Muscle fatigue over 100 arrows: Naderza 2024 study

Twenty Polish traditional archers, fourteen men and six women averaging thirty years of age, with five and a half years of practice, shoot one hundred arrows in a single session. Before starting, after the first fifty and after the second fifty, the electrical activity of six muscles of the string arm is measured during a maximum voluntary contraction: middle and posterior deltoid, upper, middle and lower trapezius, infraspinatus. For each muscle the mean and maximal amplitude of the signal are recorded, along with the median frequency of its spectrum, which is the classic fatigue index because it falls as a muscle tires.

The picture that emerges is not uniform, and this is the most important thing to know.

Two muscles show the fatigue signature, and they show it between the fiftieth and the hundredth arrow. The infraspinatus falls in mean amplitude from 162.0 to 113.2 microvolts (p = 0.033), in peak from 357.7 to 218.5 (p = 0.018) and in median frequency from 60.7 to 49.3 hertz (p = 0.021): amplitude and frequency fall together, which is the coherent picture. The lower trapezius falls in peak from 408.5 to 258.3 microvolts (p = 0.029).

Two others go the opposite way. In the middle deltoid the mean amplitude after one hundred arrows is higher than at rest, 224.6 against 182.3 microvolts (p = 0.006). In the upper trapezius the mean amplitude rises at every step, from 130.2 to 164.9 after fifty arrows (p = 0.008) and to 175.5 after one hundred (p < 0.001), and the peak from 325.0 to 404.5 and to 498.4 (p = 0.013 and p = 0.005). In the posterior deltoid the peak after one hundred arrows is higher than at rest, 742.9 against 619.4 (p = 0.020), and its median frequency rises rather than falls, from 61.9 to 66.5 after fifty and to 65.6 after one hundred (p < 0.001), which is the opposite of a fatigue sign. The middle trapezius changes in nothing.

Those who habitually shoot more than one hundred arrows per session do not respond differently from those who shoot fewer: no interaction between time and group in any of the six muscles, and no difference between the two groups on any measure. The authors say so.

The abstract, however, summarises it thus: amplitude tends to rise from baseline to fifty arrows, with significant declines observed after one hundred, indicating muscle fatigue. That sentence describes the infraspinatus and the lower trapezius, and inverts the others: in the middle deltoid and the upper trapezius the value after one hundred arrows is significantly higher than the starting one, not lower.

A cross-sectional study with repeated measures, declared as following the STROBE guidelines. Approval from the bioethics committee of the Medical University of Gdańsk dated 14 December 2023, with a resolution number, written consent, and the principles of Helsinki.

The hundred-arrow threshold is not arbitrary, and the article gives its provenance: it is the number coaches routinely advise not to exceed in a session. It is the same threshold the registry's claim rests on.

Convenience sampling among the archers of a regional club, recruited through announcements at the club and on social media. Of the fifty considered, thirty were excluded for upper limb injuries or refusal, leaving twenty. Inclusion criteria: training at least twice a week over the past six months, good health with no injury or illness in the preceding six months, being over eighteen, attending every phase. Excluded were upper limb injuries within the last six months, pain in shoulder, elbow or wrist, hypermobility, and neurological or connective tissue disease.

The twenty are traditional archers competing in traditional tournaments: a mean age of thirty with a deviation of 6.8, seventy-eight kilograms, one hundred and seventy-six centimetres, five and a half years of practice with a deviation of 4.8, a declared frequency of 1.6 ± 0.8 training days a week and 111.0 ± 46.4 arrows per session. They were split by how many arrows they habitually shoot, declared in a questionnaire before the study: thirteen with one hundred or fewer (86.2 ± 20.6) and seven with more than one hundred (157.1 ± 46.4).

The measurements were taken at the turn of 2023 and 2024 at the archers' training facility, individually, in the afternoon around four o'clock, after forty-eight hours of rest. The first immediately after the warm-up and before starting, the second five minutes after the first fifty arrows, the third after the second fifty.

Only the string arm is measured, the right one in nineteen cases out of twenty. Surface electrodes positioned according to the SENIAM recommendations, with the skin shaved, abraded and cleaned with alcohol. The signal filtered between 15 and 500 hertz, sampled at 1500 hertz with a 16-bit converter, full-wave rectified and smoothed with the root mean square over a moving window of three hundred thousandths of a second. Each maximum voluntary contraction lasts three seconds.

The analysis uses a mixed analysis of variance to study the interactions between time and group, with partial eta squared and Bonferroni-corrected pairwise comparisons, in JASP 0.18.3, with a threshold of 0.05. Normality checked with Kolmogorov and Smirnov, homogeneity with Levene's test.

No measure of force accompanies the electromyography: of the maximum voluntary contraction the electrical signal is recorded and not the force produced. And no score was collected.

