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Journal of Human Kinetics volume 66/2019, 99-109 DOI: 10.2478/hukin-2018-0051 99
Section II‐ Exercise Physiology & Sports Medicine
1 - Faculty of Psychology, Education Sciences and Sport Blanquerna–Ramon Llull University, Barcelona, Spain.
2 - Institut Francesc Macià. Departament d'ensenyament. Generalitat de Catalunya. Spain.
3 - Department of physiology, University of Barcelona, Barcelona, Spain.
Authors submitted their contribution to the article to the editorial board.
Accepted for printing in the Journal of Human Kinetics vol. 66/2019 in March 2019.
Physiological and Psychological Changes at the End
of the Soccer Season in Elite Female Athletes
by
Jose Morales1, Vicenç Roman2, Alexandre Yáñez1, Mònica Solana-Tramunt1,
Juan Álamo3, Antón Fíguls2
This study compares and describes relationships among stress-recovery indices, the heart rate variability index,
and the Cooper and Yo-Yo IR1 tests among female soccer players during the last six weeks of the competitive season.
Sixteen female soccer players engaged in a pre-test of all of the variables. After having their training monitored for six
weeks, a post-test was administered. The results revealed significant (p < 0.05) differences in the specific stress-recovery
scales of the RESTQ-sport and in the frequency-domain variables of the HRV, although there were no significant
differences in the general stress or general recovery scales. The Yo-Yo IR1 test, the Cooper test scores, and the means of
the time-domain HRV variables did not exhibit any significant differences between the pre- and the post-test. The RMSSD
variations exhibited very large and large correlations with the performance test and the RESTQ-sport variables,
respectively. The variations in the HRV frequency-domain variables exhibited significant moderate and large correlations
among the variations of the RESTQ-sport scales. Monitoring athletes at the end of the season may reveal contradictions
between some variables. To help with the interpretation of these scales, some external aspects, such as athlete strain and
monotony of training, should be considered.
Key words: RESTQ-sport, HRV, Yo-Yo IR1, Cooper test, monotony.
Introduction
The competitive season in soccer is
characterized by different performance states of
players due to the application of different training
loads (TLs) that affect the stress-recovery (SR)
status of each athlete (Dupont et al., 2004; Flatt et
al., 2017). According to Thorpe et al. (2015), TL
patterns vary considerably between the playing
season and the preseason because of differences in
training and match volume. However, to the best
of our knowledge the number of studies involving
monitoring TLs and SR status of female soccer
players using various tools simultaneously in-
season is much smaller than the number of studies
focusing on male soccer players, and smaller than
those concerning athletes participating in other
sports. It is accepted that the final period of the
season is decisive for evaluating the final success of
a soccer team. In this sense, the control of TLs and
their psycho-physiological effects during this
period has an impact on players’ performance, and
knowledge of these data provides valuable
information to optimize the training process
(Borresen and Lambert, 2009).
Studies of team sports, especially soccer,
have been characterized by attempts to quantify
training and competition loads using different
systems. Nowadays, there are different options for
TL assessment during a soccer match, including
the GPS which allows researchers to assess several
TL indices (Buchheit et al., 2014; Malone et al.,
2015), heart rate (HR) monitors, blood lactate or gas
exchange measurements (Borresen and Lambert,
100 Physiological and psychological changes at the end of the soccer season in elite female athletes
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2009), and other inexpensive and easy-to-apply
options such as the Rate of Perceived Exertion
(RPE) Session (RPEsession) (Foster et al., 1995) that
have been used in previous studies focusing on
soccer players (Algrøy et al., 2011).
Heart rate variability (HRV)
measurements have been used to measure internal
TLs and overtraining in soccer (Flatt et al., 2017).
Heart rate variability refers to variations in beat
intervals or correspondingly in the instantaneous
HR in different situations. Various studies have
used HRV to better understand the status of the
Autonomic Nervous System (ANS) and stress
induced by TLs; this stress interferes with the
sympathetic-parasympathetic ANS balance. The
relationship between ANS and HRV differs during
activity and immediate recovery situations
compared with during recovery periods
(Kaikkonen et al., 2007). Accurate HRV
assessments require stationary conditions;
therefore, it is preferable to measure HRV a
significant amount of time before or after exercise
or during immediate recovery states (Kaikkonen et
al., 2007; Task Force of the European Society of
Cardiology and the North American Society of
Pacing and Electrophysiology, 1996).
