Jou nal o Human Kine ics olume 88/2023, 259–270 DOI: 10.5114/jhk/163561 259
Sec ion III – Spo s and Physical Ac i i y
1 Spo s and Educa ion Depa men , Uni e si y o he Basque Coun y (UPV/EHU), Vi o ia-Gas eiz, Spain.
2 Physio he apy Depa men , Uni e si y o he Basque Coun y (UPV/EHU), Leioa, Spain.
* Co espondence: [email p o ec ed]
Accep ed o publishing in he Jou nal o Human Kine ics ol. 88/2023 in July 2023.
Regional Hype ophy: The E ec o Exe cises a Long
and Sho Muscle Leng hs in Rec ea ionally T ained Women
by
Ai o Zabale a-Ko a 1,*, Eneko Fe nández-Peña 1, Jon To es-Unda 2,
Maide F ancés 2, Asie Zubillaga 1, Jo dan San os-Conceje o 1
The aim o he p esen s udy was o analyse he ole o exe cises' esis ance p o ile in egional hype ophy.
Thi y-eigh heal hy women comple ed a 9-week esis ance aining p og am consis ing o ei he 4 se s o 12 epe i ions
o oli ional ailu e o inclined bicep cu ls (INC g oup) o p eache cu ls (PREA g oup), h ee imes pe week. P e- and
pos -in e en ion muscle hickness was measu ed using B-mode ul asound imaging wi h a linea -a ay ansduce . Scan
acquisi ion si es we e de e mined by measu ing 50%, 60% and 70% o he dis ance be ween he pos e io c es o he
ac omion and he olec anon. S a is ical signi icance was se a p < 0.05. No egion o he INC g oup g ew when compa ing
p e- o pos -in e en ion. The 70% egion o he PREA g oup g ew signi ican ly (muscle hickness inc eased om 2.7
±
0.43 cm o 2.94
±
0.44 cm). We ound no g ow h di e ences be ween egions when analysing pe g oup (p = 0.274),
egion (p = 0.571) o g oup* egion (p = 0.367). Ou esul s show ha he dis al egion o he a m g ows in esponse o
he p eache cu l ha places he highes amoun o s ain in he ange o mo ion in which he a m muscles a e mo e
elonga ed.
Keywo ds: muscle g ow h; selec i e hype ophy; s eng h; a iable esis ance; muscle a chi ec u e
In oduc ion
Muscle g ow h, also known as muscle
hype ophy, is a complex p ocess highly
dependen on mechanical o ce (Schoen eld e al.,
2021; Wacke hage e al., 2019). I is ela ed o
pe o mance imp o emen s in many spo s (S o ey
and Smi h, 2012), and since a high muscle mass
implies a lowe mo ali y isk in di e en
popula ions, i is impo an o heal h
p o essionals o know how o p esc ibe exe cise
app op ia ely (Sedlmeie e al., 2021; S ikan han e
al., 2016; S ikan han and Ka lamangla, 2014;
Wanname hee e al., 2007).
Muscle does no g ow homogeneously
(F anchi e al., 2018c; Ma a e al., 2011; Na ici e al.,
1989; Nosaka and Sakamo o, 2000) as i can di e
be ween he heads o a muscle and e en be ween
he di e en egions o a single head (Zabale a-
Ko a e al., 2020). This phenomenon, known as
egional hype ophy, has d awn a conside able
amoun o a en ion in ecen yea s (Diniz e al.,
2020; Maeo e al., 2021; Ma ins-Cos a e al., 2021).
Se e al ac o s seem o in luence egional
hype ophy, including exe cise selec ion, a
di e en numbe o epe i ions wi h a no malized
ime unde ension (Ma ins-Cos a e al., 2021; Wilk
e al., 2021), ime spen in he concen ic and
eccen ic phases o an exe cise (Diniz e al., 2020),
aining a di e en muscle leng hs (Maeo e al.,
2021) o e en pe o ming only concen ic/eccen ic
exe cises (F anchi e al., 2014, 2018c). In all hose
s udies, applied muscle o ce appea s o be an
impo an ac o ha somehow shapes which
egion o muscle will g ow.
Recen ly, Zabale a-Ko a e al. (2021)
ound ha exe cise selec ion migh elici di e en
egional hype ophy s imuli. In ha s udy,
au ho s es ed whe he egional hype ophy
ound a e pe o ming leg ex ensions was
di e en o he one elici ed by squa s pe o med on
260 Regional Hype ophy
Jou nal o Human Kine ics, olume 88/2023 h p://www.johk.pl
he Smi h machine in young men. Fo ha pu pose,
hey di ided subjec s in o wo g oups and each
g oup pe o med one exe cise. A e he
in e en ion, hype ophy o wo egions in wo
di e en muscle heads was compa ed be ween and
wi hin egions. The au ho s ound ha exe cise
selec ion had an in luence on egional
hype ophy, as i was di e en e en i bo h
g oups had ollowed he same olume and
in ensi y p o ocol. Howe e , since he exe cises
s udied had di e en esis ance p o iles (meaning
hey placed s ain in di e en pa s o he ange o
mo ion (RoM)), i was no possible o know
whe he he egional hype ophy epo ed was
due o he exe cise selec ion o because he
maximum esis ance ha he in ol ed join s had o
o e come occu ed a di e en muscle leng hs.