The abstract does not describe the article's results. It says amplitude rises from baseline to fifty arrows and then declines significantly after one hundred, indicating muscle fatigue. In the results the significant declines after one hundred arrows occur in two muscles out of six, the infraspinatus and the lower trapezius, and they are declines relative to fifty arrows. In the others the direction is opposite and statistically detectable: in the middle deltoid the mean amplitude after one hundred arrows is higher than at rest (224.6 against 182.3 microvolts, p = 0.006), in the upper trapezius it rises at every step up to 175.5 against 130.2 (p < 0.001), and in the posterior deltoid the peak after one hundred arrows is higher than at rest (742.9 against 619.4, p = 0.020). Whoever reads the abstract takes away a uniform picture of giving way that the data do not show.

There is then a result running against fatigue that the article does not comment on: in the posterior deltoid the median frequency rises, from 61.9 hertz at rest to 66.5 after fifty arrows and 65.6 after one hundred, with p below 0.001. Median frequency falls as a muscle tires; here it rises, and in a muscle central to the draw.

The electromyography is accompanied by no measure of force. The signal is recorded during a contraction declared to be maximum voluntary, but of that contraction only the electrical signal is known, not how many newtons it produced. An amplitude that falls during a maximal contraction may mean fatigue, or a smaller effort: after one hundred arrows, an archer pushing a little less on the dynamometer produces the same decline. It is the limit that weighs most on the interpretation, and it applies both to the infraspinatus declines and to the deltoid increases.

The methods describe the design with the numbers inverted: two assessments for three groups, while there are three assessments (rest, fifty, one hundred) on two groups (thirteen and seven archers). It does not change the analysis, but it is the sentence meant to tell a reader which analysis was done.

One pair of values comes from the row above. For the upper trapezius the time effect on median frequency is reported as F equal to 2.948 with p equal to 0.822 and eta squared 0.011: an F of 2.948 on 2 and 18 degrees of freedom gives p equal to 0.078, and those two numbers, 0.822 and 0.011, are identical to those of the interaction row just above, where F was 0.197. The conclusion does not change, since 0.078 remains above the threshold, but the published value is not that test's.

The normalisation is described and not used. The methods explain that normalisation was to the maximum voluntary contraction as a reference level, and then every outcome is reported in absolute microvolts. Since the measurement is itself a maximal contraction, those microvolts are raw amplitudes, and as such they do not compare between people or with the values of other studies.

On the sample, two things. The inclusion criterion asked for at least two training sessions a week over the past six months, and the sample declares 1.6 ± 0.8 days a week: the group described does not meet the criterion by which it was selected. And they are traditional archers competing in traditional tournaments, with five and a half years of practice and a mean age of thirty: the movement, the draw weight and the hold of traditional archery are not those of Olympic recurve, so the transfer has to be argued rather than assumed.

The comparison between the two habit groups, finally, runs on thirteen and seven people, and the group of seven is too small for the absence of an interaction to say anything: that those habitually shooting more than one hundred arrows do not respond differently is consistent with the data, but also with lacking the sensitivity to see it. No score was collected, so nothing links these signals to accuracy, and only the string arm was measured.

This is the only study that stops exactly at one hundred arrows, and the threshold was not chosen at random: the article says it is the number coaches advise not to exceed in a session. So it is the right place to look, and what is seen there is more interesting than a simple yes.

Not all of the shoulder gives way, and it does not give way in the same manner. Between the fiftieth and the hundredth arrow the infraspinatus, one of the muscles holding the head of the humerus in place, falls both in amplitude and in median frequency: that is the coherent picture of fatigue, and the lower trapezius accompanies it with a lower peak. At the same time the deltoids and the upper trapezius raise their activation, and the upper trapezius raises it at every step. Read together, this is the pattern a coach recognises: when the deep stabilisers let go, the work shifts to the superficial ones, which pull the shoulder up. It is the electrical description of an archer who after eighty arrows starts holding with the neck.

What this study cannot say, and it is worth remembering, is how much of that decline is fatigue and how much is reduced effort: of the maximal contraction the electrical signal is recorded but not the force produced, so an archer pushing a little less at the end of a session produces the same number. And no score was measured, so nothing says those signals cost arrows.

One result deserves to be known by anyone planning volumes: those who habitually shoot more than one hundred arrows per session do not respond differently from those who shoot fewer. With seven people in that group it is a weak result, but it points towards saying that getting used to high volumes does not protect against the stabilisers giving way.

Two warnings about transfer. These are traditional archers, with a movement and a hold different from Olympic recurve, and only the string arm was measured: of the bow arm nothing is known. The registry keeps this work as the most direct measurement available on the hundred-arrow threshold, with the non-uniform picture it shows, and notes that the article's abstract describes it as a general collapse that its own data do not show.