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European Journal of Sport Science
-
ORIGINAL PAPER
OPEN ACCESS
Comparison Between Shoulder Flexed and Extended
Positions in Elbow Flexion Resistance Training on
Regional Hypertrophy and Maximum Strength: Preacher
versus Bayesian Cable Curls
Parsa Attarieh
1
| João Pedro Nunes
2,3
| Saeed Khani
1
| Saman Negahdar
1
| Amirali Goli
4
| Hamed Nazarirad
1
|
Shahriar Nazarirad
5
| Shima Mojtahedi
1
| Kazunori Nosaka
3
| Rahman Soori
1
1
Department of Exercise Physiology, Faculty of Sport Sciences and Health, University of Tehran, Tehran, Iran |
2
Physical Education and Sport Center,
Londrina State University, Londrina, Brazil |
3
School of Medical and Health Sciences, Edith Cowan University, Joondalup, Australia |
4
Department of
Biological Sciences in Sport, Faculty of Sport Sciences and Health, Shahid Beheshti University, Tehran, Iran |
5
Department of Physiology, Division of Sports
Physiology, Faculty of Medicine, Çukurova University, Adana, Turkey
Correspondence: Parsa Attarieh (parsa.attarieh@gmail.com) | Rahman Soori (soori@ut.ac.ir)
Received: 15 July 2024 | Revised: 18 February 2025 | Accepted: 25 February 2025
Funding: The authors received no specic funding for this work.
Keywords: exercise selection | inhomogeneous hypertrophy | muscle architecture | strength training
ABSTRACT
In the present study, the effects of resistance training on regional hypertrophy and maximum strength of the elbow exor
muscles were compared between elbow exion exercises performed with different shoulder joint angles (~50° of exion vs.
extension) while matched for resistance proles. In a within‐subject design, 15 young men (25.6 �2.1 y; 77.3 �6.8 kg;
175.1 �5.7 cm) underwent a resistance training program twice a week for 10 weeks (3–5 sets, 8–12RM), and their arms were
dominant‐side balanced, randomly assigned to one of the two conditions according to elbow exion exercises: unilateral cable
curl with shoulder exed (Preacher curl; PREA) or unilateral cable curl with shoulder extended (Bayesian curl; BAYE). B‐mode
ultrasound imaging was used to measure changes in muscle thickness of the biceps brachii and brachialis at proximal, mid, and
distal arm regions, and one‐repetition maximum tests were completed in each respective trained exercise before and after
training. Both conditions showed signicant increases in muscle thickness (p<0.05) with no signicant differences between
them (p>0.05) across the biceps brachii proximal, mid, and distal regions (relative change [Hedges' g effect size]; PREA:
6%[0.51], 7%[0.49], 7%[0.53]; BAYE: 9%[0.73], 9%[0.62], 9%[0.62]) and brachialis (PREA: 10%[0.72]; BAYE: 8%[0.65]). Similarly,
signicant improvements in maximum strength were observed (p<0.05), with equivalent results between conditions (PREA:
28%[0.85], BAYE: 37%[1.22]; equivalence testing, p‐values =0.061, 0.637). In conclusion, the shoulder joint angle does not seem
to affect muscle hypertrophy and maximum strength gains after different elbow exion exercises matched for resistance proles.
1
|
Introduction
Neuromuscular adaptations to resistance training (RT) pro-
grams are inuenced by the manipulation of variables such as
training intensity, volume, and frequency (B. Schoenfeld
et al. 2021), as well as exercise selection, which is often over-
looked (Kassiano et al. 2022). Exercises can be characterized
according to several features (e.g., number of joints involved,
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly
cited.
© 2025 The Author(s). European Journal of Sport Science published by Wiley‐VCH GmbH on behalf of European College of Sport Science.
European Journal of Sport Science, 2025; 25:e12279 1 of 9
https://doi.org/10.1002/ejsc.12279
apparatus used, and resistance prole), and recent ndings
indicate that improvements in muscle size and strength are
affected by the exercised muscle length (Kassiano et al. 2023;
Oranchuk et al. 2019).
