Emotional Self-Regulation in Primary Education: A Heart Rate-Variability Biofeedback Intervention Programme

Ci a ion: A i ze a, A.;
A anbe i-Ruiz, A.; So oa, G.;
Mindeguia, R.; Ola za, A. Emo ional
Sel -Regula ion in P ima y Educa ion:
A Hea Ra e-Va iabili y Bio eedback
In e en ion P og amme. In . J.
En i on. Res. Public Heal h 2022,19,
5475. h ps://doi.o g/10.3390/
ije ph19095475
Academic Edi o : Raphael M. He
Recei ed: 4 Ma ch 2022
Accep ed: 28 Ap il 2022
Published: 30 Ap il 2022
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In e na ional Jou nal o
En i onmen al Resea ch
and Public Heal h
A icle
Emo ional Sel -Regula ion in P ima y Educa ion: A Hea
Ra e-Va iabili y Bio eedback In e en ion P og amme
Ai o A i ze a 1,*, Aina a A anbe i-Ruiz 1, Go e i So oa 2, Rosa Mindeguia 1and Amaiu Ola za 1
1
Depa men o Basic Psychological P ocess and De elopmen , Uni e si y o he Basque Coun y (UPV/EHU),
20018 San Sebas ian, Spain; [email p o ec ed] (A.A.-R.); [email p o ec ed] (R.M.);
amaiu [email p o ec ed] (A.O.)
2Depa men o Clinical and Heal h Psychology and Resea ch Me hodology,
Uni e si y o he Basque Coun y (UPV/EHU), 20018 San Sebas ian, Spain; go e i.so [email p o ec ed]
*Co espondence: ai o [email p o ec ed]; Tel.: +34-943-01-8332
Abs ac :
This s udy in es iga ed he bene i s o using a bio eedback in e en ion p og amme o ain
child en in con olling hei hea a e a iabili y (HRV) h ough slow-paced b ea hing in eal ime.
HRV bio eedback in e en ions ocused on showing subjec s o b ea he such ha hei HRV numbe s
ise, imp o ing hei sel - egula ion. The HRV bio eedback in e en ion, ocused on b ea hing, was
conduc ed wi h p ima y educa ion s uden s aged be ween 7 and 11 yea s. The p og amme consis ed
o i e bio eedback sessions, whe e s uden s we e augh o b ea he six long and slow pai s o b ea hs
pe minu e, o inc ease hei HRV. A e pa icipa ion in he p og amme, s uden s, ega dless o
gende , inc eased hei HRV in a s a is ically signi ican ashion wi h a la ge e ec , bu his e ec was
no he same o all ages. HRV bio eedback in e en ions a e a ely applied in schools and gi en he
e ec i eness o he in e en ion o imp o e HRV in child en, he applied implica ions o ou esul s
in educa ional se ings a e discussed, especially aking in o accoun he child en’s ages.
Keywo ds:
bio eedback in e en ion; hea a e a iabili y; child en; poly agal heo y; Hea Ma h
emWa e so wa e
1. In oduc ion
In childhood, emo ions a e expe ienced wi h g ea in ensi y and wi h low capaci y o
emo ional egula ion [1] which may ha e a nega i e impac on psychosocial skills, school
pe o mance and well-being [
2
,
3
]. Du ing p ima y educa ion, he capaci y o emo ional
sel - egula ion is s ill unde de elopmen which o e s an oppo uni y o implemen in-
e en ions wi h he goal o imp o ing emo ional sel - egula ion abili ies [
4
]. Speci ically,
in e en ions based on bio eedback o he HRV and ocused on b ea hing ha e been shown
o be e ec i e in imp o ing emo ional sel - egula ion capaci y in child en [5].
Bio eedback is a b oadly used me hod o ain people o olun a ily con ol ce ain
physiological unc ions, such as b ea hing, which consis s o p o iding use s wi h ins an a-
neous in o ma ion on a ia ions ha occu in hei own physiological ac i i y [
6
]. Using
hea a e a iabili y-based bio eedback p og ammes, by means o b ea hing p ac ise, he
subjec s lea n o b ea h such ha hea a e a iabili y (HRV) inc eases [
7
,
8
]. In his ega d,
i was obse ed ha adequa e HRV bio eedback eaches people o b ea he a a equency o
app oxima ely six b ea hs pe minu e [9,10].
As a as age is conce ned, i has been obse ed ha in child en he deg ee o HRV
and sel - egula ion capaci y a e ela ed. Di e en s udies ha e shown ha g ea e HRV
e lec s be e psychosocial adjus men in he childhood popula ion [
11
,
12
]. Child en wi h
beha iou p oblems display lowe HRV [
13
,
14
], howe e , we do no ha e enough e idence
abou he di e en ial e ec i eness ha , ega ding age, a bio eedback aining p og amme
based in b ea h pacing, may ha e on child en om 7 o 11 yea s old in P ima y Educa ion.
