In the last few years epidemiological surveys have shown correlation between low endurance capacity of the trunk extensors and low back trouble. In this report two methods for the determination of trunk extensor endurance are compared. In method I the fixated subject is lying prone with the cranial border of the iliac crest at the edge of a couch. The endurance time for maintaining the upper part of the body horizontal was measured (max. 240 s). In method II the standing subject performed a horizontal isometric pull on a strain gauge force transducer equivalent to 60% MVC of the trunk extensors. The time until complete exhaustion in the muscles (inability to maintain the preset force level) was determined. The methods were applied to two groups of normal, healthy subjects: 1) 23 female (22-61 years) and 53 male (27-60 years) postmen. 2) 10 male students (20-37 years). The results show that method II is preferable to method I, not least in the field of ergonomics. Method II is easily practicable and does not demand expensive or complicated equipment. Furthermore this method gives reliable results suitable for statistical preparation, and is not influenced by anthropometrical factors.