eters show an almost identical trajectory and very similar pattern
to the time domain parameters (● ▶ Fig. 2). This behaviour
was consistent with the fact that SD1 directly reflects parasympathetic
activity, while SD2 has an inverse behaviour to sympathetic
stimulus.
It is very likely that these coherent changes in the time domain
and the Poincaré plot could be an indicator of the fatigue status
of the group.
The Stress Score (SS) values and the sympathetic-parasympathetic
ratio (S/PS ratio) were determined according to the proposal
by Naranjo et al. [29], and were found to be of great use in
their follow-up throughout the season, since the equilibrium
between the sympathetic and parasympathetic system, as regards
accumulated workload could be analysed with a simple piece of
numeric information. If we analyse these values according to the
percentile distribution proposed by the authors [29], it was
observed that an SS of 10 and an S/PS ratio of 0.5 marks the limit
of the values obtained in soccer players of this level, and that
values of 8 and 0.2, respectively, would indicate a possible alert.
In this follow-up, we can observe (● ▶ Fig. 3) that only at the
beginning and at the end of the season were “alert values” found,
and that at no time could it be said that the group was outside
the upper limits. However, at an individual level, some increased
values were detected at certain times and were reported to the