psyg-12-724070 Sep embe 14, 2021 Time: 19:52 # 1
ORIGINAL RESEARCH
published: 20 Sep embe 2021
doi: 10.3389/ psyg.2021.724070
Edi ed by:
Be na d J. Ma in,
Uni e si y o Michigan, Uni ed S a es
Re iewed by:
Ma ia Gab iela Ga cia,
Uni e sidad San F ancisco de Qui o,
Ecuado
Jane S. Du ek,
Uni e si y o Ne ada, Las Vegas,
Uni ed S a es
*Co espondence:
Rod igo Rami ez-Campillo
[email p o ec ed]
Special y sec ion:
This a icle was submi ed o
Mo emen Science and Spo
Psychology,
a sec ion o he jou nal
F on ie s in Psychology
Recei ed: 11 June 2021
Accep ed: 27 Augus 2021
Published: 20 Sep embe 2021
Ci a ion:
To es-Banduc M,
Rami ez-Campillo R, And ade DC,
Calleja-González J, Nikolaidis PT,
McMahon JJ and Com o P (2021)
Kinema ic and Neu omuscula
Measu es o In ensi y Du ing D op
Jumps in Female Volleyball Playe s.
F on . Psychol. 12:724070.
doi: 10.3389/ psyg.2021.724070
Kinema ic and Neu omuscula
Measu es o In ensi y Du ing D op
Jumps in Female Volleyball Playe s
Maximiliano To es-Banduc1,2, Rod igo Rami ez-Campillo3*, Da id C is obal And ade4,
Julio Calleja-González5, Pan elis Theo Nikolaidis6, John J. McMahon7and
Paul Com o 7,8,9
1Escuela de Kinesiología, Facul ad de Ciencias de la Salud, Uni e sidad de Las Amé icas, Viña del Ma , Chile, 2Escuela
de Ciencias de la Salud, Uni e sidad de Viña del Ma , Viña del Ma , Chile, 3Depa men o Physical Ac i i y Sciences,
Uni e sidad de Los Lagos, Oso no, Chile, 4Cen o de In es igación en Fisiología y Medicina de Al u a, Facul y o Heal h
Science, Uni e sidad de An o agas a, An o agas a, Chile, 5Depa men o Physical Educa ion and Spo , Facul y
o Educa ion and Spo , Uni e si y o he Basque Coun y, Vi o ia-Gas eiz, Spain, 6Exe cise Physiology Labo a o y, Nikaia,
G eece, 7Di ec o a e o Psychology and Spo , School o Heal h and Socie y, Uni e si y o Sal o d, Sal o d, Uni ed Kingdom,
8Ins i u e o Spo , Physical Ac i i y and Leisu e, Ca negie School o Spo , Leeds Becke Uni e si y, Leeds,
Uni ed Kingdom, 9Cen e o Exe cise and Spo s Science Resea ch, Edi h Cowan Uni e si y, Joondalup, WA, Aus alia
The aim o his s udy was o assess d op jump (DJ) pe o mance a iables (jump heigh ,
con ac ime, and eac i e s eng h index) concomi an o su ace elec omyog aphy
(sEMG) o lowe limb muscles du ing DJs om di e en d op heigh s (in ensi ies).
The eccen ic and concen ic phase sEMG om he gas ocnemius medialis, biceps
emo is, and as us medialis muscles we e assessed du ing all es s, wi h sEMG
ac i i y no malized o maximal olun a y isome ic con ac ion (MVIC). In a c oss-
sec ional, s udy, 10 ama eu emale olleyball playe s (age 22.1 ±1.8 yea s; body mass
72.9 ±15.2 kg; heigh 1.70 ±0.08 m) comple ed DJs om six heigh s [15–90 cm
(DJ15 o DJ90)]. Du ing DJs he e was no jump- a ge box o ebound on o. Resul s o
one-way analysis o a iance (ANOVA) showed ha he jump heigh , con ac ime, and
eac i e s eng h index we e no signi ican ly (p>0.05) di e en be ween d op heigh s.
Mean biceps emo is eccen ic and concen ic sEMG anged om 27 o 50%, al hough
wi hou signi ican di e ences be ween d op heigh s. Mean gas ocnemius medialis
eccen ic and concen ic sEMG emained ela i ely cons an (∼60–80% MVIC) ac oss
DJs heigh s, al hough eccen ic alues eached 90–120% MVIC om DJ75 o DJ90.
Mean a ia ions o ∼50–100% MVIC o eccen ic and ∼50–70% MVIC o concen ic
sEMG ac i a ions we e obse ed in he as us medialis ac oss DJs heigh s. The biceps
emo is eccen ic/concen ic sEMG a io du ing DJ45 (i.e., 1.0) was lowe (p= 0.03)
compa ed o he a io obse ed a e DJ90 (i.e., 3.2). The gas ocnemius medialis and
as us medialis eccen ic/concen ic sEMG a io we e no signi ican ly di e en be ween
d op heigh s. In conclusion, jumping pe o mance and mos neu omuscula ma ke s
we e no sensi i e o DJ heigh (in ensi y) in ama eu emale olleyball a hle es.
Keywo ds: olleyball, eam spo , spo s, human physical condi ioning, esis ance aining, plyome ic exe cise,
muscle con ac ion, elec omyog aphy
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To es-Banduc e al. Jump In ensi y in Volleyball Playe s
INTRODUCTION
Volleyball is a eam spo cha ac e ized by pe iods o sho
du a ion (i.e., 3–9 s), high-in ensi y ac i i ies, in e spe sed
wi h pe iods (i.e., 10–20 s) o eco e y (Ga cía-De-Alca az
e al., 2020). Al hough he ac ions pe o med by playe s may
a y in e ms o hei indi idual oles, ela ed o echnical
and ac ical equi emen s, accele a ions, decele a ions, jumping,
ball-s iking, and mul idi ec ional locomo ion a e common
mo emen s (Sheppa d e al., 2007). In pa icula , jumping abili y
has p e iously been shown o be ela ed o be e pe o mance
in olleyball (Zi and Lido , 2010). In ac , sco ing ac ions (i.e.,
spike, block, and se e) a e mainly pe o med while jumping
e ically (Sheppa d e al., 2007). Indeed, he e is a signi ican
inc ease in he numbe o jumps pe se (113.5–181.3 jumps),
om young o eli e playe s in men’s olleyball (De Alca az
e al., 2017). Acco dingly, wi h he p inciple o aining speci ici y
olleyball playe s should sys ema ically engage in jump- ela ed
aining p og ams o imp o e spo s pe o mance (Gabbe ,
2016), in a phased, sequen ial, manne which also includes he
de elopmen o maximal o ce p oduc ion cha ac e is ics (i.e.,
s eng h) (Lloyd e al., 2011).
