Editing Lactic acid fermentation (section)

==== Lactate fermentation and muscle cramps====
{{main|Muscle contraction}}
Human (and other eukaryote) cells can produce ATP from glucose without oxygen in a process called [[glycolysis]]. This is not as efficient as respiration, but provides a high instantaneous output, and is hence used by some muscle cells. Glycolysis consumes ADP, Pi, glucose, and NAD+ to produce ATP, pyruvate, and NADH. Through lactate fermentation, pyruvate and NADH are turned into lactate and NAD+, thereby regenerating the NAD+ required for more glycolysis.

During the 1990s, the lactic acid hypothesis was created to explain why people experienced burning or muscle cramps that occurred during and after intense exercise. The hypothesis proposes that a lack of oxygen in muscle cells results in a switch from cellular respiration to fermentation. Lactic acid created as a byproduct of fermentation of pyruvate from glycolysis accumulates in muscles causing a burning sensation and cramps.

Research from 2006 has suggested that acidosis isn't the main cause of muscle cramps. Instead cramps may be due to a lack of [[potassium]] in muscles, leading to contractions under high stress. 

Animals, in fact, do not produce lactic acid during fermentation. Despite the common use of the term lactic acid in the literature, the byproduct of fermentation in animal cells is lactate.<ref name="Robergs">{{cite journal |last1=Robergs |first1=Robert |last2=McNulty |first2=Craig |last3=Minett |first3=Geoffrey |last4=Holland |first4=Justin |last5=Trajano |first5=Gabriel |title=Lactate, not Lactic Acid, is Produced by Cellular Cytosolic Energy Catabolism |journal=Physiology |date=December 12, 2017 |volume=33 |issue=1 |pages=10–12 |doi=10.1152/physiol.00033.2017 |pmid=29212886 |url=https://journals.physiology.org/doi/full/10.1152/physiol.00033.2017}}</ref> 

Another change to the lactic acid hypothesis is that when sodium lactate is inside of the body, there is a higher period of exhaustion in the host after a period of exercise.<ref>{{cite journal | vauthors = Cairns SP | title = Lactic acid and exercise performance : culprit or friend? | journal = Sports Medicine | volume = 36 | issue = 4 | pages = 279–91 | date = 2006-04-01 | pmid = 16573355 | doi = 10.2165/00007256-200636040-00001 | s2cid = 765242 }}</ref>