rate. Therefore this is the highest intensity at which a steady state of lactate can be sustained (also referred to as maximum lactate steady state). Anaerobic Threshold is expressed either in speed (m/s), or in Power Watt, or Watt/kg bodyweight.

Body Muscle

The amount of muscle mass as a percentage of the whole body mass.

Body Water

The amount of water mass as a percentage of the whole body mass.


CarbMax refers to the intensity at which the carbohydrate combustion matches the maximal uptake of carbohydrates. The latest scientific literature shows that an uptake of carbohydrates of 60 to maximum 90g per hour is possible. The actual possible uptake rate depends on the kind of carbohydrate (mixture of different forms, such as glucose and fructose). In any case – as it stands for now – it isn’t possible to go higher then 90g per hour. You will find this zone of 60g-90g marked as a red area in the load characteristics. CarbMax is the intensity (speed or power) at which 90g of carbohydrates is combusted. At higher intensities carbohydrate combustion exceeds the maximum possible uptake, resulting in carbohydrate depletion over time. This cannot be reversed during the actual exercise, but only after, during recovery.

Creatine Phosphate (CrP or PCr)

A substrate stored in the muscle cells. The breakdown of creatine phosphate into creatine and phosphate enables the muscle to produce energy. The depletion of creatine phosphate in the muscle leads to complete exhaustion. Creatine phosphate gets resynthesized out of creatine and phosphate by energy supplied in the aerobic metabolism.


Efficiency refers to the relation between produced mechanical power, and the energy per time produced by the muscle metabolism. In sports, where mechanical power output cannot be easily measured, such as swimming for example, efficiency is often related to speed instead of power. In fact, there it is possible to differentiate between two levels: one is the transfer from metabolic power or energy, to mechanical power or energy. This gross efficiency is used in power-based sports such as cycling. The other level is the transfer from mechanical power to speed. This relationship is highly determined by the drag an athlete experiences – for example aerodynamic drag in cycling or hydrodynamic drag in swimming. If mechanical power cannot be measured, it is useful to summarize the two levels into one level and use the relationship between energy produced by the muscle and speed. To determine the exact energy produced by the muscles is very difficult. The fuel sources need to be known exactly, but are difficult to assess in an experimental trial. Typically, it is easier to measure, and can be put into practical application- using the oxygen demand instead. The oxygen demand (VO2tot – metabolic demand) is related only to oxygen used to produce ATP in the muscles, and not additional oxygen, that might be needed in for non ATP producing processes – such as extra oxygen needed in the beta oxidation of fatty acids.

Energy Demand equation (EBG Term A,B,D)

The relation between moving speed (running speed, swimming speed etc.) and the energy demand – expressed as oxygen demand (see also efficiency) is expressed as a mathematical equation. The terms A,B, and D are the three terms of this equation. A is a static value, B is a linear value and D is a cubic value. Example: in a sport like swimming the terms could look like: A=5 (resting VO2); B=0,1 (expressing a small linear increase of energy demand), D=15 (expressing a large energy increase with speed). In Swimming, the cubic term D is larger compared to a sport like running. This is because of the influence of the hydrodynamic drag of the swimmer and the higher density of water compared to air.


FatMax refers to the maximum fat combustion rate. It describes an intensity – speed or power – at which the combustion of fat for energy production is at the highest. With increasing intensity, the percentage of fat combustion as a fuel for energy production decreases. However, the energy amount needed increases with an increase in intensity. Therefore, fat combustion builds a sweet spot – FatMax. FatMax has a value of energy – like kcal – per hour or minute. It cannot be backwards calculated in grams of fat because the conversion depends on what type of fats have been combusted.

Lack of pyruvate (LOP)

The amount of pyruvate which would be needed to saturate the aerobic metabolism to 100%. In a simplified way, it can be stated as lack of lactate. Lactate gets converted quickly to pyruvate, the latter to enter the aerobic metabolism as a fuel. The lack of pyruvate (LOP) therefore equals the amount of lactate that can get combusted in the aerobic metabolism – additional to the gross lactate production.

Lactate accumulation

The rate at which lactate accumulates over time. Normally expressed in mmol/l/min. Tob e found in steady state conditions once intensity exceeds anaerobic threshold.

Lactate combustion / aerobic lactate combustion

Lactate combustion refers to the amount of lactate which is cleared by combustion per minute. A typical value is mmol/l/min. From a quantitative point of view, the only way to combust lactate in the working muscle is to use it as a fuel in the aerobic metabolism (mainly through the step of transforming it into pyruvate). For this reason, it becomes clear the amount of lactate which can be combusted – or the rate – depending on the aerobic metabolism. In fact, the maximal rate at which lactate can be combusted in the aerobic metabolism is limited by the actual rate of the aerobic metabolism. Even the upper limit is determined by the rate of aerobic metabolism. The effective rate of lactate combustion is also dependent on the actual lactate concentration. At low concentration of lactate, the effective combustion rate is lower then the maximum possible combustion rate. At high lactate concentration, the limit by the aerobic metabolism comes into play.

