In rehabilitation robotics, a human-in-the-loop system implies safety depends on:

• A. A system where the user actively participates in control or supervision; safety depends on user input as well as device autonomy.
• B. A system where the device runs entirely without any user input.
• C. A system where safety depends on user input as well as device autonomy.
• D. A system with external supervision only.

Answer: (C)

In rehabilitation robotics, safety in a human-in-the-loop system comes from the collaboration between the person and the machine. The user provides intent, effort, and real-time feedback, while the device runs its autonomous control and safety mechanisms (like limiting forces, adapting assistance, and fault handling). The overall safety is not guaranteed by the user alone or by the device alone; it emerges from how well the human input and the device’s autonomous actions work together. If you relied only on the device without user input, or only on external supervision, the system could fail to respect user intent or to react to disturbances in real time. Therefore, safety depends on both user input and device autonomy—the joint, interactive system.