In . J. En i on. Res. Public Heal h 2022,19, 5475. h ps://doi.o g/10.3390/ije ph19095475 h ps://www.mdpi.com/jou nal/ije ph
In . J. En i on. Res. Public Heal h 2022,19, 5475 2 o 14
In o de o o e a comp ehensi e heo y on child en’s capaci y o sel - egula ion
h ough bio eedback p og ammes, he Poly agal Theo y should be men ioned. This
heo y add esses he in e ela ion be ween he agus ne e and he emo ional expe ience
allowing us o associa e sel - egula ion abili ies wi h alues o HRV. The agus ne e is
he en h c anial ne e and is he main ne e in he pa asympa he ic di ision de e mining
emo ional sel - egula ion [
15
]. P ima y educa ion child en comple ely possess he agus
ne e sys em [
16
,
17
] and he en al- agus b anch and he do sal- agus b anch o he
agus ne e, p o ide an inhibi o y en y o he hea h ough he pa asympa he ic ne ous
sys em ( educing hea a e) and in luence HRV ou comes.
The agus ne e sys em is hie a chically s uc u ed in o h ee sequen ial unc ional
sub-sys ems: (a) The en al agal complex o myelina ed agus, (b) The sympa hoad enal
sys em, and (c) The do sal agal complex o non-myelina ed agus [
18
,
19
]. When he
en i onmen is pe cei ed o be sa e, he en al agal complex is ac i a ed, leading o an
inc eased in luence o he myelina ed agal channels ha slow down hea bea equency,
inc ease HRV, and inhibi igh -o - ligh mechanisms o he sympa he ic ne ous sys em.
This physiological s a e makes i possible o he p e on al co ex’s s uc u es o wo k
p ope ly, which a e in cha ge o a en ion and sel - egula ion, bo h o which a e di e en-
ially de eloped o a child o 7 yea s old and one o 11 yea s old. Howe e , and despi e
p ima y educa ion child en comple ely possessing he agus ne e sys em, we s ill do no
ha e enough e idence o know how e ec i e an HRV and b ea hing based bio eedback
p og amme can be dependen on he age o he child en
The a o emen ioned HRV can be assessed wi h se e al analy ical oci, al hough he
mos commonly used a e equency domain analysis (powe spec al densi y) and ime
domain analysis [
20
,
21
]. As i has consis en ly been shown in he li e a u e, HRV is consid-
e ed a measu emen o physiological emo ional sel - egula ion [
22
–
26
] and a bioma ke
o psychopa hology [
27
]. High HRV also has been ela ed wi h lowe le els o us a ion
and highe pe o mance le els [
28
] and posi i e psychological adjus men in child en,
adolescen s, and he adul popula ion [
27
,
29
], including, o example, empa he ic esponses
o o he people in dange [
30
,
31
], social compe ence [
32
], and posi i e social in e ac ions
amongs equals [33].
Low HRV is he esul o sup essing he agal b ake. Supp ession o he agal b ake
en ails disappea ance o he pa asympa he ic in luence wielded by he en al agus, and
inc eased ca dio ascula pace, which educes HRV. The subjec i e emo ional expe ience
unde his neu ophysiological s a e is a a iable deg ee o ension, malaise, and anxi-
e y [
34
,
35
]. In e ms o psychological egula ion, educed HRV has been associa ed wi h
educed capaci y o sel - egula ion and cogni i e unc ions ha a e p ima ily loca ed in
he p e on al co ex [26,36–38].
Th ough b ea h con ol, heal hy people can inc ease hei own HRV by modi ying
espi a o y equency, h ough slowe and s eadie b ea hing [
39
,
40
] by means o he
agus ne e’s in luence on he sinoa ial node o he hea , slowing he hea a e, and
inc easing HRV [
36
,
41
,
42
]. The high HRV gene a ed h ough olun a y b ea hing is a
sui able emo ional sel - egula ion measu e [43,44].
HRV bio eedback can be conduc ed by placing a de ice on a pe son ha connec s o
a compu e and p o ides eal- ime in o ma ion on hei HRV. By obse ing he impac
ha b ea hing has on HRV in eal ime, one lea ns o b ea he ( h ough ial and e o
and eedback), and o imp o e hei emo ional sel - egula ion capaci y [
7
]. In his sense,
scien i ic li e a u e has shown ha bio eedback in e en ions ocused on b ea hing, inc ease
HRV bo h in he adul popula ion [
45
–
50
] and in he childhood popula ion [
50
,
51
]. Fo
example, Van de Zwan e al. [
52
] conduc ed an HRV bio eedback in e en ion ocused
on b ea hing o 5 weeks, analysing he p og amme’s e ec on he well-being o p egnan
and non-p egnan women. A e he in e en ion, bo h g oups had educed anxie y and in-
c eased well-being. In o de o be e ackle s ess du ing exams, Deschod -A sac e al. [
53
]
conduc ed a 5-week in e en ion on HRV bio eedback ocused on b ea hing, wi h uni e -
si y a hle es. A e he in e en ion, he expe imen al g oup signi ican ly imp o ed HRV.
In . J. En i on. Res. Public Heal h 2022,19, 5475 3 o 14
This imp o emen was main ained o 12 weeks. Posko ino a e al. [
54
] conduc ed an HRV
bio eedback in e en ion in one single session wi h 20 Seconda y School s uden s (15 and
16 yea s old), in o de o inc ease he pa icipan s’ HRV as a p o ec i e esou ce agains
in e ne addic ion diso de s. A e he in e en ion, pa icipan s’ HRV was signi ican ly
inc eased, and co ela ion analyses showed a signi ican nega i e co ela ion be ween in-
c eased HRV and sco es ob ained in measu ing in e ne addic ion. Mei e al. [
9
] conduc ed
an in e en ion wi h 32 adolescen s be ween 13 and 18 yea s o age, also in one single HRV
bio eedback session. A e he in e en ion, a signi ican inc ease in HRV was obse ed,
and mo e signi ican han ano he g oup o s uden s who ecei ed al e na i e ea men in
an au ogenous aining session.
