Health and Nutrition
Bicarbonate
In exercise that causes fatigue within a few minutes, such as racing over 800 m or 1500 m, a major part of the energy supply comes from the breakdown of carbohydrate without the muscles using oxygen in the process. The process does not involve oxygen and is therefore referred to as being anaerobic, and the carbohydrate used is mostly the muscle's store of glycogen, so it is known as anaerobic glycogenolysis. The breakdown is not complete – to carbon dioxide and water – as in lower intensity exercise, but stops at the stage of pyruvate (pyruvic acid), one of the intermediate stages. There is normally plenty glycogen available to last through a race but there is a shortage of one of the other chemicals (a compound known as nicotinamide adenine dinucleotide, which is conveniently shortened to NAD) involved in the process. By converting the pyruvate to lactate, the muscle can regenerate the NAD and allow the breakdown of glycogen – and therefore the supply of energy – to continue.
This has the disadvantage of not releasing all of the energy available in the carbohydrate, but this is more than compensated for by the fact that the process is very rapid. This means that energy can be supplied at a high rate, allowing the muscle to produce a high power: in other words, it lets you run fast. Although this allows higher rates of resynthesis of adenosine triphosphate (ATP) - the fuel used by the working muscles - than can be achieved by aerobic metabolism, when the carbohydrate is broken down completely to carbon dioxide and water, the capacity (the amount of energy that can be produced) of the system is limited, and fatigue is inevitable when high rates of anaerobic glycolysis occur.
Lactic Anaerobic Metabolism
One source of energy for ATP resynthesis is from degradation of glycogen (or glucose) via glycolysis in the muscle.
This proceeds via pyruvate to either lactate by anaerobic pathways or to CO2 and H2O using oxidative (aerobic) pathways.
Lactic acid forms lactate and hydrogen ions, which make the environment acidic.
Lactate and Fatigue
Although lactate is an importance energy source for the sprinter, the lactate that forms in the muscle is accompanied by an increase in the acidity level inside the muscle cell. The increasing level of acidity has been implicated in the fatigue process, either by inhibition of key enzymes involved in metabolism, by interfering with the transport and binding of calcium which regulates muscle contraction, or by a direct effect on the contraction process itself. The acid environment also stimulates free nerve endings resulting in a painful process: the is rather like putting an acid – say vinegar (acetic acid) or lemon juice (citric acid )- on an open cut.
Acids can be neutralised by the addition of alkali, and a number of compounds have this effect. When added to the human body, sodium bicarbonate, sodium citrate and many other chemical compounds will cause the blood to become more alkaline.
If we suffer from indigestion due to excess acidity in the stomach, the answer is to take an alkaline agent that neutralises the acid. It seems reasonable to believe that taking something to make the body more alkaline prior to exercise, might increase the ability to neutralise any lactate produced, with the potential to delay fatigue and improve exercise performance. Although it is often believed by athletes and coaches - and by television commentators - that producing lactic acid is a bad thing, it can be a good thing for the middle distance runner as it allows the muscle to work at high rates. Provided we can avoid the negative effects of increasing acidity, the more lactate we can produce the better.
Muscle Acidity and Fatigue
High rates of anaerobic glycolysis (lactic acid production) cause the muscles to become more acid. This has several effects:
- Calcium binding is affected
- Some enzymes are inhibited
- Contraction is inhibited
- Free nerve endings are stimulate
