Everyone is talking about hydrogen
as the most sensible energy source for many processes. The fuel cell car, which uses hydrogen – obtained in various processes outside the car – to produce electricity, is seen as the drive system of the future.
Biology is already much further ahead! It has always used hydrogen technology, even without hydrogen filling stations! Hydrogen is obtained (produced) in the organism from energy-rich substrates – primarily from carbohydrates and fats in the citric acid cycle – and bound as NADH/H+ or FADH2. The hydrogen is then transferred to oxygen in a cascade of small steps in the respiratory chain (our fuel cell). This produces the “electricity of the organism”, the energy-rich substrate ATP! (An article on the effectiveness of the various processes follows). The “electricity” (ATP) production takes place “on demand”; only a small battery in the form of the energy-rich phosphates compensates for a rapidly increasing energy requirement at the beginning of a movement.
On top of that, we are not dependent on the sun always shining or at least the wind blowing, no, we always have our reserves, our fat depots with us (some people would benefit from a prolonged undersupply of “fuel” – a longer fast).
From the point of view of the size (value) of the depot, it is largely irrelevant in what form we attack our energy depots. Ultimately, the only thing that matters in the balance sheet is whether we have consumed or consumed more calories. The charges for switching from carbohydrates to fat and vice versa are negligible, which puts the many discussions about which substrate is used for energy production in which situation into perspective! When losing weight, it’s all about the calorie balance!
Energy metabolism during exercise
Resting conditions
At rest, under basal metabolic conditions, the body obtains its energy primarily from the combustion of glucose and fatty acids. The ratio of oxidized glucose to oxidized fatty acids depends largely on whether the person has just eaten, i.e. can offer a lot of glucose, or whether they have not consumed any calories for a long time. In this case, they primarily burn fatty acids.
In spiroergometry, it is possible to determine quite precisely under resting conditions how many calories are consumed and whether they come from the burning of glucose or fatty acids. (s. indirect calorimetry). This is possible because 1 mole ofCO2 per mole of oxygen is formed when glucose is burned in isolation, but only 0.7 mole ofCO2/mole of O2 when fatty acids are burned.
Start of a load
At rest, our energy-providing systems are switched to base load conditions. The organism only provides as much chemical energy as is needed. However, a reservoir of energy-rich phosphates (ATP and creatine phosphate) is available in order to be prepared immediately – almost explosively – for flight or fight. The intensification of the aerobic energy supply, i.e. the energy supply in which oxygen is consumed, for the combustion of glucose takes a few seconds, that of fatty acids even a little longer. In this phase, a non-oxidative (anearobic) energy supply via lactate takes place if required. Glucose is broken down, providing only 2 molecules of ATP.
If you consider that 32 molecules of ATP are formed from 1 molecule of glucose during oxidation, the aerobic metabolism (i.e. with the consumption of oxygen), it becomes clear that the anaerobic energy supply is only a kind of emergency power generator that is switched off again when the aerobic energy supply starts. Most of the lactate is still in the muscle cells at this point and is immediately transported to the mitochondria while being converted to pyruvate. transported to the mitochondria and broken down there in the citric acid cycle.
Physical strain
We have obtained most of the data on energy supply under physical exertion from spiroergometric exercise testsin which the physical exertion is increased at different intervals, either in short-term, small-step intervals (ramp test) or in larger increments every three to four minutes (step test). This test measures, among other things, how muchCO2 is exhaled (VCO2) and how much O2 is taken in via the breath (VO2). The ratio of VCO2 to VO2, the respiratory quotient, or better the respiratory exchange rate (RER), allows a conclusion to be drawn about how much energy has been provided from fatty acids or glucose through oxidation. For details see : Indirect calorimetry. On the considerable misinterpretations as a result of buffering of lactate formation and the hypervetilation are discussed in detail in the corresponding chapters.
With this procedure, there is an increase in lactate in the blood from a certain load (threshold) – much earlier in poorly trained people than in well-trained people. The increase in lactate in the blood results inCO2 exhalation via the lungs as a result of buffering, which is independent of the provision of energy(for details see fat burning pulse). If the release ofCO2 as a result of buffering is not taken into account, then the increase in the quotient of VCO2 / VO2 (the respiratory quotient, RQ or better the RER, the respiratory exchange rate) is incorrectly interpreted as a decrease, indeed as a cessation of fat burning during very intensive physical exertion.