In his ealm, o he in e en ions in HRV bio eedback we e also p o en e ec i e. Fo
example, in e ms o he uni e si y popula ion, HRV bio eedback in e en ions ocused on
b ea hing, imp o ed pa icipan s’ HRV [
45
,
49
], and in e ms o he school-aged popula ion,
s uden s pa icipa ing in HRV bio eedback in e en ions also imp o ed HRV [
47
,
50
,
51
,
55
].
The e o e, li e a u e consis en ly shows bio eedback in e en ions ha e a posi i e
impac on pa icipan s HRV, especially in adolescen s and adul s. Less e idence is ga he ed
on he impac o hese p og ams in child en om 7 o 11 yea s old. The e o e, he main
goal o his esea ch was o examine he e ec i eness o a bio eedback b ea h pacing
aining p og amme on HRV in child en a p ima y school, aking in o accoun he age o
he pa icipan s.
Based on p e ious esul s, we expec ha ; compa ed o a con ol g oup, he alues
o he HRV o he expe imen al g oup will be highe han he con ol g oup alues a e
he in e en ion.
Rega ding he abo e-men ioned neu o-ana omical de elopmen p ocesses, we will
explo e i he lowe neu o-ana omical ma u i y p og ess a lowe ages migh also a ec he
e ec i eness o he in e en ion p og amme, so as o obse e be e HRV esul s as he age
o he pa icipan s inc eases.
Finally, in e ms o gende , we did no ind simila esea ch conduc ed on school-aged
popula ions o examine di e ences based on gende , which is possibly explained by limi ed
sample sizes. In o he age anges, Hill e al. [
56
] examined 172 s udies mainly ocused on
he adul popula ion. The esul s showed ha , in compa ison wi h men, women displayed
g ea e ampli ude in HRV. B une o e al. [
57
] conduc ed a s udy wi h 41 adolescen s
(20 boys and 21 gi ls), aged 12–17 yea s, whe e no s a is ically signi ican gende di e ences
we e ound in HRV sco es. Finally, in he s udy conduc ed by Aziz e al. [
58
], upon
compa ing HRV pa ame e s be ween 33 gi ls and 37 boys, hey obse ed ha only boys
had lowe sco es han gi ls in only h ee ou o 11 HRV pa ame e s (SDNN, LF, and SD2).
The e o e, we also aim o in es iga e i he e we e gende di e ences in HRV alues be o e
and a e he in e en ion p og amme.
2. Ma e ials and Me hods
2.1. Sample
The expe imen al and con ol g oups we e di ided in o he h ee cycles: 29.2% be-
longed o he i s cycle (2nd g ade, M = 7.58 yea s and SD = 0.38), 57.7% o he second
cycle (3 d and 4 h g ades, M = 8.93 yea s old and SD = 0.85), and he emaining 13.1% we e
hi d-cycle s uden s (5 h and 6 h g ades, M = 11.04 yea s old and SD = 0.91).
Pa icipan s we e s udying in p ima y educa ion in wo di e en public schools
using he Ama a Be i Educa ion Sys em which seeks o educa e s uden s using e e yday
p oblems and o ganizing hei e e yday lea ning p ocess in hema ic spaces (Mu umendi
and La ea public schools). The expe imen al and con ol g oups we e di ided in he h ee
cycles: 29.2% belonged o he i s cycle (2nd g ade, 7 yea s old), 57.7% o he second cycle
(3 d and 4 h g ades, 8–9 yea s old), and he emaining 13.1% we e hi d-cycle s uden s (5 h
and 6 h g ades, 10–11 yea s old).
S uden pa icipa ion was olun a y and consen ed o by he school boa d, pa en s,
and gua dians. Class ooms we e andomly assigned o expe imen al and con ol g oups,
In . J. En i on. Res. Public Heal h 2022,19, 5475 4 o 14
howe e , all child en, excep hose wi h a clinical diagnosis (i.e., hype ac i i y, dep ession
o anxie y diso de s) belonging o hose class ooms pa icipa ed in he s udy. So, child en
we e no andomly assigned o he ea men /non- ea men condi ions.
The s udy had a a ou able epo om he e hics commi ee o esea ch wi h hu-
mans, hei samples, and hei da a (M10-2020-318) om he Uni e si y o he Basque
Coun y/Euskal He iko Unibe si a ea (UPV/EHU). E hical aspec s equi ed o esea ch
wi h humans we e sc upulously ollowed (in o med consen , igh o in o ma ion, pe sonal
da a p o ec ion, con iden iali y gua an ees, non-disc imina ion, no cos , and possibili y o
lea e he s udy du ing any o i s phases).
2.2. Design
Gi en he inhe en cha ac e is ics o he na u al g oups (p ima y educa ion class ooms)
and he na u al con ex (in e en ion akes place a he school), a quasi-expe imen al
in e en ion was designed wi h a con ol g oup. Fi e HRV sco es we e aken om all
expe imen al pa icipan s. The i s measu emen o session one (S1) is he p e- ea men
measu emen and in o ms abou he baseline HRV numbe s. The i h measu emen
o session i e (S5) is he pos - ea men measu emen . Fo he con ol g oup only wo
measu es we e aken in session one (S1) and session i e (S5) and a he same pe iod o
ime as he expe imen al g oup.