Resistance exercises that stimulate the muscles at longer muscle
lengths seem to evoke greater hypertrophy (Kassiano et al. 2023;
Oranchuk et al. 2019; Ottinger et al. 2023). This can be easily
accomplished by training in lengthened muscle positions either
with partial range of motion exercises or isometric contractions
(Kassiano et al. 2023; Oranchuk et al. 2019). However, the tradi-
tional dynamic full range of motion exercises is the basis of the RT
prescription (B. Schoenfeld et al. 2021). In this sense, among the
variety of exercises that can be done while training in the tradi-
tional form, opting for exercises that focus on longer muscle
lengths is a practicable option. For bi‐articular muscles, this in-
volves selecting exercises where the proximal joint of the target
muscle remains in an anatomical or neutral position rather than a
muscle‐shortened position—for example, plantar exion with
extended knee versus exed knee (Kinoshita et al. 2023), or knee
extension with extended hip versus exed hip (Larsen et al. 2024)
—or training in pre‐stretched positions rather than neutral
(shorter) positions (Maeo et al. 2021,2023; Stasinaki et al. 2018).
Although the literature on this topic is still limited, the benets
of longer‐length training appear to depend on the muscle
analyzed. While the triceps surae, hamstrings, and quadriceps
seem to experience greater growth with training at longer
lengths, evidence regarding the biceps brachii remains con-
icting (Kassiano et al. 2023; Ottinger et al. 2023). Shoulder
extension lengthens the biceps brachii (Iwane et al. 2023), and
training an elbow‐exion exercise with the shoulder extended
probably favors the hypertrophic response in comparison to
training in a pre‐shortened position. Alternative hypotheses
suggest that the biceps may not experience greater hypertrophy
when training at longer muscle lengths because it cannot reach
the very descending portion of the force–length curve (Ottinger
et al. 2023). Another possibility is that after pre‐lengthening or
pre‐shortening the biceps brachii (Murray et al. 2000), the bra-
chialis may take on a greater role in the exercise, receiving a
larger stimulus (Kawakami et al. 1994; Nosaka and Saka-
moto 2001), and this shift could reduce potential differences in
biceps growth between exercises. However, these hypotheses
remain to be tested.
Previous studies in which researchers sought to explore the
inuence of training the biceps brachii in different lengths have
limited generalizability. In studies where the effect of varying
shoulder positions was analyzed, the compared exercises also
differed in their resistance proles (Costa et al. 2021; Kassiano
et al. 2025; Korta et al. 2023; Vendruscolo et al. 2024); conse-
quently, muscle length was not isolated as a factor, making it
difcult to determine its specic impact on hypertrophy and
strength adaptations. Moreover, in many cases, other compound
exercises involving elbow exion were included in the training
program (Costa et al. 2021; Nunes et al. 2020; Vendruscolo
et al. 2024), further introducing confounding factors. Finally,
hypertrophy was often assessed considering changes in overall
elbow exor muscle thickness (measured as the distance be-
tween the most supercial muscular arm region and the bone)
without distinguishing between the biceps brachii and bra-
chialis (Costa et al. 2021; Kassiano et al. 2025; Korta et al. 2023;
Sato et al. 2021; Vendruscolo et al. 2024). In such situations, it is
not possible to determine whether the training effects on hy-
pertrophy stem from the biceps or the brachialis. Isolating the
biceps in measurements is essential for determining the effects
of training it at different lengths, as well as exploring whether it
exhibits inhomogeneous regional hypertrophy, as observed in
other muscles. For instance, performing leg extensions with
greater hip exion has been shown to impair both acute and
long‐term proxies of proximal rectus femoris hypertrophy
(Mitsuya et al. 2023; Larsen et al. 2024). It remains to be
investigated whether altering joint position affects the regional
hypertrophy of other muscles.
