## 3 Results
### Heart Rate, Rate of Perceived Exertion, and Muscle Oxygen Saturation  
The HR results for each condition over time (measured at six points: baseline, 20%, 40%, 60%, 80%, and 100% of the test) are shown in Figure 4A. [PERSON]'s test for sphericity indicated a violation of the sphericity assumption for the time factor and the condition \(\times\) time interaction, which justified the use of Greenhouse-Geisser corrections for these analyses. The results revealed no statistically significant differences in HR between the different tDCS locations (F\({}_{(1.866,\,26.130)}\) = 1.543; \(p=0.233;\,\eta_{p}^{2}\) = 0.099). However, a significant main effect  
Figure 3: Total number of repetitions. *: Statistically significant differences with SHAM; **: Statistically significant differences with SHAM and DLPFC.  
of time on HR was observed (F\({}_{(2.180,\,\,30.524)}=235.416\); \(p<0.0001\), n\({}_{p}^{2}=0.944\)), indicating a substantial increase in HR during the test to exhaustion. No significant interaction was found between the tDCS condition and time (F\({}_{(2.784,\,\,38.976)}=0.738\); \(p=0.526\); n\({}_{p}^{2}=0.050\)), suggesting that HR modulation did not vary throughout the task by tDCS location.  
Regarding the RPE results (Figure 4B), [PERSON]'s test for sphericity revealed a violation of the sphericity assumption for both the time factor and the condition \(\times\) time interaction, justifying the use of Greenhouse-Geisser corrections. A two-factor repeated-measures ANOVA showed significant main effects for the condition factor (F\({}_{(2,\,\,50)}=4.969\); \(p=0.011\); n\({}_{p}^{2}=0.166\)), the time factor (F\({}_{(2.167,\,\,54.180)}=564.845\); \(p<0.0001\); n\({}_{p}^{2}=0.958\)), and the condition \(\times\) time interaction (F\({}_{(5.276,\,\,131.898)}=2.971\); \(p=0.015\); n\({}_{p}^{2}=0.103\)). Bonferroni-adjusted post-hoc comparisons indicated significant differences in RPE over time under the tDCS stimulation conditions (SHAM, DLPFC, and M1), with no statistically significant differences in RPE between conditions at baseline (\(p>0.05\)). Subsequent analyses showed significant increases in RPE, which were particularly noticeable from 40% of the test onwards. Statistically significant differences were observed between the SHAM and M1 conditions at 60% (\(p=0.003\); \(d=0.682\)) and 80% (\(p=0.030\); \(d=0.589\)) of the test. No statistically significant differences were detected at any of the time points between SHAM and DLPFC, nor between DLPFC and M1.  
For the SmO\({}_{2}\) values (Figure 4C), [PERSON]'s test of sphericity indicated a violation of the sphericity assumption for both the condition factor and the time factor, as well as for the condition \(\times\) time interaction. The two-way repeated-measures ANOVA revealed a significant main effect for the condition factor (F\({}_{(1397,\,\,16,\,762)}=4.441\); \(p=0.040\); n\({}_{p}^{2}=0.270\)), indicating distinct impacts across conditions. Furthermore, a significant main effect of time was observed (F\({}_{(1.971,\,\,23.647)}=17.197\); \(p<0.0001\); n\({}_{p}^{2}=0.589\)), reflecting substantial changes in SmO\({}_{2}\) over time. In contrast, the interaction between condition and time was not statistically significant (F\({}_{(2.354,\,\,28.250)}=1.995\); \(p=0.148\); n\({}_{p}^{2}=0.143\)), suggesting no statistically significant differences in SmO\({}_{2}\) modulation among the various tDCS locations over time.