# A Systematic Literature Review of Intelligent Data Analysis Methods for Smart Sport Training
## 3 Research Methodology
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Database Name** & **URL** & **No. Total Results** & **No. Included Results** \\ \hline ACM Digital Library & dl.acm.org & 33 & 20 \\ IEEEXplore & ieeeexplore.ieee.org & 316 & 41 \\ ScienceDirect & sciencedirect.com & 113 & 16 \\ Scopus & scopus.com & 490 & 87 \\ Google Scholar & scholar.google.com & 17,900 (270)E & 43 \\ \hline Total & & & 180 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Databases with search results and total after removed duplicates. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **ACM DL** & **IEEEX** & **ScienceD.** & **Scopus** & **G. Scholar** \\ \hline ACM Digital Library & / & 0 & 0 & 1 & 1 \\ IEEEXplore & 0 & / & 1 & 10 & 3 \\ ScienceDirect & 0 & 0 & / & 3 & 6 \\ Scopus & 1 & 10 & 3 & / & 7 \\ Google Scholar & 1 & 3 & 6 & 7 & / \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Databases’ matrix with duplicates shown between each database:database pair. * Google Scholar results were searched until there were at least two consecutive pages of non-relevant results (20), so a total of 270 results were inspected. The attributes identified for each study are shown in Table 3. When research proposed general solutions/models for sport training across multiple disciplines but the model was tested and/or used only on a specific discipline or athletes from a specific discipline, that discipline was identified as the only sport of application in the Table. Differentiation between team and individual sports was done on an individual basis, and was determined from each piece of research individually (e.g., tennis may in some cases refer to 1 vs. 1 matches, and in another to 2 vs. 2 matches). The training phases presented were referenced from [6], and their maturity was identified according to the [11] abstraction of H2020 European Union Technology Readiness Level (TRL) [7]. The proposal [11] mapped the nine levels of TRL to the four ordinal values:  
* Idea (TRL 0-3). * Validation (TRL 6-7). * Production (TRL 8-9). By inspecting the title, keywords and the abstract 207 studies were initially selected for review, out of which 27 were duplicates. The remaining 180 studies were selected for full text inspection. However, we could not find the full text for 25 of the studies, but this is of no concern, since the unavailable studies were of dubious origin, and we did not detect them to be cited in any of the papers (when inspected on Google Scholar). Of the 155 fully available studies, 109 were selected as relevant for our literature review and 46 were excluded. The whole review process is shown briefly in Figure 2.  
The field of smart sports training has been rising in popularity over the last few years, as demonstrated in Figure 3. The first identified study was from the year 2006, and between 2006 and 2012, one to four studies were published in the field each year. Its popularity started increasing sharply \begin{table}
\begin{tabular}{c c c} \hline \hline
**Attribute Category** & **Attribute** & **Range** \\ \hline Reference & Reference no. & [citation number] \\  & Authors & - \\  & Title & - \\  & Year of publication & - \\ Sport & Type & individual, mixed (e.g., tennis in pairs), team \\  & Name & name of the sport \\ Research & Methods used & algorithms identified in Section 4 \\  & Focus & - \\  & Result & - \\ Training phases & Planning & 0—not addressed, 1—idea, 2—prototype, 3—validation, 4—production \\  & Realization & \(|\) | | \\  & Control & \(|\) | \\  & Evaluation & \(|\) | \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Attributes screened in the reviewed studies. Figure 2: Review process. from the year 2013 onward, with no less than four research studies in any of the following years. Of the research studies, 23 and 22 of them in this review were published in 2018 and 2019, respectively, which contrasts sharply with previous years. The data for 2020 are of a different shade and hue, since the year is still in progress and we anticipate more research to be published.