Plyome ic exe cises a e o en used in jump- ela ed aining
p og ams o imp o e jumping abili y, which play a pi o al
ole in olleyball pe o mance (Zi and Lido , 2010). In ac ,
olleyball is conside ed a e y “explosi e” and as -paced spo
in which plyome ic aining is widely used (Sil a e al., 2019).
The d op jump (DJ) is a common plyome ic d ill, especially
among olleyball playe s (Zi and Lido , 2010;Sil a e al.,
2019) and comp ises o a apid ansi ion be ween he eccen ic-
concen ic [i.e., s e ch-sho ening cycle (SSC)] muscle ac ions
(Heide schei e al., 1996), allowing g ea e muscle ac i a ion and
o ce ia s imula ion o he muscle spindle (Peng e al., 2011).
The al e na ing eccen ic-concen ic muscle wo k also leads o
he accumula ion o po en ial elas ic ene gy ( ia he se ies and
pa allel elas ic componen s), consequen ly allowing mo e wo k
o be pe o med in he concen ic phase (Taube e al., 2012).
Howe e , op imal d op heigh when pe o ming DJs o p omo e
muscle pe o mance is inconclusi e (Rami ez-Campillo e al.,
2013), especially ega ding DJ in ensi y.
Commonly, a hle es pe o m DJs a inc eased heigh s o a
g ea e aining in ensi y s imulus (Peng e al., 2011), as a g ea e
d op heigh esul s in an inc eased du a ion o accele a ion,
leading o an inc eased eloci y o he cen e o mass and
he e o e an inc eased momen um on impac wi h he g ound.
In his sense, i has been sugges ed ha in ensi y could be
e alua ed by examining a a ie y o kinema ic pa ame e s (e.g.,
jump heigh ) and by assessing he ac i a ion o muscle by su ace
elec omyog aphy (sEMG) (Ebben e al., 2008). In p ac ical
e ms, acu e inc eases in sEMG du ing aining exe cises may
lead o g ea e aining- ela ed adap a ions, as sugges ed in
p e ious s udies wi h eam-spo a hle es (Se ne e al., 2014).
Howe e , he in e p e a ion o his mus be done wi h cau ion
conside ing he e is no simple closed- o m o equa ion ha
desc ibes his ela ionship (Disselho s -Klug and Williams, 2020).
The sEMG is commonly used as a ma ke o in ensi y in s eng h
aining exe cise (K ommes e al., 2017), wi h a quad a ic inc ease
in oo -mean-squa e ampli ude o he sEMG signal ac oss o ce
le els om 20, 40, 60, 80, and 100% o maximal olun a y
con ac ion (Lenha d e al., 2009). Mo eo e , g ea e in ensi y
usually allow g ea e aining- ela ed adap a ions (ACSM, 2009).
Rega ding DJs, i has been shown ha g ea e d op heigh s may
ha e a signi ican e ec on sEMG achie ed du ing he ebound
jump (Abooda da e al., 2014), wi h g ea e sEMG ac i i y du ing
DJs execu ed om a 60 cm box (DJ60) han om a 40 cm
(DJ40) (Bobbe e al., 1987b) o 20 cm box (DJ20) (Peng e al.,
2011), sugges ing g ea e plyome ic jump in ensi y om g ea e
d op heigh s. Simila ly, he use o DJ heigh ha allow a hle es
o achie e maximal eac i e s eng h index may o e g ea e
aining-induced adap a ions (Rami ez-Campillo e al., 2018b).
In his sense, ou comes such as eac i e s eng h index o sEMG
can be used as a p oxy o po en ial adap a ions. Howe e ,
no all s udies ag ee wi h hese asse ions (Ebben e al., 2008).
Mo eo e , al hough powe ou pu and eac i e s eng h may
augmen wi h ini ial inc eases in box d op heigh , i d op heigh
con inues o inc ease he o e all muscle pe o mance may be
nega i ely a ec ed (Flanagan and Comyns, 2008), i he a hle e
does no possess he app op ia e o ce p oduc ion capabili ies
equi ed o apidly decele a e and accele a e hei cen e o
mass. Indeed, such ela ionships may be modula ed by a hle e’s
cha ac e is ics, such as he sex o he a hle e and hei ela i e
s eng h capabili ies, he la e being pa icula ly ele an among
emales, including emale olleyball playe s (Beckham e al., 2019;
Fuchs e al., 2019).
Al hough some esea che s ha e assessed kinema ic and
neu omuscula measu es o in ensi y du ing SSC ac ions (Ebben
e al., 2008;Ebben e al., 2011), whe he he esul s om such
s udies a e eplicable in olleyball playe s is a ma e o u he
esea ch. P e iously, jumping pe o mance and neu omuscula
ma ke s (And ade e al., 2020), as well as biomechanical
ou comes (Peng e al., 2019) in male olleyball playe s, we e
sensi i e o DJ heigh , al hough no in a clea dose- esponse
ashion. Rega ding emale olleyball playe s, he lack o s udies
p eclude analysis o such phenomenon, al hough i seems ha
impo an di e ences be ween male and emale olleyball playe s
may be hypo hesized (Fuchs e al., 2019). Conside ing he
lack o plyome ic aining s udies conduc ed among emales
compa ed o males (Rami ez-Campillo e al., 2018a) and he
inc eased pa icipa ion o emales in olleyball, pa icula ly a
ama eu le el, mo e esea ch on his issue is needed. This may
help s eng h and condi ioning coaches o p esc ibe adequa e
plyome ic aining loads, as needless ex a aining (e.g.,
excessi e DJ heigh s) may expose a hle es o g ea e inju y isk,
especially among emales (B umi e al., 2016).
