Data Analysis

The Statistical Package for the Social Sciences (SPSS) version 21.0 was used as a tool for data analysis. Statistical analyses included descriptive statistics such as

percentages and means and standard deviations.

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1 _{It is worth adding that, as the initial purpose of the study was to investigate long-lasting}

effects, the collection of saliva during the five weeks of the protocol (in this case educational sessions) was not considered as necessary. The idea of including four instances of saliva collection in every HRVT was created to be able to monitor how biochemical markers develop before and after each session of HRVT, whether any effects of HRVT last for some time and compare those with what was expected (Adam, Hoyt & Granger, 2011). In this way, the cost of the consumables needed for the analyses of the samples was considerably restricted as well, which made the realization of the study more feasible.

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Other statistical analyses were repeated- measures analyses of variance (ANOVA), paired-samples t-tests used for post-hoc comparisons, and repeated-

measures (mixed model) analyses of covariance (ANCOVA). The level of significance for all statistical analyses was set at the .05 alpha level. The variables measured during this study are summarized in Appendix B.1. First, we explore the impact of HRVT on key aspects of HRV, such as RMSSD and LF, with the former being considered to be the primary time-domain metric to reflect vagally-mediated changes in HRV and a more reliable index than short-term SDNN and pNN50 (Shaffer & Ginsberg, 2017), whereas the latter is affected by both SNS and PNS and maximization of it would be desirable. Other key aspects of HRV are investigated as described below, as well as the impact of HRVT on biochemical and psychophysiological aspects of stress. Therefore, the

following tests were conducted:

✓ A repeated-measures analysis of covariance – mixed model - (ANCOVA) was conducted to investigate:

➢ whether there were statistically significant differences in the root mean square of the successive differences (RMSSD) recorded for the participants of the experimental group during their post-intervention testing session (i.e. Post-Intexp) compared to the RMSSD recorded for the participants of the

control group during their post-intervention testing session of (i.e. Post- IntCtrl), controlling for the RMSSD recorded during the participants’ pre-

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➢ whether there were statistically significant differences in the power of the low frequency range (LF) recorded for the participants of the experimental group during their post-intervention testing session (i.e. Post-Intexp)

compared to the LF recorded for the participants of the control group during their post-intervention testing session of (i.e. Post-IntCtrl), controlling

for the LF recorded during the participants’ pre-intervention testing session (i.e. Pre-Intexp and Pre-IntCtrl).

➢ whether there were statistically significant differences in the standard deviation of normal-to-normal R-R intervals (SDNN) recorded for the participants of the experimental group during their post-intervention testing session (i.e. Post-Intexp) compared to the standard deviation of

normal-to-normal R-R intervals (SDNN) recorded for the participants of the control group during their post-intervention testing session of (i.e. Post- IntCtrl), controlling for the standard deviation of normal-to-normal R-R

intervals (SDNN) recorded during the participants’ pre-intervention testing session (i.e. Pre-Intexp and Pre-IntCtrl).

➢ whether there were statistically significant differences in the proportion of the number of pairs of successive NN (R-R) intervals that differ by more than 50ms divided by the total number of NN (R-R) intervals (i.e. pNN50) recorded for the participants of the experimental group during their post- intervention testing session (i.e. Post-Intexp) compared to the pNN50

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intervention testing session of (i.e. Post-IntCtrl), controlling for the pNN50

recorded during the participants’ pre-intervention testing session (i.e. Pre- Intexp and Pre-IntCtrl).

➢ whether there were statistically significant differences in the mean ratio low frequency to high frequency (LF/HF) recorded for the participants of the experimental group in the post-intervention testing session (i.e. Post-Intexp)

compared to the LF/HF recorded in the post-intervention testing session of the participants in the control group (i.e. Post-IntCtrl), controlling for the

LF/HF recorded in the participants’ pre-intervention testing session (i.e. Pre- Intexp and Pre-IntCtrl).

➢ whether there were statistically significant differences in the cortisol levels detected in the participants of the experimental group before the post- intervention testing session (i.e. Post-Intexp) compared to the cortisol levels

detected in the participants of the control group before their post-

intervention testing session of (i.e. Post-IntCtrl), controlling for the cortisol

levels detected before the participants’ pre-intervention testing session (i.e. Pre-Intexp and Pre-IntCtrl).

