Not sure about more specifics, patient might have been voluntary or forced, but he hides a keyboard to connect into himself when alone and hacks himself to enable escape. Implant control autonomous systems, and control metabolism, make himself stronger, etc. Ends up escaping and never recovered by the facility later, using his implant for his own benefit.
The patient might have been overweight computer geek at the start, but the implant help him lose the fat and get into super physical shape.