F om a biomechanical s andpoin as he inc eased d op heigh
esul s in inc eased d op du a ion and he e o e accele a ion, his
would esul in a highe impac eloci y, inc eased momen um,
and so a highe b aking ne impulse (Bobbe e al., 1987a). Due
o he a o emen ioned biomechanical conside a ions, inc eased
d op heigh s may impose a subop imal in ensi y- ela ed s imulus
i he a hle e does no possess he app op ia e o ce p oduc ion
capabili ies equi ed o apidly decele a e and accele a e hei
cen e o mass. E en among male olleyball playe s, whom
usually ha e g ea e s eng h le el compa ed o emales, inc eased
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To es-Banduc e al. Jump In ensi y in Volleyball Playe s
d op heigh may no be an app op ia e in ensi y- ela ed s imulus
(And ade e al., 2020). Mo eo e , al hough eac i e s eng h
index and jump heigh may augmen wi h ini ial inc eases in
box d op heigh , u he d op heigh inc eases a e expec ed
o educe eac i e s eng h index and jump heigh (Flanagan
and Comyns, 2008). The e o e, he main aim o his s udy was
o assess maximal jumping pe o mance and neu omuscula
ac i i y in lowe limb muscles o ama eu emale olleyball
playe s a e DJ om di e en d op heigh s, using ma ke s such
as eac i e s eng h index, jump heigh , con ac ime, and sEMG.
We hypo hesized ha inc easing he d op heigh du ing DJ will
induce g ea e con ac ime among ama eu emale olleyball
playe s, wi h g ea e sEMG, al hough educed eac i e s eng h
index and jump heigh .
MATERIALS AND METHODS
Expe imen al App oach o he S udy
This s udy ollowed a c oss-sec ional design. Female olleyball
playe s we e assessed o he e ec s o box heigh du ing DJ
on sEMG, eac i e s eng h index, jump heigh , and con ac
ime. Jumps we e comple ed om 15-, 30-, 45-, 60-, 75-,
and 90 cm boxes.
Pa icipan s
Ten emale ama eu olleyball playe s (age, 22.1 ±1.8 yea s; body
mass, 72.9 ±15.2 kg; heigh , 1.70 ±0.08 m; body mass index,
25.1 ±4.2 kg/m2) pa icipa ed in his s udy. The pa icipan s
posi ions we e as ollow: middle-blocke (n= 2), libe o (n= 1),
spike (n= 5), and opposi e-spike (n= 2). A hle es we e
ec ui ed du ing he compe i i e pe iod, whe e hey usually
comple ed one egional-le el compe i ion pe week. A hle es
pa icipa ed in egula olleyball aining sessions o 2 h pe
day, 3 days pe week, du ing 3 mon hs p io o inclusion in
his s udy. All a hle es had ≥2 yea s o egula aining and
compe i ion expe ience in olleyball. A ec ui men in his s udy,
mos o he olleyball aining p ac ice was de o ed o echnical
and ac ical d ills. Mo eo e , he pa icipan s had no egula
expe ience wi h esis ance aining o s uc u ed plyome ic
aining in he 3 mon hs p eceding his s udy, pa icula ly wi h
DJs. Inclusion c i e ia we e: (i) heal hy by sel - epo (hea
and pulmona y disease, and ecen su ge ies); (ii) comple ion o
an exhaus i e heal h ques ionnai e; (iii) wi hou inju y his o y
in he pas 3 mon hs p io o es ing (con i med by checking
hei aining logs wi h he eam head coach). Exclusion c i e ia
we e: (i) any condi ion conside ed o a ec muscle unc ion
(e.g., ecen bone ac u es) o he measu emen p o ocol (e.g.,
he nia ed discs); and (ii) being on medica ions conside ed o
a ec dependen a iables (e.g., anabolic s e oids). The me hods
and p ocedu es used we e app o ed by he local uni e si y
(CODE: N◦155/2018-code 195.18) and we e based on he la es
e sion o he Helsinki decla a ion.
Da a Collec ion
To inc ease es ing eliabili y and minimize lea ning e ec s,
pa icipan s we e amilia ized wi h es ing p o ocols du ing
wo 1-h sessions, he week be o e measu emen s. Du ing
amilia iza ion, pa icipan s comple ed a maximal olun a y
isome ic con ac ion (MVIC) es on day one and a se ies o
DJ es s on he nex amilia iza ion session, wi h ≥48 h om
p e ious MVIC es ing. Du ing es ing sessions, he pa icipan s
pe o med he MVIC and (a e 5 min o eco e y) DJs on
he same day (a oiding eposi ioning o he elec odes). The
day be o e a es ing session, pa icipan s we e ins uc ed o
pe o m a low-in ensi y wo kou and main ain hei die a y
ou ine. A s anda dized wa m-up was comple ed be o e each
es ing session including 5 min o ee unning and 5 min o
dynamic jumps and dynamic s e ching (And ade e al., 2015).
All jump es s we e pe o med on he olleyball cou whe e he
pa icipan s ained and compe ed. Pa icipan s we e asked o use
he same spo ga men s, including he shoes ha hey usually
wo e du ing aining and/o compe i ion. The sEMG ac i i y was
eco ded du ing each es . All measu emen s we e conduc ed on
he same labo a o y, unde con olled empe a u e and humidi y
condi ions. Al hough we did no con ol o ho mone s a us no
mens ual cycle phase, all he pa icipan s we e eumeno heic
and did no ake any ho monal con acep i e. Fu he mo e,
p e ious wo ks did no ind di e ences in he DJ (Sipa iˇ
ciené
e al., 2013) pe o mance o e he cou se o an o a ian mens ual
cycle. All es s we e conduc ed and a he same ime o day o
a oid he in luence o ci cadian hy hms.
An h opome y
S anding heigh (m) and body mass (kg) we e assessed
using a s adiome e /mechanical scale (SECA, model 220,
Hambu g, Ge many) wi h p ecisions o 0.1 cm and 0.1 kg,
espec i ely. Subjec s we e es ed in ligh clo hing (shoes we e
emo ed). The body mass index was calcula ed om he wo
measu emen s (kg·m−2).
Maximal Volun a y Isome ic Con ac ion
Following a ho ough explana ion o he es ing p ocedu es, he
a hle es comple ed a speci ic wa m-up by comple ing se e al
submaximal con ac ions o he knee ex enso and plan a
lexo muscula u e. A e he wa m-up, a hle es comple ed h ee
knee and ankle ex ension and lexion non- amped MVIC ials
on an isokine ic dynamome e (BiodexR
, Sys em 3 P o, NY,
Uni ed S a es) (see Figu e 1A), wi h 1 min es ing among ials
(Ebben e al., 2010). Fo all MVIC a emp s, he g a i y e ec
o que was ob ained by weighing he limb wi h he isokine ic
de ice, and he pa icipan s we e ins uc ed o pe o m a
maximal e o , gi en hem he ins uc ion o “ y o ex end you
leg (o oo ), as ha d as you can.” Ve bal encou agemen was
p o ided du ing maximal a emp s. Each MVIC ial las ed 4–
5 s. Du ing he knee ex ension es , he pa icipan s sea ed in he
dynamome e so ha hei hip and knee join s we e posi ioned
a ∼90◦angles. S ap was w apped ∼3 cm abo e he la e al
malleolus o he a hle e’s ankle (dominan side), as well as a he
high, wais , and ches . Ca e was aken o align he cen e s o
o a ion o he knee join and dynamome e . In he ankle lexion
MVIC es , he dynamome e o ien a ion was se a 90◦, wi h a
il a 0◦, sea o ien a ion a 90◦, sea back il a 70–85◦, oo pla e
il a 0◦, and knee lexion a 20–30◦. The axis o o a ion was se
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To es-Banduc e al. Jump In ensi y in Volleyball Playe s
in neu al posi ion, we e axis passes h ough he body o alus,
ibula malleolus, and h ough o jus below he ibial malleolus.
