Trunk extensor-to-flexor muscles strength and endurance disproportion are major factors in the aetiology of low-back pain. There are still insufficient studies on the assessment and training of the trunk flexors'endurance compared with the extensors. Decreased trunk flexor muscles' endurance is linked to incidences of chronic and recurrent low-back pain. Therefore, normative database of abdominal muscles' endurance are important in identifying alterations of the trunk musculature from normal and in clinical evaluations of disability or rehabilitation outcome in low-back pain. Furthermore,...