Which reaction type occurs in muscles during intense exercise?

During intense exercise, muscles often operate under low oxygen conditions, which leads to a specific type of anaerobic metabolism known as lactic acid fermentation. This process allows for the continuous production of ATP when the demand for energy surpasses the oxygen supply available for aerobic respiration.

In lactic acid fermentation, glucose is partially broken down to produce energy, resulting in the formation of lactic acid as a by-product. This mechanism is vital for short bursts of high-intensity activity, such as sprinting or heavy lifting, where the muscle cells require quick energy but cannot get sufficient oxygen to conduct aerobic respiration efficiently.

In contrast, aerobic respiration, while more efficient in terms of ATP yield, requires oxygen and is not sufficient during short, intense exercise when the body cannot uptake oxygen quickly enough to meet energy demands. Alcoholic fermentation is not relevant in human muscle cells, as it primarily occurs in yeast and some types of bacteria, and the electron transport chain specifically functions during aerobic respiration, again requiring oxygen. Thus, during intense exercise, lactic acid fermentation is the correct and essential pathway for energy production in muscles.