Despi e his limi a ion, hose indings sugges ha
ega ding he leg ex ension, he ac ha he hip
join does no mo e while he knee ex ends may
elici mo e s imuli o he ec us emo is muscle.
Fo he Smi h machine squa s, i can be in e ed
om hose esul s ha he as us la e alis ge s
mo e g ow h s imuli in exe cises ha a e simila o
squa s.
Compa isons be ween exe cises wi h
di e en esis ance p o iles such as bicep p eache
cu ls and inclined bicep cu ls, de ined as he
deg ee o esis ance in each pa o he RoM o a
join , ha e been epo ed p e iously (Maeo e al.,
2021; Wakaha a e al., 2013), bu no wi h he
speci ic aim o epo ing he e ec s o esis ance
p o iles on egional hype ophy. This may ha e
con ounding e ec s on ou in e p e a ion o he
esul s and hus, he aim o he p esen s udy was
o analyze he ole o exe cises wi h di e en
esis ance p o iles in egional hype ophy. Fo
ha pu pose, inclined bicep cu l and p eache
bicep cu l exe cises we e compa ed in h ee
di e en egions o he a m. The i s exe cise
places he highes amoun o s ain ( ep esen ed as
he g ea es di icul y o he exe cise) a he end o
he exe cise (Loss and Cando i, 2008), when he
a m is a 90–100º lexion, while he la es places he
highes amoun o s ain a he beginning (Loss and
Cando i, 2008), wi h a conside able amoun o
elonga ion in he biceps b achii and b achialis
muscles. In addi ion, we decided o pe o m he
s udy in ec ea ionally ained women, as mos
egional hype ophy s udies ha e analyzed his
phenomenon in men. We hypo hesized ha he
p eache cu l would elici g ea e muscle g ow h in
he dis al pa o he biceps, as epo ed by
p e ious esea ch in which he highes s ain
occu ed when he muscle was elonga ed (Nosaka
and Sakamo o, 2000).
Me hods
Pa icipan s
Thi y-eigh heal hy women joined his
s udy. Pa icipan s we e equi ed o mee he
ollowing inclusion c i e ia: 1) women wi h an age
anging be ween 18 and 45 yea s; 2) lack o
musculoskele al diso de s in he uppe limbs a
leas one yea p io o he beginning o he s udy,
and 3) a esis ance aining expe ience o a leas 6
mon hs p io o he beginning o he s udy.
A o al o 31 pa icipan s inished he
s udy. Two pa icipan s d opped ou because hey
es ed posi i e o SARS-COVID19 and i e
pa icipan s d opped ou o pe sonal easons no
ela ed o he s udy. W i en in o med consen was
ob ained om each pa icipan a e a ho ough
explana ion o he es ing p o ocol, he possible
isks in ol ed and he igh o e mina e
pa icipa ion a will was p o ided. The s udy was
app o ed by he Ins i u ional Re iew Boa d o he
Uni e si y o he Basque Coun y UPV/EHU ( e .
118/2019) and all p ocedu es we e conduc ed in
acco dance wi h he Decla a ion o Helsinki (2013).
Pa icipan s we e analyzed by he in en ion- o-
ea p inciple in o de o a oid he isk o bias
(McCoy, 2017) e en i wo pa icipan s did no
each 90% o a endance o he planned aining
sessions. A p io i sample size calcula ions we e
ca ied ou acco ding o he AIPE app oach (Ab e
al., 2020) pe o med wi h he ESCI so wa e (Ab e
al., 2020). This analysis e ealed ha o ob ain a
95% con idence in e al wi h a s anda dized mean
di e ence o 0.4 be ween g oups (Ab e al., 2020)
and a wid h o 0.8 (0.4 in each side o he poin
es ima e), each g oup should include a leas 49
pa icipan s. Un o una ely, we we e unable o
each such a high numbe o pa icipan s, hus he
isk o a ype II s a is ical e o is high.
