lactic acid medical information?

Question

How does lactic acid affect the body?

Answer 1

Lactic acid is ONE of the 'waste byproducts' resulting from the chemical reactions that result in muscle contraction
The expression "lactic acid" is used most commonly by athletes to describe the intense pain felt during exhaustive exercise, especially in events like the 400 metres and 800 metres. When energy is required to perform exercise it is supplied from the breakdown of Adenosine Triphosphate (ATP). The body has a limited store of about 85 grms of ATP and would use it up very quickly if we did not have ways of resynthesising it. There are three systems that produce energy to resynthesise ATP: ATP-PC, lactic acid and aerobic.

The lactic acid system is capable of releasing energy to resynthesise ATP without the involvement of oxygen and is called anaerobic glycolysis. Glycolysis (breakdown of carbohydrates) results in the formation of pyruvic acid and hydrogen ions (H+). A build up of H+ will make the muscle cells acidic and interfere with their operation so carrier molecules, called nicotinamide adenine dinucleotide (NAD+), remove the H+. The NAD+ is reduced to NADH which deposit the H+ at the electron transport gate (ETC) in the mitrochondria to be combined with oxygen to form water (H2O).

If there is insufficient oxygen then NADH cannot release the H+ and they build up in the cell. To prevent the rise in acidity pyruvic acid accepts H+ forming lactic acid which then dissociates into lactate and H+. Some of the lactate diffuses into the blood stream and takes some H+ with it as a way of reducing the H+ concentration in the muscle cell. The normal pH of the muscle cell is 7.1 but if the build up of H+ continues and pH is reduced to around 6.5 then muscle contraction may be impaired and the low pH will stimulate the free nerve endings in the muscle resulting in the perception of pain (the burn). This point is often measured as the lactic threshold or anaerobic threshold or onset of blood lactate accumulation (OBLA).

The process of lactic acid removal takes approx. one hour, but this can be accelerated by undertaking an appropriate warm down which ensures a rapid and continuous supply of oxygen to the muscles.

The normal amount of lactic acid circulating in the blood is about 1 to 2 millimoles/litre of blood. The onset of blood lactate accumulation (OBLA) occurs between 2 and 4 millimoles/litre of blood. In non athletes this point is about 50% to 60% VO2 max and in trained athletes around 70% to 80% VO2 max.