Schildkröt sling trainer Fitness: The gym that fits in your pocket - The Schildkröt sling trainer Fitness is a versatile training device that takes up little space and fits in any drawer or travelling bag. At the same time, you can train every part of your body with just one piece of equipment. You can quickly and easily adjust the belt length to your body size or for the corresponding exercise using the metal buckles. The constant instability during the exercises forces the body to make reactive compensatory movements. In addition to coordination, this also strengthens the deep muscles: this can promote a healthy posture and prevent everyday complaints such as back and neck pain.