Lower back load in archery: Ji 2024 study

Thirteen university students, most of them from an archery club, shot two bows of 20 and 25 pounds at two targets with their centres 1.0 and 1.4 metres above the ground, at 10 yards. Using 17 inertial sensors and a digital human model, the authors estimated, at the point of the draw they considered most risky, the compression on the disc between the fourth and fifth lumbar vertebrae (L4/L5) and the angles of the shoulders, elbows and trunk.

Mean compression ranged from 511.02 to 558.46 newtons in the women and from 581.02 to 665.26 in the men, depending on the condition; the authors speak of about 80 N more in the men, but in the table the difference runs from 63 to 127 N. Compression was linked mainly to body mass (r = 0.62) and less to trunk flexion (r = 0.40), and did not clearly rise from the 20 lb to the 25 lb bow.

The only significant difference in joint angles between men and women concerned the left shoulder, the bow arm for a right-handed archer, with the 25 lb bow: the men held it more abducted, 83.39 against 74.70 degrees at the low target and 84.39 against 75.78 at the high one (p = 0.04 and 0.03). With the 20 lb bow at the high target the men flexed the right shoulder, on the string side, by about 13 degrees more (46.67 against 33.76), with p = 0.06.

Participants were aged 19 to 26 and had widely varying experience; a certified coach took everyone through the shot sequence, and each could warm up before every change of bow. Each person repeated four tasks five times, always in the same order: the 20 lb bow at the low and then the high target, then the 25 lb bow at the same two. String force was measured with a digital force gauge (SF-500) at a fixed draw length.

Movement was recorded with the Xsens MVN Awinda system, with sensors on the head, shoulders, upper arms, forearms, hands, sternum, pelvis, thighs, lower legs and feet, and streamed in real time to a second model in Siemens' JACK ergonomics software, built from each participant's measurements. In the chosen pose, with both hands under load, the software calculated lumbar compression from the posture and the force applied by each hand. The comparisons were a two-way analysis of variance, by task and sex, and correlations between pairs of variables.

The condition with the 25 lb bow and the low target reports exactly the same values as one of the conditions in the companion paper in Sensors, by the same group on the same thirteen participants: the two papers share at least part of their data. The two conditions with the high target, in turn, reappear with the same values, rounded, in a 2025 paper by the same group in Applied Sciences, where they are presented as shots at 10 yards: as a result the 25 lb bow at 10 yards has different values in the Sensors paper and in the 2025 one.

Lumbar compression was not measured but calculated by a model, which depends on the forces assigned to the hands and on the posture reconstructed from the sensors. The paper does not compare the values with any risk threshold, so on its own it cannot say whether 500 or 600 newtons is a lot or a little, and it ignores other loads on the spine such as shear or twisting. The forces measured with the gauge are not reported, while the text gives the weight of the two bows as 9 and 11 kg, which match the draw weights expressed in kilograms rather than the mass of a bow: it is not clear which value went into the calculation.

The sample is 13 people, and the paper does not say how many were men and how many women, or what level each was; the companion paper gives 7 men and 6 women, with all four experts among the men, so the sex differences may also reflect experience and body mass. Bows of 20 and 25 pounds at 10 yards are far from competition conditions, and the order of tasks was fixed. The text has some inconsistencies: the correlation of 0.62 is described as both moderate and high, and one p value is attached to a different condition from the one in the table. The idea that a different posture reduces injuries is the authors' proposal: nobody was followed over time and no injuries were recorded.

For anyone who shoots, the study is mainly a proof of method: it shows that wearable sensors and a digital model can estimate posture and lumbar load during the shot without a camera laboratory. The values found, with light bows in a group of students, do not show that shooting is hard on the back, or harder for heavier people; they show that in the model the estimated load rose with body mass and with forward trunk flexion.

The observation closest to the range concerns the bow shoulder: with the heavier bow the men held it higher than the women. The authors put this down to differences in strength, which they did not measure. Their closing recommendations, to train upper body strength, control body weight and keep the back and shoulders straight, are general advice that the study does not test.