Archery technique and EMG: Nishizono 1987 study

Two Japanese studies presented together at a biomechanics conference. In the first, eleven channels of electromyography were recorded on five men aged 18 to 28: two beginners with three months of shooting, one middle-level archer with five years, and two champions, the winner of the 1978 All Japan field championship and the winner of the 1981 US Open. The two best had a higher maximal drawing strength (36.2 and 40.2 kilograms against 29.7, 34.1 and 31.1) and a wider finger stretch.

In the beginners' traces, what stands out is strong biceps activity, an imbalance between the muscles of the right and left sides (trapezius and deltoid) and a sudden discharge on the right at the moment of release. In the two champions the picture is the reverse: a very active deltoid and a weak biceps during the draw, similar activity on both sides, a clear cessation of muscle activity at the instant of release, and back and shoulder activity that stays at the same level for 1.5 to 1.7 seconds after the release instead of switching off at once.

The second study puts numbers on that cessation, which the authors call the silent period. Twelve men aged 18 to 24, split into three groups by their usual scores, shot 20 arrows at 8 metres, at intervals of 15 to 20 seconds. In the best group the deltoid silence appeared in 70% to 100% of shots, with a latency of 110 to 120 milliseconds from the clicker and a release reaction time of 170 to 180 milliseconds; in the other two groups it appeared less often. During the deltoid silence the pectoralis major stayed almost still, a sign that this is not simple reciprocal inhibition between agonist and antagonist, and the extensor digitorum began to act precisely while the deltoid was silent. Filming at 200 frames per second shows the fingers starting to open 25 milliseconds before the release, with arm and shoulder steady.

In the first study, signals were collected from eleven sites: trapezius, deltoid, biceps, triceps and flexor carpi ulnaris on both sides, plus the extensor digitorum on the right. A strain gauge fitted to the bow and a high-speed cine camera were used to identify the instant of release. The results are presented as traces, one archer per figure, alongside the bow strain curve and the sequence of body positions at intervals of five hundredths of a second (1.3 hundredths for one of the two champions).

In the second study the twelve participants, healthy and without neurological disorders, were split into three skill groups according to their usual mean score. Each shot 20 arrows from a line 8 metres from the target, with 15 to 20 seconds between arrows. The strain gauge on the bow gave bow strain and the moment of release; an electrical contact on the clicker, the metal strip fixed to the side of the bow, gave the signal that starts the reaction. A camera at 200 frames per second filmed the movement of the hand. For each participant, five traces of deltoid, pectoralis major and extensor digitorum were superimposed, aligned on the release signal, and from these came the rate at which the silent period appeared, its latency from the clicker, and the time from the clicker to the mechanical response of the bow.

Five archers in the first study and twelve in the second, and in the first the results are single traces commented on in words: there is no statistics, no mean, no quantified comparison between skill groups. What one reads is the authors' description of their own figures. In the second study, level is defined by the usual mean score, but those scores are not reported, the number of archers in each of the three groups is not stated, and the rate at which the silence appears is given as a range for the best group with no comparative test.

The distance of 8 metres makes the shot a laboratory movement: at that range the target is not a precision task, and the scores of the arrows analysed were not recorded, so whether the silent period goes with good arrows or merely with good archers is unknown. Bow type and draw weight are not given in either study.

The figure of 18 kilograms of tension released at the loose is read off a single trace. Surface electromyography on the forearm also picks up neighbouring muscles, and the extensor digitorum was recorded only on the right, that is, on a string hand assumed to be the right one for everybody. The document is a nine-page conference paper, reviewed differently from a journal article, and the available copy is a scan with some character recognition errors.

This is the oldest source in the registry on the deltoid silent period, the observation that in the best archers the activity of the muscle holding the draw switches off for an instant around the release. Here it is seen in the two champions of the first study and in the best group of the second, where it appeared in seven shots out of ten and in some archers in all of them.

For someone who shoots, the useful reading is not the silence itself, which nobody can feel or decide on, but the timings around it: less than two tenths of a second passed between the clicker and the string leaving, the fingers began to open a fortieth of a second before that, and through that interval arm and shoulder stayed still. What is a single movement for the archer is, in the traces, a sequence with a definite order.

The other part, the comparison between beginners and champions on how the work is shared out, should be taken as a description of two traces rather than as a criterion: back and shoulders active instead of the biceps, the two sides symmetrical, a follow-through held for more than a second. These are three observations on two archers, collected in 1987, which come back in later work but are not quantified here.