['Although abdominal muscle morphology is symmetrical in the general population, asymmetry has been identified in rotation sports. This asymmetry includes greater thickness of obliquus internus abdominis (OI) on the non-dominant side in cricketers. Cricket fast bowlers commonly experience low back pain (LBP) related to bowling action, and this depends on trunk muscle control. This study aimed to compare abdominal muscle thickness between fast bowlers with and without LBP.', 'Cross sectional descriptive study.', 'Twenty-five adolescent provincial league specialist fast bowlers (16 with and 9 without LBP) participated. Static ultrasound images (US) of OI, and obliquus externus (OE) and transversus abdominis (TrA) were captured on the dominant and non-dominant side in supine.', 'Total combined thickness of OE, OI and TrA muscles was greater on the non-dominant than dominant side (p=0.02) for fast bowlers without LBP, but symmetrical for those with pain. Total thickness was less on the non-dominant side for bowlers with pain than those without (p=0.03). When individual muscles were compared, only the thickness of OI was less in bowlers with LBP than those without (p=0.02). All abdominal muscles were thicker on the non-dominant side in controls (p<0.001) but symmetrical in LBP.'] Is symmetry , not asymmetry , of abdominal muscle morphology associated with low back pain in cricket fast bowlers?