Plank circuit and archery accuracy: Yachsie 2023

Twelve male archers aged 16 to 18, selected from the twenty-two at a centre in Yogyakarta, did eighteen sessions of a plank circuit, three times a week, with a measure of arm strength and a shooting test at 40 metres before and after. There was no comparison group.

The published means go down. Arm strength goes from 443.92 kg, range 188 to 621 with a standard deviation of 152.0, to 419.58, range 242 to 552 with a standard deviation of 112.6; the shooting score goes from 547.00, range 424 to 639, to 535.08, range 461 to 587. The text commenting on the table states instead that both means rose, and the two t tests reported give values of 41.894 and 55.001 with eleven degrees of freedom and p = 0.000, from which the authors conclude that the circuit increased strength, accuracy and arm endurance.

The numbers do not hold together. Thirty-six arrows, as the method states, are worth at most 360 points: a score of 547 does not fit. The introduction to the same article reports that on that strength instrument the archers in this setting averaged 8.3, a figure with no relation to the 443.92 kg in the table. And a third set of numbers appears in the discussion, which mentions monthly scores at 40 metres of between 322 and 332.

The design is a before and after on a single group, with no control. Of the twenty-two archers at the centre, twelve were chosen by purposive sampling, on the criteria of being male and aged between sixteen and eighteen.

The circuit has seven plank stations: basic plank, elbow plank, single leg plank, plank arm reach, side plank, elevated side plank and archer plank. The athlete moves from one station to the next until the lap is complete, and after a full lap there is a three-minute break. The stated dosage is 60 to 70% of a one-repetition maximum, thirty seconds of recovery, three to five repetitions, one to three sets and three minutes between sets.

There are two measures. Arm strength with the Holding Bow Digit Test, expressed in kilograms, an instrument for which the authors quote a validity of 0.895 against a table value of 0.344. Accuracy with thirty-six arrows at 40 metres, adding up the value of each arrow, with validity 0.895 and reliability 0.944 quoted from an earlier paper of their own. The analysis includes a Kolmogorov-Smirnov normality test, a Levene homogeneity test and t tests on the means.

Nothing else about the shooting is given: no bow type, no target face, no number of ends, and no mention of who scored. Nor does the paper say who ran the training, or what the archers did in their own shooting sessions over the same six weeks.

The problem is not at the edges, it is in the data. The two means in the table fall between before and after, while the text, the results and the conclusions all speak of an increase in both: this record reports the numbers as printed, with no way of saying which of the two versions describes the experiment. The units do not hold: a score of 547 over thirty-six arrows exceeds the possible maximum of 360, and an arm strength of 443.92 kg on a bow-holding test does not square with the average of 8.3 that the same article reports for that instrument in its introduction. The t values, 41.894 and 55.001 with eleven degrees of freedom, are not compatible with standard deviations of 152 and 82 points in twelve participants.

Even without these contradictions the design would not allow the circuit to be credited with what is observed. There is no comparison group, so six weeks of ordinary shooting practice, of growth in boys of sixteen to eighteen and of familiarity with the two tests all enter the result alongside the planks. The dosage is stated as a percentage of a one-repetition maximum, which is not defined for an isometric hold, and the three to five "repetitions" of a plank remain ambiguous. The twelve archers were chosen deliberately out of twenty-two, not at random.

What remains is the programme, described station by station, and that is the part of the article that can be read with profit. On what the programme produces, this source is not able to give a measurement.

For someone who shoots there is nothing to take away about effect. A circuit of seven plank variations, eighteen sessions over six weeks, is a plausible and well described piece of training, but this article does not allow anyone to say whether it changed arm strength or the score at 40 metres, because the published measures go one way and the text goes the other, and because the score reported is not compatible with the arrows reported.

In the registry the source stays as a documented example of a body-weight programme for young archers, and as a reminder of why every figure has to be read off the table rather than off the conclusion.