Muscle activity and skill in archers: Shinohara 2018

Thirty Japanese high-school and university archers, all men and all right-handed, were ranked by their score over 72 arrows at 70 metres and split into three groups of ten: elite 633.0 ± 16.7 points out of 720, pre-elite 593.0 ± 8.3 and beginners 557.5 ± 19.3. In a laboratory, shooting at a target 2 metres away, they had six muscles on the string side recorded with surface EMG along with three joint angles, over the second preceding the click.

The muscle that separates the levels is the lower trapezius of the drawing arm: 54.0 ± 15.7% of maximum voluntary contraction in the elite, 39.4 ± 10.6% in the pre-elite and 34.0 ± 11.1% in the beginners, significantly different from both other groups (p < 0.05 and p < 0.01) and with an effect size the authors class as moderate to high. The ratio of upper to lower trapezius goes from 2.33 ± 1.02 in the beginners to 1.45 ± 0.58 in the pre-elite and 1.23 ± 0.97 in the elite: as level rises, the load shifts from the upper to the lower part of the trapezius. The arms go the other way. The biceps brachii works less in the elite than in the other two groups (p < 0.05) and the triceps less than in the beginners (p < 0.05); in every group the triceps stays between 10 and 20% of maximum contraction.

On the angles, the elite hold the drawing shoulder less open, 99.0 ± 4.5 degrees of abduction against 105.8 ± 6.5 in the pre-elite and 107.2 ± 4.0 in the beginners, and the elbow less flexed, 138.3 ± 5.0 degrees against 143.3 ± 2.0 and 143.6 ± 3.7. Horizontal shoulder extension does not separate the groups, and neither do the upper trapezius, the middle deltoid and the posterior deltoid. Height, body weight, body mass index and draw weight did not differ between the groups; age and years of practice did.

The measurements were taken in an indoor biomechanics laboratory, not on the shooting field. After upper-limb stretching and a few practice shots, each archer shot five arrows at a target 2 metres away, aiming each time at a mark 1 centimetre across. The score that defines the three groups comes instead from 72 arrows at 70 metres, shot on a separate occasion. Archers with a history of shoulder dislocation or surgery, with cervical symptoms or with documented injuries of the shoulder complex were excluded, as was anyone reporting pain during the experiment.

The movement was filmed by five cameras synchronised at 200 frames per second, with four reflective markers 10 millimetres across on the radial styloid process, the lateral epicondyle, the acromion and the spinous process of the seventh cervical vertebra, all on the right. The instant analysed is the fall of the clicker, taken as full draw. Coordinates were obtained with a direct linear transformation: shoulder abduction is the angle between the vertical and the acromion-to-epicondyle line, horizontal extension the angle between the C7-to-acromion line and the acromion-to-epicondyle line in the horizontal plane, elbow flexion the angle between the acromion-to-epicondyle line and the epicondyle-to-styloid line, also in the horizontal plane. Between-trial repeatability was high: intraclass correlation coefficients above 0.97 for the kinematics and above 0.82 for the EMG.

Surface EMG, with Ag/AgCl electrodes 2 centimetres apart centre to centre, recorded the upper trapezius, lower trapezius, middle deltoid, posterior deltoid, biceps brachii and triceps brachii, with the reference electrode on the left olecranon. The signal was converted at 1 kHz, full-wave rectified and integrated over the second preceding the fall of the clicker. Each value is expressed as a percentage of that muscle's maximum voluntary contraction, measured three times before the shots in manual muscle testing positions, with 3-second isometric contractions against manual resistance, then averaged. The comparison between the three groups is a one-way analysis of variance followed by Scheffé's test, with the threshold at 5%.

The design is cross-sectional, and the three groups do not differ in score alone: they also differ significantly in age and in years of practice. The higher lower-trapezius activity in the elite may therefore be a result of years of shooting as much as a cause of the score, and the study does not separate the two. The authors' conclusion, that raising the score calls for training the lower trapezius, goes beyond what this design can show.

The link between muscles and score is indirect. The EMG comes from five arrows shot in a laboratory at 2 metres, the score from 72 arrows at 70 metres shot on a separate occasion, and there is no measurement of where any of the analysed arrows landed. The authors list this among their limitations, along with the absence of competition pressure. There is also no marker on the trunk, so sideways trunk tilt is not quantified and may have affected the abduction angle, which is one of the very variables separating the groups; the authors flag this and recommend correcting for it in future measurements.

The sample is men only, Japanese, at high school and university. «Elite» here means the ten highest scorers out of thirty, at 633 points out of 720: a good level, not that of a senior national team. With ten archers per group the distributions overlap a good deal, and the standard deviation of the lower trapezius in the elite is 15.7 percentage points on a mean of 54.0.

Two points in the text do not agree. The results describe the upper-to-lower trapezius ratio as significantly higher in the elite than in the beginners, while the figures (1.23 against 2.33) and the discussion say the opposite, that it is lower in the elite: this record follows the figures and the discussion. The EMG filter is described as high-pass at 500 Hz and low-pass at 20 Hz, which taken literally would pass nothing; a band between 20 and 500 Hz, as is usual, is the reasonable reading, but that is what the text says. The percentages of maximum contraction for biceps and triceps are not reported in the body of the paper, which gives only the note that the triceps stays between 10 and 20%.

The mechanical explanation, that the lower trapezius fixes the scapula to the spine, rests on kinesiology textbooks rather than on measurements made here; one of the two citations offered in support is a book on Amazonian ethnobotany, which has no bearing on the matter. The available text is the accepted version before typesetting, without the tables: the figures in this record come from the body of the article.

The most useful finding is the comparison between two parts of the same muscle. It is not the trapezius as a whole that separates the levels: the upper trapezius works the same way at every level, while the lower trapezius goes from 34% to 54% of maximum contraction from beginners up to elite. This is the measurement behind the instruction to draw with the back and not to lift the shoulder, and it says something precise: the point is not to switch off the upper part of the trapezius, which stays active in everyone, but to add work in the lower part. The ratio between the two, falling from 2.33 to 1.23, sums up the same shift in a single number.

The arms go the other way. In the elite the biceps and triceps work less, and the biceps is less active even with the elbow less flexed. For an archer this is the simplest check to run on yourself: a drawing arm pulling with the biceps is a sign that the work is not coming from the scapula.

On the angles, the elite had the drawing shoulder 7 to 8 degrees less open and the elbow about 5 degrees less flexed than the other two groups. These are group means, not a position to copy: within each group the spread is 4 to 6 degrees, and the study did not measure trunk tilt, which changes how the shoulder angle reads. Rather than a numerical target they point to a direction: a drawing arm more closed, not more open.

None of these figures says that training the lower trapezius will raise your score. The study photographs thirty archers once, and those with the higher scores also had more years of shooting behind them. What remains is a pointer to where to look when checking your own position at full draw, and one more reason why scapular stability work sits in archers' programmes.