From a psychological perspective,
different instruments are useful for assessing
stress-recovery situations and internal TLs during
training and these instruments can be also used to
detect a possible overtraining situation or to
prevent an injury. Kellmann and Kallus (2001)
developed the Recovery Stress Questionnaire for
Athletes (RESTQ-sport), an instrument to measure
SR balance in athletes. The RESTQ-sport has been
used in soccer (Laux et al., 2015), and its
application is important for both competitions and
training sessions because it enables evaluations of
the current situation and expectations of
performance in upcoming games or training
sessions.
Since performance in soccer depends on
many factors, the use of a variety of psychological
and physiological variables, together with a
detailed description of the characteristics of
training, is justified. Therefore, the objectives of
this study were: (i) to describe the TL of the last
mesocycle of the season, (ii) to compare the results
of performance, psychological and physiological
tests before and after the final mesocycle, and (iii)
to establish a relationship between the chosen
variables of the different domains evaluated. We
hypothesized that there would be significant
differences between the initial and the final values
due to the accumulated effect of training.
Methods
Participants
Sixteen professional female soccer players
from the Club de Fútbol Levante-Las Planas
(Barcelona) competing in the Spanish First
Division (age: 23.25 ± 5.07 years; body mass: 60.94
± 9.55 kg, body height: 1.61 ± 6.89 m, and body
mass index: 23.55 ± 2.11 kg/m2) participated in the
study.
After being fully informed verbally and in
writing of the purposes and potential risks of the
study, the subjects provided their written consent
to participate in the investigation. The study and
its protocol were reviewed and approved by the
Ramon Llull University internal review board and
conducted in accordance with the latest version of
the Declaration of Helsinki.
Design and Procedures
We collected data during pre-test and post-
test sessions, just after Easter Week holidays. The
data collection occurred one week immediately
after the second mesocycle of the season. Between
tests, the soccer players continued with their last
mesocycle training program, and the re-test was
performed before the last week of the competitive
period.
All testing sessions were completed 2 hours
prior to the start of training. During the testing
sessions, we measured HRV and collected RESTQ-
sport questionnaire information. The subjects also
performed the Cooper test and, after 48 hours, the
Yo-Yo IR1 test. The researchers responsible for
data collection were blinded to the participants
and the information was codified and statistically
treated by other researchers.
Six players were excluded to avoid HRV
disturbances because they were in their luteal
menstrual period; this phase is known to affect
HRV results (de Zambotti et al., 2013).
HRV analysis
In order to obtain accurate data, we applied
The Task Force of the European Society of
Cardiology and the North American Society of
Pacing and Electrophysiology criteria to all of the
HRV measurements. The HRV was always
recorded at 5 pm (2 hours before training), and the
by Jose Morales et al. 101
© Editorial Committee of Journal of Human Kinetics
athletes were instructed to avoid any stimulants,
thermogenics and alcohol for at least 48 hours. The
testing room conditions were standardized (quiet,
no distractions, temperature of 20-22°C).
The subjects were asked to remain still and
breathe at a pace between 10-12 cycles per minute
without speaking or making any movements.
These conditions were maintained during the pre-
and the post-test. The female athletes were fitted
with HR monitors and given 5 minutes to rest in a
supine position prior to the data collection.
Interbeat (RR) interval recordings were obtained
during the next 5 minutes of each subject using a
validated portable HR monitor (Polar® RS810,
Kempele, Finland). This series of HR monitors had
been validated for HRV recordings (Giles et al.,
2016). The RR recordings were downloaded using
the accompanying Polar software (Polar® Precision
Performance) and exported for later analysis of
time- and frequency-domain measures of HRV
using Kubios v2.0 HRV software (Biosignal
Analysis and Medical Imaging Group at the
Department of Applied Physics, University of
Kuopio, Kuopio, Finland).
Based on the original RR intervals, the
following variables were calculated: the standard
deviation of the RR-intervals (SDNN), the root-
mean-square successive difference of intervals
(RMSSD).
We analyzed different HRV variables in the
frequency domain, which were obtained by
analyzing the spectral analysis density of the RR
signal. As recommended by the Task Force (Task
Force of the European Society of Cardiology and
the North American Society of Pacing and
Electrophysiology 1996), we performed spectral
analysis with a Fast Fourier Transformer to
quantify the power spectral density of the low-
frequency (LF; 0.04–0.15 Hz) and high-frequency
(HF; 0.16–0.40 Hz) bands.
