Side-to-side asymmetry in absolute and relative muscle thickness of the lateral abdominal wall in cricket pace bowlers

Background. The abdominal musculature plays a protective role against lower-back injury. Knowledge of the asymmetry in abdominal wall thickness in healthy, injury-free cricket pace bowlers may provide a useful platform against which pathology could be assessed and the effects of training could be evaluated.Objective. To compare side-to-side differences in absolute muscle thickness and activity of the abdominal musculature and to compare these measurements at the start, with those at the end of a cricket season among a group of amateur pace bowlers.Methods. This was a controlled longitudinal prospective study. Rehabilitative ultrasound imaging was used to assess abdominal muscle thickness in 26 right-handed, injury-free cricket pace bowlers at the start and at the end of a cricket season. Thickness measurements were done at rest, during an abdominal drawing-in manoeuvre (ADIM) and the active straight-leg raise (ASLR) on the left (-L) and right (-R).Results. The absolute thickness of the non-dominant obliquus abdominis internus (OI) was higher than that of the dominant OI at the start (p=0.001; ES=0.87) as well as at the end of the cricket season (p=0.001; ES 1.09). At the start of the season, the percentage change during the ADIM, thus muscle activity, was higher for the non-dominant OI than for the dominant OI (p=0.02; ES=0.51). Absolute thickness of the dominant obliquus abdominis externus (OE) at rest was significantly higher at the end of the season compared with the start of the season (p=0.0001; ES=0.85). During ASLR-R, the activity of the left transversus abdominis (TA) was significantly higher than that of the right TA during ASLR-L (p=0.03) when measured at the end of the season.Conclusion. This study highlights the possible muscle adaptations in absolute muscle thickness and activity as a consequence of the asymmetrical bowling action.