Release measured by sound in archers: Heller 2012

Seven recurve archers from the German junior and senior national teams (two men and five women, mean age 24.3) shot 30 arrows at 18 metres indoors while a microphone behind them recorded the sound of every shot. From the audio signal the author picked out three moments: the clicker falling, the shot and the arrow hitting the target. From these he calculated the time between clicker and shot and the arrow's average speed, together with their variation from shot to shot.

Mean time between clicker and shot ranged from 144.40 to 175.96 milliseconds depending on the archer, and its coefficient of variation from 3.94% to 7.25%. Mean score, measured to a tenth of a ring, ranged from 9.42 to 10.13. Of the four variables measured, only the variability of the clicker-to-shot time explained the differences in score: on its own it accounted for 66% of them (adjusted R² 0.66, p = 0.02), and the archers with the most consistent timing had the highest averages. When the analysis was repeated seven times, each time leaving one archer out, the result held, with values between 0.66 and 0.75.

Neither the mean clicker-to-shot time nor arrow speed, mean or variability, was linked to score. The author concludes that what matters is not how quickly the archer reacts after the clicker but how repeatably.

The system uses off-the-shelf parts: an AKG C 480 B microphone at face height about half a metre behind the archer, connected to a Focusrite audio interface recording at 96 kHz and 24 bit, and the free software Audacity. Three sounds can be told apart in the signal: the click of the clicker, the thud of the limbs returning to shape at the end of the power stroke, taken as the moment of the shot, and the impact on the target. Average speed is the flight time over the 18 metres, corrected for the time the sound of the impact takes to travel back to the microphone.

Each archer shot ten ends of three arrows with their own bow, with no time limit, on the 40 cm vertical triple face, and was told to aim for the highest score. Every arrow was scored to a tenth of a ring, with 11 for the exact centre. The four variables (mean and coefficient of variation of clicker-to-shot time and of speed) were entered in a forward stepwise multiple linear regression, with mean score as the outcome.

Seven archers with 30 arrows each is a small sample, as the author acknowledges, and with four candidate variables and seven data points a stepwise regression tends to find a link even where it is weak. Leaving out one archer at a time shows that the result does not depend on a single person, but it is no substitute for a check on a different group. The comparison is between archers: the study does not look at whether, within the same archer, arrows with an unusual timing score worse.

The time measured is not the pure reaction after the clicker: it ends when the limbs return to shape, so it also includes the string pushing the arrow. Archers who are consistent in timing may well be consistent in many other aspects of the shot, and timing variability may be a sign of skill rather than a cause of it. The idea that the shot starts before the click is heard, as a motor programme with no correction on the way, comes from another study: these data are compatible with it but do not test it. Everything was measured at 18 metres indoors, and the author calls for the result to be checked outdoors and at longer distances.

The study shifts the focus from how quickly an archer shoots after the clicker to how consistently. In these seven archers the mean time mattered little, while the variation from shot to shot did: in the archer with the highest average a coefficient of 3.98% on about 176 milliseconds works out at a standard deviation of roughly 7 milliseconds, and in the least consistent 7.25% on about 156 at roughly 11. These are differences of a few milliseconds, hard to perceive, and the study does not say how to work on them.

The most concrete part is the tool. A good microphone, an audio interface and free software are enough to measure the clicker-to-shot time over a training end, without attaching anything to the bow. A coach might use it to follow an archer over time; it does not, however, say what to change if variability is high.