Editing Grasshopper (section)

=== Jumping ===

Grasshoppers jump by extending their large back legs and pushing against the substrate (the ground, a twig, a blade of grass or whatever else they are standing on); the reaction force propels them into the air.<ref>{{cite web |last1=Heitler |first1=W.J. |title=How Grasshoppers Jump |url=http://www.st-andrews.ac.uk/~wjh/jumping/ |publisher=University of St Andrews |access-date=3 April 2015 |date=January 2007 |url-status=live |archive-url=https://web.archive.org/web/20150924123105/http://www.st-andrews.ac.uk/~wjh/jumping/ |archive-date=24 September 2015 }}</ref> A large grasshopper, such as a locust, can jump about a metre (20 body lengths<!--5 cm body=1/20 m-->) without using its wings; the acceleration peaks at about 20&nbsp;g.<ref>{{cite web |last1=Heitler |first1=W.J. |title=Performance |url=http://www.st-andrews.ac.uk/~wjh/jumping/perform.htm |publisher=University of St Andrews |access-date=13 April 2015 |date=January 2007 |url-status=live |archive-url=https://web.archive.org/web/20150319133858/http://www.st-andrews.ac.uk/~wjh/jumping/perform.htm |archive-date=19 March 2015 }}</ref>

They jump for several reasons; to escape from a predator, to launch themselves into flight, or simply to move from place to place. For the escape jump in particular there is strong selective pressure to maximize take-off velocity, since this determines the range. This means that the legs must thrust against the ground with both high force and a high velocity of movement. A fundamental property of [[muscle contraction#Force-length and force-velocity relationships|muscle]] is that it cannot contract with high force and high velocity at the same time. Grasshoppers overcome this by using a [[catapult]] mechanism to amplify the [[Power (physics)#Mechanical power|mechanical power]] produced by their muscles.<ref>{{cite web |last1=Heitler |first1=W.J. |title=Energy and Power |url=http://www.st-andrews.ac.uk/~wjh/jumping/power.htm |publisher=University of St Andrews |access-date=5 May 2015 |date=January 2007 |url-status=live |archive-url=https://web.archive.org/web/20141118101313/http://www.st-andrews.ac.uk/~wjh/jumping/power.htm |archive-date=18 November 2014 }}</ref>

The jump is a three-stage process.<ref>{{Cite journal | doi = 10.1007/BF00219055|pmid=7707268| title = Motor patterns during kicking movements in the locust| journal=Journal of Comparative Physiology A| volume = 176| issue = 3 |pages=289–305| year=1995| last1=Burrows | first1 = M.|s2cid=21759140}}</ref> First, the grasshopper fully flexes the lower part of the leg (tibia) against the upper part (femur) by activating the flexor tibiae muscle (the back legs of the grasshopper in the top photograph are in this preparatory position). Second, there is a period of co-contraction in which force builds up in the large, [[Pennate muscle|pennate]] extensor tibiae muscle, but the tibia is kept flexed by the simultaneous contraction of the flexor tibiae muscle. The extensor muscle is much stronger than the flexor muscle, but the latter is aided by specialisations in the joint that give it a large effective mechanical advantage over the former when the tibia is fully flexed.<ref>{{cite journal |author= Heitler, W.J. |year= 1977 |title= The locust jump III. Structural specialisations of the metathoracic tibiae |journal= Journal of Experimental Biology |volume= 67 |pages= 29–36 |doi= 10.1242/jeb.67.1.29 |url= http://jeb.biologists.org/content/jexbio/67/1/29.full.pdf |url-status= live |archive-url= https://web.archive.org/web/20161019094114/http://jeb.biologists.org/content/jexbio/67/1/29.full.pdf |archive-date= 19 October 2016 }}</ref> Co-contraction can last for up to half a second, and during this period the extensor muscle shortens and stores elastic strain energy by distorting stiff cuticular structures in the leg.<ref>{{Cite journal | pmid=1159370 | year=1975 | last1=Bennet-Clark | first1=H.C. | title=The energetics of the jump of the locust ''Schistocerca gregaria'' | journal=The Journal of Experimental Biology | volume=63 | issue=1 | pages=53–83 | doi=10.1242/jeb.63.1.53 | url=http://jeb.biologists.org/content/63/1/53.1.long | url-status=live | archive-url=https://web.archive.org/web/20170103003849/http://jeb.biologists.org/content/63/1/53.1.long | archive-date=3 January 2017 | url-access=subscription }}</ref> The extensor muscle contraction is quite slow (almost isometric), which allows it to develop high force (up to 14&nbsp;N in the desert locust), but because it is slow only low power is needed. The third stage of the jump is the trigger relaxation of the flexor muscle, which releases the tibia from the flexed position. The subsequent rapid tibial extension is driven mainly by the relaxation of the elastic structures, rather than by further shortening of the extensor muscle. In this way the stiff cuticle acts like the elastic of a [[catapult]], or the bow of a bow-and-arrow. Energy is put into the store at low power by slow but strong muscle contraction, and retrieved from the store at high power by rapid relaxation of the mechanical elastic structures.<ref>{{cite book |author=Biewener, Andrew A. |title=Animal Locomotion |url=https://books.google.com/books?id=yMaN9pk8QJAC&pg=PA172 |year=2003 |publisher=Oxford University Press |isbn=978-0-19-850022-3 |pages=172–175 |url-status=live |archive-url=https://web.archive.org/web/20171127023307/https://books.google.com/books?id=yMaN9pk8QJAC&pg=PA172 |archive-date=27 November 2017 }}</ref>