## 2 Materials and Methods
### Data Processing and Data analysis  
From the cardiac activity pre-processed records with a 0.5 Hz component filtered, we separated three sections of corresponding segments of measurements, one before the HIMS application (Group A), one during the HIMS application (Group B), and one after the HIMS application (Group C). All records had the same length. Subsequently, we used the Pan-Tompkins method to identify the R-waves [27]. Furthermore, we obtained individual RR interval vectors, i.e., time intervals between individual R-waves. We processed collected data sets of RR intervals by standard methods, i.e., time-domain analysis, and frequency analysis [19] and by nonlinear analysis--The Recurrence quantification analysis (RQA) [28]. Concerning the time-domain analysis, parameters of mean RR interval (meanRR) and mean heart rate values (meanHR) were obtained. In this case, these are the standard arithmetic means of the given parameters. Moreover, we got long-term variability parameters through the standard deviation  
Figure 2: Example of electrocardiogram during high-induction magnetic stimulation procedure with detailed ECG curve with applied pulses. of NN (normal-to-normal) intervals (SDNN) and the standard deviation of heart rate (SDHR) [19]. The number of adjacent RR intervals differing by more than 50 ms (NN50), the number of such intervals to the total number of RR intervals (pNN50), and Root mean square of successive RR interval differences (RMSSD) were selected as further parameters. These parameters are used for longer signals [19] but are stated to get the complete standard analysis. Frequency analysis uses the power spectral density (PSD), which is based on the conversion of signals into the frequency spectrum using a Fourier transform (FT), or more precisely, a Discrete Fourier transform (DFT) because of the discrete signal. Standard FT, or rather DFT, considers an equidistantly sampled signal. Thus, in the case of HRV, this requirement is not met. For this purpose, a so-called Lomb periodogram is used, which was developed for the modification of non-equidistantly sampled data. The acquired power spectrum of HRV is then divided into frequency bands, each of which is associated with different functional effects on RR intervals [29]. In the case of the frequency analysis, outputs in individual frequency bands defined for HRV in the range of low frequencies (LF), i.e., absolute power of low-frequency band (0.04-0.15 Hz) and in the band of high frequencies (HF), i.e., absolute power of the high-frequency band (0.15-0.4 Hz), were monitored. An LF and HF ratio (LF/HF) was obtained by mentioned parameters, and it is used as an indicator of sympathovagal balance, i.e., a balance indicator of the sympathetic and parasympathetic activity of the neural system [19]. Given the nonlinear nature of biological signals, data were further evaluated using the method based on the chaos theory method--the RQA, described further [28]. Monitored parameters, or more precisely, their values were statistically compared before and after the HIMS application. We rejected the null hypothesis of normal distribution based on the Jarque-Berra test [30]. Regarding the rejection and the fact that paired data were compared, a [PERSON] test, which is the non-parametric alternative to the one-way ANOVA with repeated measures and post-hoc analysis ([PERSON] and [PERSON]'s approach [31]), was carried out to statistically compare the state before, during and after the HIMS application [32]. Statistical significance is presented in the form of _p_-values, where \(p\) < 0.05 indicates a statistically significant difference between compared groups because data were tested at the significance level of \(\alpha=5\)%. Individual p-values represent the result of [PERSON]'s test. The _p_-value indicates that there is a statistically significant difference between the pairs of study groups. However, the Friedman test itself does not determine between which particular pairs these differences exist. Therefore, mentioned post-hoc analysis was used.