with respect to their relationship with the sympathetic or parasympathetic
system. Thus, in the time domain, use is made of
the SDNN, rMSSD and pNN50 [41], and for the non-linear methods,
the diameters of the Poincaré plot [24] were used. As well as
these, it was also decided to measure the sympathetic stress
indices (Stress Score) and the sympathetic-parasympathetic
ratio (S/PS index), recently described by Naranjo et al. [29] and that
seem to provide more information than the SD1/SD2 ratio, which,
according to the majority of authors, is of questionable significance.
Likewise, we have made the classic measurement of complexity
in time series, using the SampEn [37], the significance of
which has never been examined in high level athletes over time.
As can be observed in ●▶ Fig. 1, the behaviour of the 3 variables
measured in the time domain was practically identical, and was
always above the references values set by the Task Force [41]. If
we accept that the 3 represent parasympathetic activity [41], a
lower initial zone that covers the pre-season and first month of
competition is observed, and then later, a recovery of the parasympathetic
tone at rest that, with variations, is maintained at a
high level until the final phase of the competition (April and
May) in which the accumulation of games, and probably their
decisive importance, means that there should be a decrease in
this at-rest parasympathetic tone. Likewise, the Poincaré param