Lactate concentration

The concentration of lactate expressed in mmol/l. This is referred to as concentration in the blood (where it can be measured easily) or in the muscle.

Lactate distribution space

The amount of mass in which lactate gets distributed as a percentage of whole body mass. As lactate is water-soluble, the lactate distribution space is related to the body water mass.

Lactate production

Lactate production describes the amount of lactate produced per time. The common value is mmol/l/min. In contrast to lactate concentration, is a flux rate, which adapts very quickly to a change of intensity. Lactate production is not the same as lactate accumulation. Lactate production refers to the gross lactate production in glycolysis and therefore does not account for lactate combustion.

Metabolic demand

Metabolic demand refers to the amount of energy needed for a certain intensity. It would be applicable to express metabolic demand in energy over time – like the mechanical power output as measured by a powermeter on a bike (for example is in Watt = J/s). However, for easy comparison with other physiological metrics, metabolic demand is expressed in needed oxygen uptake. This is a common term in the literature named ‘VO2tot’ – describing the total oxygen needed for a certain power output or speed. As it is expressed in ml/min/kg, it is very comparable to the actual oxygen uptake (VO2) and other metrics. The relation of metabolic demand (VO2tot) to speed or power describes the efficiency.

Multi Athlete Metabolic Profiling

The visualization of up to 3 performance assessment’s – either of the same athlete or of different athletes. This can be done with real data, or virtual data to visualize the effect of individual metabolic metrics on the overall performance of the athlete.

Muscle mass used

The percentage of the total body muscle mass that is used in specific sporting exercise

O2 per Watt Equivalent

The amount of oxygen needed to produce one Watt of power.

Percentage of VO2Max @ AT

Expresses the usage of VO2max at anaerobic threshold. The higher the percentage, the higher fraction of the actual VO2max which can be sustained without accumulating lactate.

Single Athlete Metabolic Profiling

The visualization of the results of the actual performance status of a single athlete.

Sum of squared errors

In a fitting of data to a curve, the delta value between fitted and measured values are taken, squared and afterwards summed up. This provides a statistical value expressing the quality of the fitting. The smaller the sum of squared errors the smaller are the differences between measured and fitted (=calculated) data.

Virtual Test

A copy of a real dataset of a performance assessment in which one or more physiological metrics have been manipulated. A virtual test allows a coach (and athlete) to visualize the effect of a change in a single performance related metric (efficiency, body composition, VO2max, etc.) on the overall, or a specific performance of the athlete.

VLa and VLamax

The origin of the term VLamax is similar to VO2max. The ‘V’ should carry a dot above, and expresses a flow rate. The ‘La’ stands for lactate, and the ‘max’ for maximum. Therefore, VLamax refers to the maximum lactate production rate. The value used is either mmol/l/min (VLa), or mmol/l/s (VLamax). Lactate production is an important marker in sports performance because: 1) it is generated by the combustion of carbohydrates. The more lactate produced – the more carbohydrates consumed. 2) with every single molecule of lactate produced, energy for muscle contraction is released. 3) the rate – not the concentration(!) – of lactate production is an important indicator for the performance or capacity of glycolytic energy production. As lactate is the end product of glycolysis, the more lactate produced in a certain amount of time- the more energy is produced in the glycolytic (anaerobic) metabolism (in vivo, the equilibrium between pyruvate and lactate, is heavily on the side of lactate!). Therefore we can refer to Vlamax as maximum glycolytic (anaerobic) capacity

VO2 and VO2max

The ‘V’ in VO2max should carry a dot above it. V-dot originates in fluid dynamics and stands for volumetric flow rate. The ‘O2’ in VO2max stands for oxygen. ‘Max’ in VO2max stands for maximum. These three put together stands for maximum oxygen uptake. The common value is ml/min or related to the body mass: ml/min/kg body mass. Often, VO2max is mistaken for the amount of oxygen that is inhaled or even by the amount of air that is inhaled. Oyxgen uptake or VO2, refers to amount of oxygen that actually stays in the body to be used in aerobic metabolism. Only a fraction of the inhaled air (at sea level approx. 20.9%) consists of oxygen, and a huge amount of this is exhaled. The oxygen that actually is taken up by the body, is only a fraction of that ventilation. The body, or more precisely the muscles, in the case of sports, use oxygen in the aerobic metabolism to produce energy for the needed movements. The rate of energy produced for muscle contraction is related to the oxygen uptake. Therefore VO2max is often described as maximum aerobic capacity.


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