Abstract: A training device for the human or animal body includes a balance body with a movable centre of mass and a holder with which the balance body can be carried. The holder includes a harness with connectors for connecting to a torso of the body and with a cavity in which the balance body is at least partially received and fixed. The harness particularly includes a first part with connector for attaching to a back of the user and a second part connected releasably to the first part. The first part and the second part adjoin each other so as to form a cavity which is open on both sides and in which the balance part is at least partially received in substantially fitting manner.