The dominan ankle o he a hle e (de e mined by asking he
pa icipan he p e e ed leg used o kick a ball) was a ached o
he dynamome e wi h an ankle a achmen de ice, in addi ion o
he use o s aps a he ches and wais .
D op Jump Tes s
D op jump heigh s we e andomly selec ed om 15-, 30-,
45-, 60-, 75-, and 90 cm boxes (DJ15, DJ30, DJ45, DJ60,
DJ75, and DJ90, espec i ely) (see Figu e 1A), and pa icipan s
comple ed 3 ials a each andomly selec ed heigh . An elec onic
con ac ma (Axon Jump 4.0, Bioenginee ing Spo s, A gen ina)
(see Figu e 1B) was used o measu e con ac ime (ms) and
ligh ime, he la e o which was used o calcula e jump
heigh . Besides, he eac i e s eng h index was calcula ed as
jump heigh /con ac ime (mm·ms−1), as p e iously desc ibed
(Flanagan and Comyns, 2008). Playe s jumped wi h a ms akimbo
and s epped o he box wi h he leading leg s aigh o a oid any
ini ial upwa d p opulsion du ing DJ execu ion. Upon landing,
hey we e ins uc ed o jump o maximal heigh and minimal
con ac ime in o de o maximize eac i e s eng h index
(Ba nes e al., 2007). They had 30 s o es be ween jumps
and 60 s be ween heigh s (And ade e al., 2020). O no e,
each a hle e comple ed 18 o al jumps (i.e., 3 ials ×6 box
heigh s). Maximal pe o mance (e.g., jump heigh ) was mos
commonly achie ed du ing he i s o second ial (i.e., in 36
o 60 maximal jumps), sugges ing lack o lea ning e ec om
epea ed ials. Addi ionally, pilo s a is ical analyses indica ed
ha he mean o he bes alue ( om 3 ials) yielded simila
esul s (i.e., ou comes p>0.05 be ween DJ heigh s). Conside ing
ha maximal jumping pe o mance may be mo e ecologically
alid o olleyball playe s, he bes pe o mance ial (highe
eac i e s eng h index alue, associa ed jump heigh , and con ac
ime) was used o s a is ical analysis as p e iously sugges ed
(And ade e al., 2020).
Su ace Elec omyog aphy
The sEMG da a was acqui ed (T igno Wi eless Sys em, Delsys,
Na ick, MA, Uni ed S a es) and used o quan i y muscle ac i i y.
A e wa m-up he skin was ca e ully sha ed, ab aded and
cleansed wi h alcohol p io o applica ion o EMG +IMU
senso (T igno A an i Senso , Delsys, Na ick, MA, Uni ed S a es),
whose sample a e o he EMG signal is 1950 and 148 Hz
o he accele ome e . As p e iously sugges ed (And ade e al.,
2020) he elec odes we e placed on he muscle belly su ace
o he biceps emo is, gas ocnemius medialis and as us
medialis muscles o he dominan leg acco ding o he “Su ace
Elec omyog aphy o he Non-In asi e Assessmen o Muscles
(SENIAM)” ecommenda ions.1The elec odes we e secu ed
wi h adhesi e ape (3M, Canada). The sEMG signals om each
elec ode we e ampli ied (inpu impedance 120 k; signal o
noise a io 750; in e -elec ode dis ance o 10 mm) (Ebben
e al., 2008) and gain ange o 500–5000. Su ace elec odes
we e connec ed by Wi-Fi o a base s a ion (T igno Base S a ion,
1h p://www.seniam.o g
T igno Wi eless Sys em, Delsys, Na ick, MA, Uni ed S a es) and
s eamed con inuously o a compu e h ough an analog o digi al
con e e (G-42, HP no ebook compu e , Uni ed S a es). The
sEMG da a was managed wi h compu e so wa e (EMGwo ksR
,
Delsys, Na ick, MA, Uni ed S a es). All da a we e cen e ed and
il e ed wi h a 10 Hz high-pass and a 500 Hz low-pass second
o de in ini e impulse esponse (IIR) Bu e wo h il e .
Su ace elec omyog aphy and IMU da a eco ding
The oo mean squa e (RMS) was used o assess sEMG eco ded
du ing jump es ing (Ebben e al., 2008). Da a we e calcula ed
using a 60 ms mo ing window. Da a we e analyzed o iden i y he
p e- and pos -con ac muscle bu s iming and he magni ude o
ac ion o he jump (Ebben e al., 2010). The RMS was e alua ed
as p e iously sugges ed (Gonzalez-Izal e al., 2012):
RMS =s1
nX
n
x2
n
whe e Xn is he alue o he sEMG signal and n is he sample
numbe . Du ing DJ he eccen ic and concen ic sEMG ac i i y
was eco ded, coupled wi h an ine ial measu emen uni o
de ec each phase (T igno A an i EMG +IMU Senso , Delsys,
Na ick, MA, Uni ed S a es). To his aim, he IMU was placed
a 1/3 on he line be ween he ip o he ibula and he ip o
he medial malleolus. Beha io analysis o he IMU accele a ion
signal du ing a DJ was conduc ed in a pilo session be o e he
es ing sessions. A e he applica ion o 10 Hz ini e-impulse-
esponse (FIR) il e , signal ec i ica ion, and low-pass il e ed
wi h a 5 Hz FIR il e , bo h using a Blackman window (i.e.,
accele a ion impac il e ), an ini ial peak a he beginning o he
DJ was no ed, co esponding o ini ial DJ g ound con ac (s a
o he eccen ic phase), isually de e mined as he inc ease in
he ampli ude o he accele a ion (abo e baseline). The ea e ,
he peak p og essi ely descended un il e u n o baseline (i.e.,
end o he ini ial peak, end o he eccen ic phase, and s a
o he concen ic phase). Ano he peak was obse ed a e he
ligh phase o he DJ. Using da a om con ac ime and ligh
ime, calcula ions allowed he iden i ica ion o he eccen ic and
concen ic phases. F om hese eco dings, eccen ic/concen ic
a io was calcula ed. Each RMS sEMG da a was exp essed as
a pe cen age o MVIC (Walke e al., 2012) using he highes
sEMG eco ded du ing MVIC ials (And ade e al., 2020). The
eliabili y o hese measu es has p e iously been es ablished
(Gonzalez-Izal e al., 2012).
