Clicker and final pull: Edelmann-Nusser 2006 study

By gluing a strain gauge to the clicker, the authors measured how many millimetres the draw length changes during the final pull, that is in the two or three seconds in which the archer, having aimed, draws the arrow back until the clicker falls. Seven junior archers, two men and five women aged 16 to 19, all of them competitors at the Junior World Championships and the German national championships, each shot 66 arrows at 30 metres indoors. Mean scores per arrow run from 9.31 points for the first archer to 8.72 for the seventh, with ranges from 8 to 10 for the best two and from 5 to 10 for the last.

The archer with the highest mean started the final pull between three and two seconds before the click and drew the arrow back by about 5 mm in a regular manner: the three curves shown are not identical, but they are very much alike. The second archer split the final pull into two movements, a fast one and then a slow one, and in the last second an increase of about 2.5 mm was enough to take the clicker past the point; he repeated this double action in all 66 shots, with the slow part usually lasting less than two seconds.

In the two archers with the lowest means, the worst arrows showed interruptions. The sixth, in his three shots scoring 5, 6 and 6, stopped pulling when the clicker had almost gone past and let the tension go, so that the draw length decreased, before starting again: this is what archers on the field call shrinking. The seventh, in two of his three worst shots, all scoring 6, stopped without letting the tension go and held the draw length nearly constant for a moment before resuming. All the arrows shown in the figure of ordinary shots, for four different archers, scored 9 or 10. The authors conclude that irregularities, and shrinking in particular, may weigh on the score, and note that among archers of this level the differences in regularity are far less obvious than those described in an earlier study of a mixed-level group.

The clicker is a strip of spring steel 5 cm long and half a centimetre wide, fixed to the window of the riser, which during aiming rests on the shaft a few millimetres behind the point of the arrow. Because of the taper of the point, any movement of the arrow forwards or backwards changes the bending of the strip, and from the known shape of the point the course of the draw length can be reconstructed. The bending was read by a strain gauge (model FAE-A6304J-12-S6E from BLH) glued to the clicker and connected to an amplifier by a thin four-metre cable, which leaves the archer free to move. That was the whole point of the work: the previous method, with an electromechanical device fixed between the grip and the limb, was slow and awkward to mount.

Each archer shot with their own bow, 11 ends of six arrows at 30 metres indoors on an 80 cm ten-ring target face, with no time limit and the instruction to score as highly as possible. The score of each arrow was noted and a mean was worked out for each archer. In the figures the time axis runs from three or four seconds before the clicker falls to the fall itself, taken as time zero, and the vertical scale is 15 mm.

There is no statistical analysis. The link between irregularity and score is a correspondence between the two archers with the lowest means and the bumpiest curves, judged by eye: nobody counted how many irregular final pulls produced low-scoring arrows and how many produced high ones, and those 462 arrows in all remain largely outside the figures, which show three shots per archer chosen as examples, and for the weaker archers the three lowest-scoring ones. Shrinking proper was clearly seen in one archer only.

The archers are seven, all young and all good: the authors themselves say that among athletes of this standard the differences in regularity are faint, which makes the study ill-suited to establishing what an irregularity costs. The measurement is indirect, it depends on the shape of the arrow point and on the clicker's position, and the paper gives neither a measurement error nor a calibration; nor does it say how much of the bending might come from lateral movement of the arrow rather than from movement back and forth. One distance only, indoors, on an 80 cm face. There is also an observation by the authors that cuts against the simple reading: the second archer's pause, which in someone else would be read as a fault, is his own automatism and goes with the second-highest mean in the group.

The study puts numbers on something an archer feels but cannot see: how far the arrow moves during the final pull and over how long. In these juniors the final pull takes the last two or three seconds and moves the arrow by a few millimetres, between about 2.5 and 5 depending on the archer, and in the archer who scored most the shape of that movement repeated itself almost unchanged from one arrow to the next.

The two observations that remain point in different directions. On one side, in the archer who showed it, the worst arrows are the ones in which the draw length went backwards before the click, the shrinking that coaches recognise from the movement itself; on the other, a pull split into a fast part and a slow one, which from outside looks like a pause, belonged to the second-best score in the group, because that archer did it every time. What the study suggests, then, is that repeatability counts for more than the shape of the curve, and it suggests this from seven people read by eye.

On the practical side the main result is the instrument: a strain gauge on a clicker, with a thin cable, gives the course of the draw length immediately after the shot, which is why it became a routine diagnostic tool for the German junior national team. Whether seeing it helps to change it is another question: no archer here was followed while trying to correct their own shrinking.