Archers' balance and visual disturbance: Wada 2020

The study compares 24 archers, 35 ball-sport athletes (tennis, baseball, football and rugby) and 34 people who did no sport, all in their early twenties. Each stood on a platform inside a large box dotted on the inside; at a given moment the box suddenly moved towards them and then swung back and forth, with ever smaller movements. To the person watching it looks as if the surroundings are moving, and the body tends to follow.

In all three groups the forward-backward sway of the centre of pressure jumped as soon as the box started, then settled. The difference lay in how quickly balance came back. In the first trial the archers swayed significantly less than the non-athletes at 15 and 20 seconds after the start and less than the ball-sport athletes at 20 seconds; in the second the difference from the non-athletes at 15 and 20 seconds remained; in the third the three groups could no longer be told apart. In the preliminary trial, done with eyes closed, sway did not change in any group.

The authors infer that archers rely less on vision to keep their balance and more on information from muscles and joints, and that it is archery training that shifts this weighting. They explain the disappearance of the differences in the third trial by anticipation: after two repetitions everyone knew what was coming and the body prepared for it.

The box measured 150 by 120 by 70 centimetres. After the preliminary trial with eyes closed, participants stood in socks with their feet on drawn outlines, so the stance was always the same, and looked at the dots while the box moved towards them and then swung at 0.42 Hz for 60 seconds with a damped amplitude. The sequence was repeated three times in a row. A stabilometer recorded side-to-side and forward-backward movement of the centre of pressure separately, at 100 samples per second with a 10 Hz filter. The authors calculated the standard deviation of the signal over 5-second windows, from 10 seconds before to 25 seconds after the box started, and compared the groups window by window with the Wilcoxon rank-sum test.

The archers were 10 men and 14 women with a mean age of 21.1 years; the ball-sport athletes 21 men and 14 women (21.3 years); the non-athletes 17 and 17 (22.9 years). Nothing is said about bow type, level or years of shooting. The data are old: the study was completed before July 2003 and a short abstract appeared in 2004 in a Japanese balance research journal; the full paper came out in 2020.

Of the three groups only the archers matter here, and almost nothing is known about them: not their discipline, not their level, not how long they had been shooting. The comparison is cross-sectional, so it cannot say whether archery changes the way people balance or whether those who already rely less on vision get on better in archery; the role of training is the authors' hypothesis. The proprioceptive explanation is inferred too, since nobody measured proprioception: the same result could be read as a different habit of not being pulled along by movement at the edges of the visual field.

The findings are few and fragile. The paper shows them only in a graph, with no numerical values or effect sizes; there are many comparisons (three groups, seven windows, three trials) and no correction for multiple testing; the differences appear in two windows out of seven and vanish on the third repetition. Side-to-side sway was recorded but does not appear in the results, apart from one example trace. Finally, the stimulus is far from shooting: on the platform people stand without a bow looking at moving dots, whereas on the line the archer looks at a still target with the bow at full draw.

For anyone who shoots, the study says little directly. It suggests that archers, faced with a visual disturbance filling the whole field of view, regain their balance a few seconds sooner than ball-sport athletes or people who do no sport. This fits the idea that stability on the line draws on what the feet and body feel and not only on the eyes, but it does not demonstrate it, because nothing about shooting was measured: neither aiming nor score.

Similar situations do occur in competition, such as flags and banners moving at the sides, spectators, or the archer next to you shifting on the line. The study did not test them and says nothing about how much they affect aiming. It only shows that in the laboratory the difference between archers and non-archers appeared in a couple of 5-second windows, of unknown size, and disappeared once the disturbance became predictable.