This is the "original" arm-power prototype (although in about its 20th iteration). The bike is my own custom recumbent. The frame is my own design. It was put together by a professional framebuilder 20+ years ago. I first started working on adding arm power to it around 2000.
The arm motion is "controlled." The arm levers are connected – via a push-pull rod, or "power link" – to the crank assembly. That makes the rowing motion very smooth and efficient. The inertia of your feet and legs on the cranks carries the arm levers through top- and bottom-dead center.