The HF band reflects vagal modulation, and
the LF band reflects both sympathetic and
parasympathetic influences. Furthermore, the
LF/HF ratio was examined as an indicator of
sympatho-vagal balance (Bosquet et al., 2008).
RESTQ-sport test analysis
The RESTQ-sport recovery-stress
questionnaire was used (Kellmann and Kallus,
2001) to determine the perceived stress of seasonal
activities.
The soccer players had to answer 77 questions
related to 19 different scales. In addition, the
RESTQ-sport scores were classified as general
stress scores (mean of 7 scales), general recovery
scores (mean of 5 scales), sport-specific stress
scores (mean of 3 scales), and sport-specific
recovery scores (mean of 4 scales). The final score
of each scale was the mean of the points obtained
in each item. Each subject’s answer was checked
based on a Likert scale with values ranging from 0–
6.
The Spanish version of the RESTQ-sport was
used, which had been validated by Gonzalez-Boto
et al. (2009). This version demonstrated high
reliability with a Cronbach Alpha index ranging
from 0.77 to 0.94 and significant correlations with
the Profile of Mood States questionnaire and the
RESTQ-sport scales.
Performance tests
The Cooper test was conducted taking into
account the aspects described by McArdle et al.
(2010) (i.e., a 200-m track with markings every 50
m). All the subjects were familiarized with the test
protocol, and they performed a warm up of 2 min
of running and 3 min of stretching. To begin the
test, a "GO" command was given and the timer was
started. During the test, athletes were kept
informed of the remaining time at the end of each
lap (200 m). Once the test ended after 12 minutes,
the distance that the athlete covered, rounded to
the nearest 50 m mark, was registered.
The Yo-Yo IR1 test was performed following
the protocol proposed by Bangsbo et al. (2008) after
completion of a specific warm-up. The Yo-Yo IR1
test consisted of repeated 20-m runs back and forth
between two markers with a progressive increase
in speed, which was governed by an audio player.
Between each 40-m run, the athlete recovered with
10 s of jogging (shuttle runs of 2×5 m). The test
consisted of 4 runs at 10–13 km·h-1 (0–160 m) and
another 7 runs at 13.5–14.0 km·h-1 (160–440 m).
From this point on, the players completed 8
additional runs, each 0.5 km·h-1 faster than the
previous one. The test was completed when the
athlete reached voluntary exhaustion or failed to
maintain her running pace in synchrony with the
audio recording (i.e., she failed to achieve the
markers twice in the same stage). The Yo-Yo IR1
course lines were marked with cones 20 m
apart with additional cones set 5 m behind the
starting line for use during recovery.
The athletes wore HR monitors to record the
102 Physiological and psychological changes at the end of the soccer season in elite female athletes
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final HR attained during the test.
Training program characteristics
The athletes underwent the same training
program for 6 weeks and focused on specific
objectives of the end of the competitive period. The
TL was characterized by using specific high-
intensity and decreased volume loads. The
recovery time was sufficient to ensure that the
athletes were fit during competition (Figure 1).
We monitored internal TLs using the HR-
based approach of Edwards (1993) and the RPE-
based approach of Foster et al. (2001).
The method of Edwards (1993) is based on the
time accumulated in five HR zones and is
calculated analyzing each zone (zone 1: 50–60% of
HRmax; zone 2: 60–70% of HRmax; zone 3: 70–80% of
HRmax; zone 4: 80–90% of HRmax; zone 5: 90–100% of
HRmax). The calculation was made by summing the
number of minutes in each zone multiplied by the
zone number. The HR assessment was made using
a portable HR monitor (Polar® RS810), and the
recordings were downloaded using the
accompanying Polar® software.
The method proposed by Foster et al. ( 2001)
requires subjects to rate the intensity of training 30
min after the end of the session using the Borg’s
Category Ratio-10 (CR-10) RPE scale. The TL is
calculated by multiplying the duration of exercise
by the RPEsession score.
We collected RPEsession scores and the scores of
the Edwards method and calculated the mean of
the week-long values of all of the subjects. At the
same time, the week-long monotony was
calculated according to Foster (1998) by dividing
the mean of the week-long TL from RPEsession by its
standard deviation. The monotony is a
measurement of variability of training across one
week. If the TL is always high or always low
during the week, the monotony value will be high.
