Exercise-related transient abdominal pain (ETAP) affects 40–60% of the physically active population, is detrimental to performance but of unknown aetiology. Excessive movement of abdominalperitoneum is one proposed mechanism. Transversus abdominis (TrA) function may play a role reducingin the incidence of Exercise-related transient abdominal pain via the tensioning of the thoracolumbar fascia or increasing intraabdominal pressure. The aim of this study is to identify any relationship betweentransversus abdominis function and exercise-related transient abdominal pain, hypothesing that thosewith stronger transversus abdominis will have lower incidence of exercise-related transient abdominalpain.Design: Observational study design.Methods: Trunk muscle strength was measured clinically using the functional Sahrmann test. Contraction of transversus abdominis was measured by ultrasound imaging of resting muscle size and calculatingthe change in thickness with a voluntary contraction. Participants completed questionnaires describingany exercise-related transient abdominal pain symptoms, and were divided into four groups depend-ent upon frequency of any symptoms (never, yearly, monthly and weekly). Between group differenceswere analysed using analysis of covariance, with Bonferroni correction adjusting for age and training ofparticipants using STATA. Poisson regression determined incident rate ratios for relevant variables.Results: Data was obtained from fifty runners (28 male, 25.8 ± 7.0 years). Sahrmann test score andfrequency of Exercise-related transient abdominal pain were significantly different between groups(p = 0.002) with asymptomatic runners having significantly higher Sahrmann test scores (stronger mus-cles) than weekly and yearly Exercise-related transient abdominal pain groups (p = 0.001, p = 0.02). Therewere significant between group differences for resting transversus abdominis thickness (p = 0.034) butnot for transversus abdominis thickness change (p = 0.555).Conclusions: Participants who had stronger trunk muscles and larger resting Transversus abdominis sizeexperienced Exercise-related transient abdominal pain less.