2.3. Ins umen s and Ma e ials
As ollows, a desc ip ion o he ins umen s and ma e ials used a e desc ibed.
Reco ding shee (ad hoc): A documen was speci ically p epa ed o eco d he da a
ob ained om each s uden in each session h oughou he in e en ion. I con ains he
HRV sco es om he i e sessions.
HRV: Hea Ma h EmWa e so wa e was selec ed o his s udy [
59
], whose e icacy has
been p o en in di e en s udies [
5
,
50
,
55
]. This is a non-in asi e ins umen ha measu es
HRV in eal ime h ough a senso placed on he ea lobe. Using a ma hema ical algo i hm,
he EmWa e so wa e ans o ms he collec ed da a (e.g., RMSSD, SDNN...) in o low,
medium, and high cohe ence a ios. These low, medium and high cohe ence a ios a e
di ec ly ela ed o HRV ampli ude a es. Thus, a low cohe ence le el ma ches low HRV,
a medium cohe ence le el ma ches medium HRV, and a high cohe ence le el ma ches
high HRV.
A e each session, he applica ion shows he HRV sco es by dis ibu ing 100 poin s
in h ee le els (1) A low cohe ence le el, o low HRV, shown in ed; (2) An in e media e
cohe ence le el, o in e media e HRV, shown in blue; and (3) A high cohe ence le el, o
high HRV, shown in g een. These sco es a e se o h on he eco d shee and used o la e
s a is ical analyses.
Two EmWa e so wa e applica ions we e used [
59
]: Cohe ence Coach and Balloon Game.
By applying Cohe ence Coach, child en lea n o b ea he ollowing he hy hm o a mo ing
ball on he compu e sc een, lea ning o b ea he six b ea hs pe minu e in he ollowing
ashion: when he ball goes upwa d, pa icipan s mus b ea he in h ough he nose, and
when he ball goes down, hey mus also b ea he ou h ough he nose.
The applica ion named Balloon Game is an in e ac i e game whe e s uden s p ac ise
he ype o b ea hing lea ned in he Cohe ence Coach applica ion, bu wi hou ollowing
he hy hm o he ball. Speci ically, in he Balloon Game applica ion, a ho -ai balloon
appea s, lying o e di e en scena ios wi h a iable deg ees o speed, depending on he
pa icipan s’ pace o b ea hing. I hey b ea he unde pa ame e s simila o hose lea ned
in he Cohe ence Coach applica ion, he jou ney will be as e , while i hey do no b ea he
unde hese pa ame e s, he jou ney will be slowe .
In . J. En i on. Res. Public Heal h 2022,19, 5475 5 o 14
2.4. P ocedu e
The p og amme was implemen ed in wo phases. Fi s , since he in e en ion was de-
signed o he u o o ain s uden s indi idually, he p e-in e en ion phase was designed,
whe e eache s we e ained o lea n o use he EmWa e so wa e’s Cohe ence Coach and
Balloon Game applica ions [
59
] so ha , la e on, hey could apply his in e en ion o
s uden s. This aining’s goal was wo- old. On one hand, he objec i e was o each how
o use he p og amme and he ins umen s necessa y o use i in he class oom in o de
o ake indi idual HRV measu emen s h oughou he in e en ion. On he o he hand,
o help eache s o unde s and he ela ionship be ween s eady, calm b ea hing, and HRV.
Teache aining las ed 8 h.
Secondly, o he expe imen al g oup, he applica ion phase o he in e en ion
p og amme consis ed o i e sessions. One session pe week was held indi idually wi h
each s uden . Each session las ed app oxima ely 15 min and was conduc ed in he same
physical space (a class oom p epa ed o his end). The idea is o each gi l and boy o
conduc hei session he same days and imes o he week. The di e en ac i i ies p oposed
we e di ec ed by he usual eache s who had been p e iously ained and we e supe ised
by a membe o he esea ch eam. Mo eo e , he HRV sco es ob ained on each eco d o
each session we e collec ed on a eco d shee made o his end. A de ailed s ep by s ep
desc ip ion o he bio eedback aining p og amme can be ob ained by he au ho s. Table 1,
summa izes he in e en ion p o ocol bo h in in e en ion and con ol g oups.
Table 1. In e en ion p ocesses o in e en ion and con ol g oups.
G oups S1 S2 S3 S4 S5
In e en ion HRV-
Base line
B ea h T aining +
HRV-Balloon Game
Connexion
B ea h T aining +
HRV-Balloon Game
Connexion
HRV-Balloon
Game Connexion
HRV-Balloon
Game Connexion
Con ol HRV-
Base line 1 No aining No aining No aining HRV-Base line 2
3. S a is ical Analysis
In o de o obse e i HRV sco es we e signi ican ly di e en upon comple ion o
aining, we conduc ed he Wilcoxon signed- ank es compa ing a e ages be o e and a e
he aining sessions. La e , a S uden - es analysis was pe o med o examine i a e ages
be ween p e- es and pos - es low HRV and high HRV by cycles we e di e en . We also
analysed he gende di e ences in HRV by using a a iance analysis o HRV esul s in S1
and S5 based on gende and inally, o examine i he e ec i eness o he p og amme was
s able om session o session and aking in o accoun he age o he pa icipan s, we used
an ANOVA analysis using a MIXED me hod.
