HAPTREX is a robotic retrofit system that closes the cost and data gap of digitizing strength training by upgrading the machines gyms already own. Commercial gyms face a bad choice today: keep analog equipment that produces no meaningful workout data, or spend roughly USD 20,000 per smart machine, writing off usable assets. HAPTREX changes the equation. It bolts onto existing machines and replaces weight plates with software-controlled robotic resistance. Its bidirectional force-feedback loop measures the user while controlling the load in real time, enabling isotonic, isokinetic, isometric, and velocity-based training, automated strength assessment, AI coaching, and Auto Spotting. Every movement is continuously recorded at 1 kHz, including force, position, velocity, and range of motion. At one-tenth the cost of replacement, HAPTREX turns every strength machine gyms already own into a connected, software-defined platform for training, assessment, and human performance data.