## 4 Discussion  
The first objective of the study was to analyze differences between EE\({}_{\text{Spiro}}\) and EE\({}_{\text{LPM}}\) during the team handball GBPT. As hypothesized, EE\({}_{\text{Spiro}}\) was greater compared to EE\({}_{\text{LPM}}\) during the entire test and all single heats. One explanation is that the metabolic power method [9] estimates EE for locomotion only on horizontal acceleration and not correctly for non-locomotive actions (e.g., passes, throws) and other movements (e.g., tackles, jumps) [13]. The second objective was to analyze the correlation between EE\({}_{\text{Spiro}}\) and EE\({}_{\text{LPM}}\). Correlation results for the entire test and all single heats were not significant (\(0.18\leq p\leq 0.99\)), with small correlation coefficients (\(r\leq 0.44\)). As previously explained, we suggest that a relatively large part (e.g., passes, throws, tackles, and jumps) of the total EE was undetected by the LPM system (shown by the difference between EE\({}_{\text{Spiro}}\) and EE\({}_{\text{LPM}}\)) and that this undetected EE in the EE\({}_{\text{LPM}}\) was not systematic. This was similar in all heats and therefore independent of inter-heat variations in movements and intensities. The third objective was to develop a regression model that predicts EE\({}_{\text{Spiro}}\) based on EE\({}_{\text{LPM}}\). This regression model may have the potential to use the more practicable LPM system and the metabolic power model for EE [9] instead of the impractical spiroergometry (the gold standard). The results have shown that the regression analyses were not feasible. The fourth objective was to investigate the REE compared with the EE during a pre-activated motionless rest for the estimation of net EE\({}_{\text{Spiro}}\). REE was very small \begin{table}
\begin{tabular}{c c c c c c c c c} \hline  & **Entire Test** & **H1** & **H2** & **H3** & **H4** & **H5** & **H6** & **H7** & **H8** \\ \hline \(r\) & 0.32 & 0 & 0.26 & 0.33 & 0.44 & 0.15 & 0.26 & 0.16 & 0.25 \\ \(p\) & 0.34 & 1 & 0.43 & 0.33 & 0.18 & 0.69 & 0.46 & 0.66 & 0.49 \\ \hline \end{tabular}
\end{table} 
Table 2: Pearson correlation coefficients (\(r\)) and significance level (\(p\)) between energy expenditure via spiroergometry and via local position measurement system for the entire test and every single heat (H1–H8). Figure 3: Energy expenditure via spiroergometry (EE\({}_{\text{Spiro}}\)) and via local position measurement (EE\({}_{\text{LPM}}\)) of the entire game-based performance test (GBPT) of one participant (P01). (\(6.8\pm 0.6\%\) of the gross EE\({}_{\text{Spiro}}\)) and the subtraction of REE did not affect the statistical results (difference and correlation analyses for the entire test and all single heats). We suggest that REE affects the underestimation of EE\({}_{\text{LPM}}\) in comparison with EE\({}_{\text{Spiro}}\) only to a limited degree. For an accurate comparison of EE\({}_{\text{LPM}}\) and EE\({}_{\text{Spiro}}\), EE during a pre-activated, motionless rest would be the more meaningful factor than REE, because the metabolic power method cannot estimate the increased EE for the internal processes in a pre-activated state. However, it seemed that the EE in the pre-activated, motionless rest were affected by EPOC after warm-up, because the EE exceeded common values during standing. A total of 86.5 \(\pm\) 7.8% of the gross EE\({}_{\text{Spiro}}\) across participants hardly represent valid EE for the pre-activated, motionless rest, and were therefore not subtracted for further analyses. The effect of additional EE during a pre-activated, motionless rest and potential EPOC after warm-up was also seen in an increased EE\({}_{\text{Spiro}}\) at the beginning of the GBPT (Figure 3). To compare the results in EE in the current study with previous studies during the various tasks at different intensity levels [32], the EE results were also presented as kJ/min (see Table 1).