## 3 Results
### The Results of the Frequency Domain Index  
The ANOVA showed that, regarding LF, the interaction between the measurement time and intervention program of HF was significant (F(1,56) = 3.215, \(p\) = 0.025), and there was a significant main effect for time (F(1,14) = 39.344, \(p\) = 0.000) in group A; the interaction between the measurement time and intervention program of HF was significant (F(1,56) = 3.316, \(p\) = 0.000), and there was a significant main effect for time (F(1,14) = 103.179, \(p\) = 0.000) in group B. According to the post-hoc test, the intervention effects of programs II, III, and IV in group A were significant, and the maximum change rate of program II was \(-\)20.880%; in group B, the intervention effects of programs I, II, and III were significant, and the maximum change rate of program II was \(-\)23.528% (Table 3 and Figures 3C and 4C). Regarding LF, there was no interaction between the measurement time and intervention program, but there was a significant main effect for time (F(1,14) = 58.706, \(p\) = 0.000) in group A; there was no interaction between the measurement time and intervention program, but there was a significant main effect for time (F(1,14) = 101.460, \(p\) = 0.000) in group B. According to intra-group statistics, the intervention effects of programs I, II, III, and IV in group A were significant, and the maximum change rate of program II was 20.616%; in group B, the intervention effects of programs I, II, III, and IV were significant, and the maximum change rate of program I was 32.631% (Table 3, Figures 3D and 4D).  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Indicators**} & \multirow{2}{*}{**Program**} & \multicolumn{4}{c}{**Moderate Physical Fatigue**} & \multicolumn{4}{c}{**Severe Physical Fatigue**} \\ \cline{3-8}  & & **T** & \(p\) & **Rate (\%)** & **T** & \(p\) & **Rate (\%)** \\ \hline \multirow{8}{*}{RMSSD} & I & \(-\)1.405 & 0.182 & 12.1 & \(-\)6.394 & 0.000 & 32.6 \\  & II & \(-\)5.050 & 0.000 & 25.4 & \(-\)3.407 & 0.004 & 24.6 \\  & III & \(-\)3.959 & 0.001 & 18.3 & \(-\)3.362 & 0.005 & 26.1 \\  & IV & \(-\)3.483 & 0.004 & 17.5 & \(-\)3.706 & 0.002 & 14.9 \\  & V & \(-\)0.785 & 0.446 & 7.7 & \(-\)1.082 & 0.298 & 7.6 \\ \hline \multirow{8}{*}{SDNN} & I & \(-\)3.617 & 0.003 & 14.8 & \(-\)4.907 & 0.000 & 40.2 \\  & II & \(-\)5.689 & 0.000 & 27.9 & \(-\)5.245 & 0.000 & 32.1 \\  & III & \(-\)3.175 & 0.007 & 17.2 & \(-\)3.607 & 0.003 & 33.1 \\  & IV & \(-\)3.284 & 0.005 & 19.0 & \(-\)3.948 & 0.001 & 30.7 \\  & V & \(-\)1.705 & 0.110 & 9.6 & \(-\)1.873 &Figure 3: Comparison of the effects of tDCS intervention programs on the indicators of HRV and HbO\({}_{2}\) after physical fatigue. Note: \(\blacksquare\) means moderate physical fatigue; \(\blacksquare\) means severe physical fatigue. (**A**) Difference of different tDCS intervention programs on RMSSD before and after intervention. (**B**) Difference of different tDCS intervention programs on SDNN before and after intervention. (**C**) Difference of different tDCS intervention programs on LF before and after intervention. (**D**) Difference of different tDCS intervention programs on HF before and after intervention. (**E**) Difference of different tDCS intervention programs on HbO\({}_{2}\) before and after intervention.