# Adjustable Stiffness-Based Supination-Pronation Forearm Physical Rehabilitation
## 1 Introduction
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Device** & \begin{tabular}{l} **Supination–Pronation** \\ **Torque (Nm)** \\ \end{tabular} & \
\begin{tabular}{l} **ROM** \\ \end{tabular} &
\begin{tabular}{l} **Characteristics** \\ \end{tabular} \\ \hline MIT MANUS 1998 [29], 2005 [30] & 1.85 & 180\({}^{\circ}\) & Active and passive device configured to assist arm joints movement and hand grasping training through a graphic module that provides a series of video games that the patient must complete. \\  & & & Performs wrist bend, adduction, extension, and arm stretching. It has a mechanism to achieve forearm rotation and elbow bend and stretching. \\  & & & A lightweight and compact wrist and forearm rehabilitator with pneumatic actuators and force compensation control. \\  & & & Practical device for clinical implementation with two bearings that provide mechanical robustness and easy to use for the supination–pronation ROM. \\  & & & Facilitates rehabilitation of the forearm in supination–pronation, wrist in flexion-extension, and radial-ulnar deviation. It is shown to provide grip force measurements. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of wrist–forearm rehabilitation devices. Figure 1: Supination–pronation of the entire ROM. The study reported in this paper focuses on the development and control of an original adjustable stiffness rehabilitation device that is lightweight and accessible. This rehabilitation meets the needs of wrist-forearm supination-pronation rehabilitation protocols that consider the tracking of a cyclic trajectory and the regulation of its stiffness, representing the torque that potential users need to overcome in order to regain strength in their muscles. No individuals with specific medical conditions (physical affectations) participated when performing the experimental tests reported in this paper. A healthy volunteer signed an informed consent document to participate in the experimental tests oriented to evaluate the performance of the device. The study is not oriented to clinical studies related to the evolution of patients' medical conditions using the adjustable stiffness rehabilitation. This paper presents a new medical device focusing on its performance under a closed-loop control configuration in order to track specific trajectories and adjust the system's stiffness. Rehabilitation depends on the intensive and continuous practice of movements and exercises. Physical rehabilitation consists of three exercise phases: passive, active-assisted, and active [37; 38]. In conventional therapy sessions, for passive exercises, also known as passive ROM exercises, a therapist helps in moving muscles and joints through their full ROM and the patient does not exert any effort. Active-assisted exercises are executed when the patient's muscles are weak; i.e., the patient has difficulty in performing the exercises by himself/herself; then, a therapist assists movements. Active exercises are performed when the patient can move without assistance; in this phase, external resistance that helps in increasing power and endurance of the muscles is useful and desirable. Supination-pronation rehab exercises help regain motion and build strength in one of the most crucial body parts: the forearm. Without the proper functioning of this part of the body, performing ADL would be difficult and is even impossible. When a patient is performing rehabilitation for the forearm, the following general guidelines are recommended in [38; 39; 40]: