Motion analysis in kyudo: Koyama 2018 study

Fifteen students from a Japanese high school kyudo club, with experience ranging from six months to three years, each shot two arrows in front of a video camera. The authors looked at two aspects of kai, the full-draw phase in which the archer holds before the release: how much the position of the right elbow changed between the first and second arrow, and how long kai lasted before the release (hanare).

The elbow was more consistent in the students with more years of practice. The most regular student moved by 0.706 mm in one direction and 0.881 mm in the other between shots; the least regular, a first-year, by 36.274 mm and 9.463 mm. Timing also followed experience: the whole sequence, from raising the bow to the final position, took between 12 and 26 seconds, and between the two arrows it changed by a second at most in the experienced students and by up to 7 seconds in the beginners. The two third-year students, both selected for their prefecture's team at the national games, held kai for 2 seconds on both shots; second-years ranged from 2 to 5 seconds and first-years from 2 to 11. The coach asks for at least 5 seconds, and the authors note that many of the school's most experienced archers held for 2 seconds or less: a sign of hayake, the early release that kyudo regards as one of its most serious faults.

The archers were members of a school club with a coach who has led it for more than thirty years: from first-years who had just started up to third-years, with grades, for those who had one, from third kyu to second dan. Markers were placed on the elbows and wrists and a frontal video camera filmed the shots; using Photron's TEMA software the authors extracted two coordinates in millimetres for the right elbow during kai and compared them between the first and second arrow. The durations of the phases (from raising the bow to the draw, from the draw to kai, from kai to release, from release to the final position) were measured in seconds by the coach.

Each archer shot two arrows because some first-years could not manage more. There is no statistical analysis: the results are shown as charts of individual archers ordered by years of practice. At the end the authors asked the experienced archers why they released so early, and they report their answers.

Two arrows per archer are too few to speak of consistency: a difference between two shots may come down to one poor shot. There is a single frontal camera, so the elbow is tracked in one plane, and the paper does not say how the two coordinates relate to the line of draw. The times were taken by the coach and are given to the nearest second, and the text does not say with what. There is no statistical test, years of practice go together with age and strength, and no measure is linked to the target: we do not know who hit the mato, the target.

The paper was presented at a symposium and did not go through a peer-reviewed journal. The English title refers to archery, but the study is about kyudo alone, with its own bow, its 28 metre distance and its eight-stage sequence. The explanations of hayake, partly physical and partly mental, come from a few of the archers' answers rather than from any measurement.

For archers in western disciplines the study offers no figures to carry over, but it shows two familiar things. The first is that with years of practice the movement settles down even in its details: the elbow returns to almost the same point and the timing from one arrow to the next becomes similar. The second concerns time at full draw: the school's best archers, the ones picked for the national games, released after 2 seconds even though they had been told to hold for at least 5.

The answers collected by the authors describe the problem from the inside: the sense of having found the moment when the arrow goes to the centre, the urge to release before giving way, and the release going off by itself even when trying to hold. In western archery a similar account comes with target panic. The study, though, neither measures nor explains the mechanism, and it does not say whether a longer kai would have helped those archers hit more often.