Muscle activity in kyudo: Kamei 1971 study

One of the first studies anywhere in which the muscle activity of an archer during the shot can be seen written out on paper. The authors recorded surface electromyography from fourteen muscles of the neck, shoulders and arms in three kyudo practitioners of different levels, a fourth dan, a second dan and a beginner, shooting at the makiwara with their usual technique. Running on the same chart alongside the electromyography were the tension on the bow, the breath, the angle of the right elbow and the instant the arrow left.

The sequence described follows the stages of kyudo. As the bow is raised, all the muscles recorded show a weak discharge. Moving into the draw, the shoulder of the bow arm and that of the drawing arm abduct, the right elbow starts to flex and the tension on the bow rises: in the fourth dan the elbow reaches full flexion after about 5 seconds, in the second dan after about 5.5, and there the bow tension becomes constant. Over that stretch the discharge of the teres major, deltoid and triceps of both arms increases, along with the extensor carpi ulnaris of the bow arm, which fixes the wrist; the biceps stay active throughout the draw. The authors read the increase in both teres major muscles as the sign that the draw is carried by the muscles of the back, which close the rear of the body.

Then the still stretch begins. The fourth dan stays in it for about 3.5 seconds, the second dan for about 5, with the tension on the bow held steady; according to the abstract the beginner stays in it for about 2 seconds against the expert's 5. At release the difference is clear: the beginner contracts every muscle of the upper body, the expert releases them together, and the authors think this is where the unsteady release of someone without experience comes from. The curve of the force applied to the bow also behaves in two ways: it rises smoothly in the expert and oscillates in the beginner.

The electromyography is surface EMG from fourteen muscles: sternocleidomastoid, trapezius, teres major, deltoid, biceps brachii and triceps brachii on both sides, plus the extensor carpi ulnaris on the left and the flexor carpi radialis on the right. Recorded alongside were the breath with a thermistor, the tension applied to the bow with a semiconductor strain gauge, the movement of the right elbow with an electrogoniometer and the departure of the arrow with a microswitch. Every signal went to the same pen oscillograph, so the timings of one channel can be read next to those of the others.

The three participants shot at the makiwara, the bundle of straw at very short range on which kyudo practitioners work on the movement itself, using the technique they usually trained with. As a reference the authors also recorded electromyography at maximal tension under static, balanced conditions. The analysis follows four of the eight stages of kyudo, from raising the bow to the release, and proceeds muscle by muscle: for each one it describes when the discharge increases and in which stage, without quantifying the amplitudes.

Three people, one per level, so every comparison between expert and beginner is a comparison between two individuals: the 2 seconds against 5 of holding still are the times of two men, not the means of two groups, and the two experienced practitioners fall in the opposite order to the one expected (the fourth dan holds for about 3.5 seconds, the second dan for about 5). The number of arrows recorded is not stated, and the electromyography amplitudes are not normalised to a maximal contraction: the paper describes which muscles switch on and when, not how much.

The movement measured is shooting at the makiwara, where neither target nor score exists: no result in this study is linked to an arrow landing near the centre. The discipline is kyudo, with a technique, a bow and timings of its own, and the registry counts its practitioners as archers without carrying its numbers over to recurve. The instruments are those of 1971, with the pen traces read by eye.

One limit of this record should be stated too: in the copy available, the last pages of the paper, where the beginner's trace, the discussion and the conclusions are, are images from which no text can be extracted. What is read here comes from the first pages and the English abstract; the details on the beginner, in particular, rest on the abstract alone.

This is a historical study, and its value for anyone shooting today is to show that something coaches say out loud was already readable on a trace in 1971. In the two experienced practitioners the force on the bow rose smoothly and, at the moment of release, the muscles of the upper body let go together; in the beginner the force oscillated during the draw and at release everything contracted. The difference lies not in which muscles are used, which are the same, but in how they behave over time.

The other point of interest is the increase in the teres major on both sides during the draw, which the authors read as showing that the movement is carried by the back. That is a reading of traces, not a measurement of force, and it concerns kyudo, where the archer draws standing with an asymmetric bow and long timings.

Nothing in this study says how many points an archer scores, because shooting at the makiwara is not scored. In the registry it counts as evidence on kyudo archers for claims about the release and about muscle activity during the draw, and a claim resting on this study alone would be resting on three people measured half a century ago.