Arm muscles in archery: Dorshorst 2022 study

The study comes from anthropology: researchers who examine the bones of ancient populations use the shape and symmetry of the humerus to judge whether those people shot bows, yet almost nobody had measured which muscles are actually working in each arm during the shot. The authors recorded the electrical activity of eight muscles on each side in nine men as they drew a recurve bow, and compared the draw arm with the bow arm during the drawing phase.

In the draw arm the biceps (both as total activity and as peak) and the latissimus dorsi (as total activity, p = 0.004 for both) were more active. In the bow arm the lateral deltoid and the two measured heads of the triceps, long and lateral, were more active, with p values between 0.004 and 0.039. Anterior and posterior deltoid did not differ between sides; pectoralis major appears in the charts, but the text does not discuss its comparison. The traces from a single archer show a spike in the draw-arm biceps just before the halfway point of the draw, a spike in the bow-arm lateral deltoid at around 40%, and then the bow-arm triceps staying high through the whole second half, as the elbow reaches extension. In the authors' view the overall level of activation is similar in the two arms, but achieved with different muscles.

The participants were nine men recruited through flyers on the University of Massachusetts campus at Amherst and in local gyms, mean age 22. Experience was self-reported: four had shot for less than a year and five for 8 to 15 years. Only one drew with the left hand, using a left-handed bow of the same type. Everyone shot the same standard recurve, which according to the paper had a draw weight of 0.45 kg, chosen so that anyone could reach full draw without losing form.

The target was 6.1 metres from the front foot, at chest height, a distance imposed by the size of the laboratory. Each archer shot 10 arrows, with as much time as they wanted and an optional rest between shots. Surface electromyography (Delsys Trigno, 2,000 samples per second) tracked latissimus dorsi, pectoralis major, biceps, the three parts of the deltoid and two heads of the triceps on both sides, with values expressed as a percentage of each muscle's maximum voluntary contraction. Eleven Qualisys cameras at 200 Hz, with markers on the bow and arrow, defined the start and end of the draw. Only the draw phase was analysed, since it was the one with the highest activity, using two measures: integrated activity and peak activity. Beginners and experienced archers did not differ, so they were pooled into one group and the two sides were compared with the Wilcoxon test.

The biggest limitation is the bow. A draw weight of 0.45 kg, about one pound, is far below what any archer shoots: the authors themselves point out that Olympic recurves average around 48.5 lb. With such a light load the muscles do much less work, and there is no way of knowing whether they would work in the same order and proportions with a real bow. The figure is also low enough to suggest a unit error in the paper, but the text gives it twice.

The archers were recreational and did not shoot regularly through the year, and experience was only self-reported: the authors warn that their experienced group might count as beginners by any performance standard. The comparison between beginners and experienced archers, four against five, had little chance of detecting differences, so pooling them does not show that they shoot the same way. Holding at full draw, the release and deep muscles such as brachialis and the scapular muscles, which surface electromyography cannot reach, are all left out; the time traces are shown for one archer only. Electrical activity, finally, is not a measure of force or of load on the bone.

For archers the study confirms a division of labour that coaches have long described: the bow arm pushes with deltoid and triceps, the draw arm pulls with latissimus and biceps, and the bow-arm triceps really comes in as the elbow straightens in the second half of the draw. A spike in the draw-arm biceps halfway through the draw, seen in one archer with a bow that has almost no weight, is not enough to say that archers rely too much on the arm, nor to judge anyone's technique.

It changes nothing in an archer's training or physical preparation. The study is mainly useful to people who read ancient bones, and as an example of how much draw weight and sample level matter: finding out which muscles work in a real archer needs trained archers shooting their own bows, and the aiming and release phases too, which are missing here.