S a is ical Analyses
The da a used in he s a is ical analyses is a ailable om he
co esponding au ho upon easonable eques .
The Shapi o–Wilk (n<50) and Le ene es s, espec i ely
analyzed he no mali y and homoscedas ici y o he ou come
a iables. When he da a did no con on o he es o no mali y
and/o homogenei y o a iance, hey we e log ans o med and
we e back ans o med o p esen a ion pu poses.
Da a a e p esen ed as mean ±SEM. The wi hin-session
(be ween- ial) eliabili ies o all dependen a iables we e
assessed by calcula ing in a-class co ela ion coe icien s and
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To es-Banduc e al. Jump In ensi y in Volleyball Playe s
FIGURE 1 | Se up used o e alua e he pa icipan s in he s udy. (A) Isokine ic o maximal olun a y isome ic con ac ion and boxes (i.e., 15 cm heigh each) used
du ing d op jumps and (B) con ac ma , wi h pa icipan wa ming up be o e measu emen s.
coe icien o a ia ion and he associa ed 95% con idence
in e als. As p e iously sugges ed, in a-class co ela ion
coe icien s alues <0.5, be ween 0.5 and 0.75, be ween 0.75 and
0.9, and >0.9 we e in e p e ed as poo , mode a e, good, and
excellen eliabili y, espec i ely, based on he lowe bound 95%
con idence in e al (Koo and Li, 2016).
To calcula e he sample size, alida ed (Faul e al., 2007)
s a is ical so wa e (GPowe ; Uni e si y o Dusseldo ,
Dusseldo , Ge many) was used. Gi en he s udy design
(one g oups and six epea ed measu es), a mode a e e ec size
(Cohen’s ) = 0.6–1.2 (And ade e al., 2020), alpha-e o <0.05,
he non-sphe ici y co ec ion € = 1, he co ela ion be ween he
epea ed measu es = 0.5, and a desi ed powe (1-βe o ) = 0.95,
he o al sample size esul ed in six pa icipan s. Conside ing
po en ial d opou s, he minimal ini ial sample size was se a 10
pa icipan s. Conside ing he cha ac e is ics o he sample (i.e.,
emales; ama eu le el) and he es [i.e., e y sho du a ion
(<1 s pe ial)], a eliabili y h eshold was se a ≤10% o he
coe icien o a ia ion (S okes, 1985).
A se ies o epea ed measu es one-way ANOVA es s we e
used o compa e dependen a iables collec ed du ing he DJ.
When a signi ican F- alue was achie ed, Bon e oni pos hoc
p ocedu es we e pe o med o loca e he pai wise di e ences
be ween he means. E ec sizes (ES) we e de e mined by
calcula ing pa ial e a-squa ed (η2
p) de i ed om ANOVA
analysis, con e ed o Cohen’s d alues as p e iously ou lined
(F i z e al., 2012) and in e p e ed using he con en ions
ou lined o spo sciences: <0.2, i ial; 0.2–0.6, small; >0.6–1.2,
mode a e; >1.2–2.0, la ge; >2.0–4.0, e y la ge; >4.0, ex emely
la ge (Hopkins e al., 2009). Signi icance was se a an a p io i
alpha le el o p<0.05. All s a is ical calcula ions we e pe o med
using STATISTICAR
So wa e (Ve sion 8.0, S a So , Inc., Tulsa,
OK, Uni ed S a es).
RESULTS
Fo he DJ pe o mance a iables con ac ime, jump heigh ,
and eac i e s eng h index, he in a-class coe icien s we e
calcula ed, o each o he six d op heigh s, yielding 18
calcula ions, and 8 demons a ed good eliabili y, 7 mode a e
eliabili y, and 3 poo eliabili y, based on he lowe bound
95% con idence in e als o in a-class co ela ion coe icien s
(Table 1). The gene al end was o eliabili y o educe wi h
an inc ease in d op heigh . Rega ding he coe icien o a ia ion,
12 ou o 18 calcula ions achie ed he ≤10% h eshold, wi h a
gene al end o educed eliabili y in he eac i e s eng h index.
The lowes con ac ime was achie ed in he DJ30
(375.2 ±41.7 ms), and he highes was achie ed in he
DJ90 (460.6 ±50.0 ms), wi h a di e ence o ∼23%, al hough no
signi ican (i.e., i ial) di e ences we e obse ed be ween d op
heigh s (Table 2). Fu he mo e, he jump heigh o he a hle es
anged om 27.7 o 29.3 cm, and om 0.66 o 0.87 mm·ms−1 o
eac i e s eng h index, wi hou signi ican di e ences be ween
any d op heigh s (Table 2).
The sEMG o he biceps emo is du ing he eccen ic phase
a ied om 32% (DJ75) o 50% (DJ90), al hough wi hou
signi ican di e ences be ween any d op heigh s (Table 2).
Simila ly, he biceps emo is concen ic sEMG ac i a ion a ied
be ween 27 and 42%, wi hou signi ican di e ences be ween
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To es-Banduc e al. Jump In ensi y in Volleyball Playe s
TABLE 1 | Reliabili y [in a-class co ela ion coe icien (ICC) and coe icien o a ia ion (CV)] o d op jump pe o mance a iables.1
DJ15 DJ30 DJ45 DJ60 DJ75 DJ90
Con ac ime
ICC 0.95 (0.82–0.99) 0.96 (0.84–0.99) 0.96 (0.84–0.99) 0.91 (0.69–0.98) 0.97 (0.87–0.99) 0.86 (0.38–0.97)
CV 8.8% (6.0–16.6%) 9.3% (6.3–17.6%) 9.2% (6.3–17.5%) 11.8% (8.0–22.6%) 6.2% (4.1–12.2%) 9.6% (6.1–22.3%)
Jump heigh
ICC 0.96 (0.84–0.99) 0.92 (0.71–0.98) 0.91 (0.67–0.98) 0.94 (0.76–0.98) 0.87 (0.53–0.97) 0.92 (0.60–0.99)
CV 4.9% (3.3–9.0%) 4.4% (3.4–9.2%) 6.0% (4.1–11.2%) 4.8% (3.2–8.9%) 8.7% (5.8–17.4%) 8.4% (5.3–19.4%)
Reac i e s eng h index
ICC 0.93 (0.76–0.98) 0.93 (0.72–0.98) 0.93 (0.75–0.98) 0.93 (0.73–0.98) 0.82 (0.40–0.96) 0.80 (0.20–0.96)
CV 11.2% (7.6–21.4%) 11.7% (8.6–24.3%) 12.3% (8.3–23.5%) 11.2% (7.6–21.3%) 13.6% (9.0–27.8%) 9.4% (6.0–21.9%)
1Values in pa en hesis include 95% con idence in e als.
