## 2 Materials and Methods
### Assessment Sessions  
Assessment sessions were performed at 2 time points, before starting (T0) and after completing (T1) the training program. Each session took approximately 1.5 h to complete and was performed on separate days from typical training sessions to avoid fatigue. The evaluation involved both upper extremities and included robotic and non-robotic measures, such as strength and clinical tests. For each limb, the robotic assessment evaluated:  
1. Active and passive wrist ROM in flexion/extension and radial/ulnar deviation. Participants moved actively or were passively moved by the WristBot towards each direction until they reached maximal excursion. The outcome measure was maximal wrist rotation in degrees recorded by encoders along each direction. 2. The ability to track a target moving in the space identified by flexion/extension and radial/ulnar deviation. Without any assistive force, participants actively moved the handle of the robot to follow a target over a Lissajous figure (figure-eight shape) for 3 min. The pronation/supination plane was locked during the task. For each participant, the size of the figure never exceeded the 80% of the active ROM previously assessed. The trajectory was described by the following law of motion Equation (1): \[\left\{ \begin{array}{c}x=80\%*\min(ROM)*\sin\left(\frac{2\pi t}{T}\right) \\ y=80\%*\frac{1}{2}\min(ROM)*\sin\left(2*\frac{2\pi t}{T}\right)\end{array} \right.\] (1) where \(\min(ROM)\) is the minimum active ROM among the four directions assessed and \(T=30\) s (the duration of a complete lap). Outcome measures computed from these data were the Tracking Error (TE) and the Figural Error (FE). TE was defined as the mean angular distance in degrees between end-effector and target position at each time point. This outcome measure evaluated the performance, taking into account the difference in velocity between the end-effector and the target. TE was computed starting from the data recorded by the encoders along the flexion/extension (\(x\) [deg]) and radial/ulnar deviation (\(y\) [deg]) planes. Robot encoders recorded angular data, i.e., rotations along each degree of freedom. The measure is obtained through Equation (2): \[TE=\frac{\sum_{i=1}^{N}\sqrt{\left(x_{T,i}-x_{H,i}\right)^{2}+\left(y_{T,i}-y_{ H,i}\right)^{2}}}{N}\] (2) where \(T\),\(i\) and \(H\),\(i\) are the target and the end-effector positions at each time sample and \(N\) is the total number of time samples. FE was measured to characterize performance as the trajectory of the participant from the ideal figure-eight shape (target trajectory), regardless of differences of speed between target and end-effector. FE was measured in degrees and computed as shown in Equation (3): \[dist_{AB}(i) =\min_{j}\parallel A_{i}-B_{j}\parallel i=1,2,\ldots n\] \[dist_{BA}(j) =\min_{i}\parallel A_{i}-B_{j}\parallel j=1,2,\ldots m\] (3) \[FE =\frac{\sum_{i=1}^{i}dist_{AB}(i)+\sum_{i=1}^{m}dist_{BA}(j)}{n+m}\] where \(A\) and \(n\) are the time series (\(A[x(t)\),\(y(t)]\)) and total samples of the target trajectory and \(B\) and \(m\) are the time series (\(B[x(t)\),\(y(t)]\)) and total samples of the end-effector trajectory [20]. Assessment of strength included:  
1. Maximum grip force to measure overall grip strength. This was performed twice on each limb and the highest force in kg was recorded (Jamar Smart Digital Hand Dynamometer, Performance Health, Warrenville, IL, USA). 2. Grip force endurance test to measure muscular endurance on each limb. Participants gripped the dynamometer at 50% of their maximum grip force and the time tofatigue in seconds (defined as when the participant could no longer hold 50% of their maximum for 2 consecutive seconds) was recorded. 3. Maximum isometric wrist force measured in kg was determined for flexion/extension and radial/ulnar deviation using a stationary load cell (Model: BG 500, Mark-10 Corporation, New York, NY, USA). Finally, clinical outcome measures included: 1. 19-Hole Peg Test (9-HPT) was performed twice on each limb.