However, if high and low TLs are intercalated
during the training week, the monotony score will
be moderate or low. The training strain is a value
that represents the stress to which the athlete was
exposed during the entire training week. It is
obtained by multiplying the weekly TL (including
the load of the competition) by the training
monotony score. A week of higher TLs along with
a high monotony score yields very large training
effort values.
Statistical analysis
We performed statistical analyses using the
Statistical Package for Social Science version 22.0
(SPSS, Inc., Chicago, IL, USA). A significance level
of p < 0.05 was used for all the tests. The Shapiro-
Wilk test was applied to test for a normal
distribution of the data. A repeated-measures
ANOVA of internal TL variables was carried out to
check for differences during the six weeks of
training. We relied on a paired t-test to compare the
differences between the pre- and post-test scores
for all dependent variables (HRV, RESTQ-sport,
and the performance test). Moreover, Pearson
product-moment correlations were used to
quantify the relationships between pre- and post-
test changes in HRV, RESTQ-sport and
performance variables. Finally, we evaluated the
correlation of all the dependent variables in the
post-test with the final result of the monotony and
the training strain of the last week of training.
Results
Training load variables
A main effect of the time factor was observed.
Significant differences in the variables quantifying
the TLs according to the mesocycle week and the
Edwards method (F(5,45) = 39.45, p < 0.05; η2p = 0.39)
and RPEsession (F(5,45) = 47.36, p < 0.05; η2p = 0.31)
were noted. Figure 1 shows the values of the
different training variables. For the variables that
did not fulfill sphericity based on the Mauchly test,
the degrees of freedom were adjusted using the
Huynh-Feldt method. The monotony (F(3.55,32.88) =
6.67, p <0.05; η2p = 0.29) and the training strain
(F(3.15,30.18) = 16.65, p < 0.05; η2p = 0.21) also revealed
significant differences between the different weeks
of training. Pairwise comparisons were performed
using the Bonferroni post hoc tests and are shown
in Figure 1.
HRV variables
The means of the HRV variables did not
exhibit any significant differences in either the time
domain or in the pre- or post-test. We found
significant differences only in the frequency
analyses that used normalized units. There was a
significant increase (p < 0.05) in LF (t15 = 4.19; p =
0.001; r = 0.73) and the LF/HF ratio (t15 = 4.4; p =
0.001; r = 0.75) and a significant decrease in HF (t15
= 4.23; p = 0.001; r = 0.74) between the pre- and the
post-test. Descriptive analyses are provided in
Table 1.
Stress/recovery variables
Contrast analysis was used to compare the
by Jose Morales et al. 103
© Editorial Committee of Journal of Human Kinetics
means of RESTQ-sport results and the stress-
recovery perception of the subjects. There were
significant differences in sport-specific stress (t15 = -
4.95; p = 0.001; r = 0.79) and sport-specific recovery
(t15 = -5.9; p = 0.001; r = 0.84) between the pre- and
the post-test scores. No significant differences were
observed in the general stress or the general
recovery scales (Figure 2).
Performance variables
There were no significant differences between
the means of the performance tests in the pre- and
the post-test scores. Both tests’ scores had
increased, yet not significant results in the Cooper
test (t15 = -2.08; p = 0.58) and the Yo-Yo IR1 test (t15 =
-1.73; p = 0.11) (Figure 3).
Correlations between dependent variables
A very large, significant correlation was
found between ∆RMSSD and ∆Yo-YoIR1 (r = 0.84;
p = 0.02) and the Cooper test (r = 0.78; p = 0.03).
∆RMSSD also exhibited a large and significant
correlation with the RESTQ-sport variables,
∆general stress (-0.61; p = 0.01), ∆specific stress (r =
0.58; p = 0.01), ∆general recovery (r = 0.64; p = 0.003),
and ∆specific recovery (r = 0.50; p = 0.009). The
other HRV time-domain variables exhibited non-
significant, but moderate correlations with
the RESTQ-sport and the performance test
variables (r = 0.34–0.45; p > 0.05).
