Editing Marathon (section)

===Glycogen and "the wall"===
{{Main|Hitting the wall}}
[[Carbohydrate]]s that a person eats are converted by the [[liver]] and [[muscle]]s into [[glycogen]] for storage. Glycogen burns rapidly to provide quick energy. Runners can store about 8 [[joule|MJ]] or 2,000 [[calorie|kcal]] worth of glycogen in their bodies, enough for about 30&nbsp;km/18–20 miles of running. Many runners report that running becomes noticeably more difficult at that point.<ref>{{cite web|url=http://www.half-marathon-running.com/HittingTheWall |archive-url=https://web.archive.org/web/20170322111711/http://www.half-marathon-running.com/HittingTheWall |url-status=dead |archive-date=22 March 2017 |title=Hitting the wall for marathon runners |publisher=Half-marathon-running.com |access-date=22 August 2009 }}</ref> When glycogen runs low, the body must then obtain energy by burning stored fat, which does not burn as readily. When this happens, the runner will experience dramatic [[fatigue]] and is said to "[[hitting the wall|hit the wall]]". The aim of training for the marathon, according to many coaches,<ref name=glyco>{{cite web |url=http://e-articles.info/e/a/title/Lesser-Known-Dangers-Associated-With-Marathons/ |title=Lesser-known Dangers Associated with Running a Marathon |last=Klein |first=Michael |date=3 October 2008 |work=E-articles.info |archive-url=https://web.archive.org/web/20130117044405/http://e-articles.info/e/a/title/Lesser-Known-Dangers-Associated-With-Marathons/ |archive-date=17 January 2013}}</ref> is to maximize the limited glycogen available so that the fatigue of the "wall" is not as dramatic. This is accomplished in part by utilizing a higher percentage of energy from burned fat even during the early phase of the race, thus conserving glycogen.{{citation needed|date=July 2012}}

Carbohydrate-based "[[energy gel]]s" are used by runners to avoid or reduce the effect of "hitting the wall", as they provide easy to digest energy during the run. Energy gels usually contain varying amounts of sodium and potassium and some also contain caffeine. They need to be consumed with a certain amount of water. Recommendations for how often to take an energy gel during the race range widely.<ref name=glyco />

[[File:Boston marathon mile 25 helper 050418.jpg|thumb|A runner getting encouragement at Mile 25 of the Boston Marathon]]
Alternatives to gels include various forms of concentrated sugars, and foods high in simple carbohydrates that can be digested easily. Many runners experiment with consuming energy supplements during training runs to determine what works best for them. Consumption of food while running sometimes makes the runner sick. Runners are advised not to ingest a new food or medicine just prior to or during a race.<ref name=glyco /> It is also important to refrain from taking any of the non-steroidal anti-inflammatory class of pain relievers ([[NSAIDs]], e.g., [[aspirin]], [[ibuprofen]], [[naproxen]]), as these drugs may change the way the kidneys regulate their blood flow and may lead to serious kidney problems, especially in cases involving moderate to severe dehydration. NSAIDS block the [[COX-2]] enzyme pathway to prevent the production of prostaglandins. These prostaglandins may act as inflammation factors throughout the body, but they also play a crucial role in maintenance of water retention. In less than 5% of the whole population that take NSAIDS, individuals may be more negatively sensitive to renal prostaglandin synthesis inhibition.<ref>{{cite journal|last=Brater|first=D. Craig|title=Effects of nonsteroidal anti-inflammatory drugs on renal function: focus on cyclooxygenase −2–selective inhibition|journal=The American Journal of Medicine|date=17 January 2000|volume=107|issue=6|pages=65–70|doi=10.1016/S0002-9343(99)00369-1|pmid=10628595}}</ref>