Measu es
Measu emen s we e pe o med wo days p io
o he beginning o he aining p og am and 72–96
h a e i s end. Measu emen s las ed ~30 min and
es ing sessions we e ca e ully scheduled o ensu e
ha he same numbe o hou s we e le since he
by Ai o Zabale a-Ko a e al. 261
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license.
end o he aining p o ocol. Du ing he day o he
i s measu emen s, pa icipan s we e andomly
alloca ed in o he INC and PREA g oups, using he
RANDOM unc ion o an Excel 2016 sp eadshee .
T aining P og am
The wo expe imen al g oups ained bo h
a ms, despi e he ac ha only one a m was
analyzed. This was made o a oid any po en ial
c oss-educa ion e ec (Lee and Ca oll, 2007).
Pa icipan s in he INC g oup comple ed a 9-week
esis ance aining p og am consis ing o 4 se s o
12 epe i ions o inclined bicep cu ls h ee imes
pe week, pe o ming each se o muscula ailu e.
Inclined bicep cu ls consis ed o pe o ming bicep
cu ls wi h a dumbbell while lying supine on a
bench wi h 45º inclina ion. The exe cise began wi h
he o ea m pe pendicula o he loo , and ended
when he elbow eached a leas a 90º angle, ne e
going beyond 110º. Pa icipan s in he PREA g oup
comple ed he same aining p o ocol, bu
pe o med he p eache bicep cu l ins ead o he
inclined bicep cu l. The p eache bicep cu l
consis ed o pe o ming bicep cu ls wi h a
dumbbell on a Sco bench. A Sco bench is a
speci ic kind o a bench consis ing o a 50º inclined
pla o m whe e he pa icipan places he a m
while pe o ming he cu ling mo emen . The
exe cise began wi h he o ea m pa allel o he
loo o sligh ly below, and ended when he
o ea m o med a 75º angle wi h he loo , ne e
eaching a posi ion pe pendicula o he loo .
Pa icipan s in bo h g oups we e eques ed o keep
he hand always comple ely supina ed o a oid he
po en ial impac ha he o ea m posi ion has on
he ec ui men o elbow lexo s (Kleibe e al.,
2015). They we e also eques ed no o pe o m any
o he biceps b achii o pulling exe cises (also
known as back exe cises), ha would di ec ly o
indi ec ly a ec he s imulus p o ided by he
exe cises o he s udy. To make i easie o
pa icipan s o o ganize hei aining sessions
wi h he condi ions o he s udy, hey we e o e ed
di e en aining plans acco ding o he numbe o
days hey wan ed o ain. They we e also
encou aged no o pe o m s enuous pulling o
bicep-demanding ac i i ies du ing he pe iod o
he s udy.
Weekly aining olume consis ed o 12
weekly se s (Baz-Valle e al., 2018) o he biceps
b achii exe cise and a ied be ween 60 and 85 se s
o he es o he muscles (depending on he
numbe o days ha each subjec ained). This
amoun o weekly se s ollows cu en guidelines
o weekly esis ance exe cise olume o maximize
muscle g ow h (Baz-Valle e al., 2022).
T aining was p og ammed in a lexible
ashion: on he i s day, pa icipan s we e old o
adjus he weigh so ha hey could each
muscula ailu e a 12 epe i ions. Fo ha pu pose,
pa icipan s we e old o choose a weigh ha
would make hem each, bu no exceed 12
epe i ions on hei exe cise. I hey we e able o
pe o m 1–3 ex a epe i ions wi h he chosen
weigh , hey had o use he nex hea ies dumbbell.
I he weigh di e ence be ween dumbbells was
oo high (in some gyms, he weigh di e ence
be ween one dumbbell and he nex hea ies one is
2.5 kg, and as mos pa icipan s li ed 10 kg, ha
would be a 25% inc ease), pa icipan s we e gi en
wo op ions: hey could li a hea ie weigh and
pe o m as many epe i ions as possible ying o
each 12, o pe o m mo e epe i ions han 12,
always eaching oli ional ailu e. Pa icipan s
we e sugges ed o li a hea ie weigh i hey
could pe o m mo e han 6 epe i ions wi h i o o
pe o m mo e epe i ions i hey el hey could no ,
bu o ne e exceed 18 epe i ions. We conside
ha he ac ha pa icipan s did no pe o m he
same numbe o epe i ions occasionally did no
ha e any e ec on he esul s, as muscle size
imp o emen s a e no a ec ed by he numbe o
epe i ions pe o med when he epe i ion ange
does no exceed 20 o go unde 6 (Baz-Valle e al.,
2018; Schoen eld e al., 2021).
As he du a ion o each o he phases o an
exe cise seems o induce egional hype ophy
(Diniz e al., 2020), he eccen ic phase o he
exe cise had o las 2 s, and he concen ic phase o
he exe cise had o be pe o med as as as possible
o pa icipan s in bo h g oups. This was
emphasized many imes o pa icipan s because i
is known ha a longe ime unde ension can elici
g ea e muscle g ow h (Bu d e al., 2012).
