# Intra-Reliability of a Wearable Near-Infrared Sensor for Monitoring the Intensity of Exercise
## 3 Results  
Figure 2 shows the mean \(\pm\) 95% CI of SmO\({}_{2}\) during exercise at intensities of 50-250 W in both tests. The within-within-subjects ANOVA revealed no statistically significant effects for session (\(F_{1,12}\) = 0.97, \(p\) = 0.34, \(\eta^{2}\) = 0.07) or the interaction between session and workload (\(F_{4,48}\) = 0.19, \(p\) = 0.94, \(\eta^{2}\) = 0.02) (Figure 2). We do not show results for factor workload, because it exceeds our testing hypothesis. Figure 2: Distribution of muscle oxygen saturation percentage levels (SmO\({}_{2}\)) by workload and test. The boxplots show the distribution of SmO\({}_{2}\) (\(y\)-axis) measured at different workloads (\(x\)-axis) of 50, 100, 150, 200, and 250 W for two different tests. Each workload is represented twice, corresponding to Test 1 and Test 2, respectively. The horizontal lines within each box represent the medians, while the red points and error bars indicate the means and their corresponding 95% confidence intervals. The individual points outside the boxes represent data points that are either outliers or leverage points. The results of relative and absolute reliability indices for each workload are displayed in Table 1. For the ICC, SmO\({}_{2}\) showed substantial (50 W and 100 W) and almost perfect (150 W, 200 W, and 250 W) levels of reliability. Moreover, the CV demonstrated excellent reliability during all tested intensities (<10%). The comparison of the SEM and the SWC values induces marginal sensitivity to detect a change for each workload. The Bland-Altman analysis revealed a small bias for SmO\({}_{2}\) at intensities of 50 W (0.54%), 100 W (1.31%), 150 W (1.08%), 200 W (1.31%), and 250 W (0.61%) (Figure 3). Limits of agreement were approximately \(\pm\)5% for all workloads, with the exception of 150 W, which demonstrated slightly higher variability (\(\pm\)6.1%). The majority of data points fell within the LoA, suggesting a strong concordance between the two tests. This pattern indicates that the differences observed between the first and second test measurements are minimal and fall within an acceptable tolerance range. The regression analysis of these differences produced equations characterized by low slopes (ranging from 0.002 to 0.21), accompanied by Pearson's correlation coefficients approaching null values (ranging from 0.04 to 0.31), all with \(p\)-values exceeding 0.05. Consequently, these results suggest an absence of a systematic bias in the measurement differences as the magnitude of the SmO\({}_{2}\) varies. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Workload** & **50** & **100** & **150** & **200** & **250** \\ \hline SmO\({}_{2}\) (\%) T1 & 48.2 \(\pm\) 6.8 & 46.2 \(\pm\) 6.8 & 43.5 \(\pm\) 7.5 & 39.4 \(\pm\) 9.0 & 33.8 \(\pm\) 10.6 \\  & [44.1, 52.3] & [42.1, 50.4] & [39.0, 48.1] & [33.9, 44.8] & [27.4, 40.2] \\ \hline SmO\({}_{2}\) (\%) T2 & 47.7 \(\pm\) 5.9 & 44.9 \(\pm\) 6.2 & 42.5 \(\pm\) 6.6 & 38.1 \(\pm\) 10.9 & 33.2 \(\pm\) 10.6 \\  & [44.1, 51.3] & [41.2, 48.7] & [38.5, 46.4] & [31.5, 44.7] & [26.8, 39.5] \\ \hline ICC & 0.721 & 0.765 & 0.898 & 0.878 & 0.906 \\  & [0.30, 0.91] & [0.41, 0.92] & [0.71, 0.97] & [0.66, 0.96] & [0.72, 0.97] \\ \hline CV (\%) & 7.2 & 6.9 & 5.1 & 9.1 & 9.9 \\  & [5.1, 11.2] & [5.0, 11.4] & [3.7, 8.5] & [6.5, 15.0] & [7.1, 16.5] \\ \hline SEM (\%) & 3.4 & 3.1 & 2.2 & 3.5 & 3.3 \\  & [2.5, 5.7] & [2.3, 5.2] & [1.6, 3.6] & [2.5, 5.8] & [2.4, 5.5] \\ \hline SWC (\%) & 1.3 & 1.3 & 1.4 & 2.0 & 2.1 \\  & [0.9, 2.1] & [0.9, 2.2] & [1.0, 2.3] & [1.4, 3.3] & [1.5, 3.5] \\ \hline MDC (\%) & 9.5 & 8.8 & 6.1 & 9.7 & 9.2 \\  & [6.8, 15.7] & [6.3, 14.4] & [4.4, 10.1] & [7.0, 16.1] & [6.6, 15.3] \\ \hline \end{tabular}
\end{table} 
Table 1: Muscle oxygen saturation (SmO\({}_{2}\)) values and reliability indicators across different workloads.