In contrast to resting conditions, a simple estimation of the ratio of glucose to fat burning in this type of exercise test is therefore only possible if the proportion ofCO2 resulting not from metabolism but from the buffering of lactate is also determined by determining the blood gases (Lotz et al 2019). First of all: the proportions of glucose and fat used for energy production do not change significantly even at maximum load!
The RER can also be used to draw conclusions about the energy supply through the oxidation of glucose or fatty acids during exercise without additional blood gas analysis if the lactate is examined in steady state, i.e. if the lactate has not risen over a period of approx. 10 minutes, i.e. with constant continuous exercise.
With increasing exertion, there is a further increase in lactate in the blood. As lactate is formed from glucose without the use of glucose, i.e. anaerobically, many people still speak of a transition from an aerobic metabolism to a mixed aerobic/anaerobic metabolism when the lactate in the blood increases, and of an anaerobic metabolism when it increases further.
But how high is the proportion of lactate detectable in the blood in energy production during exercise?
The literature almost always states that the increase in lactate indicates that the provision of energy for exercise is increasingly anaerobic, i.e. takes place to an increasing extent without oxygen consumption. However, if the proportion of anaerobic metabolism in the provision of energy was significant, then it would be expected that the oxygen consumption per watt in the upper performance range would be significantly lower than in the purely aerobic range.
However, the figure above shows that there is by no means a decrease in oxygen consumption with increasing exertion (measured in watts). As the oxygen consumption/watt is not significantly lower in the so-called anaerobic range than at low levels of exertion, the proportion of lactate in the energy supply and the proportion of anaerobic metabolism in the energy supply for the various exertion levels will be calculated below in a collective that we examined. However, only the proportion of lactate that appears in the blood is included in the calculations. The much larger proportion of lactate, which is formed intracellularly as an intermediate product of glucose metabolism, but is then immediately processed oxidatively in the mitochondria, has nothing to do with anoxidative metabolism!
The calculation is based on data that we collected from 8 athletes who were subjected to a step test with an increase in load of 40 watts every 4 minutes (Lotz. et al, 2019 ). In addition to the lactate determination, a blood gas analysis and a respiratory gas analysis (spiroergometry) were carried out on these test subjects. The details of the examination are presented in the chapter “Fat burning pulse“.
The starting point for the calculation is the data listed in Table 3 on the “Fat burning pulse” page, using the RER corrected for the effect of buffering.
The calorie consumption per minute for the respective exercise level in the form of the oxidation of glucose or fatty acids was taken from the publication (Lotz et al, Table 3), reduced by the respective resting metabolic rate. A calorie content of 4 kcal/g glucose or 9 kcal/g fatty acids was assumed. The molecular weight of glucose was assumed to be 180 g x mol-1, for fatty acids palmitic acid (256 g x mol-1) was used as a representative for others. The formation of ATP from 1 mol glucose was assumed to be 32 mol ATP, for 1 mol palmitic acid 129 mol ATP.
The table shows that working muscles below the 1st lactate threshold gain less than 1 percent of the additional energy consumed from the release of lactate into the blood. At loads between LT1and LT2, glycolysis contributes just under 1.3 percent to the additional energy production. Even under maximum load, anaerobic glycolysis accounts for less than 2.5% of the ATP supply.
However, this calculation does not take into account how much lactate is formed intracellularly during intensive exercise and then oxidized in the same cell or absorbed and burned by other organs. It can be assumed that the amount of lactate that is eliminated from the blood by cells not involved in muscular activity increases with the concentration of lactate in the blood. The magnitude of lactate uptake during exercise can be reliably estimated from the lactate decay curves following exercise. Decrease rates of more than 1 mmol lactate/l/min are not achieved even by very well-trained athletes after an endurance exercise.
If the lactate elimination during the maximum load is added to the lactate increase, then under maximum load the proportion of lactate in the additional energy supply can be calculated to be less than 5%!
In the figure above, the ratios from the table above are visualized. We hope that the minimum proportion of energy production resulting from anaerobic metabolism can still be seen as a red line on a cell phone!
To use the term “anaerobic metabolism” for the small amounts of anaerobically provided energy is not helpful in my opinion! downright misleading!
Since the anaerobic metabolism accounts for less than 5% of the energy supply up to the maximum load, the lactate thresholds should not be referred to as aerobic or anaerobic thresholds. (see also which meaning ….)