Biological processes during endurance stress
The human body works similar to an engine. It needs fuel (ATP/adenosine triphosphate) to perform. Performance in this case is endurance.
However, the body does not have only one petrol tank like the engine, but three types of “fuel” are available to it. The smallest energy store in the human body is the creatine phosphate store (KrP), it provides its energy immediately and is therefore required for very short and very high loads such as sprinting. The second, somewhat larger storage unit consists of sugar (glucose/carbohydrates) and is important for endurance exercises of medium intensity (running at about 11 km/h).
The third energy store is the fat store. The fat storage of a normal-weight man is 100,000 kcal of energy, which would be sufficient for about 30 marathons. Although fats are very rich in energy and even marathon runners have a surplus, it is very difficult to convert them into energy (fat metabolism).
This is also the reason why the human body falls back on sugar when it is under a higher load. Lactate measurements are used to objectively assess sporting performance. Lactate values provide considerably more information about sporting stress and performance than heart rate and have therefore been used in competitive sports for decades.
However, due to the high effort and cost-benefit considerations, professional lactate measurement in leisure sports makes little sense. In the field of sports science, lactate has long been a synonym for lactic acid. However, according to recent research, lactate cannot be acidic, as lactic acid breaks down into protons and lactate.
Protons are positively charged particles and lactate is negative. Therefore one should assume that lactate is basic and not acidic. Here you can get detailed information about
- Lactate level test
With increasing exposure, the lactate concentration in the blood rises until the point is reached where the accumulation corresponds to the level of degradation.
This is called the lactate steady-state. This range is around 4 mmol/litre and is considered a guideline value for sporting performance. In short: in the fitness and health sector, the 4 mmol/l limit should not be exceeded.
During endurance training, above all the cardiovascular system is trained, over a certain period of time respiratory rate, respiratory volume, heart rate and stroke volume are increased and trained. For this we need energy, which our body has to provide. As with every effort, our body first relies on existing energy reserves in the form of ATP (adenosine trisphosphate, fuel of the cell) and creatine phosphate (phosphate supplier for used ATP).
It then begins to generate new ATP through glycolysis, i.e. the metabolism of carbohydrates. This occurs first anaerobically, then aerobically (without/with oxygen). After a certain start-up time, aerobic glycolysis can provide a continuous supply of energy as long as the effort is not too great, so that oxygen consumption and intake are in equilibrium.
Under aerobic, i.e. oxygen-rich conditions, the fat metabolism is then also noticeably boosted. The fat metabolism is also increased in the first few minutes with the other energy sources, but gains in importance especially during longer work (from 30-45 min) when the carbohydrate and protein stores are used up. Long endurance training with an appropriate load level at which enough oxygen is available (you can still talk, basic endurance I) thus serves to burn fat.
The maximum oxygen intake is the gross criterion for aerobic endurance performance. The name oxygen uptake is misleading, because it does not mean the maximum uptake of oxygen by breathing, but the utilization of the oxygen taken up by breathing in the cardiovascular system. Indicators for the maximum oxygen uptake (VO2max) are the cardiac output per minute (HMV) and the arterio-venous oxygen difference (a-v DO2).
Cardiac output is the amount of blood that the heart pumps into the circulation in one minute. The arterio-venous oxygen difference is the difference between the oxygen content in the pulmonary artery (venous blood) and the arterial blood, i.e. the difference in “O2” that is pumped in and out. It is calculated from the product of (HMV) and (a/vDO2).