Shot timing and posture in recurve: Lau 2023

Sixteen young recurve archers, 11 boys and 5 girls with a mean age of 16, from the Terengganu state team and the Pahang sports school in Malaysia, shot 36 arrows at 70 metres in front of a side-on video camera. The authors split them into two groups by total score: the eight on 285 out of 360 or more and the eight below. For every shot they then timed four phases and measured how far the elbow of the drawing arm sat off the draw force line.

The median score per arrow was 8 in the better group and 7 in the other. The better group stayed longer at aim (phase 3, from full draw to release: median 3.38 seconds against 2.72), had a shorter phase after the release (phase 4, to the end of the follow-through: 2.40 against 2.72) and took longer over the whole shot (10.46 against 9.74 seconds). The first two phases, raising the bow and drawing, did not differ. Nor did the elbow angle: 4 degrees at anchor in both groups, and 59 and 59.5 degrees after the release.

Pooling all 576 arrows, score was statistically linked to only two measures: the length of phase 4 (r = -0.111) and the elbow angle after the release (r = -0.083). Arrows with a shorter final phase and a less deviated elbow scored slightly more on average, but correlations this low account for about 1% of the variation in score, or less.

The camera (a Sony HDR-CX160) stood on a tripod 1.5 metres from the archer, side-on, at sternum height, and filmed at 30 frames per second. The coach spotted each arrow's score through a telescope, and it was checked again when the arrows were collected. The four phases, taken from a 1993 biomechanics study, were: from raising the bow to the pre-draw; from the pre-draw to full draw and anchor; from full draw to the release, that is, aiming; and from the release to the end of the follow-through. The phases were timed on the video with the free software Kinovea.

For posture the authors placed three reflective markers: on the wrist of the bow hand, on the back of the wrist of the drawing hand and on the point of the elbow. The angle between the line joining the two wrists and the line from wrist to elbow was taken as the elbow's deviation from the draw force line. Anchor posture was measured on the frame before the release and release posture on the tenth frame after it. The groups were compared with the Mann-Whitney test and the links with score with Spearman correlation, using the single arrow as the unit: 288 per group, 576 in all. All the archers were right-handed and none had been injured in the previous three months.

The heaviest limitation is statistical. There are 16 archers, but every comparison treats each arrow as an independent data point: 288 arrows per group, 576 in all. Arrows from the same archer resemble one another, so the very small p values (below 0.001 for phases 3 and 4) say little about how well the difference holds between people. The groups were also formed from the same score, in the same session, in which the times were measured. The two correlations with score likewise reach significance because of the number of arrows, and they remain very weak.

At 30 frames per second the times are accurate to about 3 hundredths of a second, which is enough for phases lasting seconds; the text, though, also says the videos were converted to 0.04 seconds per frame, and it is unclear which figure applies. The elbow angle "at release" is taken ten frames after the string leaves, roughly a third of a second later: it describes where the arm ended up in the follow-through, not the posture at the instant the string leaves the fingers. The view is side-on only and two-dimensional, as the authors acknowledge.

The end of the follow-through has no precise criterion, and its length may also depend on the outcome of the arrow, which the archer sees or senses. The explanations offered (more strength to hold the aim, heavier stabilisers in the better group, time pressure in the weaker one) were not measured. The sample is made up of state-level teenagers who all follow the same Korean technical method, and on aiming time the results run opposite to studies of elite archers, as the authors themselves point out.

The study does not show that aiming for longer earns more points. Among these young archers the better ones stayed at aim about seven tenths of a second longer and finished the shot a little sooner after the release, but aiming time, taken arrow by arrow, was not linked to score. One possible reading is that steadier archers can hold full draw without hurrying while less experienced ones let go sooner; the study does not test this, and other work on world-class archers has found the opposite.

For anyone filming their own shooting, the useful part is the method: an ordinary camera side-on, a tripod and free software are enough to time the phases of a shot and see how consistent they are from one arrow to the next. They are not enough to study the release, which at 30 frames per second falls entirely between two images.

On the elbow the two groups were the same, at about 4 degrees at anchor. The link between elbow position after the release and score is too weak to become a technical rule: it only lends mild support to the idea that arrows shot with the arm finishing more in line tended to land slightly closer to the centre.