This week I am writing on the side of lactate build up is advantageous during exercise.
The author argued for that lactic acid accumulation inside muscle fibers is not responsible for muscle fatigue. In fact, the reason that muscle fatigue occurs is due to the disturbance of any of the steps in excitation-contraction (EC) coupling in muscles. There are several types of muscle fatigue, and each one is caused by different attributes of exercise. One major type of fatigue is caused by the buildup of potassium ions in the transverse-tubular or T tubular systems. The other type of fatigue occurs by direct or indirect effects of the accumulation of metabolites, as we discussed in class earlier this week. And finally, the reduction of calcium ions released from the sarcoplasmic reticulum (SR) can indirectly cause muscle fatigue.
Lactate ions in the cytoplasm of muscle cells, even at high concentrations, do not impair EC coupling. Along with this, high concentrations of hydrogen ions, a by-product of the breakdown of lactate, has few, if any, harmful effects on EC coupling. This is because normal controlled calcium release is little, if at all, inhibited by low pH, which would incur with high concentrations of hydrogen ions in the body. In fact, in a single intact muscle fiber, decreasing pH from 7.1 to less than 6.7 does not cause or accelerate the onset of fatigue, but actually slows its onset! An increase in intracellular acidity can increase cytoplasmic calcium and consequent activation of contractile apparatus, because SR calcium pumps bind and requester calcium even more so at acidic pHs. This would actually reverse the reduction of calcium ions, which as I mentioned above, is one of the causes of muscle fatigue.
Another cause I mentioned, is the accumulation of metabolites during exercise. I found an article on google scholar (did not find one I liked on pubmed,) that researched biomarkers of peripheral muscle fatigue during exercise. The article kept mentioning how their was an increase in lactic acid accumulation in increased exercise intensity and how that proved muscle fatigue, however gave no evidence to support that. Meanwhile, they were mentioning other metabolites that we spoke of earlier this week, such as ammonia, hypoxanthine and xanthine, that have been proven to disrupt EC coupling.
Lactate is helping us out people! We <3 lactate.
Source: https://bmcmusculoskeletdisord.biomedcentral.com/articles/10.1186/1471-2474-13-218