4. Resul s
Once he in e en ion was comple ed, he i e HRV sco es collec ed on he eco d
shee s we e p ocessed and analysed. Below we p esen he esul s o he Wilcoxon signed-
ank es compa ing a e ages be o e and a e he aining sessions. We deemed i essen ial
o obse e whe he HRV sco es we e signi ican ly di e en upon comple ion o aining. In
addi ion, sco es om he baseline (S1) we e compa ed wi h hose om session i e (S5). I
should be men ioned ha he c i e ia used by Kelley and P eache [
60
] we e ollowed o
in e p e he e ec size.
In e ms o low HRV, o he expe imen al g oup he a e age le els we e signi ican ly
highe a he baseline (S1; M= 62.70) han a e he in e en ion (S5; M= 31.80), z=
−
10.26,
p< 0.05, =
−
0.53. Fo medium HRV, he a e age le els we e lowe on he baseline session
(S1; M= 14.50) han a e he in e en ion (M= 23.08) z=
−
5.98, p< 0.05, =
−
0.34. Finally,
o high HRV, he a e age le els we e lowe on he baseline session (S1; M= 23.04) han
a e he in e en ion (M= 79.52), z=
−
12.37, p< 0.05, =
−
0.71. Compa ing hese same

In . J. En i on. Res. Public Heal h 2022,19, 5475 6 o 14
alues o he con ol g oup, no s a is ical di e ences could be obse ed in any o he h ee
le els o HRV. Low HRV alues (S1; M= 60.21); (S5; M= 62.70), z= 0.87, p> 0.05, = 0.13.
Fo medium HRV, (S1; M= 16.76) and S5 (M= 17.09) z= 0.73, p> 0.05, = 0.12. Finally, o
high HRV, (S1; M= 24.17) and S5 (M= 24.98) z= 0.44, p> 0.05, = 0.04.
As he e we e no s a is ical di e ences o he con ol g oup, we examined di e ences
jus o he expe imen al g oups and aking in o accoun he main goal o his in es iga ion,
ha is o examine i he e we e di e ences be ween age anges. As ollows, wi h he
analysis by age anges ( i s , second and hi d cycle), in Table 2, i can be obse ed ha
he e is a di e en ial e ec o age in ela ion o high HRV. Wi h changes being s a is ically
signi ican in all cycles, a lowe e ec size is obse ed in he i s cycle (7 yea s old), being
a mode a e e ec size. In he second cycle, a la ge e ec size is obse ed and in he hi d
cycle, he bigges e ec size is obse ed.
Table 2. Compa ison o S1* and S5* a e ages by high HRV and cycles.
P e-Tes Pos -Tes S uden ’s Cohen’s d
N M SD M SD p d
To al 300 23.26 29.56 79.52 60.47 0.000 −1.250
Cycle 1 87 26.61 31.93 49.77 51.10 0.000 −0.558
Cycle 2 175 23.78 29.75 94.99 60.56 0.000 −1.577
Cycle 3 38 13.16 19.88 76.39 54.84 0.000 −1.692
* S1 and S5 numbe s e e o sessions 1 and 5.
In ela ion o esul s by ages o low HRV in Table 3, we also obse e he p og amme’s
di e en ial impac . In his case, wi h he change e ec being s a is ically signi ican in all
cycles, he e ec ’s lesse size occu s again in he i s cycle, his being a mode a e e ec size.
In he second cycle, we obse e a la ge e ec size. And in he hi d cycle, he g ea es e ec
sizes o all cycles occu .
Table 3. Compa ison o S1–S5 a e ages by low HRV and cycles.
P e-Tes Pos -Tes S uden ’s Cohen’s d
N M SD M SD p d
To al 299 62.63 30.78 32 30.07 0.000 −1.007
Cycle 1 87 62.16 33.09 31.45 37.23 0.000 −0.506
Cycle 2 174 61.39 31.01 25.32 27.26 0.000 −1.238
Cycle 3 38 69.37 23.18 30.95 29.12 0.000 −1.469
In o he wo ds, as he child en a e olde , he g ea e he impac o he p og amme
(measu ed h ough he inc eased high HRV and educed low HRV).
In o de o gi e an answe o he hi d explo a o y hypo hesis, we analysed he gende
di e ences in HRV. Table 4shows he esul s.
None o he HRV sco es compa ed be ween gi ls and boys in sessions one and i e
showed s a is ically signi ican esul s. Thus, he e a e no di e ences be ween bo h gende s
in HRV alues.
A his poin o he s udy, we also asked i he e ec i eness o he p og amme is s able
om session o session ac oss he i e sessions and also i he e a e any di e ences in each
session ega ding he age o he pa icipan s. In o de o answe o hese ques ions, he
e olu ion o high HRV alues om session o session was examined by an ANOVA analysis
using a MIXED me hod. The ixed e ec es ima ion showed ha he inc ease o he high
HRV obse ed in each session was s a is ically signi ican . See Table 5.
In . J. En i on. Res. Public Heal h 2022,19, 5475 7 o 14
Table 4. Va iance analysis in HRV esul s in S1* and S5* based on gende .
