A mechanical resistance assembly employs a resilient strap which is stretched by the use of a pulley system pulled by the user. The assembly has an adjustable mechanical advantage and in a preferred use thereof being selectively coupled to a rigid, stable frame in any one of a variety of different configurations...http://www.google.fr/patents/US4521013?utm_source=gb-gplus-shareBrevet US4521013 - Resilient type exercising device
