Insoles and compound shooting: Wu 2022 study

Fifteen Taiwanese compound archers at university level, with national competition experience, shot fifteen arrows at 30 metres wearing a flat insole and fifteen more wearing an arch-support insole, standing on a pressure plate. With the arch support the mean score per arrow rose from 9.58 to 9.74 points, a small difference but a consistent one across the group (p < 0.001), worth 2.4 points over the fifteen arrows shot.

The movement of the centre of pressure under the feet shrank almost everywhere. Fore and aft it went from 4.55 to 1.56 centimetres under the left foot (p = 0.022) and from 3.95 to 1.86 under the right (p < 0.001); taking both feet together, from 2.51 to 1.34 centimetres fore and aft and from 6.75 to 2.61 sideways (p = 0.014 in both cases). The area covered by the sway, by contrast, changed only under the right foot, from 9.38 to 8.87 square centimetres (p = 0.033), and did not change under the left foot or overall.

The load was also redistributed: with the arch support the rear of the left foot carried 40.18 per cent of the weight instead of 43.72 (p = 0.016), and the front of the right foot 22.75 instead of 20.21 (p = 0.014). The other two zones did not change.

Every participant held the bow with the left arm and drew with the right, had 7.4 years of practice on average and no limb injury in the preceding six months. A preliminary sample size calculation, based on sway data from an earlier study, indicated that eleven people would be enough.

The test took place indoors, with the target at 30 metres, so as to remove wind, sun and rain. All wore shoes of the same make and model and started with the flat insole, then moved to the arch-support one: the same order for everyone. Fifteen minutes of warm-up with stretching and ten to fifteen arrows came first. In each condition fifteen arrows were shot in ends of three, with two minutes per end and arrow retrieval in between, as in an individual compound match, where an end is worth a maximum of 30 points.

Under the feet was a pressure plate; on the face, at the anchor point, a round pressure sensor 1.8 centimetres across marked the moment the hand arrived in position. The two instruments sampled in synchrony at 1,000 hertz, and five seconds of data were taken from the appearance of the anchor signal. From these came the excursion of the centre of pressure fore and aft and sideways, for each foot and for both together, the resulting area and the share of pressure on four zones, front and rear of each foot. The two insoles were compared with paired t tests.

The authors state two limitations: the test was run indoors and there was no control group. The second one matters more than their wording suggests. Everyone shot first with the flat insole and then with the arch support, with no alternation of the order and no readaptation break: any effect of warming up, of getting used to the plate or of simply progressing through the session lands on the side of the arch support. Nobody could be unaware of which insole they were wearing, which weighs on an outcome such as the score.

The differences are also small: the effect size on the score is 0.38, a value the authors themselves class as small, and none of the measures reaches 0.50. The standard deviations of the sway are huge compared with the means, 4.55 centimetres with a deviation of 4.64 in the left foot: inside that figure sit archers who differ a great deal from each other, and the average tells us little. The sway area, which is the summary measure, did not change on the left foot or across both feet, while the two linear excursions did.

Information that would be needed is missing: the sex of the participants, the shape of their feet, whether they already used insoles, and the article reports a training volume of 36 hours a week that reads like a misprint. Finally, the five second window from the anchor covers aiming and release but is not tied to the instant of release, and the score was collected over fifteen arrows at a single distance.

The idea underneath is familiar to anyone who shoots: a score is built on a base that does not move, and contact with the ground is the last link in the chain. This study is one of the few to try changing something in that link and to measure stability and score together, and to do so on compound archers, who appear in balance studies far less often than recurve ones.

What it found is less sway under the feet and sixteen hundredths of a point more per arrow with an insole that supports the arch. Sixteen hundredths per arrow is nothing and is a great deal, depending on where you compete: over fifteen arrows it comes to 2.4 points. The fact remains that everyone shot first without and then with, which is the easiest way to obtain an improvement, and that the sample is fifteen people.

There is nothing here on which insole, for which foot, nor on what happens after weeks of use; and an insole that changes how the foot loads is something the foot has to digest, not an accessory to try on the day of a competition. Anyone with pain in the foot or the sole falls outside the scope of this study: that is an assessment for a physiotherapist.