Approximately 40–60% of runners at some time experience the performance-diminishing condition of exercise-related transient abdominal pain (ETAP), more commonly referred to as the running or side stitch. Although ETAP incidence increases with consumption of foods,and is reduced with age and training volume,the precise cause of ETAP symptoms remains unclear.Recent literature has proposed several different aetiologies of ETAP, including irritation of the parietal peritoneum, cramping of the abdominal musculature, diaphragmatic ischaemia and stress ofthe peritoneal and subdiaphragmatic ligaments. Morton and colleagues observed that in those who regularly experience ETAPthe most common locations for pain is the left and right lumbarregions of the torso and this location is consistent with pain fromthe intercostal nerves, which also service the parietal peritoneum.ETAP is regularly provoked when participating in activities thathave a significant amount of force transmission through the trunk,for example running and horse riding, and appears less commonly in cycling.During activities involving large displacementsof the abdomen (running/horse riding) or rotation (swimming)it is thought that there is excessive movement of the abdominal contents, which stresses the surrounding somatic anatomical structures.The local stabilising muscles of the spine, including transversus abdominis (TrA), internal obliques, lumbar multifidus,quadratus lumborum, pelvic floor muscles and the diaphragm,are involved in providing protection of the spinal column whilestationary and during functional movements.Their role in providing protection against posterior trunk musculoskeletal pain has previously been established, with Hodges and colleagues repor-ting evidence that a loss or delay of feed-forward activation of TrAis associated with chronic and recurrent low back pain.Therole of these muscles in controlling the more anterior trunk painassociated with ETAP has not been established.Contraction of the TrA leads to decreased abdominal circumference via increased tension of the thoracolumbar fascia.Thisdecreased abdominal circumference along with the cocontractionof the diaphragm and pelvic floor muscles produces an increasein intraabdominal pressure. Either or both of these variables may be influencing factors on the mobility of the abdominal contents. Therefore, we hypothesise that better TrA function mayreduce abdominal content mobility and contribute to a reducedincidence of ETAP. Consequently, this study investigated TrA
function in relation to frequency of ETAP experienced by the physicallyactive population to determine if TrA contraction and strength isgreater in those who are asymptomatic of ETAP in comparison tothose who are symptomatic of ETAP.