## 2 Research Methodology
### Search Strategy
#### 2.2.1 Search String  
In this study, the search string has been defined on the basis of the PICO strategy [33; 34]. This strategy considers that the four essential elements to be addressed in any clinical research question are Population (P), Intervention (I), Comparison (C), and Outcomes (O). _Population_ refers to the patient or the problem to be addressed, which in the context of our SMS is determined by the studies that describe remote rehabilitation systems for young patients. The _intervention_ represents the exposure to be considered, defined in the SMS described herein by the interaction paradigms and devices that allow the rehabilitation system to be used remotely (mainly at home), the gamification techniques or serious games included in the system to complete the physical therapy or rehabilitation, and the adaptation capabilities provided by the system depending on the user needs. The _comparison_ refers to the analysis regarding the effect produced by the intervention on the group that receives it and on the group that does not receive it; however, this is not applicable to systematic mapping studies, since their main objective is to characterize the studies available in the literature. Finally, \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**ID** & **Question** & **Motivation** \\ \hline \multirow{3}{*}{MQ1} & \multirow{3}{*}{In which places are the rehabilitation systems used?} & To determine if the system is designed to be used at home, preventing the patient from being checked by the therapist on the rehab centre. \\ \cline{3-3}  & & \\ \hline \multirow{3}{*}{MQ2} & What is the communication mechanism between the user of the rehabilitation system and the therapist? & To know how the patient receives the feedback provided by the therapist. \\ \hline \multirow{3}{*}{MQ3} & \multirow{3}{*}{What are the devices used by the system?} & To discover the devices most frequently used in rehabilitation systems to capture the movements of the patient. \\ \cline{3-3}  & & \\ \hline \multirow{3}{*}{MQ4} & \multirow{3}{*}{Which interaction paradigms are used?} & To explore the different paradigms used to interact with the system. \\ \cline{3-3}  & & \\ \hline \multirow{3}{*}{MQ5} & \multirow{3}{*}{Which interaction styles are used?} & To identify which are the interaction styles most used. \\ \cline{3-3}  & & \\ \hline \multirow{3}{*}{MQ6} & Is there any methodology that therapists should follow to define the rehabilitation therapy? & To know if exergames should be designed and created following certain steps. \\ \hline \multirow{3}{*}{MQ7} & Do the rehabilitation systems provide any support for adapting and customising rehabilitation exercises? & To determine if the system is capable of personalizing the exercises based on the patient’s needs and his or her evolution throughout the therapy. \\ \hline \multirow{3}{*}{MQ8} & Do the systems provide any capability to automatically generate the exergames? & To know if the rehabilitation system is able to facilitate efficiently the creation of exergames. \\ \hline \multirow{3}{*}{MQ9} & Do the systems include any gamification technique? & To identify whether the rehabilitation systems include gamification or serious games to motivate young patients. \\ \hline \multirow{3}{*}{MQ10} & \multirow{3}{*}{What are the gamification techniques used?} & To explore the main and frequent gamification techniques used by the rehabilitation systems. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mapping questions and their motivations. the _outcome_ includes the results which are of interest, that is, the devices, paradigms and techniques used to develop remote rehabilitation systems based on gamification and serious games for young patients and supporting adaptation capabilities to the user needs. Table 2 summarizes the strategy used to define the search string.