Para archers' kinematics: Kim 2021 study

Seven Paralympic recurve archers from the Korean national team were captured in three dimensions while shooting six arrows: four in the ARW2 class, who shoot seated in a wheelchair (paraplegia or a comparable impairment), and three in the ARST class, who shoot standing. They were aged between 43 and 52.

The wheelchair archers took longer over the draw, 2.228 seconds on average against 0.985, and over the hold, 4.414 against 3.042 seconds. These are the only statistically significant differences in timing; release and follow-through did not differ. Forward-backward trunk inclination was around 70 degrees in the wheelchair archers and around 77 in the standing ones, but the difference was not significant, and the same applied to sideways inclination, between 7 and 10 degrees in both groups. The centre of the upper body moved more front to back during the draw in the wheelchair archers (1.013 against 0.292); on the other axes and in the other phases, and in all movements of the bow's centre, the groups did not differ. The score over the six arrows was 57 for the wheelchair group and 56 for the standing group.

The authors infer that archers who shoot seated, without support from the legs, need more time to find their balance during the draw.

Testing took place at 20 metres, a distance chosen so that the motion analysis system could be set up: 12 Eagle 4 infrared cameras (Motion Analysis) at 120 frames per second, placed in front, behind, at the sides and on the diagonals, plus a video camera at 30 frames per second. Twenty-eight reflective markers were fixed to the trunk, arms and bow. The body centre is that of the upper body alone, without the legs, and the bow's centre is derived from three points: the nocking point and the two limb tips.

The shot is divided into four phases: the draw up to anchor, the hold up to the start of the release, the release up to the moment the arrow has left the bow, and the follow-through until the rotating bow passes waist height. The groups were compared with a t-test for each variable, with a threshold of p < 0.05; the published version adds confidence intervals and Hedges' g, very large for the timings (2.359 for the draw). Repeatability over the six arrows, measured with the intraclass correlation coefficient, was 0.852. The ARW1 class, with more severe impairment, and compound archers were excluded. The wheelchair archers had on average 15.3 years in the sport, the standing archers 8.6.

With four archers on one side and three on the other, a t-test picks up only very large differences and cannot rule out small ones: a mean difference of six to seven degrees in trunk inclination is not significant partly for this reason. There are many tests, run one at a time without correction, and a result or two may have come up by chance. The task, six arrows at 20 metres in a laboratory, is far from a competition at 70 metres, and the two groups also differed in years in the sport and in sex, not just in class.

The units of some measures are unclear: the movement of the body centre has no unit in the preprint and is given in metres per second in the published version, and how it was calculated is not explained. The training suggestions in the discussion, such as shortening the timings through stability work or training the deltoid, were not tested. The December 2020 preprint, which the registry used as its reference, gives t values in the text that differ from its own table; this record follows the published version, where text and table agree.

For anyone coaching wheelchair archers, the study gives some of the few reference figures available for archers at this level: the draw and the hold lasted 1.24 and 1.37 seconds longer than in standing archers, while the release was just as quick, under 0.33 seconds in both groups, and the score was almost the same. In these national-team ARW2 archers, then, an average hold of over 4 seconds went with a good score.

The study does not say whether shortening the timings would improve the score: that is the authors' idea, drawn from research on archers without impairments. The greater front-to-back movement of the trunk during the draw fits with the lack of support from the legs, but it was measured in four people.