The variations in the HRV frequency-domain
variables exhibited some significant moderate and
large correlations among the variations of RESTQ-
sport, ∆HF and ∆specific recovery (r = 0.68; p =
0.007), ∆HF and ∆specific stress (r = 0.61; p = 0.02),
∆HF and ∆general stress (r = 0.55; p = 0.02), ∆LF/HF
and ∆specific recovery (r = 0.48; p = 0.01), ∆LF/HF
and ∆specific stress (r = 0.31; p = 0.04), ∆LF/HF and
∆general stress (r = 0.55; p = 0.04), ∆LF and ∆specific
stress (r = 0.38; p = 0.04). The remainder of the
variables did not exhibit any significant
correlations; all were small or moderate (r = 0.16–
0.36; p > 0.05).
Training monotony exhibited high and
significant correlations with some variables of
RESTQ-sport, specific stress (r = 0.71; p = 0.02) and
specific recovery (r = -0.66; p = 0.03). There were
moderate correlations with the variable HRV of the
frequency domain HF (r = 0.48), LF (r = 0.41) and
LF/HF (r = 0.45). The remaining HRV variables did
not exhibit any significant correlations and were
low or very low in value.
Training strain exhibited high and moderate
correlations with RMSSD (r = -0.70; p = 0.01), Yo-Yo
IR1 (r = 0.44), and the Cooper test (r = 0.41). The
remaining variables did not exhibit any significant
correlations and were low or very low in value.
Table 1
Heart rate and HRV variable comparisons between the pre- and post-test.
Variable Pre‐test Post‐test
HR 58.25 (2.42) 58.11 (3.12)
Time-domain HRV
MeanRR (ms) 957.15 (42.94) 917.23 (64.04)
STDRR (ms) 65.96 (9.07) 96.03 (11.68)
MeanHR (1/min) 62.84 (2.46) 76.97 (11.08)
STDHR (1/min) 4.11 (0.35) 10.88 (2.4)
RMSSD (ms) 72.56 (14.36) 76.6 (9.11)
Frequency-domain HRV
LF(u.n.) 43.12 (3.77) 60.84 (3.63) *
HF(u.n.) 56.14 (3.72) 38.47 (3.63) *
LF/HF ratio 0.76 (0.13) 1.58 (0.22) *
The data are expressed as mean (standard error of the mean).
*Indicates a significant difference (p < 0.05) between the pre- and post-test.
104 Physiological and psychological changes at the end of the soccer season in elite female athletes
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Figure 1
Quantification of TLs of the team's weekly mean. 1 Means significant
differences compared to week 1, 2 Means significant differences compared to week 2,
and 3Means significant differences compared to week 3.
Figure 2
Differences in RESTQ-sport scales (general stress scores, general recovery, sport-specific stress,
and sport-specific recovery). The columns represent the mean and the error bars represent
the standard error of the mean. *Indicates significant differences (p < 0.05).
by Jose Morales et al. 105
© Editorial Committee of Journal of Human Kinetics
Figure 3
Differences in performance tests (Cooper and Yo-Yo IR1). The columns represent the mean
and the error bars represent the standard error of the mean.
*Indicates significant differences (p < 0.05).
Discussion
The results revealed significant changes
between the initial measurement and some of the
analyzed variables at the end of the female soccer
players’ season. These changes can be observed in
the differences between the RESQT-sport scores
and the HRV results at the beginning and the end
of the analyzed mesocycle. In contrast, there were
no differences between the pre-test and the post-
test in the Cooper test or the Yo-Yo IR1 results,
although the planning strategy was focused on
tapering at the end of the season to obtain peak
performance in the athletes. Therefore, our results
were only partially consistent with our initial
hypothesis because not all of the variables
exhibited significant differences between the pre-
and the post-test.
The coaches decided on a progressively
decreasing TL during the last 3 weeks of the
mesocycle. These changes, which consisted of a
decrease in intensity and an increase in the number
of tactical sessions, were consistent with the
training methods documented in other studies
that followed the same kind of a program to
improve performance after a tapering period
(Milanez et al., 2014). The TL assessment results
during the mesocycle were consistent with the
coaches’ strategies. Both the methods of Edwards
and RPEsession exhibited a progressive reduction
in the TL over the last 3 weeks. Furthermore, there
was a notable increase in monotony scores during
the last three weeks. At the same time, the training
strain did not decrease in the same proportion as
the TLs represented by the RPEsession and
Edwards indices. Previous studies have used
monotony scores with psychological and
physiological TL assessments (da Silva et al., 2015).
