The idea that lactic acid buildup causes muscle fatigue is preposterous. Lactic acid buildup is not only irresponsible for the fatigue and decreased muscular performance, but rather other sources of fatigue can be discovered in different muscle groups. During performance it can be observed that the excitation-contraction coupling steps are impaired when under high stress. One example of this can be observed in the transverse-tubular system has a buildup of potassium ions. This system is in the direct vicinity of muscle-fibers, so a buildup of ions during exercise would impair the muscle fibers’ abilities to keep sodium ion equilibrium. A buildup of inactive sodium inside the fibers leads to the inactivation of action potentials, and in turn a slower functioning muscle fiber.
Another explanation for the fatigue and limited performance of muscles can be observed in the accumulation of metabolites coupled with a limited level of substrate. When muscle fibers (especially fast-twitch muscle fibers) exert energy, they utilize a wide variety of substrates to fuel themselves. In many cases, a great increase in energy use in fast-twitch fibers can cause ATP in the tissues to decrease to extremely low levels, and subsequently a decrease in the glycogen stores as the cells try to keep up with the rate of ATP use.
Since lactate does not affect the excitation-coupling steps it can be determined that it is not responsible for muscle fatigue. The higher level of hydrogen ions do not lead to any change in the pathway, or a greater production of metabolites that would lead to muscle fatigue. It could even be argued that the lower pH brought on with higher lactate concentrations actually aid the muscles in fighting fatigue, as chloride ions are retained better and action potentials can be maintained when the cell is functioning at a high rate. In the absence of lactate it has been observed that the action potentials are inhibited faster, and this is directly related to muscle fatigue and performance.
The point-counter point argument has been explored further in other articles as well. A study found in the American Physiological Society determined that the cause of muscle fatigue during high-intensity exercises was not actually lactic acid buildup, but rather a buildup of phosphate ions due to the breakdown of creatine phosphates. During high-intensity exercises our bodies rely on anaerobic sources of energy, so increased lactate levels should be irrelevant to the function and fatigue of muscle cells. This falls in line with the claim made in the point-counterpoint article, and further goes to show why lactic acid buildup does not affect the function or fatigue of muscular tissues.
Works Cited
Westerblad, Håken, et al. “Muscle Fatigue: Lactic Acid or Inorganic Phosphate the Major Cause?” Physiology, American Physiological Society, 1 Feb. 2002, www.physiology.org/doi/full/10.1152/physiologyonline.2002.17.1.17.
