Cross-education of Skill and Strength in Healthy People Subjected to an Upper-limb Disuse Model

Fine Manual Dexterity

Fine manual dexterity will be assessed using the Functional Dexterity test (FDT). Using a stopwatch, the evaluator records the total time in seconds that the participant takes to complete the task.

Force control

In a seated position with the elbow flexed, participants will perform isometric contractions to reach a target torque guided by real-time visual feedback. The accuracy of maintaining these contractions in the wrist flexor and extensor muscles will be assessed using a Humac Norm isokinetic dynamometer (Computer Sports Medicine, Inc., Stoughton, MA, USA). Participants will perform a continuous 60-second isometric contraction exercise. During this period, participants will adjust their force level to between 10% and 30% of their maximum voluntary contraction (MVC) at 10-second intervals. Three attempts will be performed per limb. The Root Mean Square Error (RMSE) will be recorded.

Gross Manual Dexterity

This gross manual dexterity will be assessed using the same task performed during the experimental group's contralateral manual dexterity training. Specifically, participants will complete 15 trials, moving cylinders of varying weights across a gridded board following a sequence displayed on a smartphone. The time required to complete these 15 trials will be recorded.

Handgrip strength

Maximum lumbrical and cylindrical grip strength will be assessed using a Jamar Plus+ digital hand dynamometer. The highest value from three attempts will be recorded for each assessment

Joint Position Sense Test

Proprioception: Wrist flexion-extension joint position sense will be assessed using the Joint Position Sense Test (JPST). All measurements will be conducted with a Humac Norm isokinetic dynamometer (Computer Sports Medicine, Inc., Stoughton, MA, USA). Three attempts will be made per limb. The absolute error (difference in degrees between 30° and the angle achieved during the test) will be recorded.

Left/right judgment

Left/right judgment will be assessed using the Recognise™ application (Noigroup, Adelaide, Australia). Performance on the laterality judgment task was quantified using the Inverse Efficiency Score (IES), calculated as the average reaction time of correct responses divided by the proportion of correct responses (IES = RT / PC). 3 blocks of 20 images (60 images total). Maximum exposure time: 5 seconds per image.

Physical activity level

Weekly metabolic equivalents (MET-min/week) will be calculated using the validated Spanish version of the Global physical activity questionnaire (GPAQ).

Psychological Distress

Psychological Distress, including symptoms of depression, anxiety, and stress, will be assessed using the 21-item Depression, Anxiety and Stress Scale (DASS-21). This self-report instrument will be used to quantify the severity of emotional distress across these three domains. This scale has a minimum score of 0 and a maximum of 126 points (total score calculated by doubling the sum of the 21 items). Higher scores in DASS-21 indicate greater psychological distress.

Sleep Quality:

Sleep disturbances and overall sleep quality will be assessed using the Pittsburgh Sleep Quality Index (PSQI). This scale has a minimum score of 0 and a maximum of 21 points (higher scores indicate worse sleep quality)

Daily steps

Physical activity will be monitored using a Xiaomi Band 9 smartwatch (number of daily steps), which participants will wear throughout the seven-day mobilization period.