Final answer:
Lactic acid fermentation is less efficient than cellular respiration, producing only 2 ATPs per glucose molecule and leading to the accumulation of lactic acid which can cause muscle fatigue. It is a short-term solution during high-intensity exercise when oxygen is limited.
Step-by-step explanation:
Lactic acid fermentation in muscle cells is considered not as good a use of glucose as cellular respiration because it is much less efficient in producing adenosine triphosphate (ATP). During cellular respiration, one glucose molecule can produce up to 36 to 38 ATPs, while lactic acid fermentation yields only 2 ATPs per glucose molecule. Additionally, lactic acid fermentation leads to the accumulation of lactic acid in the muscles, which may contribute to muscle fatigue. This is particularly evident during intense exercise when the body's demand for energy exceeds the oxygen supply, and cells resort to lactic acid fermentation to maintain ATP production.
Lactic acid fermentation allows the recycling of NAD+ from NADH, which is crucial for glycolysis to continue. However, this pathway is not sustainable for long-term energy needs due to its low efficiency and the by-products that can contribute to muscle discomfort. The lactic acid produced can be transported out of the muscles and converted back into usable energy in the liver via the Cori cycle, but this process requires additional oxygen, contributing to the notion of "oxygen debt" after intense exercise.