Pa icipan s we e also eques ed o es a leas 48
h be ween aining sessions. Res ing be ween
epe i ions was no allowed, and pa icipan s had
o es om 3 o 5 min be ween se s. T aining
sessions ook place a gyms in which each
pa icipan usually exe cised. To es whe he
pa icipan s pe o med he exe cises wi h he
co ec echnique and wi h he igh in ensi y, each
pa icipan had o send a ideo pe o ming an
262 Regional Hype ophy
Jou nal o Human Kine ics, olume 88/2023 h p://www.johk.pl
e ec i e se o he main esea che a e e e y
session. Pe o ming exe cises wi h a bad echnique
o 3 o mo e sessions was an exclusion c i e ion,
al hough none o he pa icipan s me i .
Pa icipan s egis e ed he weigh li ed in each se
in a mobile phone APP (Dudysolu ions e sion 2.3,
2020 Spain) so ha hey could see he weigh li ed
and he epe i ions pe o med in p e ious sessions,
and y pe o m be e .
Muscle Thickness
Muscle size/ hickness was measu ed using
B-mode ul asound imaging (GE LOGIQTM e, GE
Heal hca e, WI, USA) wi h a linea -a ay
ansduce (code 12 L-RS, a iable equency band
4.2–13.0 MHz, ield o iew 3.7 mm) by an
expe ienced echnician. Measu emen s we e
pe o med wi h pa icipan s in a supine posi ion,
wi h a ms and legs ex ended and elaxed. P io o
es ing, pa icipan s emained in his posi ion o
10 min o allow o s abiliza ion o no mal body
luids. The echnician hen applied a wa e -soluble
ansmission gel (Aquasonic 100 Ul asound
T ansmission gel; Pa ke Labo a o ies Inc.,
Fai ield, NJ, USA) o each measu emen si e and a
9 MHz ul asound p obe was placed pa allel o he
issue in e ace wi hou dep essing he skin. When
he quali y o he image was deemed as
sa is ac o y, he echnician sa ed he image o he
ha d d i e. Scan acquisi ion si es we e de e mined
by measu ing 50%, 60% and 70% o he dis ance
be ween he pos e io c es o he ac omion and he
olec anon as pe o med in p e ious esea ch
(Ma a e al., 2011). When de e mined, a ci cle was
d own a ound he ci cum e ence o he a m in
hose h ee spo s. A e ha , he cen e o he biceps
b achii muscle was calcula ed as a line be ween he
co acoid p ocess and he an e ocubi al c es . Th ee
scans we e aken in he place we e bo h lines
c ossed a 50%, 60% and 70% o he de e mined
leng h. Muscle hickness (MT) was conside ed he
a e age o he h ee measu emen s. Thickness was
measu ed using he line s aigh unc ion o ImageJ
so wa e (Kim e al., 2020) in he cen e o he scan
(Figu e 1). The echnician ha pe o med he scans
was blinded o he exe cises ha each pa icipan
had pe o med. Measu emen s we e aken on he
igh side o he body.
An h opome ic Measu emen s
One day be o e and 3–4 days a e he 9-week
in e en ion, an h opome ic cha ac e is ics o
pa icipan s we e measu ed. Pa icipan s we e
weighed on a calib a ed digi al scale whils
wea ing minimal clo hing. Body heigh was
measu ed wi h a s adiome e a ached o he scale
wi h pa icipan s s anding shoeless and head
aligned in he ho izon al F ank u plane. Eigh -
si e skin old measu emen s (in mm) we e aken
om he biceps b achii, iceps, scapula ,
abdominal, sup ailiac, high and medial cal si es
acco ding o s anda d p ocedu es using a skin old
calipe (Ha penden1, Ba y In e na ional, Wes
Sussex, UK). All skin olds we e measu ed o he
nea es 1 mm and he mean o h ee eadings was
eco ded as he inal alue o each si e. All body
composi ion measu emen s we e aken by he
same in es iga o 24–48 h be o e and 72–96 h a e
comple ion o he aining p o ocol. Body a
pe cen age (%BF) was es ima ed using he
equa ion p oposed by Faulkne (Faulkne , 1966). I
was measu ed o ensu e ha pa icipan s s ayed in
a no mo-calo ic o a calo ic-su plus s a us, and o
a oid con ounding ac o s in he ul asound scans.
In some pa icipan s, i was no easy o dis inguish
whe e he muscle ended and we e he skin and
subcu aneous a began. I a pe cen age does no
inc ease, any inc ease in a m hickness canno be
a ibu ed o an inc ease in a mass.