any d op heigh s (Table 2). Simila ly, gas ocnemius medialis
eccen ic sEMG ac i a ion emained ela i ely cons an be ween
DJ15 and DJ60 (∼60–70%), wi h an inc ease up o 117% in
DJ90, al hough hese we e no signi ican be ween d op heigh s
(Table 2). Fo he gas ocnemius medialis concen ic sEMG, no
signi ican di e ences we e obse ed be ween any d op heigh s,
wi h ac i a ion a ying be ween 63 and 76% (Table 2). The
as us medialis eccen ic sEMG, al hough ini ially showed a
educ ion om DJ15 (∼69%) o DJ30 (∼55%), he ea e a
ela i ely cons an inc ease was no ed up o a maximum o 104%
achie ed a e DJ90 (Table 2), al hough hese we e no signi ican
(Table 2). The as us medialis concen ic sEMG highligh ed no
signi ican a ia ion (52–72%) be ween d op heigh s (Table 2).
The biceps emo is eccen ic o concen ic sEMG a io was
ela i ely cons an be ween DJ15 o DJ75, howe e , compa ed o
he a io achie ed a e DJ45 (i.e., 1.0), a signi ican (p= 0.03;
η2
p=0.21; d= 1.0, mode a e) g ea e a io was obse ed a e
DJ90 (i.e., 3.2) (Figu es 2A,B). The gas ocnemius medialis
eccen ic o concen ic sEMG a io showed a educ ion om
DJ15 (i.e., 1.5) o DJ45 (i.e., 0.9), and he ea e a ela i ely
cons an inc ease up o DJ90 (i.e., 1.7), al hough wi hou
signi ican di e ences be ween d op heigh s (Table 2). The as us
medialis eccen ic o concen ic sEMG a io showed a ia ions
be ween 1.0 (DJ30) and 2.5 (DJ90), al hough wi hou signi ican
di e ences be ween d op heigh s (Table 2).
DISCUSSION
The main aim o his s udy was o assess jumping pe o mance
and neu omuscula ac i i y in lowe limb muscles o emale
olleyball a hle es a e DJ om di e en d op heigh s, using
pa ame e s such as eac i e s eng h index, jump heigh , con ac
ime, and sEMG. Based on a p e ious s udy (And ade e al.,
2020), we hypo hesized ha inc easing he d op heigh du ing
DJ will no ensu e g ea e kinema ic and neu omuscula
measu es o in ensi y du ing plyome ic jumps in emale
olleyball playe s. Indeed, aside om a g ea e biceps emo is
eccen ic/concen ic sEMG a io a e DJ90 compa ed o
DJ45, no signi ican di e ences we e no ed be ween d op
heigh s o he ou comes analyzed in emale olleyball playe s.
The e o e, jumping pe o mance and neu omuscula ma ke s
we e no sensi i e o DJ heigh wi hin hese ama eu emale
olleyball a hle es.
No signi ican di e ences in con ac ime we e no ed be ween
DJ15 o DJ90 box heigh s, whe eas a ∼23% inc ease (al hough
no signi ican ) in con ac ime was no ed in he DJ90 compa ed
o p e ious d op heigh s. Rela edly, he eac i e s eng h index,
al hough did no a ied signi ican ly ac oss he di e en d op
heigh s, he lowes alue (i.e., 0.7) was achie ed a e DJ90, a
∼22% educ ion compa ed o he highes eac i e s eng h index
alue achie ed in he DJ30 (i.e., 0.9). Such educ ion almos
pe ec ly mimics he inc ease in he con ac ime obse ed in
he DJ90. A hle es commonly pe o m DJs a inc eased heigh s
o a g ea e aining-in ensi y s imulus (Peng e al., 2011),
wi h some s udies showing g ea e sEMG ac i i y a e DJs
execu ed om a 60 cm box (DJ60) han om a 40 cm (DJ40;
i.e., males) (Bobbe e al., 1987b) o 20 cm box (DJ20; i.e.,
males and emales) (Peng e al., 2011). Al hough his may
sugges g ea e plyome ic jump in ensi y om g ea e d op
heigh s, ou esul s, in con as sugges ha nei he g ea e
sEMG occu ed no g ea e kinema ic (i.e., jump heigh , eac i e
s eng h index, and con ac ime) pe o mance. Di e ences
be ween he esul s o p e ious s udies and ou esul s a e no
easy o explain. Howe e , pa icipan ’s sex seems no a key
ac o , as p e ious s udies in male olleyball playe s also ound
ha inc easing he d op heigh du ing DJs does no ensu e
a g ea e aining in ensi y (And ade e al., 2020). Mo eo e ,
simila o ou indings, some s udies also ha e no ed ha
g ea e DJ heigh may, in ac , educe pe o mance (i.e., eac i e
s eng h index and jump heigh ), o bo h ained and un ained
pa icipan s (Flanagan and Comyns, 2008). The e o e, using
g ea e d op heigh may no always be an e icien s a egy o
inc ease aining in ensi y o emale olleyball playe s, as an
impo an educ ion in eac i e s eng h index de elopmen may
be induced, and a subop imal eac i e s eng h index du ing
aining may limi maximiza ion o aining-induced adap a ions
(Rami ez-Campillo e al., 2018b). Mo eo e , a g ea e d op
heigh box could inc ease e ical g ound eac ion o ces ( GRF)
(Jensen and Ebben, 2007;Ebben e al., 2008, 2011). E en a
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To es-Banduc e al. Jump In ensi y in Volleyball Playe s
TABLE 2 | Compa ison o d op jump pe o mance a iables and su ace elec omyog aphy (%MVC) be ween d op heigh s.
