Machines, apparatuses, systems and methods for providing adjustable tension to a cable system using a pivotally mounted leverage mechanism that employs an adjustably positionable weight. Embodiments are used in exercise and other muscle strengthening devices, and may include an electronic control system for monitoring, recording a user's progress, and for altering or releasing tension to the cable system based on feedback from the user. Embodiments include a user interface for inputting information for particular exercises or workouts, as well as outputting/downloading information following exercises or workouts. Other embodiments allow adjustment to the starting point of the lifting bar so that such machines may be used for bench presses, squats, cleans or curls.