Core training and sway in archers: Suppiah 2017

Twelve young Malaysian archers from a development programme, 6 boys and 6 girls aged 13 to 19 (mean 14.6), were randomly split into two groups. All carried on with their normal training; one group added eight weeks of bodyweight exercises for the trunk muscles. Measurements were taken at the start, after four weeks and at the end: some physical tests (plank, push-ups, sit-ups, sit and reach), the range of movement of the centre of pressure on a force platform while shooting, and the score over six arrows at 50 metres.

In the training group the centre of pressure range perpendicular to the line of shot fell from 193.52 to 24.21 after four weeks and to 20.62 at the end; in the controls it went from 172.27 to 123.77 and then to 144.31 (no unit is given). The difference between groups was significant after four weeks (F = 7.952, p = 0.018) and at the end (F = 10.899, p = 0.008). Parallel to the line of shot the groups also differed at four weeks (F = 7.887, p = 0.019) and at eight (F = 11.105, p = 0.008). Between weeks four and eight the training group improved no further, which the authors put down to school exams cutting attendance. In the training group alone, centre of pressure range correlated strongly with score (0.924 at the end), but the scores themselves are not reported.

The trunk sessions lasted about 45 minutes including warm-up and consisted of bodyweight exercises chosen for the muscles that control front-to-back and sideways sway; the paper does not list them or say how many sessions a week there were. The force platform was built specially for the study and recorded forces and moments during each shot, from which the shift of the centre of pressure on both axes was calculated. The score came from a single end of six arrows at 50 metres, on a range set up like a competition. The plank was held to exhaustion on the elbows. The analysis used a mixed analysis of variance with time as the repeated factor, Cohen's d for effect sizes and Pearson correlations between sway, plank and score.

Six archers per group is very few, and how the boys and girls were spread between groups is not stated. The training group started with a larger range, and an 87% drop in four weeks is far more than one would expect from trunk exercises: with no unit, no reliability data for the platform and no indication of which phase of the shot was measured, it is hard to know what actually changed. The controls did no extra sessions, so the effect may also come from the added time and attention.

The score, which appears in the title, is over six arrows and its values are never reported. The correlations are calculated on the six trained archers and are positive: read as printed, a larger range goes with a higher score, the opposite of what the authors argue. There are other inconsistencies: Cohen's d values for the plank are identical to those for sway; the abstract gives an F of 7.952 for week eight that the table assigns to week four; the text calls the correlation between plank and score non-significant with p = 0.077, which in the table is the week-four value, whereas at week eight the table gives p = 0.030; and the age range is 13-18 in the abstract and 13-19 in the methods.

The study suggests that in adolescent archers trunk work added to shooting may reduce the sway measured during the shot, and that the effect stalls when sessions are missed. The size of the change, however, is so large and the numbers so inconsistent that the result should be taken as a signal to be checked, not as a measure of the effect.

On score the study allows no conclusion: the values are missing and the correlation reported points the opposite way to the conclusion. The programme is not described well enough to repeat. For anyone coaching young archers what remains is the idea, which also comes up in other studies of archers, that trunk stability is one of the qualities worth developing, with no direct evidence that it turns into points.