An interactive exercise system with apparatus and methods to optimize muscle strength for rehabilitation, to improve or maintain fitness, and to enhance the performance of athletes. The system uses an electronically controlled linear actuator to generate resistance against the muscular force exerted by the user. The system includes sensors configured to detect acceleration, speed, velocity, position, direction of movement, duration, and the force applied by the user. A control system preferably continuously monitors the sensors, and instantaneously adjusts the adaptive actuator. This provides a proportional counterforce to the user force throughout the entire range-of-motion. A display panel allows the user to interact with the system in real-time. The objective of the user is to synchronize the exercise performance with a selected target goal, by correlating the user's movement relative to a position on a display panel.