➢ whether there were statistically significant differences in the cortisol levels detected in the participants of the experimental group immediately after the post-intervention testing session (i.e. Post-Intexp) compared to the

cortisol levels detected in the participants of the control group immediately after their post-intervention testing session of (i.e. Post-IntCtrl), controlling

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for the cortisol levels detected immediately after the participants’ pre- intervention testing session (i.e. Pre-Intexp and Pre-IntCtrl).

➢ whether there were statistically significant differences in the a-amylase levels detected in the participants of the experimental group before their post-intervention testing session (i.e. Post-Intexp) compared to the a-

amylase levels detected in the participants of the control group before their post-intervention testing session of (i.e. Post-IntCtrl), controlling for the a-

amylase levels detected before the participants’ pre-intervention testing session (i.e. Pre-Intexp and Pre-IntCtrl).

➢ whether there were statistically significant differences in the a-amylase levels detected in the participants of the experimental group immediately after their post-intervention testing session (i.e. Post-Intexp) compared to

the a-amylase levels detected in the participants of the control group immediately after their post-intervention testing session of (i.e. Post-IntCtrl),

controlling for the a-amylase levels detected immediately after the

participants’ pre-intervention testing session (i.e. Pre-Intexp and Pre-IntCtrl).

✓ Furthermore, a repeated-measures analysis of variance (ANOVA) was conducted to investigate:

➢ whether there were statistically significant differences in the a-amylase levels of the experimental group participants collected before the HRVT compared to the other three instances of collection, that is, immediately after, 45 minutes later and 90 minutes after the end of the HRVT.

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➢ whether there were statistically significant differences in the cortisol levels of the participants of the experimental group collected at the same time from Session 1 to Session 8 (i.e. seven measurements X four different times of collection).

➢ whether there were statistically significant differences in the a-amylase levels of the participants of the experimental group collected at the same time from Session 1 to Session 8 (i.e. seven measurements X four different times of collection).

✓ Additionally, a repeated-measures analysis of covariance – mixed model - (ANCOVA) was conducted to investigate:

➢ whether there were statistically significant differences in the total electrical activity recorded in the trapezius muscles (EMG) in the post-intervention testing session of the participants in the experimental group (i.e. Post-Intexp)

compared to the EMG recorded in the post-intervention testing session of the participants in the control group (i.e. Post-IntCtrl), controlling for the

electrical activity recorded in the trapezii of the participants’ pre- intervention testing session (i.e. Pre-Intexp and Pre-IntCtrl).

➢ whether there were statistically significant differences in the skin

conductance levels (SC) recorded in the post-intervention testing session of the participants in the experimental group (i.e. Post-Intexp) compared to the

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the control group (i.e. Post-IntCtrl), controlling for the SC recorded in the

participants’ pre-intervention testing session (i.e. Pre-Intexp and Pre-IntCtrl).

➢ whether there were statistically significant differences in the skin

temperature levels (TEMP) recorded in the post-intervention testing session of the participants in the experimental group (i.e. Post-Intexp) compared to

the TEMP recorded in the post-intervention testing session of the

participants in the control group (i.e. Post-IntCtrl), controlling for the TEMP

recorded in the participants’ pre-intervention testing session (i.e. Pre-Intexp

and Pre-IntCtrl).

Appendix B.1 outlines the different parameters measured during the different sessions of the study.

In sum, better understanding of psychophysiological/biochemical responses to the newly-introduced 5-week slow-breathing strategy is important. First, as stress management and, as an extent of that, emotional control, in general, is one of the key issues an athlete faces prior to competition, strategies for better mental preparation are needed. Second, if HRV training is proposed as an intervention, then understanding whether a single 20-minute session has acute effects and/or within a 5-week period have increasing or gradually attenuated as well as long-lasting benefits is important. In the current study, the following three research questions were addressed: (A) Does a single 20-minute HRV training session create acute biochemical effects? (B) With the passage of time within the 5-week period of the suggested protocol, are there any increasing or attenuated effects? (C) Are there any long-lasting effects recorded two

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weeks after the completion of the 5-week protocol? Answering these questions will result in a clearer understanding on the benefits of HRV training on emotional control.

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3.3 RESULTS