Die a y Guidelines
To a oid he po en ial o die a y
con ounding, pa icipan s we e gi en a documen
in which hey we e ins uc ed o each 2 g·kg−1 o
p o ein in ake. Fi s , hey we e augh how o
calcula e hei p o ein needs acco ding o hei
bodyweigh . Then, hey we e ins uc ed on how o
each ha amoun wi h examples o di e en
dishes and we e eques ed o include a leas 20 g
o p o ein pe meal di ided in o 3 o 5 meals wi h
a leas 3 hou s be ween hem. Pa icipan s we e
also ained o be in an eucalo ic die o sligh
ene gy su plus. Pa icipan s also ag eed no o ake
any supplemen s ha could in e e e wi h he
s udy ou comes (such as c ea ine o whey p o ein).
Design and P ocedu es
As he aim o ou s udy was o e alua e he
e ec s o esis ance p o iles, wo exe cises wi h
di e en esis ance p o iles we e chosen o he
p esen s udy: inclined bicep cu ls and p eache
cu ls. The i s one places he highes s ain a he
by Ai o Zabale a-Ko a e al. 263
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end o he exe cise, wi h he elbow in a 90º–100º
posi ion, wi h he o ea m pa allel o he loo
(Figu e 2). As some people usually lex he elbow
o a g ea e deg ee in his exe cise and ou aim was
o make he end o he concen ic phase he ha des
pa o he RoM, pa icipan s we e eques ed no o
lex he elbow mo e han 110º. The esis ance
inc eased along he RoM o he exe cise, ha is, an
ascending esis ance cu e (Figu e 2). The second
one places he highes s ain a he beginning o he
exe cise, wi h he elbow in a 0º posi ion (Figu e 2).
The esis ance dec eased along he RoM o he
exe cise, ha is, a descending esis ance cu e. To
minimize he in luence ha he esis ance o o he
exe cises may ha e on he adap a ions o he
exe cises included in he s udy, pa icipan s could
no pe o m any addi ional exe cise ha included
an ac i e elbow lexion, i.e., nei he exe cises ha
di ec ly a ge ed he bicep such as biceps cu ls, no
exe cises ha indi ec ly ained i such as pull ups.
E en i no pe o ming exe cises ha in ol ed
elbow ex ension was sugges ed o he pa icipan s,
hey we e allowed o do hem.
To assess muscle g ow h, MT measu emen s
we e pe o med. MT was chosen ins ead o he
c oss sec ional a ea (ACSA) as pe o ming eliable
ACSA measu emen s wi h an ul asound
appa a us is di icul and ope a o dependan
(He nández-Belmon e e al., 2022). MT was
de ined as he hickness o all muscles in he a m
(biceps b achii and b achialis) in he ield-o - iew
o he p obe, om he skin in e ace o he
hume us. This s udy was designed o e alua e he
e ec s o wo exe cises be ween g oups. Fi s , we
pe o med a wi hin- egion analysis, o e i y
whe he any o he egions g ew in esponse o he
exe cise pe o med. Second, o compa e g ow h
be ween egions, a be ween- egion analysis was
pe o med a e wa ds.
S a is ical Analysis
We es ed all a iables o no mal
dis ibu ion (Shapi o-Wilk es ) and homogenei y
o a iance (Le ene’s es ). An independen sample
es was used o check o signi ican di e ences
in MT and %BF a iables p io o he beginning o
he s udy. I he esul s o he Le ene’s es we e
signi ican , he Welch’s co ec ion me hod was
used. To analyze MT di e ences be ween egions,
i s , we ans o med he inc eases in MT in o
pe cen age inc eases (%MT). Then a wo-way
ANOVA was pe o med wi h %MT as a dependen
a iable (Fac o 1: g oup, ac o 2: egion). When
he e we e signi ican F alues o he main e ec s
o in e ac ions, he Tukey pos -hoc es was used. To
analyze wi hin- egion changes in muscle
hickness, a pai ed sample es we e applied o
compa e PRE and POST measu emen s. In he
wi hin- egion analysis, he Wilcoxon’s signed ank
es was used when he a iable did no ha e a
no mal dis ibu ion. E ec sizes o he ANOVA
we e calcula ed as Pa ial η squa ed (ηp2). They
we e conside ed i ele an (< 0.01), small (0.01–
0.06), medium (0.06–0.14) and la ge (> 0.14) (Goss-
Sampson, 2019). E ec sizes o pai ed sample -
es s we e calcula ed using Cohen’s d, and we e
conside ed i ial (< 0.2, i ial), small (0.2–0.49 ),
mode a e (0.5–0.79) and la ge (≥ 0.8) (Cohen, 1988).