DJ15 DJ30 DJ45 DJ60 DJ75 DJ90 ANOVA ou comes
G oup F(5, 50),
p- alue (η2
p)
Con ac ime (ms) 384.8 ±34.2 375.2 ±41.7 392.8 ±45.9 377.6 ±39.5 383.1 ±34.9 460.6 ±50.0 F= 0.5, p= 0.78 (0.05)
Jump heigh (cm) 27.7 ±1.8 29.3 ±1.6 29.2 ±1.5 27.8 ±1.4 29.0 ±1.5 28.8 ±1.6 F= 0.2, p= 0.96 (0.02)
Reac i e s eng h (mm.ms−1) 0.76 ±0.01 0.87 ±0.10 0.84 ±0.11 0.80 ±0.08 0.80 ±0.07 0.66 ±0.07 F= 0.7, p= 0.66 (0.06)
BF EC (%MVC) 39.3 ±9.3 37.0 ±8.9 37.7 ±11.0 42.5 ±11.0 31.6 ±4.5 50.0 ±16.2 F= 0.3, p= 0.92 (0.03)
BF CON (%MVC) 28.6 ±6.8 30.0 ±7.1 36.0 ±7.6 41.8 ±16.1 29.5 ±5.2 27.1 ±12.6 F= 0.3, p= 0.90 (0.03)
GM EC (%MVC) 72.7 ±8.9 62.3 ±12.5 59.4 ±8.1 67.8 ±11.0 93.9 ±11.7 117.1 ±30.3 F= 2.3, p= 0.06 (0.19)
GM CON (%MVC) 63.4 ±9.2 62.9 ±8.3 75.3 ±7.0 65.2 ±5.7 64.7 ±6.3 76.3 ±4.9 F= 0.7, p= 0.66 (0.06)
VM EC (%MVC) 68.6 ±9.0 54.8 ±6.6 75.2 ±8.2 95.0 ±18.2 96.0 ±11.4 104.4 ±24.5 F= 2.1, p= 0.08 (0.18)
VM CON (%MVC) 52.5 ±7.0 65.4 ±8.9 72.3 ±11.8 52.0 ±11.0 64.4 ±9.8 58.1 ±14.4 F= 0.6, p= 0.68 (0.06)
BF EC/CON a io 1.6 ±0.4 1.4 ±0.2 1.0 ±0.1 1.7 ±0.3 1.5 ±0.5 3.2 ±0.9aF= 2.7, p= 0.03 (0.21)
GM EC/CON a io 1.5 ±0.4 1.1 ±0.2 0.9 ±0.2 1.2 ±0.3 1.6 ±0.3 1.7 ±0.6 F= 1.1, p= 0.38 (0.1)
VM EC/CON a io 1.4 ±0.2 1.0 ±0.2 1.2 ±0.2 2.4 ±0.7 1.8 ±0.4 2.5 ±0.9 F= 1.8, p= 0.13 (0.16)
Da a a e mean ±SEM.
BF, biceps emo is; CON, concen ic; DJ15-DJ90, d op jump om 15 o 90-cm boxes, espec i ely; GM, gas ocnemius medialis; EC, eccen ic; MVC, maximal olun a y
con ac ion; VM, as us medialis.
aSigni ican ly g ea e compa ed o DJ45 (p <0.05). η2
p: pa ial e a-squa ed. Bold alues: highes pe o mance and sEMG alues o each a iable ac oss d op heigh s.
FIGURE 2 | Eccen ic (EC) o concen ic (CON) su ace elec omyog aphy (sEMG) a io in he biceps emo is (BF), gas ocnemius medialis (GM), and as us medialis
(VM) muscles o emale olleyball a hle es. (A) Rep esen a i e sEMG eco ding om BF, GM, and VM o one a hle e pe o ming d op jumps om 15 cm (DJ15) and o
90 cm (DJ90). (B) No e ha compa ed o he EC/CON sEMG BF a io achie ed a e DJ45 (i.e., 1.0), a signi ican ly (p= 0.03) g ea e a io was obse ed a e DJ90
(i.e., 3.2). Da a a e showed as median and in e qua ile ange, n= 10. *Signi ican ly (p= 0.03) g ea e a e DJ90 compa ed o DJ45.
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To es-Banduc e al. Jump In ensi y in Volleyball Playe s
DJ30 may induce GRF ≥4 imes body mass in emales a hle es
(McNai and P apa essis, 1999), po en ially con ibu ing o
knee ins abili y and non-con ac ACL inju y (Yu and Ga e ,
2007). The e o e, o ama eu emale olleyball a hle es, in o de
o inc ease pe o mance and educe inju y isk, he use o
mode a e heigh boxes (e.g., ≤DJ30) may be p e e ed o e
g ea e box heigh s.
O no e, al hough no signi ican concen ic o eccen ic sEMG
di e ences we e shown be ween DJ box heigh s, he highes
alues o sEMG ac i i y usually occu ed om g ea e DJ box
heigh s, al hough he jumping pa ame e s (i.e., eac i e s eng h
index) achie ed ela i ely be e pe o mance a lowe DJs box
heigh s. Reduced jumping pe o mance om highe DJ box
d op heigh s migh be ela ed o neu omuscula inhibi ion,
which se es as a p o ec i e mechanism o p e en muscle and
endon inju y om excessi e s ess in he muscle- endon uni
(Komi, 2008). Howe e , a g ea e jumping pe o mance may
no necessa ily coincide wi h RMS o sEMG ac i i y (And ade
e al., 2020). This migh be explained by he eu iliza ion
o elas ic ene gy due o he in e ac ion be ween con ac ile
elemen s and a se ies o elas ic elemen s (Bobbe e al.,
1996), gea ing g ea e jumping pe o mance independen o
elec ical ac i i y. This no ion is ein o ced by he ac ha
a g ea e DJ box heigh (i.e., 90 cm), a ∼23% inc ease in
con ac ime was no ed compa ed o lowe d op heigh (i.e.,
15 cm), hus inc easing elas ic ene gy loss due o a p olonged
SSC (Asmussen and Bonde-Pe e sen, 1974), yielding a ela i ely
educed jumping pe o mance and an inc eased sEMG ac i i y.
