Kinematics of the recurve release: Santosh Kumar 2024

The same five recurve archers as in the authors' other paper, men of international level from the SAI centre in Sonipat, were measured at release at 70 metres on five linear quantities: the height of the centre of mass (mean 100.46 cm), the height of the centre of gravity (100.79 cm), the height of the arrow at release (170.93 cm) and a quantity called body force alignment, right and left, expressed as a percentage (43.58% and 56.61%), which the paper does not define and which seems to mean the share of weight on each side. Performance is the arrow score, averaging 9.97 points (range 9.9 to 10).

With the significance threshold of 0.878 that applies to five people, the authors find score linked to the height of the centre of mass (r = -0.893), of the centre of gravity (0.878, exactly on the threshold) and of the arrow (-0.945); right (0.360) and left (0.770) force alignment are not. Among the variables they report -0.960 between centre of mass and centre of gravity, 0.887 between centre of mass and arrow height, -0.959 for left-side alignment (the text leaves unclear whether with the centre of mass or with arrow height) and 0.935 between centre of gravity and left-side alignment. The authors read the negative sign as a hint that a lower centre of mass goes with better scores.

The filming set-up is described in more detail here than in the companion paper. The camera named is a Casio EX-F1 (60 to 300 frames per second), yet the text describes six cameras: one in front at eye level, one overhead 2 metres from the archer, one behind at 6 metres, one in front for bow verticality, one level with the clicker 6 metres from the box for arrow height and angle, and one 10 metres away at 30 degrees from the target to record the impact. The archer stood in a 1 by 1 metre box on the shooting line and shot 6 arrows on the whistle; elsewhere the text mentions three trials per archer instead. The centre of the target was 5 feet above the floor. Measurements were taken at release with Siliconcoach Pro 8 and Tracker and correlated with score using Pearson's correlation in SPSS 20; the methods also announce a linear regression whose results never appear.

The same limits apply as in the paper on angles: five archers scoring between 9.9 and 10 (standard deviation 0.044) cannot link any measurement to performance, because one archer differing slightly from the others on two variables is enough to produce a very high correlation. Here there are also problems of definition. For a person standing still on Earth, centre of mass and centre of gravity are the same point, yet they are treated as two variables and come out correlated in opposite directions (-0.960), while the text says they fall together. The conclusion reports a positive correlation between arrow height and performance, but the coefficient given is -0.945. The paper does not explain how the centre of mass or the weight distribution was obtained, which would normally require a body segment model and a force plate, neither of which is mentioned. The measured differences are tiny (the centre of mass ranges from 100 to 101.11 cm), probably below the precision of a video measurement. The same sample appears in the authors' paper on release angles. The registry flags the journal as having questionable editorial standards.

For an archer this study changes nothing. The idea that lowering the centre of gravity improves scores does not come from these data, which cannot support it, and there is no indication of how posture or the weight split between the feet affects the arrow. What remains are some descriptive values for five high-level archers, such as an arrow about 171 cm off the ground at release, which depend on stature (around 6 feet) more than on technique.