Wearable breathing sensor for archers: Romano 2019

A team of engineers from Campus Bio-Medico University in Rome, with ENEA and the Sant'Anna School, presents two elastic chest bands, each carrying a fibre optic sensor embedded in a small silicone block, intended to record archers' breathing and heartbeat while they shoot. The work has two parts. In the first, on four archers, motion capture measured how much the chest wall deforms during a complete shot and during quiet breathing, to decide where to place the bands so that the shot would not overstretch them. The upper right chest deformed by up to 58% during the shot and was ruled out; the other regions stayed between 18% and 38%. Of the two lines chosen, one stretched by more than 8% during quiet breathing in all four archers; the other stretched by 3 to 16% during the shot.

In the second part two healthy volunteers, with no indication of whether they were archers, wore the bands while breathing, simulating a shot and holding their breath. The signal followed breathing on both bands; the small movements caused by the heartbeat were visible only during breath-holding, when breathing did not mask them. The paper reports no rates and no comparison with a reference instrument: it shows the traces and presents the system as a first step.

Each sensor is a fibre Bragg grating (wavelength 1547 nm, 10 mm grating) enclosed in a Dragon Skin silicone block measuring 90 by 24 by 1 mm: when the chest expands the band stretches it and the reflected wavelength shifts. To choose the position, four archers (two men and two women) had 42 markers on the front of the chest, filmed by eight BTS infrared cameras; the chest was divided into three regions per side (upper rib cage, lower rib cage, abdomen), and the maximum deformation was calculated for each pair of markers during a complete shot and during four quiet breaths. The upper left side was also excluded to avoid soft tissue movement, especially in the women.

The bands were tested on a 37-year-old man and a 22-year-old woman, with an optical interrogator recording at 250 Hz: five quiet breaths, a simulated shot, a breath-hold, five more breaths and a second breath-hold held as long as possible, the whole sequence repeated twice.

It is a very small feasibility study. The archers' level and discipline are not given, and each shot only once; the bands were never worn during real shooting, only by two volunteers simulating the movement. There is no ECG or spirometer for comparison, so it is not known how accurately the bands measure breathing or heart rate: the authors leave that to future work. The heartbeat also shows only during breath-holding: the paper does not show whether it can be read during the simulated shot, when the chest moves more.

The band positions were chosen from chest deformation during the shot, but the motion capture could not see cardiac movement, so closeness to the heart was only taken into account, not measured. There is also a small inconsistency: the abstract refers to Dragon Skin 10 silicone, the main text to Dragon Skin 20.

For anyone shooting today the study changes nothing: it does not say how to breathe or when to release, and it does not measure performance. It is of interest to anyone following research on wearable instruments, because it shows two things. The first is that during the shot the archer's chest, especially the upper right part, deforms far more than during quiet breathing, so a badly placed sensor would measure the movement rather than the breathing. The second is that a light band can follow breathing, while the heartbeat can so far be read only during breath-holding; that the bands do not disturb the shot is the authors' aim, not yet tested on archers in training.