Force sensors in archery: the grip, the string, the fingers and force plates

What a force sensor measures

A force sensor turns a deformation into a number. Archery studies use three kinds: strain gauges, fine metal grids glued to a bending part, whose resistance changes as the metal stretches; force-sensitive resistors, films less than a millimetre thick that conduct more when squeezed; and force plates, rigid platforms that read the push of the feet in three directions. Unlike electromyography, which records muscle activity, these read a force directly, but only at the point where the sensor sits and only in the direction it was built for.

The grip

In 1992 Martin and colleagues, the first in the registry to measure the hand on the grip, taped fifteen force-sensitive resistors onto the grip of fifteen American recurve archers, eight of Olympic standard and seven less accomplished, and calibrated each sensor with nine loads from 0 to 37.4 newtons: of the 225 calibration curves, 79% had a coefficient above 0.96. The archers shot 72 arrows at 30 m, but only 18 were recorded, at 40 Hz, one sample every 25 ms.

The moments by which the hand would rotate the bow, however, were estimated, not measured: each sensor was weighted by an approximate distance, so the resulting moment arms are numbers without units. With that estimate, pressure distribution was linked to the point of impact in one archer in fifteen vertically and three in fifteen horizontally, hence the claim that the distribution of grip pressure does not predict where the arrow goes. What separated the two groups was vertical repeatability from shot to shot, higher in the better archers (p = 0.045), which underpins the claim on more consistent grip pressure. The instrument also changed the equipment: the archers felt the grip was thicker, though they said their grip and technique were not affected.

In 2007 a Japanese group read the hand through the bow. Koike and colleagues glued six pairs of strain gauges above and below the grip of purpose-built kyudo bows and calibrated them on a rig with a load cell: the force estimated by the sensors and the force read by the cell lay on the line y = 0.99x + 0.82. Nineteen practitioners shot, but the published traces cover only six: there the upward push moment was between 1 and 5 Nm and the torsion about 0.6 Nm. The calibration is sound, the experiment much less so, because those traces are read by eye, without statistics.

To see what a force does to the arrow, the archer is removed. In 2008 a mechanical rig holding Japanese bows varied only the torsion at the grip, up to about 14 Nm, and at 28 m the point of impact moved from one side of the target to the other. It is the clearest measurement behind the claim that bow torsion moves the arrow, and it also shows the claim's limit: no study in the registry has measured torsion and point of impact in the same shot of a recurve archer.

The string and the clicker

No study in the registry has put a sensor on the string during an archer's shot. Strain gauges on the bow, on the other hand, are the first force sensors in the registry: in 1971 Kamei and colleagues used one to follow the tension of the bow in three kyudo practitioners, and in Nishizono's studies of 1984 and 1987 the bending of the bow served to mark the moment of release. String tension is read by strain gauges only on a 1997 launching rig, where nobody is shooting. On archers, what has been measured in the final draw is a displacement. Leroyer in 1993 used a displacement sensor fixed to the grip: in the last 5 seconds before the clicker the drawing hand moved back by about 5 mm. In 2006 Edelmann-Nusser and colleagues glued a strain gauge onto the clicker blade, which bends more or less depending on where it rests on the tapered point, and among seven juniors the best archer drew the arrow back by about 5 mm over two to three seconds; the same system, with aiming recorded alongside it, returns in a second paper on the same archers. Neither gives a calibration or a measurement error. The full story is in the line on the final draw.

The fingers

Here too nothing has been measured on archers: finger-sensor studies use bow-like frames and people who do not shoot. In 2017 eight men pressed on four six-axis sensors, holding half of their maximal force, and then let go. In 2023 an aluminium bow frame weighing 1.53 kg was drawn to 40% of maximal finger strength by eight men with no shooting experience. The load is a fraction of a real draw weight and no string slides off the fingers, which is why the claim on the finger flexors before the clicker rests on electromyography and not on a force.

Force plates

A force plate gives two different things: the path of the centre of pressure, covered on the posturography page, and the forces themselves, that is how much load each foot carries. For the forces, the layout of the plates matters. With a single plate under both feet, as in the 2019 study of 27 recurve archers, the split between the legs cannot be measured, though the paper's discussion does. With a plate under the front foot only, in the 2014 single case, half the picture is visible: a peak of 44.12 kg in an archer weighing 84. What is needed is a reading for each foot, as in a Russian study from 2023 of eleven young archers: in their usual stance the load leaned towards the front leg, by 7.83% in compound and 29.50% in recurve, and with the front foot turned into a T stance it moved onto the back leg. The claim that the weight sits more on the front leg is contested, and the two studies against it are exactly the one with a plate under one foot and the one inferring load from a horizontal force.

The simplest check is to add up. In the Turkish study from 2010, with two plates, before the release the legs carried 39.0 and 32.6 kg, together far more than the archers' declared mean body mass of 54 kg, and the paper does not explain it. That is why the drop in foot load at the release can be seen, but its size is uncertain.

Pressure plates are a grid of small sensors showing where the load sits under the sole: among the fifteen compound archers of the insole study, 43.72% of the pressure was under the heel of the bow-side foot, the premise of the claim on arch-support insoles. Plates also mark time: Spratford and colleagues marked the release with a microphone, helped by a sudden change of moment that the plate recorded in every archer, and in a French study with two plates at 1,000 Hz the centre of pressure moved by 15-20 mm at the release, eight to ten times the sway during aiming. This is one reason why the legs during the shot are almost still, not still.

What to check in a study using force sensors

• whether the force is measured or estimated, and whether a calibration is reported with its error;
• where the sensor sits, how much it changes the grip or the equipment, and how fast it samples compared with the milliseconds of the release;
• for force plates: one under both feet, one per foot or one under a single foot, and whether the loads add up to body weight;
• whether an archer, a person simulating or a machine does the shooting;
• how many people and how many arrows, and whether arrows were treated as independent observations, like the 108 arrows from four archers in 2010.

Design, sample and journal are weighed as explained in How we read a study.

@misc{campagna2026_enresearchmethodsforcesensorsgripstringf,
  author = {Campagna, Matteo},
  title = {Force sensors: grip, string, fingers and force plates},
  year = {2026},
  howpublished = {Research, matteocampagna.com},
  url = {https://matteocampagna.com/en/research/methods/force-sensors-grip-string-force-plates},
  note = {accessed 2026-10-16}
}