On the asymmetric Japanese bow the two limbs deform differently
3 studies
The summary today
Two bench tests, each on a single bow, find that the yumi's two limbs do not deform in the same way, and on that they agree. Where they disagree is on which tip moves more. In the first, from 2013, a carbon yumi drawn to about 700 millimetres with 300 newtons moves its upper tip by about 240 millimetres and its lower tip by about 180; after the release, though, the two tips oscillate with similar amplitudes, the upper one lagging in phase, and the motion dies out in about three seconds. In the second, from 2019, a commercial shihan-yumi measured over nine sections shows the opposite at the tips: the long limb, above the grip, rotates and bends along its whole length, so its tip moves little, while the short one rotates with little bending and its tip moves more. The difference may come down to the bows: the 2019 one has a ratio between its two sections of about 6 to 4, against the 2 to 1 of a standard-length yumi. That the upper limb does more work is also stated in a 2017 review of the materials of the Kyoto bow, but as a description of how the bow is built, not as a measurement.
Also phrased as: "yumi asymmetry"; "upper and lower limb of the Japanese bow"; "grip below the middle"; "asymmetric kyudo bow"; "yumi tips at full draw"
In practice
It is explained that the yumi is held about a third of the way up and that, for this reason, the longer upper limb works differently from the lower one, and that the bow hand has to make up for this asymmetry at the release.
Evidence
-
2013
For Equipment tests Published later
A carbon yumi on the bench, draw of about 700 millimetres, horizontal force 300 newtons: the upper tip moves by about 240 millimetres, the lower by about 180.
Motion Analysis of the Japanese Bow for Archery · Hajime Shoji, Shinya Hashimoto, Toshiaki Sakurai, Ikuo Hibino
-
2013
Context Equipment tests Published later
After the release the two tips oscillate with amplitudes of the same order, despite starting from very different deflections, with the upper tip lagging in phase; the motion has died out within about 3 seconds (video measurement).
Motion Analysis of the Japanese Bow for Archery · Hajime Shoji, Shinya Hashimoto, Toshiaki Sakurai, Ikuo Hibino
-
2013
Context Equipment tests Published later
A rigid-body model with torsional springs reproduces the upper limb well, 240 millimetres measured against 230 calculated, but not the lower, 180 against 220.
Motion Analysis of the Japanese Bow for Archery · Hajime Shoji, Shinya Hashimoto, Toshiaki Sakurai, Ikuo Hibino
-
2017
Context Equipment tests Published later
Review of the materials of Kyoto bows: base length of about 220 centimetres, a three-layer section (outer bamboo, core of different woods, inner bamboo) and the grip below the middle, so that the upper limb deforms much more than the lower. It is a structural description, with no measurement of displacement.
Materials Technology in Kyoto Bow · Hiroyuki Hamada
-
2019
For Equipment tests Published later
Commercial shihan-yumi with a ratio between its two sections of about 6 to 4, measured over nine sections and compared with a large-deflection model: the long limb rotates and bends along its whole length, so its tip moves relatively little; the short one rotates with little bending, and its tip moves more. Measurements and model agree.
Nonlinear Dynamic Analysis of a Japanese bow (Nonlinear Spring Characteristics and Dynamic Behavior) · Atsumi Ohtsuki, Shigemichi Ohshima
-
2019
Context Equipment tests Published later
The limb tips do almost all their moving in the first part of the draw, then move little and the movement turns horizontal; the angles at the two tips also change a great deal at first and then grow at an almost steady rate. Experimental and theoretical values agree well.
Nonlinear Dynamic Analysis of a Japanese bow (Nonlinear Spring Characteristics and Dynamic Behavior) · Atsumi Ohtsuki, Shigemichi Ohshima
-
2019
Context Equipment tests Published later
The bow tested is a 4.2 kg shihan-yumi, 164 centimetres long with a 157 centimetre string, mass 270 grams, with a ratio between the sections above and below the grip of about 6 to 4, against about 2 to 1 for a standard-length yumi: less asymmetric than usual.
Nonlinear Dynamic Analysis of a Japanese bow (Nonlinear Spring Characteristics and Dynamic Behavior) · Atsumi Ohtsuki, Shigemichi Ohshima
Status history
- 2013 Reported The first bench test, on a carbon yumi, measures the tips on video: at full draw, about 700 millimetres and 300 newtons, the upper tip moves by about 240 millimetres against 180 for the lower. After the release the two tips oscillate with similar amplitudes, the upper one lagging in phase, and the motion dies out in about three seconds; a rigid-body model reproduces the upper limb well, 230 millimetres calculated against 240, but not the lower, 220 against 180. A single bow, at a regional symposium: reported.
- 2017 Reported The structural explanation arrives, in a review of the materials of the Kyoto bow: a laminate of outer bamboo, a core of different woods and inner bamboo, about 220 centimetres long, with the grip below the middle, so that the upper limb deforms much more than the lower. It says why the two limbs should work differently, but does not measure the displacement: the basis is still the 2013 test, and the status does not change.
- 2019 Reported A second bench test, on a commercial 4.2 kg shihan-yumi measured over nine sections with a millimetre grid and a protractor, confirms that the two limbs work differently, but not in the way the first found: the long limb rotates and bends throughout and its tip moves little, the short one bends little and its tip moves more. The tips, moreover, do almost all their moving in the first part of the draw. Two tests in favour, but on one bow each and at odds over which tip moves more, with the 2019 bow less asymmetric than usual: they are not enough to reach corroborated, and the status stays reported.
Related
Related articles
Research lines
Cite
Campagna, M. (2026). On the asymmetric Japanese bow the two limbs deform differently (Version 1). In Evidence Registry. Retrieved 16 October 2026, from https://matteocampagna.com/en/registry/equipment/japanese-bow-asymmetric-limbs
@misc{campagna2026_yumiflettentiasimmetrici,
author = {Campagna, Matteo},
title = {On the asymmetric Japanese bow the two limbs deform differently},
year = {2026},
howpublished = {Evidence Registry, matteocampagna.com},
url = {https://matteocampagna.com/en/registry/equipment/japanese-bow-asymmetric-limbs},
note = {Version 1; accessed 2026-10-16}
}
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