## 4 Discussion

Table 10: The results of a repeated measures (within-subjects) ANOVA test assessing differences in the pairwise heart rhythm synchronization for all five groups during 15-min periods before (1), during (2) and after (3) using the Heart lock-In technique (\({}^{\text{a}}\)—Mauchly’s Test of Sphericity was violated, Greenhouse-Geisser df correction applied; \({}^{\text{b}}\)—Adjustment for multiple comparisons: Bonferroni). Note that in order to assess the pairwise heart rhythm synchronization between participants in one group, the Euclidean distance from the optimal time lag vectors of each participant to all other participants in the group was computed and mean Euclidean distance was calculated. The lower mean Euclidean distances correspond to the higher level of pairwise synchronization. It can be seen, for example, that the California’s group members’ heart rhythms were significantly more synchronized with each other during the HLI period than before and after the HLI period, etc. have widely varying levels of sensitivity to changes in the Earth's magnetic field, and can respond in opposite ways to fluctuations in the same environmental variable [49]. When looking at the LMF-HRV-correlations at individual level (shown in Appendix information) across all groups, it is clear that the same individuals degree of HRV synchronization with the LMF not only varies day to day but can also be positively correlated on some days and negatively correlated on others. However, at the group level there are some days when the majority of the participants were either positively or negatively correlated. During the study period, the overall group level trend was toward negative correlations to changes in the LMF. It is currently unclear why on some days the groups were positively correlated while on others they were negatively correlated or why on the day of the HLI the vast majority of the participants' and all the groups were strongly positively correlated with changes in the LMF. We also examined the synchronization between the group members within each of the groups before, during and after the HLI that all the groups did at the same time. Keep in mind that lower values in Figure 5 represent a higher level of synchronization among the group members. In the time period before the HLI the group members gathered together in the same rooms preparing for the HLI and as group were already tending towards being in a more coherent state. There was a clear increase in HRV coherence during the HLI period, especially in the California group which had the familiarity and practice shifting into and sustaining a coherent state. The New Zealand group who were also more familiar with meditation and the HLI also had a significant increase in HRV coherence at the group level. Previous research has shown that being in a coherent state was significantly related to the likelihood of increased pairwise synchronization between participants [50] and the findings from this study are in line with this previous finding. All of the groups pairwise HRV synchronization with the exception of the Lithuania group was significantly increased during the HLI when the group members were in a more coherent state and the Lithuania group had a high level of synchronization in the period before the HLI which is why they did not show a significant increase in pairwise synchronization during the HLI. Most of the groups synchronization significantly decreased in the period following the HLI. This is likely due to the fact that they got up and started to go about their next activity shortly after the HLI was completed. The only exception to this was the New Zealand group who stayed together after the HLI for another group activity, who remained more significantly synchronized than the pre-HLI period. Without doubts, there are other environmental factors that do affect HRV. For example, the altitude is one of the factors which does have an effect to HRV.