Muscles in compound and recurve: Vagle 2000 study

Seven experienced male archers aged 36 to 51 shot the same compound bow and the same recurve, both at 55 pounds, while surface EMG recorded 12 muscles of the shoulders and arms and a camera tracked the bow. The work is a final project for a Master of Physical Therapy at the University of North Dakota, and it describes the curves without statistical tests.

With the compound, full draw came at 29% of the time from the start of the draw to the release, and with the recurve at 59%, partly because the compound was held at full draw for three seconds and the recurve for one. Over the whole movement, activity was higher with the recurve in all 12 muscles. The largest differences were in teres major of the drawing arm (119.6%), brachioradialis of the same arm (116.9%) and triceps of the bow arm (111.9%); the smallest was in the middle deltoid of the bow arm (30.9%).

The timing ran the opposite way. With the compound the highest activity came in the first part of the draw, up to 20-26% of the cycle, and dropped after let-off; with the recurve it was highest during the hold. Looking only at the draw up to full draw, five muscles worked slightly harder with the compound (right triceps, left brachioradialis, left middle trapezius, and left posterior and middle deltoid) and the rest harder with the recurve, with differences ranging from 1.4% for the left middle trapezius to 16.5% for the right middle trapezius.

The archers were members of the Red River Archers club, right-handed, used to both bows, had shot three competitions in the previous twelve months and took part in state and national events. The compound was a 1999 Hoyt Raider Powerflex, set to 55 pounds with 75% let-off and the draw length adjusted for each archer; the recurve a Martin Hatfield takedown of 55 pounds at 28 inches. A shooting glove and arm guard were provided, or the archers could use their own glove or tab. After ten warm-up draws with an elastic band, each archer made about six draws and releases with each bow, shooting into a foam target about a metre and a half away, with the hold timed by a metronome.

The muscles recorded were posterior and middle deltoid, teres major, triceps, biceps and brachioradialis of the right, drawing arm; middle trapezius on both sides; and middle and posterior deltoid, triceps and brachioradialis of the left arm. The signal was integrated and averaged over two cycles per archer, with time expressed as a percentage of the movement, and then averaged across archers. A single camera at 60 frames per second, with three reflective markers on the bow, gave the bow and string angles in the sagittal plane.

The signal was not normalised to each muscle's maximal contraction: the approved protocol included it but the thesis does not, and the author herself writes that for this reason it cannot say how hard one muscle works compared with another or how close it is to its maximum. The comparisons are percentage differences between means, with no measure of spread and no tests, on seven people.

The three-second hold with the compound and the one-second hold with the recurve change the shape of the curves and the averages over the whole movement, because the compound spends longer in the low-load phase after let-off. The recurve was 55 pounds at 28 inches, so archers with a longer draw held more weight, while the compound was set for each archer. The approved protocol asked for archers used to a compound with a mechanical release, but the methods chapter mentions only a glove and tab and does not say how the compound was released, which matters for the forearm muscles. A target a metre and a half away, six shots per bow and a single camera are a long way from shooting in competition. The "traditional" bow here is a recurve, not a longbow, and the work did not go through external peer review.

The thesis puts figures, rough as they are, on something anyone who has shot both bows knows: with a compound the effort is in the draw, before the valley, and the hold is light; with a recurve the hardest part is the hold itself, when the full draw weight sits on the fingers. For archers switching between bows, or thinking about strength in terms of their own bow, it is a pointer consistent with the mechanics of the two.

The author's training suggestions, working through the range of motion up to let-off for the compound and on an isometric hold at the end of the draw for the recurve, are inferred from the charts and have not been tested. The activity of the bow-arm brachioradialis, concentrated at the release, is likewise explained with two hypotheses that the thesis does not put to the test.