A e age SD F
HRV N Gi ls N Boys Gi ls Boys F pCohen’s d
Low HRV S1 138 61.80 163 63.21 31.35 30.18 0.16 0.69 −0.046
Low HRV S5 138 33.82 163 30.45 31.26 29.12 0.93 0.34 0.112
Medium HRV S1 138 14.04 163 14.93 9.10 10.13 0.63 0.43 −0.093
Medium HRV S5 138 23.32 163 22.96 23.03 19.74 0.02 0.88 0.017
High HRV S1 138 24.14 163 22.35 30.09 29.10 0.28 0.60 0.061
High HRV S5 138 80.22 163 78.45 63.11 58.01 0.06 0.80 0.029
* S1 and S5 numbe s e e o sessions 1 and 5.
Table 5. E olu ion o high HRV alues om session o session in all samples.
P edic o Sum o Squa es d Mean Squa e F p
Session 1 high HVR 4616.81 2 2308.41 2.70 0.06
Session 2 high HVR 24578.54 2 12289.27 11.09 0.001
Session 3 high HVR 102411.57 2 51205.78 24.52 0.001
Session 4 high HVR 79778.77 2 39889.38 15.61 0.001
Session 5 high HVR 119275.36 2 59637.69 18.18 0.001
In Figu e 1 he g aphical e olu ion o he high HRV o all samples can be seen.
In .J.En i on.Res.PublicHeal h2022,19,xFORPEERREVIEW7o 15
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Table4.Va ianceanalysisinHRV esul sinS1*andS5*basedongende .
A e ageSDF
HRVNGi lsNBoysGi lsBoysFpCohen´sd
LowHRVS113861.8016363.2131.3530.180.160.69−0.046
LowHRVS513833.8216330.4531.2629.120.930.340.112
MediumHRVS113814.0416314.939.1010.130.630.43−0.093
MediumHRVS513823.3216322.9623.0319.740.020.880.017
HighHRVS113824.1416322.3530.0929.100.280.600.061
HighHRVS513880.2216378.4563.1158.010.060.800.029
*S1andS5numbe s e e  osessions1and5.
Noneo  heHRVsco escompa edbe weengi lsandboysinsessionsoneand i e
showeds a is icallysigni ican  esul s.Thus, he ea enodi e encesbe weenbo hgen‐
de sinHRV alues.
A  hispoin o  hes udy,wealsoaskedi  hee ec i enesso  hep og ammeis
s able omsession osessionac oss he i esessionsandalsoi  he ea eanydi e ences
ineachsession ega ding heageo  hepa icipan s.Ino de  oanswe  o heseques ions,
hee olu iono highHRV alues omsession osessionwasexaminedbyanANOVA
analysisusingaMIXEDme hod.The ixede ec es ima ionshowed ha  heinc easeo 
hehighHRVobse edineachsessionwass a is icallysigni ican .SeeTable5.
Table5.E olu iono highHRV alues omsession osessioninallsamples.
P edic o Sumo Squa esd MeanSqua eFp
Session1highHVR4616.8122308.412.700.06
Session2highHVR24578.54212289.2711.090.001
Session3highHVR102411.57251205.7824.520.001
Session4highHVR79778.77239889.3815.610.001
Session5highHVR119275.36259637.6918.180.001
InFigu e1 heg aphicale olu iono  hehighHRVo allsamplescanbeseen.

Figu e1.E olu iono  hehighHRVinallsamples.
Examining he esul s,wecouldobse e ha  hepa e no  he i s cyclewasali le
di e en  om he o alsamples.The ixede ec es ima ionindica es ha  he eisanin‐
c emen o  hehighHRV omS1 oS2,howe e  he eadec ease omS2 oS3.This
22.94
54.17
64.36
72.59
80.08
0
10
20
30
40
50
60
70
80
90
0123456
High HVR
Time
Figu e 1. E olu ion o he high HRV in all samples.
Examining he esul s, we could obse e ha he pa e n o he i s cycle was a li le
di e en om he o al samples. The ixed e ec es ima ion indica es ha he e is an
inc emen o he high HRV om S1 o S2, howe e he e a dec ease om S2 o S3. This
educ ion only happens in child en o he i s cycle, bu no in he second and hi d cycle.
See Table 6and Figu e 2.
Table 6. E olu ion o high HRV alues om session o session in cycle 1.
P edic o Es ima ion SE d pIC95% [LL, UL]
Session 1 high HVR 26.00 4.04
291.64
6.43 0.001 [18.04, 33.95]
Session 2 high HVR 42.66 4.04
291.64
10.56 0.001 [34.71, 50.61]
Session 3 high HVR 36.43 4.04
291.64
9.01 0.001 [28.48, 44.38]
Session 4 high HVR 45.80 4.15
291.64
11.02 0.001 [18.04, 33.95]
Session 5 high HVR 49.77 4.04
291.64
12.31 0.001 [18.04, 33.95]
In . J. En i on. Res. Public Heal h 2022,19, 5475 8 o 14
In he ollowing he g aphical e olu ion o he high HRV o s uden s o cycle 1 can
be seen.
In .J.En i on.Res.PublicHeal h2022,19,xFORPEERREVIEW8o 15
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educ iononlyhappensinchild eno  he i s cycle,bu no in hesecondand hi dcycle.