An in a-class co ela ion coe icien es was
pe o med o measu e he eliabili y o he
measu emen p o ocol, in a pilo s udy ca ied ou
wi h en pa icipan s. All he s a is ical analyses
we e pe o med wi h JASP 0.16 o Mac. The le el
o signi icance was se a p < 0.05, bu was hen
adjus ed using he Benjamin-Hochbe g p ocedu e
o dec ease he False Disco e y Ra e (FDR < 5%). A
pilo s udy was pe o med p e iously o es he
eliabili y o he echnician and he ul asound
appa a us. Ten seden a y pa icipan s no ela ed
o he p esen s udy unde wen MT measu emen
p o ocols in wo di e en days, wi h a leas one
week be ween each measu emen . The in aclass
co ela ion coe icien (ICC (3,1)) o he pilo s udy
was calcula ed using an Excel sp eadshee based
on a single a e , absolu e ag eemen and 2-way
mixed-e ec s model, and in e p e ed as poo (<
0.5), mode a e (0.5–0.75), good (0.75–0.9) o
excellen (> 0.9) (Koo e al., 2016).
Resul s
We ound no di e ences in he body a
pe cen age (p = 0.18) p io o he beginning o he
s udy.
Be ween-G oup and Region Analysis
The wo-way ANOVA showed no
in e ac ion o g oup (p = 0.102, ηp2 = 0.032), egion
(p = 0.370, ηp2 = 0,024) o g oup* egion (p = 0.544, ηp2
= 0.015). Fo his eason, no pos -hoc analysis was
pe o med.
264
Regional Hype ophy
Jou nal o Human Kine ics, olume 88/2023 h p://www.johk.pl
Wi hin Regions Analysis
Resul o he pai ed sample - es we e no
signi ican in he INC g oup (p = 0.95, d = 0.019; p =
0.520, d = 0.242 and p = 0.536, d = 0.193 in 50%, 60%
and 70% egions, espec i ely).
The 70% egion o he PREA g oup g ew
signi ican ly (p = 0.017, ES = 0.623), bu in con as ,
nei he he 60% egion (p = 0.071, ES = 0.503) no
he 50% egion (p = 0.347, ES = 0.263) g ew.
The in a-class co ela ion coe icien o
he echnician and he ul asound appa a us used
o he s udy was ICC (3,1) = 0.96 (CI = 0.93–0.99),
showing excellen eliabili y be ween
measu emen s, and demons a ing ou p o ocol o
be e y highly eliable (Mun o, 2005).
Table 1. Mean muscle hickness pe egion in cm (n = 32).
50% PRE 60% PRE 70% PRE 50% POST 60% POST 70% POST
INC 2.19 ± 0.28
[2.04–2.34]
2.3 ± 0.38
[2.09–2.51]
2.74 ± 0.43
[2.51–2.97]
2.24 ± 0.32
[2.06–2.41]
2.41 ± 0.23
[2.28–2.53]
2.81 ± 0.44 [2.57–
3.05]
PREA 2.13 ± 0.34
[1.97–2.28]
2.32 ± 0.43
[2.14–2.53]
2.68 ± 0.43
[2.50–2.90]
2.27 ± 0.43
[2.07–2.47]
2.5 ± 0.38
[2.33–2.68]
2.94 ± 0.44 [2.74–
3.14]*
INC, inclined biceps cu ls g oup; PREA, p eache cu ls g oup. Values a e Means
±
SD [95% CI]
* Signi ican ly di e en om PRE
Table 2. Two-way ANOVA (G oup and egion) o he %MT.
Sum o
squa es
d Mean
squa e
Fp η
p2
G oup 1336.411 1 1336.411 2.740 0.102 0.032
Region 982.326 2 491.163 1.007 0.370 0.024
G oup*
egion
597.508 2 298.754 0.613 0.544 0.015
Residuals 39992.147 82 487.709
* Signi ican alue
Figu e 1. A ep esen a i e measu emen o MT o a subjec om an Ul asound Scan.
by Ai o Zabale a-Ko a e al.
265
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license
.
Figu e 2. Incline p ess (INC) and p eache cu ls (PREA) exe cises and hei esis ance
p o iles (Loss and Cando i, 2008). A. Ini ial posi ion; B. Final posi ion; C. Resis ance
o que du ing elbow lexion.
Figu e 3. Muscle g ow h pe egion (in pe cen ages).
* signi ican ly di e en om p e
by Ai o Zabale a-Ko a e al. 267
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license.
Discussion
The main inding o his s udy was ha he
dis al egion o he a m g ew in esponse o he
p eache cu l (an exe cise wi h a descending
esis ance p o ile), while he es o he egions o
ha g oup and all he egions o he o he g oup
did no . In con as , be ween- egion compa isons
showed no g ow h di e ences. This means ha
while he wi hin- egion analysis sugges s ha he
esis ance p o ile o an exe cise seems o con ibu e
o he g ow h o a gi en egion inside he a m
muscles, esul s om he be ween- egion analysis
show ha he e may be many o he ac o s
in luencing egional hype ophy as well.