It ha s been reported than high monotony scores ar e
related to low TL variability, which may suggest
the beginning of overtraining (Foster, 1998). When
monotony and training strain were represented
together with the weekly TL (Figure 1), we could
observe that the sessions were not properly
managed, because a significant reduction in TLs
should result in a corresponding reduction in
monotony and training strain, which was not the
106 Physiological and psychological changes at the end of the soccer season in elite female athletes
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case. The increased monotony was due to low
variety in training that could have been avoided by
alternating intensity and volume between
consecutive sessions (Comyns and Flanagan,
2013). The strong correlations found between the
monotony and the specific stress and recovery
indices of the RESTQ-sport can be attributed to the
TL being more affected by psychological than
physiological factors.
The performance test scores did not exhibit
significant differences (p > 0.05) between the pre-
and the post-test of the analyzed mesocycle. There
was a little improvement in the results, which was
far from what was expected after applying a
tapering strategy during the last weeks of the
season. These results are consistent with those of
Oliveira et al. (2013), in which the changes in Yo-
Yo test performance are evident during the pre-
season, but not during the season, despite training.
Changes in the physiological performance
test (∆Yo-YoIR1 and ∆Cooper) during the last
mesocycle of the season only exhibited significant
and large correlations with ∆RMSSD. This HRV
variable did not exhibit any significant differences
between the pre- and post-test period, and yielded
similar results as the other performance variables.
These findings are consistent with those of Flatt et
al. (2017).
Meanwhile, the variables of the frequency
domain of the HRV exhibited a significant
decrease. This finding could be interpreted as
showing that the team was coming to the end of the
season and beginning to enter a phase of
overtraining or that the players displayed
relatively high indices of stress, aspects that were
not reflected by the design of the loads or a
decrease in players’ performance. Other tennis
(Thiel et al., 2011) and women’s soccer (Flatt and
Esco, 2015) studies that included an intense
training period reported that lower HRV variables
were not associated with decreased performance.
Our results are similar to those of previous Yo-Yo
IR1 test results, and the Yo-Yo IR1 improvement
was not related to the relative changes in short-
term HRV. These changes could explain the
absence of a correlation with the HRV variables
(Buchheit et al., 2011; Oliveira et al., 2013).
However, the HRV does not have to reflect the
recovery of all systems since there are many
different stressors unrelated to training (e.g., social,
educational, occupational, economic, nutritional,
travel, and time-related stress) (Flatt et al., 2017;
Tian et al., 2013).
The use of the RESTQ-sport combined
with physiological, non-invasive outcome
measurements such as HRV has several precedents
for monitoring the effects of the TL simultaneously
with changes in stress and recovery (Dupuy et al.,
2013; Morales et al., 2014; Thiel et al., 2011).
Previous studies have reported similar results
when comparing stress and physiological
variables. For instance, Morales et al. ( 2014)
reported decreased HRV values with higher levels
of stress and lower recovery after 4 weeks of
intense training with judo athletes; performance
variables exhibited a significant decrease. Other
studies have found that HRV and RESTQ-sport
showed the same behavior, but did not correlate
with athletes’ performance (Dupuy et al., 2013;
Thiel et al., 2011).
In the present study, the general stress and
general recovery indices of the RESTQ-sport did
not exhibit significant differences. Nevertheless,
the sport-specific stress and sport-specific recovery
scales demonstrated significant differences (p <
0.05). These results might suggest overtraining,
although here this conclusion has been ruled out
due the results of the Cooper and Yo-Yo IR1 tests,
which indicated stable athletes’ performance.
These findings suggest that motivational factors or
training monotony likely resulted in the higher
sport-specific stress scores and lower sport-specific
recovery at the end of the season compared with
the baseline status. In this sense, the results
presented here are in agreement with those of
Thorpe et al. (2015). This author affirmed that
psychometric variables predicted fatigue in elite
soccer players better than other markers such as
HRV or Counter-Movement Jump.
The frequency-domain HRV results
exhibited significant differences between the pre-
and post-test, indicating decreased HRV and
higher sympathetic ANS activation in response to
the stressful situation (Stanley et al., 2013).
According to Bosquet et al. (2008), HRV measured
in the frequency domain is moderately reliable, but
requires a highly standardized protocol to control
for breathing, time of the day, temperature,
luminosity, and noise, among other
factors. Recent studies have considered time-
domain variables, like the log RMSSD, to be the
best indicator for athletic monitoring because this
by Jose Morales et al. 107
© Editorial Committee of Journal of Human Kinetics
variable appears to be uninfluenced by the
breathing rate and is more reliable than frequency-
domain variables (Plews et al., 2014).