SeeTable6andFigu e2.
Table6.E olu iono highHRV alues omsession osessionincycle1.
P edic o Es ima ionSEd  pIC95%[LL,
UL]
Session1highHVR26.004.04291.646.430.001[18.04,33.95]
Session2highHVR42.664.04291.6410.560.001[34.71,50.61]
Session3highHVR36.434.04291.649.010.001[28.48,44.38]
Session4highHVR45.804.15291.6411.020.001[18.04,33.95]
Session5highHVR49.774.04291.6412.310.001[18.04,33.95]
In he ollowing heg aphicale olu iono  hehighHRVo s uden so cycle1can
beseen.

Figu e2.E olu iono  hehighHRVincycle1.
5.Discussion
Asse  o hin hes udy’shypo heses,i wasexpec ed ha  heb ea hing‐basedbio‐
eedbackp og ammewouldinc easeHRV.Ino he wo ds, ha  heHRVbio eedbackin‐
e en ionp og ammewouldbee ec i ei ,uponi scomple ion,pa icipan swe eable
oinc ease hei highHRV.I wasalsoexpec ed ha such alueswillbehighe  o  he
expe imen alg oupcompa ed o hecon olg oup.Wealsoin ended oexplo ei  he e
we edi e encesbe weenboysandgi lsand,mos impo an ly,i  heageo  hepa ici‐
pan shadane ec on he esul s.
Uponanalysing hecompa isono p e‐ es (S1)andpos ‐ es (S5)highHRVa e ages
om heexpe imen alg oup,weobse e ha in e en ionp og ammeimp o edhigh
le elso HRV.Wealsoobse ed ha compa ing he alueso  heHRV o  hecon ol
g oup, hep e‐ es andpos ‐ es  esul sdidshows a is icallysigni ican di e ences,
showing o  hisg oup hesame aluesinbo hmeasu es.The e o e,weconside  ha  he
in e en ionp og ammeinc eased heHRVo pa icipan s,whichcanbeconside edas
anindica o o  hei imp o ingcapaci y o sel ‐ egula ion.Emo ionalsel ‐ egula ionisa
undamen al ool ode elops uden s´e o ,mo i a ion,andpe sonal esponsibili y
abou lea ningand ogua an eescholas icadap a ion[14,61,62].Th oughou  hep ima y
educa ionpe iod,child enexpe iencecomplex eelingswi hou ha ingin e nalized he
abili y ocommunica eandsel ‐ egula e hei emo ionse ec i elyye .The e o e, his
26.00
42.67
36.44
46.94 49.77
0
10
20
30
40
50
60
0123456
High HVR
Time
Figu e 2. E olu ion o he high HRV in cycle 1.
5. Discussion
As se o h in he s udy’s hypo heses, i was expec ed ha he b ea hing-based
bio eedback p og amme would inc ease HRV. In o he wo ds, ha he HRV bio eedback
in e en ion p og amme would be e ec i e i , upon i s comple ion, pa icipan s we e able
o inc ease hei high HRV. I was also expec ed ha such alues will be highe o he
expe imen al g oup compa ed o he con ol g oup. We also in ended o explo e i he e
we e di e ences be ween boys and gi ls and, mos impo an ly, i he age o he pa icipan s
had an e ec on he esul s.
Upon analysing he compa ison o p e- es (S1) and pos - es (S5) high HRV a e ages
om he expe imen al g oup, we obse e ha in e en ion p og amme imp o ed high
le els o HRV. We also obse ed ha compa ing he alues o he HRV o he con ol g oup,
he p e- es and pos - es esul s did show s a is ically signi ican di e ences, showing o
his g oup he same alues in bo h measu es. The e o e, we conside ha he in e en ion
p og amme inc eased he HRV o pa icipan s, which can be conside ed as an indica o o
hei imp o ing capaci y o sel - egula ion. Emo ional sel - egula ion is a undamen al
ool o de elop s uden s’ e o , mo i a ion, and pe sonal esponsibili y abou lea ning
and o gua an ee scholas ic adap a ion [
14
,
61
,
62
]. Th oughou he p ima y educa ion
pe iod, child en expe ience complex eelings wi hou ha ing in e nalized he abili y o
communica e and sel - egula e hei emo ions e ec i ely ye . The e o e, his kind o
p og amme can be essen ial o child en’s well-being by p omo ing he abili y o sel -
egula e hei own emo ions, a en ion and beha iou .
The imp o emen o he ea men g oup in HRV obse ed in ou esea ch, ma ches esul s
obse ed in o he in e en ions wi h o he age g oups. Fo example, Kuppusamy, e al. [
63
]
ca ied ou an in e en ion wi h 520 adolescen s (13–18 yea s) o analyse he impac o a
6-mon h
p og amme ocused on olun a y b ea hing con ol on domain pa ame e s o e-
quency and HRV. A e he in e en ion, i was obse ed ha he expe imen al g oup ob ained
a s a is ically signi ican imp o emen in compa ison wi h he con ol g oup in he indica o
o HRV’s pa asympa he ic in luence. Mei e al. [
9
] conduc ed an in e en ion wi h 60 subjec s,
whe e hey analysed he di e ences in HRV o pa icipan s in wo g oups ea ed di e en ly:
one g oup wi h an HRV bio eedback session, and a g oup wi h an au ogenous aining session.
