Draw weight and energy cost in archery: Tsuji 1984

What does shooting an arrow cost in energy? Ten students from a Japanese university club, five men and five women, shot with three bows of different draw weight while the authors collected their expired air and recorded their heart rate. The cost of one arrow rises in step with draw weight: 0.47, 0.59 and 0.73 kcal for the men, with bows of 32, 42 and 51 actual pounds, and 0.27, 0.33 and 0.40 kcal for the women, with bows of 25, 35 and 45. Expressed per unit of body weight the pattern holds: from 0.08 to 0.12 kcal per arrow per ten kilograms for the men and from 0.05 to 0.07 for the women. Between draw weight and the cost of an arrow the correlation is 0.70 in the men and 0.84 in the women, falling only slightly, to 0.68 and 0.77, for the values scaled to body weight.

What a session costs in total depends on how many arrows are shot and how much walking is involved. In the trial with six arrows and a 30 metre run to collect them, the men spent 11.2, 11.6 and 12.0 kcal according to draw weight and the women 8.27, 8.52 and 9.34; in the trial with twenty-four arrows and no walking, that is four times as many shots, the men spent 20.3, 23.8 and 27.3 kcal and the women 14.2, 15.4 and 17.1. The energy demanded per minute was therefore higher when the arrows were fetched at a run than when shooting went on throughout. The RMR intensity index rises with draw weight in every condition: in the women it goes from 1.8 to 2.3 in the trial with running and from 1.1 to 1.6 in the one without, and in their discussion the authors place archery between 2.3 and 2.9, an intensity they consider modest. Heart rate climbs as soon as the end begins, stays high throughout the shooting and returns to resting values about two minutes afterwards.

The participants were members of a university club in the Osaka area, aged 19 to 22, with two or three years of practice, chosen because their draw lengths were similar (about 27 inches for the men, 26 for the women) and because in training they scored at least 320 points out of 360 at 30 metres, that is 89% of the maximum, which puts them in the upper range of student archers. The women were interviewed so that the trials could be scheduled away from their period. The bows were 66 inch Yamaha YTSL models at the three draw weights, each checked with a Takei tension gauge so that the actual weight at each archer's draw length was known.

There are three trials. In the first, six arrows were shot and then fetched with a 30 metre run; in the second, twenty-four arrows in a row with no walking; in the third, six arrows, again without walking. Energy expenditure was calculated from expired air collected during the shooting, in the two minutes that followed and at rest, and from that the authors derived basal metabolism, the RMR index, the energy of activity and the cost per arrow. Heart rate was recorded with a Sanei telemeter counting R waves. Alongside expenditure they measured height, weight, girths, grip strength, back strength, shoulder and arm strength, vertical jump and eyesight. In the last part, measured total expenditure is compared with the figure obtained by multiplying the number of arrows by the cost of one arrow and adding resting metabolism.

Ten people, a single club, and the equipment and technique of 1984. The design is a series of trials repeated on the same participants, with no comparison group, and the number of arrows stays far below that of a competition: the authors themselves recall that at the time a domestic Japanese competition meant 288 arrows over two days and an international one the same 288 over four, and that their club trained mostly at 30 and 50 metres with bows averaging 39 pounds. The cost per arrow comes from the twenty-four arrow trial alone, and the comparison between measured and estimated expenditure matches well in the men and rather less well in the women.

The female sample is heavier than the Japanese average for that age (56.6 kilograms against 50.7), which the authors put down to the amount of physical activity their course of study involved: the women in this study do not stand in for women archers in general. Values are reported as means with the half-range of the 95% confidence interval, and the relationship between draw weight and energy rests on correlation coefficients rather than on a test of the slope. The score served only to select the participants: the study measures neither accuracy nor steadiness, so it says nothing about what makes anyone shoot better. The text is in Japanese, with the abstract and tables in English.

The figure worth keeping is the order of magnitude. One arrow costs a man between half and three quarters of a kilocalorie with bows of 32 to 51 pounds, and a woman between a quarter and four tenths with bows of 25 to 45: a round of 72 arrows therefore sits in the tens of kilocalories, and no shooting session comes close to the cost of a run. A stronger bow costs more energy per arrow, almost in direct proportion to draw weight, yet even at the heaviest weight the measured intensity stays at two or three times basal metabolism.

The other figure concerns everything around the shooting. Walking or running to collect arrows weighed more per minute than shooting did, so much so that six arrows with a 30 metre retrieval cost almost as much as twenty-four arrows shot from a standing position: over a long session, then, much of the physical work lies in the walking and in holding the posture rather than in the draws themselves. Heart rate rises at once and returns to rest within a couple of minutes, which explains why a heart rate monitor on the field says more about the rhythm of the ends than about muscular fatigue. The study does not measure performance, so it is no help in choosing a draw weight: it says only that energy expenditure in archery is small and predictable from the number of arrows.