The more a Japanese bow's limbs curve outwards at rest, the heavier it is to draw
1 study
The summary today
There is only a calculation, from 2019. Two Japanese authors built a large-deformation model of the Japanese bow, asymmetric and divided into nine segments, checked it statically against a commercial bow and then varied, within the model, the curvature the segments have at rest. At equal draw, the force on the string comes out almost proportional to how much the bow is curved at rest, and the effect fades as the draw lengthens. Not all curvature works the same way, though: increasing the curvature of the three central segments raises the force, while bending the two sections between the grip and the tips further inwards lowers it. So what counts is which part of the limb is curved and in which direction, not curvature in general. The registry holds no draw-force measurement of real bows with different curvatures and everything else equal: the claim rests on a model.
Also phrased as: "curvature of the Japanese bow"; "yumi shape at rest"; "limb reflex and draw weight"; "more curved yumi, heavier draw"
In practice
Among Japanese bow archers it is said that the more the bow curves at rest, the harder it is to draw.
Evidence
-
2019
For Model Published later
A theoretical large-deformation model of an asymmetric Japanese bow, with the initial curvature of the segments varied in the calculation: at equal draw distance the force is almost proportional to the amount of initial curvature (conclusion 5), and the change in force due to initial curvature tends to shrink as the draw lengthens (conclusion 6).
Nonlinear Dynamic Analysis of a Japanese bow (Nonlinear Spring Characteristics and Dynamic Behavior) · Atsumi Ohtsuki, Shigemichi Ohshima
-
2019
Context Model Published later
In the nine-segment model, checked statically against a commercial shihan-kyū bow, increasing the positive curvature of central segments 4, 5 and 6 raises the force on the string (conclusion 1), while making the initial curvature of segments 3 and 7, the sections between the grip node and each tip, more negative, that is more inward, lowers it (conclusion 2). It is not curvature in general that makes a bow heavy: it depends on which section bends and in which direction.
Nonlinear Dynamic Analysis of a Japanese bow (Nonlinear Spring Characteristics and Dynamic Behavior) · Atsumi Ohtsuki, Shigemichi Ohshima
Status history
- 2019 Transferred The only work on the subject arrives, and it is a calculation: in a nine-segment model of the Japanese bow, checked statically against a commercial bow, the force at equal draw is almost proportional to curvature at rest, with an effect that shrinks at longer draws. The calculation also says that not all curvature counts the same way: bending the sections between the grip and the tips further inwards lowers the force. With no measurement on real bows of different curvature, the claim rests on the model alone: transferred.
Related
Related articles
Research lines
Cite
Campagna, M. (2026). The more a Japanese bow's limbs curve outwards at rest, the heavier it is to draw (Version 1). In Evidence Registry. Retrieved 16 October 2026, from https://matteocampagna.com/en/registry/equipment/japanese-bow-limb-curvature-draw-force
@misc{campagna2026_flettentireflexdurezza,
author = {Campagna, Matteo},
title = {The more a Japanese bow's limbs curve outwards at rest, the heavier it is to draw},
year = {2026},
howpublished = {Evidence Registry, matteocampagna.com},
url = {https://matteocampagna.com/en/registry/equipment/japanese-bow-limb-curvature-draw-force},
note = {Version 1; accessed 2026-10-16}
}
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