Lactic Acid
Today I will be writing in reference to an article posted on Velo News.
The link to the article is posted HERE.
Just to get things straight I am going to agree with everything that is written in this particular article. For the most part lactic acid and lactate are used interchangeably for two totally different things. Lactate plays a roll, as shown above, in the production of ATP. In reality Lactate actually serves a purpose and helps us to create more energy. As stated in the article our bodies do create an acid which is simply H+ ions. The H+ ions and Lactate leave the muscule cells together. Because of the 1:1 relationship that the H+ ions have with Lactate, Lactate levels become a good indicator for intensity. The H+ ions cause fatigue in a number of different ways. Keep in mind that H+ ions will lower the PH of blood. When the PH decreases below 6.9 phophofrutokinase becomes inhibited. As PH continues to decrease glycogen breakdown stops at a PHof 6.4. Glycogen breakdown is a main source of short term energy. More research is needed on this last part, but as of now it appears that H+ ions compete for binding sites with Ca++ for troponin binding sites. Troponin and Ca++ are responsible for cross bridge formation and ultimately responsible for muscle contraction. Because the build up of H+ ions can inhibit our bodies ability to exerciese, do work, or live, our bodies must remove the H+ ions. Our bodies contain HCO3 which acts as a buffer for the H+ ions. Ultimately, as the HCO3 buffers the H+ ions breating rate increases because our body has PH sensors. As breathing rate increases H+ levels fall keeping the body in a state of homeostasis. If exercise intensity is increased to a high level then H+ will begin to build up, because the body will not be able to buffer it and expel it through an increased breathing rate. The point where the H+ ions begin to accumulate and increase at an expontential rate is where ones lactate threshold occurs. Once again it is called lactate threshold simply because lactate is used as an indicator for the H+ ions. If the H+ ions continue to build up the athlete will eventually experience failure.
To summarize H+ ions cause the bodies PH to change, as PH changes breathing rate increases, the breathing rate must go up because the HCO3 produces CO2 in the blood, the CO2 must be expelled from the body. The reason your breathing rate goes up is not because you need more oxygen, but because you must get rid of the CO2 in the blood that is ultimately caused by the increase in H+ ions as exercise intensity increases. Next time you do efforts until failure you will know what is ultimately causing your bodies inability to continue.
Sources
Dr. Thomas Barstowe Ex. Physiology course material