Our study meets the Task Force-
standardized protocol requirements to control for
the influence of external factors (Task Force, 1996).
Even so, our results are controversial in the HRV
domain because the frequency domain exhibited
significant differences between the pre- and the
post-test and the time domain did not. The same
situation occurred in the RESTQ-sport results; only
the specific sport variables exhibited significant
differences. A possible explanation for these
results is that time-domain variables were more
sensitive to external factors because of the
increased anxiety produced by the overlap of the
school exam period with the end of the training
season and the associated decrease in motivation
(D’Ascenzi et al., 2013).
The influence of the female menstrual
cycle on HRV made it impossible to compare the
groups more than once per month. Moreover,
several previous studies have reported the effect of
the female period on physiological functions such
as HRV; sex-hormone fluctuations are basic
physiological factors that continuously affects
body functioning in women. Such studies have
found increased LF components accompanied or
unaccompanied by decreased HF components in
HRV during the luteal phase compared with the
follicular phase and indicated a predominant
sympathetic activity in the luteal phase and a
dominant vagal activity in the follicular phase (de
Zambotti et al., 2013). The majority of previous
studies based their results on analyses of
frequency-domain and non-linear HRV variables,
and it is rare to find studies that report the effect of
the female period on the time domain of HRV
variables. Recently, Brar et al. (2015) observed the
effect of the female period on HRV, and these
authors concluded that time-domain variables,
particularly the lnRMSSD, did not always exhibit
significant differences, in contrast with frequency-
domain variables. As a result, Brar et al. (2015)
were unable to easily detect period-induced
changes.
There are a number of limitations of this
study that should be considered. The most
important one pertains to the HRV data collection,
because the most recent studies (Flatt et al., 2017;
Flatt and Esco, 2015) recommend monitoring HRV
on a weekly basis by comparing the evolution of
the coefficient of variation of a single variable such
as lnRMSSD. In our study, the pre- and post-tests
were performed 6 weeks apart. Also, several HRV
variables in the temporal and frequency domains
were analyzed considering other methodological
recommendations such as the menstrual cycle of
females and breathing control for the treatment of
the data. In this sense, there was a loss of
information throughout the entire process, but it
was compensated for by greater methodological
rigor. At the same time, the follow-up throughout
the process ensured that information associated
with other load factors of training (e.g., monotony
and training strain) could be obtained. Future
research may choose to focus on combining weekly
lnRMSSD tracking and the monotony and strain
values derived from the RPEsession. Yet another
limitation of this study was the lack of a control
group to confirm the results and thus increase the
quality of the research. However, this was a high-
standard sample, and it is very difficult to gain
access to the athletes and have them participating
in time commitments beyond their normal training
routine. In the end, this study opted for an
observational design under which all subjects
underwent the same measurements and the same
training process.
In conclusion, the combined analysis of
physiological and psychological factors related to
training of a soccer team contributes much more
valuable information than if these analyses are
performed separately.
Monitoring HRV does not reflect changes
in all physiological systems. Therefore, such
monitoring needs to rely on other factors unrelated
to training such as psychological stress (social
stress, sleep, well-being, etc.).
Monotony is an index derived from the
RPEsession that can be very useful for distributing
sessions in a suitable way and thereby avoiding the
situation in which TLs act as stressors.
The analyses of different HRV domains
can reveal contradictory results in female athletes
because the frequency domain is highly affected by
the menstrual phase and cannot be assessed
during the same week for all members of an all-
female team. To avoid these disturbances, it is
preferable to analyze time-domain variables
because they are more stable and are not altered by
menstruation or by the breathing rate and
108 Physiological and psychological changes at the end of the soccer season in elite female athletes
Journal of Human Kinetics - volume 66/2019 http://www.johk.pl
stationary conditions. For this reason, this
measurement is ideal for this type of study of
female athletes. Moreover, the lnRMSSD is the
time-domain variable that exhibited a stronger
correlation with the RESTQ-sport and the Cooper
and Yo-Yo IR1 tests.
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Corresponding author:
Dr. Jose Morales,
c/ Císter, 34, 08022 Barcelona, Spain.
Tel. +34 93 253 30 00 Fax: +34 93 253 30 31
E-mail: josema@blanquerna.url.edu