Plank, arm strength and archery: Yachsie 2023 study

Twelve male archers from Yogyakarta, aged 16 to 18, did a circuit of plank exercises for 18 sessions, three a week, with an arm strength test and a 40-metre shooting test before and after. The author reports improvements in both, with enormous t values: 42.884 for strength and 35.023 for accuracy in the table, 41.894 and 34.019 in the abstract, with p given as 0.000 throughout.

The means, however, cannot be read. The descriptive table has four rows with muddled labels (pretest arm strength twice, posttest accuracy twice) and means of 444.92, 549.00, 413.58 and 437.08. If the shooting test was 36 arrows, the maximum possible is 360, so none of these means can be a score; the discussion, for its part, speaks of mean 40-metre scores between 322 and 332, taken once a month. For strength, the introduction gives a mean of 8.3 from an earlier measurement with the same instrument.

The design is a single group tested before and after, with no control. From a population of 22 archers in Yogyakarta, 12 were selected, all male and aged 16 to 18. Arm strength was measured with the holding bow digital test, an instrument proposed in Indonesia for arm strength and endurance in archers; the stated unit is the kilogram, and the paper does not describe how the test is run. Accuracy was the total of 36 arrows shot at 40 metres. Bow type and target face are not given.

The circuit had seven stations of planks and variations (shown in a figure), at an intensity of 70 to 75% of maximum heart rate estimated as 220 minus age, with 30 seconds' recovery, 3 to 6 repetitions, 3 or 4 sets and 3 minutes' rest between sets. The analysis consists of normality and homogeneity tests and a paired t test with 11 degrees of freedom.

The numbers do not hold together. With twelve people, t values of 42 and 35 mean everyone improved by almost exactly the same amount, with minimal differences between individuals: for the 36-arrow shooting test, where scores fluctuate a good deal from one end to the next, that is hard to believe. The t values differ between abstract and table; the methods name a Kolmogorov-Smirnov normality test and the results a Shapiro-Wilk test; the homogeneity table contains an entry, exercise meditation, that has nothing to do with the study; and the acknowledgements thank Banyumas Regency, which is not in Yogyakarta. The same coefficient, 0.895, is given for the validity of both instruments.

Beyond all this, a design without a control cannot separate the circuit from the shooting the archers did over the same weeks, or from familiarity with the tests.

The study does not support the claim that planks improve accuracy. With no control group, descriptive data that cannot be interpreted and statistics that change from one page to the next, the reported improvement may come from the shooting practice the archers were doing anyway. The explanation in the discussion (stronger arms, less tremor at full draw, more central arrows) is the author's reasoning, not a measurement: tremor was not recorded. The plank remains a common exercise for the trunk and shoulders; this study adds no reliable data on how it relates to shooting.