The ques ion a ises how esis ance p o ile
di e ences can make some egions g ow while he
es does no . We sugges h ee mechanisms ha
may p o ide an explana ion o his inding. The
i s mechanism may be he deg ee o elonga ion o
he muscle du ing he exe cise. E idence sugges s
ha aining a long muscle leng hs may inc ease
sa come e leng h (Wisdom e al., 2015), which may
elici u he inc eases in muscle size in he dis al
egion. Some s udies epo ha a e pe o ming
exe cises a long muscle leng hs, ascicle leng h
inc eases o a g ea e deg ee han muscle g ow h
(Valama os e al., 2018), and his may pa ly
explain why changes in MT obse ed in ou s udy
we e so small. In his ega d, ou esul s a e in line
wi h p e ious s udies like he one by Sa o e al.
(2021) ha ound a g ea e inc ease in MT o he
dis al egion o he a m (70% o he dis ance
be ween he la e al epicondyle and he ac omion)
a e pe o ming p eache cu ls a long muscle
leng hs s. sho muscle leng hs. This sugges s ha
when he a m muscles wo k a long muscle
leng hs, he dis al egion unde goes highe ension
han he es o he muscle (Nosaka and Sakamo o,
2000).
The second mechanism is ela ed o he
coo dina ion o he elbow lexo s. The b achialis
muscle is mo e p esen in he dis al egions han in
he mo e p oximal ones. In ac , in he scans o
some pa icipan s ha we e clea enough o
disc imina e be ween he biceps and he b achialis
muscles, he hickness o he b achialis a he 70%
egion was wice as he one ound a he 50%
egion. P obably, wo king a long muscle leng hs
s imula es he b achialis muscle mo e han he
biceps b achii muscle. Howe e , due o he leng h-
ension ela ionship o he elbow lexo s, elbow
lexion is no e y e ec i e a long muscle leng hs
(Ismail and Rana unga, 1978). This may ha e
s imula ed he b achialis, by a he s onges
elbow lexo (Kawakami e al., 1994), o a g ea e
deg ee han he biceps b achii in he p eache cu l
exe cise.
The hi d mechanism may be he neu al
s a egy used by each pa icipan o ace he
equi emen s o he exe cise, as p e ious esea ch
has shown ha some people ha e he abili y o
selec i ely choose muscles ha pe o m he same
exe cise (A illon e al., 2021). Recen e idence
sugges s ha he momen gene a ed by each join
can be p edic ed by decoding he neu al signal
a i ing o he muscles ( ia HD EMG
measu emen s in i o) (Sa o i e al., 2017). Fu u e
esea ch on egional hype ophy should ocus on
unde s anding he in e play be ween he
mechanical ole o a muscle egion and he neu al
signals i ecei es, as muscle hype ophy is a
esul o bo h mechanical o ces and neu al inpu s
(Alix-Fages e al., 2022).
Rega dless o he mechanisms behind he
indings o he wi hin- egion analysis, i is
su p ising ha no egion in he INC g oup g ew,
and i is e en mo e su p ising ha he be ween-
egion compa ison showed no di e ences in he
egions' g ow h. Howe e , bo h g oups had a
conside able isk o ype II s a is ical e o , as 49
pa icipan s we e needed o each su icien
s a is ical powe , and nei he g oup eached ha
numbe . Thus, he lack o g ow h may jus be a
consequence o he small sample size.
In gene al, he g ow h obse ed in he only
egion is no able (ES = 0.623, medium ES,
app oxima ely a 10% inc ease). One o he easons
why many egions did no expe ience a signi ican
g ow h may be ha MT was used o assess i .
Muscle is a 3-dimensional o gan, and as such i can
g ow in h ee dimensions. Fo ha eason, he
golden s anda d o measu e muscle g ow h is he
Magne ic Resonance Imaging (MRI) (F anchi e al.,
2018b). Un o una ely, MRI is di icul o
implemen and e y expensi e, and o ha eason
we chose o measu e MT wi h a b-mode ul asound
appa a us, cheape and easie o implemen . As
MT measu es only 1D g ow h, we may ha e
missed pa o he g ow h due o he cons ain s o
ou measu emen me hod. Ano he po en ial
sou ce o he lack o g ow h in he INC g oup is
he high d op–ou a e. Six women d opped ou
by Ai o Zabale a-Ko a e al. 267
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license.
