Device for increasing the training effect in a horse, consisting of essentially a sheet of mat-like material (1) adapting to and attachable to the horse's back. The mat-like sheet (1) is, over a substantial area, equipped with slits (9) going through the mat, in order to improve flexibility, and also of cuts (3, 4) that take up a position in essentially the area of the highest point of the horse's rear scapulae, which permits the overlapping of the parts of the mat remaining on different sides of the cut (3, 4).