Yumi History of the yumi . Early Japanese used bows of various sizes but the majority were short with a center grip . By the 3rd century BC , the bow length had grown to nearly 2 meters . This bow was called the " maruki yumi " and was constructed from a small sapling or tree limb . It is unknown when the " asymmetrical " yumi came into use but the first written record is in a Chinese manuscript from the 3rd century AD which describes the people of the Japanese islands using " a wooden bow with upper and lower limbs of different lengths , and bamboo arrows with points of bone or iron " . The oldest asymmetrical yumi found to date was discovered in Nara and is estimated to be from the 5th century . During the Heian period ( 794 - 1185 ) the length of the " yumi " was fixed at a little over two meters and the use of laminated construction was adopted from the Chinese . By the end of the 10th century the Japanese developed a two piece bamboo and wood laminated " yumi " . Over the next several hundred years the construction of the " yumi " evolved and by the 16th century the design of the " yumi " was considered to be nearly perfect . The modern bamboo " yumi " is practically identical to the " yumi " of the 16th and 17th centuries . Shape . The yumi is exceptionally tall , standing over two meters , and surpassing the height of the archer ( " ite " , 射手 ) . They are traditionally made by laminating bamboo , wood and leather , using techniques which have not changed for centuries , although some archers ( particularly beginners ) may use a synthetic yumi . The yumi is asymmetric ; According to the All Nippon Kyudo Federation , the grip has to be positioned at about two thirds of the distance from the upper tip . The upper and lower curves also differ . Several hypotheses have been offered for this asymmetric shape . Some believe it was designed for use on a horse , where the yumi could be moved from one side of the horse to the other with ease . However , the grip position had emerged before horseback archery became widespread in Japan . Others claim that asymmetry was needed to enable shooting from a kneeling position . Yet another explanation is the characteristics of the wood from a time before laminating techniques . In case the bow is made from a single piece of wood , its modulus of elasticity is different between the part taken from the treetop side and the other side . A lower grip balances it . Yet another theory is that the hand holding the yumi experiences less vibration at this point . The points one and two thirds of the distance from the upper tip are the nodes . This makes it easier for the archer to grip the yumi after shooting an arrow . String . The string of a yumi is traditionally made of hemp , although most modern archers will use strings made of synthetic materials such as Kevlar , which will last longer . Strings are usually not replaced until they break ; this results in the yumi flexing in the direction opposite to the way it is drawn , and is considered beneficial to the health of the yumi . The nocking point on the string is built up through the application of hemp and glue to protect the string and to provide a thickness which helps hold the nock of the arrow in place while drawing the yumi . Care . A bamboo yumi requires careful attention . Left unattended , the yumi can become out - of - shape and may eventually become unusable . The shape of a yumi will change through normal use and can be re - formed when needed through manual application of pressure , through shaping blocks , or by leaving it strung or unstrung when not in use . The shape of the curves of a yumi is greatly affected by whether it is left strung or unstrung when not in use . The decision to leave a yumi strung or unstrung depends upon the current shape of the yumi . A yumi that is relatively flat when unstrung will usually be left unstrung when not in use ( a yumi in this state is sometimes referred to as being ' tired ' ) . A yumi that has excessive curvature when unstrung is typically left strung for a period of time to ' tame ' the yumi . A well cared - for yumi can last many generations , while the usable life of a mistreated yumi can be very short . Yumi history . The Korekawa bow , from the late Jōmon period which ended about 400 BCE , is laminated .