om he INC g oup, while only one d opped ou
om he PREA g oup. Such a d op-ou a e
inc eases he p obabili y o a ype II s a is ical
e o . Howe e , p e ious esea ch analyzing an
exe cise wi h a esis ance p o ile p esumably
simila o he one used in he INC g oup (Nunes e
al., 2020) (maximal di icul y close o 90º o elbow
lexion) ound no g ow h a e 8 weeks o aining
(D ummond e al., 2016). The e o e, ano he
possible explana ion o he lack o g ow h
obse ed in he INC g oup may be ha his kind o
esis ance does no p o ide enough s imuli o he
g ow h o elbow lexo s. In con as , a s udy by
Nunes e al. (2020) analyzing he e y same
exe cise ound a 7% inc ease in MT. These
con adic o y indings imply ha e en i he
esis ance p o ile o an exe cise o ces he muscle
o wo k a sho muscle leng hs (which
p esumably has less po en ial o hype ophy),
he e mus be o he ac o s in ol ed.
This s udy aced se e al limi a ions.
Muscle is a h ee dimensional o gan, and o ha
eason he op imum quan i ica ion o i s g ow h is
h ee-dimensional (F anchi e al., 2018a). We
pe o med ul asound scans, which only allows o
pe o m MT o ACSA measu emen s. Since he
echniques used o measu e ACSA om
ul asound scans a e oo complex and ope a o
dependan (He nández-Belmon e e al., 2022) and
MT has a e y high co ela ion wi h ACSA
(F anchi e al., 2018a), we deemed i an accep able
way o measu e muscle g ow h. The ICC shows a
high deg ee o ag eemen be ween measu emen s,
ha can also be seen elsewhe e and con i m ha
measu ing MT wi h ul asound scans is a eliable
manne o quan i y muscle g ow h (F anchi e al.,
2018a; Palme e al., 2015). Howe e , we could no
dis inguish whe he he measu ed g ow h was due
o he biceps b achii o b achialis muscle in he
scans o many pa icipan s, which made i di icul
o d aw conclusions abou he eason o his
egional MT inc ease. A eliabili y analysis o he
skin old echnician was no pe o med, which may
also be a sou ce o po en ial e o , and inally, we
mus admi ha he be ween-g oup analysis used
in his s udy may ha e limi ed i s s a is ical powe .
This mus be aken in o accoun by esea che s
aiming o in es iga e in his ield, as a wi hin
subjec analysis using one a m as con ol may be
mo e app op ia e.
Conclusions
In conclusion, his s udy shows ha
egional hype ophy is a ec ed by he esis ance
p o ile o an exe cise. This means ha di e en
egions o a muscle will g ow in esponse o
exe cises ha place he highes di icul y in speci ic
poin s o he ange o mo ion. In pa icula , ou
esul s show ha he dis al egion o he a m g ows
in esponse o exe cises ha place he highes
amoun o s ain in he ange o mo ion in which
he a m muscles a e mo e elonga ed, bu no in
hose ha place he g ea es s ain when he a m
lexo s a e sho ened.
Acco ding o he esul s o his s udy, he
esis ance p o ile o any exe cise changes he
manne in which he in ol ed muscles g ow. Fo
example, when aiming o inc ease he size o he
elbow lexo s in he pa ha is closes o he elbow,
using exe cises in which he highes s ain is posed
when muscles a e elonga ed seems o be he bes
op ion. This is key in spo s such as bodybuilding
in which shape, size and symme y o muscles a e
e alua ed in compe i ion.
Au ho Con ibu ions: Concep ualiza ion: A.Z.-K., E.F.-P. and J.S.-C.; me hodology: A.Z.-K., J.T.-U. and
M.F.; so wa e: A.Z.-K. and J.T.-U.; alida ion: A.Z.-K., E.F.-P. and J.S.-C.; o mal analysis: A.Z.-K., E.F.-P.
and J.S.-C.; in es iga ion: A.Z.-K. and A.Z.; esou ces: A.Z.-K.; da a cu a ion: A.Z.-K. and A.Z.; w i ing—
o iginal d a p epa a ion: A.Z.-K.; w i ing— e iew & edi ing: A.Z.-K., E.F.-P. and J.S.-C.; isualiza ion:
A.Z.-K.; supe ision: A.Z.-K., E.F.-P., J.T.-U., M.F., A.Z. and J.S.-C.; p ojec adminis a ion: A.Z.-K.; unding
acquisi ion: J.S.-C. All au ho s ha e ead and ag eed o he published e sion o he manusc ip .
Funding In o ma ion: This esea ch was unded by he Basque Go e nmen , G an numbe : IT1726-22.
Ins i u ional Re iew Boa d S a emen : This s udy was conduc ed ollowing he p inciples o he Decla a ion
o Helsinki, and app o ed by he Ins i u ional Re iew Boa d o UPV/EHU (118/2019, 21 No embe 2019).
In o med Consen : In o med consen was ob ained om all pa icipan s included in he s udy.