In he p esen s udy, sEMG ac i i y was no malized o MVIC
o compensa e o di e ences in s eng h, muscle one, a
mass, and muscle geome y among o he ac o s ha may
induce bias in he esul s (Ank um, 2000). Howe e , in he
li e a u e, di e en me hodologies ha e been used o assess
neu omuscula pa ame e s (Ebben e al., 2008, 2010;Peng
e al., 2011), yielding di e en esul s. Al hough no consensus
exis s (Ebben e al., 2008;Peng e al., 2011), cu en esul s
ag ee wi h he no ion ha mode a e d op heigh s du ing DJ
allow maximiza ion o pe o mance, including olleyball playe s
(And ade e al., 2020). In addi ion, i mus be conside ed ha he
sEMG eccen ic/concen ic a io may be pa icula ly sensi i e o
changes in jumping in ensi y (And ade e al., 2020) as indica ed
by he g ea e biceps emo is sEMG eccen ic/concen ic a io
a e DJ90 compa ed o DJ45. Such esul was in line wi h a
endency o dec eased biceps emo is concen ic sEMG and
inc eased biceps emo is eccen ic sEMG a g ea e DJ heigh s.
Such indings may be ela ed o he eccen ic in ol emen o he
biceps emo is a he hip join o decele a e he cen e o mass a
landing, wi h po en ial implica ions o hams ing s ain inju y
isk educ ion (Bou ne e al., 2018).
Taken oge he , ou esul s sugges ha mo o uni
ec ui men does no change ac oss DJ box heigh s du ing
he eccen ic and concen ic phases. This obse a ion emains
o di e en muscles (biceps emo is, as us medialis, and
gas ocnemius medialis) and di e en muscle ac ions (agonis
and an agonis ). The e o e, i is deba able i a g ea e DJ
d op heigh is indica i e o g ea e in ensi y. Based on ecen
esul s, he 50–100% o maximal coun e mo emen jump heigh
may be he app op ia e indi idual ela i e d op heigh o
he DJ among olleyball playe s (Peng e al., 2019). Fu u e
s udies should analyze he e ec s o adequa e (indi idualized)
p esc ip ion o d op heigh s o he DJ on he physical
i ness and inju y isk among emale olleyball playe s, as
p e iously esol ed in o he g oups o a hle es (Rami ez-
Campillo e al., 2018a, 2019). Fu he , DJ d ills a e mean o
be pe o med usually wi h a con ac ime o <250 ms. O no e,
al hough all a hle es ha e ≥2 yea s o egula aining and
compe i ion expe ience in olleyball, is s iking ha almos
all o hem did no a ain a con ac ime <250 ms du ing he
di e en DJ heigh s. Indeed, only one o he emale olleyball
a hle es managed o achie e such a pe o mance, po en ially
highligh ing ha a hle es we e no app op ia ely condi ioned
o gain he maximal bene i s om his ask. The e o e, ela i e
s eng h on DJ pe o mance, pa icula ly among emale,
including emale olleyball a hle es (Beckham e al., 2019),
may be a ac o o s eng h and condi ioning coaches and
esea che s o conside .
Limi a ions
Some limi a ions should be acknowledged. Fi s ly, i would be
isky o ex apola e cu en indings o o he highly ained
emale olleyball g oups, especially hose wi h ex ensi e s eng h
and condi ioning p epa a ion, pa icula ly esis ance aining
p epa a ion. Secondly, du ing he DJ es ing session, all he
playe s (excep one) achie ed con ac ime >250 ms. On one side,
such con ac ime a e commonly obse ed in he jumping ac ions
o olleyball compe i ions, meaning high ecological alidi y
o he cu en indings. Howe e , i cu en indings may be
ex apola ed o DJ d ills in ol ing as SSC muscle ac ion, o
g ound oo con ac ime <250 ms, also e e ed as bounce DJ
(Bobbe , 1990), should be cla i ied in u u e esea ch. Thi dly,
d op heigh is in luenced by box heigh (Ge aldo e al., 2019),
and a modula ion o d op heigh om g ea e box heigh s (e.g.,
s epping down om he box) may ha e (inad e en ly) occu ed,
dec easing he heigh he cen e o mass d ops om. We
ecommend con olling he cen e o mass displacemen adding
cinema ic analysis o his a iable o con i m o disca d he
a o emen ioned. Fou hly, ou small sample size may aise some
ques ions on he ex e nal alidi y o hese esul s, pa icula ly
since ec ui ed a hle es comes om di e en playing posi ions
(e.g., libe o, and se e ), and wi h di e en aining backg ounds
(i.e., ≥2 yea s o olleyball expe ience). Fu u e s udies may
conside he inclusion o ama eu playe s bu wi h mo e
yea s o expe ience. Finally, he s udy design (c oss-sec ional)
does no allow in e ing cause-e ec ela ionships. The e o e,
ex apola ion o cu en indings o aining in e en ions should
be pe o med wi h cau ion.
CONCLUSION
Ou esul s show ha con ac ime, jump heigh , eac i e s eng h
index, as well as biceps emo is, medial gas ocnemius, and as us
medialis muscles sEMG (i.e., bo h concen ic, eccen ic, and
eccen ic/concen ic a io) we e no signi ican ly a ec ed by DJs
F on ie s in Psychology | www. on ie sin.o g 8Sep embe 2021 | Volume 12 | A icle 724070
psyg-12-724070 Sep embe 14, 2021 Time: 19:52 # 9
To es-Banduc e al. Jump In ensi y in Volleyball Playe s
pe o med om di e en d op heigh s (i.e., DJ15, DJ30,
DJ45, DJ60 DJ75, and DJ90), excep o a g ea e biceps
emo is eccen ic/concen ic a io om DJ90 compa ed o DJ45.
The e o e, DJ pe o mance a iables (jump heigh , con ac ime,
and eac i e s eng h index) concomi an o sEMG o lowe
limb muscles du ing DJs om di e en box heigh s (in ensi ies)
a e no sensi i e ma ke s o DJ box heigh (in ensi y) in
ama eu emale olleyball a hle es. In o he wo ds, inc easing he
box heigh s o DJs may no induce g ea e aining s imulus
(i.e., in ensi y).
DATA AVAILABILITY STATEMENT
The o iginal con ibu ions p esen ed in he s udy a e included
in he a icle/supplemen a y ma e ial, u he inqui ies can be
di ec ed o he co esponding au ho /s.
ETHICS STATEMENT
The s udies in ol ing human pa icipan s we e e iewed and
app o ed by he local uni e si y (UST, CODE: N155/2018-
code 195.18) and we e based on he la es e sion o he
Helsinki decla a ion. The pa ien s/pa icipan s p o ided
hei w i en in o med consen o pa icipa e in his
s udy.
AUTHOR CONTRIBUTIONS
All au ho s made signi ican con ibu ions, including p epa a ion
o he i s d a o he manusc ip , da a collec ion, analysis
o da a, in e p e a ion o da a, and p o ided meaning ul
e ision and eedback. All au ho s ead and app o ed he
inal manusc ip .
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