The esul s e ealed signi ican e ec s in bo h in e en ions on HRV alues.
We also ound esea ch conduc ed wi h he same Hea Ma h echnology used in ou
esea ch [
59
]. Field e al. [
64
] conduc ed an in e en ion wi h 13 pa icipan s aged be ween
26 and 62 yea s. A e he in e en ion, he expe imen al g oup showed g ea e HRV
ampli ude han he con ol g oup in a s a is ically signi ican ashion and wi h a g ea e ec
In . J. En i on. Res. Public Heal h 2022,19, 5475 9 o 14
size (d = 1.97). A i ze a e al. [
45
] conduc ed an HRV bio eedback in e en ion p og amme
wi h 152 uni e si y s uden s (a e age age = 19.6), and a con ol g oup wi h 81 uni e si y
s uden s (a e age age = 19.4), in o de o educe anxie y le els be o e exams, and hus
imp o e academic pe o mance. The esul s indica e a signi ican imp o emen in HRV
sco es, wi h an e ec size o η2= 0.77.
Rega ding he gende a iable, we obse ed signi ican di e ences be ween boys and
gi ls in HRV alues. The e ec size was low in all cases (d=< 0.3). In his ega d, i should be
men ioned ha we did no ind simila esea ch conduc ed on he schoolchild en popula ion
o examine di e ences based on gende , which is possibly explained by limi ed sample
sizes. Thus, ha ing obse ed ou esul s and hose shown in he scien i ic li e a u e [
57
,
58
],
we canno conclude ha he e a e e iden di e ences be ween boys and gi ls in HRV. Jus
like Hill e al. [
56
], we belie e ha i is necessa y o esea ch u he in o he impac o he
gende a iable on HRV o obse e mo e conclusi e esul s.
One o he goals o his a icle was also o obse e he e ec o he p og amme
depending he age o he pa icipan s. We should emembe ha , gi en he cu icula
con igu a ion o p ima y educa ion, he in e en ion p og amme in his esea ch was
applied o h ee di e en age anches: cycle one (7 yea s, n = 76), cycle wo (8–9 yea s,
n = 240), and cycle h ee (10–11 yea s, n = 47). The esul s showed ha he di e ences in
he p e- es and pos - es a e ages in high HRV we e s a is ically signi ican in all cycles.
Howe e , i is impo an o no e ha , in e ms o he e ec size, he e we e di e ences
be ween he cycles: in cycle one (
d=−0.28
), being low o mode a e, while in cycle wo
(d=−0.83) and in cycle h ee (d=−0.79), he e ec size was la ge.
In o he wo ds, in cycle one, unlike cycle wo and cycle h ee, we obse e a mode -
a e size e ec bo h in high HRV and in low HRV. As such, we may suppose ha hese
di e ences be ween cycles a e associa ed wi h sha ed p og ession ac o s inhe en o s u-
den s in cycle one. Di e ences may be jus i ied by ma u i y ac o s ela ed o he age
o 7 yea s. The e o e, speci ically heeding o he neu o-ana omical ce eb al zones o
emo ional sel - egula ion ( o example, he an e io en al cingula e co ex and he p e-
on al en omedial co ex) [
65
], and being awa e o hei de elopmen al p ocess be ween
childhood and adolescence [
66
,
67
] we can in e ha his lowe neu o-ana omical ma u i y
p og ess a 7 yea s makes i di icul o acqui e he emo ional sel - egula ion skill measu ed
in his case h ough inc eased high HRV. As such, i should be men ioned ha he esul s
obse ed in ou s udy a e also co obo a ed by hose obse ed in o he pieces o esea ch
wi h simila me hodologies [64,68,69].
6. Conclusions
Based on he esul s obse ed in his s udy, and h ough he s a is ical analyses
conduc ed a e applying ou in e en ion p og amme, we can a i m ha s uden s who
pa icipa ed in ou p og amme lea ned o inc ease hei HRV by p ac ising long, s eady
b ea hing, a a pace o six pai s o b ea hs pe minu e. These esul s all in line wi h o he
simila s udies [
23
,
67
], and hey a e in acco dance wi h he Poly agal Theo y [
19
,
70
,
71
],
which a i ms ha bio eedback p ocedu es based on b ea hing s a egies ha e an in luence
on he egula ion and imp o emen o HRV. Mo eo e , HRV bio eedback has p o en
o be an e ec i e s a egy o child en o lea n o sel - egula e and bols e olun a y
b ea hing lea ning.
A g owing body o psychological esea ch suppo s he idea ha HRV could be an
objec i e physiological measu emen o assess emo ional esponses [
22
,
23
,
72
], including
hose ela ed o emo ional egula ion [
15
,
67
,
73
]. High HRV le els co ela e o posi i e
esul s in psychological adjus men in child en [
74
–
76
], adolescen s, and adul s [
27
]. I has
also been di ec ly linked o sel - egula o y capaci ies in child en [
77
–
79
]. The imp o emen
o emo ional sel - egula ion capaci ies is e y impo an in P ima y Educa ion because
a his pe iod he e is an inc ease in academic and social demands ha can nega i ely
a ec emo ional s ess [
80
]. High HRV esul s a e posi i ely associa ed wi h emo ional
sel - egula ion abili ies, which, in u n, posi i ely in luences psychological well-being [
81
]