In this case, the physiotherapist is using Constraint-induced movement therapy.
In Constraint-induced movement therapy, the therapist forces the use of the affected arm, by restricting the movement of the arm. In this condition, the therapist block all the possible to work with an unaffected arm, which force the person to use the other arm, and hence, it helps in restoring the movement of the affected arm.
These preferences may have been advantageous in our evolutionary history, when food was less reliably available
-from quizlet
The aspect of his experimental process which is most important for obtaining reliable results is repeating his data collection many times.
