Trunk muscles in archers: Dar 2025 study

The question was whether archery, an asymmetrical and repetitive movement, leaves asymmetries in the trunk muscles. The answer, in 15 young Israeli elite archers, is that none show up. No measure separates the dominant from the non-dominant side: multifidus thickness at rest and during contraction at L4-L5 and L5-S1, thickness of the transverse abdominis and internal oblique, percentage change from rest to contraction, seconds held in the side bridge, ratio of side bridge to trunk extension. Every comparison sits above 0.05, with small to medium effect sizes; the closest to the threshold is the multifidus at rest at L4 (3.35 against 3.14 cm, p = 0.07). The side bridge hold had a median of 92 seconds on both sides, and its ratio to trunk extension was 0.81 on the dominant side against 0.76 on the other.

Mean asymmetry between the two sides, calculated as a percentage difference, runs from 5.1 to 7.9 per cent for the back muscles and from 15.4 to 18.8 for the abdominal ones, with standard deviations of the same order as the means. In individual athletes the difference between sides reached 19 per cent for the back and 47 per cent for the transverse abdominis and internal oblique. The most asymmetrical measure was not a muscle but a test: the side bridge hold, with a mean difference of 44.8 per cent between sides and a standard deviation of 31. Between males and females the only difference concerns the internal oblique on the dominant side, thicker in the males at rest (0.91 against 0.70 cm) and during contraction (1.25 against 0.90). None of the athletes reported low back pain; two reported pain in the thoracic area.

This is a retrospective analysis of medical files: the authors went back to the start-of-season screenings carried out by the physiotherapists of the sports medicine centre at the Wingate Institute, which supports Israel's Olympic and Paralympic teams, and analysed those of the archers. The sample is therefore whatever the archive held: 15 athletes, 10 male and 5 female, mean age 17.2 years, 170.6 cm and 71.8 kg, training at least seven archery sessions a week of three hours each plus two strength sessions.

Ultrasound was performed with a portable device and a 6 MHz convex transducer, always by the same physiotherapist. The multifidus was measured prone, with the transducer longitudinal and lateral to the spinous process until the L4-L5 and L5-S1 joint was identified, from the facet joint to the subcutaneous tissue, at rest and during active extension of the opposite leg. The transverse abdominis and internal oblique were measured supine with the knees flexed, transducer on the midaxillary line between the iliac crest and the ribs, at rest and during the abdominal drawing-in manoeuvre, with the image frozen at the end of expiration and the measurement taken 2 cm from a fixed reference. Each measurement was repeated twice and averaged. The clinical tests were two timed holds, the side bridge on one elbow and trunk extension prone with the legs fixed to the bench. The data were not normally distributed, so comparisons between sides used the Wilcoxon signed rank test and comparisons between sexes the Wilcoxon two-sample test, with no correction for multiple comparisons, a choice the authors state.

Fifteen athletes, five of them female, are too few to rule a difference out: a lack of significance here means that an asymmetry, if there is one, is smaller than this sample can resolve, not that none exists. The authors say so themselves, along with two other limits: the ultrasound was taken at rest and during standardised contractions, never during the draw and the release, and there is no comparison group.

The formula used for asymmetry takes the absolute difference, so it says how far the two sides diverge but not which of them is larger. A group in which half the athletes are thicker on the right and half on the left comes out asymmetrical individually and symmetrical in the comparison between sides, which is exactly the picture in these data. The largest figure, the 44.8 per cent difference in the side bridge hold, comes from a test timed to failure, which also depends on how hard someone pushes. No reliability indices are reported for this operator's ultrasound measurements. The files do not record bow type or draw weight, so the athletes' discipline is undetermined, and nothing about shooting was measured. A mean age of 17.2 years with a standard deviation of 2.7 includes athletes still growing, and the authors note that adaptations to years of asymmetrical loading may not yet have developed.

For an archer the content comes down to one thing: in fifteen young athletes shooting more than twenty hours a week, the deep trunk muscles measured by ultrasound were equally thick on both sides, and the back was more symmetrical than the abdomen. This is no guarantee that archery does not produce imbalances, since the sample is small and young and nobody was followed over time; it is the observation that at that age, under that load, differences between sides do not yet show.

Variation from one athlete to the next does show: the difference between sides reached 47 per cent for the abdominal muscles and 45 per cent for the side bridge hold. That bears on how such tests are read rather than on any programme, because a left-to-right difference measured once does not separate adaptation to shooting from the ordinary variability of people who shoot. The authors close by recommending start-of-season screening and trunk exercises, but those recommendations are not tested here: the study evaluated no programme and recorded no injuries. Pain that persists is a matter for a doctor or a physiotherapist, not for the reading of a record.