Therefore, the objective of the present study was to compare the
effects of elbow‐exion exercise training on regional hypertro-
phy of biceps brachii and brachialis, and elbow exion
maximum strength gains after two exercise conditions matched
for resistance proles: unilateral Preacher cable curl (PREA),
performed with the arms supported on an angled bench, keep-
ing the shoulder in a exed position; and unilateral Bayesian
cable curl (BAYE), similar to the commonly known incline curl,
performed with the shoulder in an extended position. Figure 1
illustrates how exercises were performed. It was hypothesized
that BAYE would present advantages over PREA at increasing
biceps brachii size (Kinoshita et al. 2023; Larsen et al. 2024;
Maeo et al. 2021,2023), whereas changes in strength would be
equivalent between conditions (Maeo et al. 2021,2023).
2
|
Methods
2.1
|
Experimental Design
A within‐subject design was carried out to compare the effects
of training the biceps brachii in different shoulder positions on
regional hypertrophy and strength gains. This design was cho-
sen to eliminate any potential inter‐individual variations on
training effects such as dietary intake, responsiveness, and
training tolerance. This study is part of a larger research project
designed to analyze the effects of RT in young male adults, but
the only elbow exion exercise was the biceps curl. The subjects'
dominant arms (preferred hand for writing) were randomly
assigned to one of the two conditions based on elbow exor
exercises, whereas the nondominant arms were assigned to the
other: PREA or BAYE. Therefore, a balanced distribution of
Summary
�Training biceps curl with the shoulder exed (PREA) or
extended (BAYE) resulted in similar moderate‐to‐large
increases in elbow exor muscle thickness and
maximum strength.
�Similar increases in muscle thickness were observed for
all analyzed sites in both conditions, that is, no regional
hypertrophy was observed.
�The biceps brachii do not seem to benet from longer‐
length resistance training nor exhibit inhomogeneous
regional hypertrophy.
2 of 9 European Journal of Sport Science, 2025
dominant and nondominant arms was achieved across the ex-
ercise conditions.
The current investigation was executed as follows: 1 week was
used for pre‐training outcome assessments, 10 weeks for the
progressive training program, and one more week for post‐
training testing (at least 72 h after the last training session).
Muscle hypertrophy was dened as changes in muscle thickness
(MT) via ultrasonography, and muscular strength was assessed
via one‐repetition maximum (1RM) tests in the respective
trained exercises. Testing and training sessions were supervised
by at least two researchers with international personal trainer
certications (1:2 participant:professional ratio) to standardize
exercise techniques and help ensure the safety of the subjects. A
40‐g dose of concentrated protein powder (Milk Protein Pro
Milk, Kalleh, Iran) was provided to the subjects after every
training session as a strategy to increase their average daily
protein intake and maximize the training responses (Morton
et al. 2018). This investigation was conducted according to the
Declaration of Helsinki and was approved by the University
Ethics Committee.
2.2
|
Subjects
Recruitment was carried out through social media and home
delivery of yers in the university area. Interested subjects
completed detailed health history and physical activity ques-
tionnaires, and were subsequently admitted if they met the
following inclusion criteria: men, 18–35 years old, free from
cardiac, orthopedic, or musculoskeletal disorders that could
impede exercise practice, not consume drug or supplement er-
gogenic aids, and not be involved in the practice of RT over the
6 months before the start of the study. Of the 38 volunteers, 21
FIGURE 1
|Top left: Biceps brachii normalized force–length curve and operating length for Preacher (PREA; shoulder exed 50°) and Bayesian
(BAYE; shoulder extended 50°) biceps curls during the 10°–140° range of motion. These were obtained using OpenSim Arm26 model (Holzbaur
et al. 2005), considering biceps brachii as a single unit (sum of short and long heads) while maintaining relative contributions of each head to the
length and active force and using muscle–tendon default parameters. Top right: Resistance proles (relative torque to elbow angle) of the trained
exercises. Bottom left and right: Example of how PREA (top) and BAYE (bottom) exercises were conducted during testing and training sessions.
Note the same hand‐pulley distance at the start of the exercises and the same arm‐cable angles between exercises at the start and end of the
range of motion. Estimated peak torques (arm‐cable angle: 90°) were at 61.5° elbow exion.
3 of 9
met the criteria, were evaluated at baseline, and began the
training program. An attendance rate of less than 80% was set as
an exclusion criterion, resulting in the exclusion of six partici-
pants. Fifteen individuals completed the study and were
included in nal analyses (age =25.6 �2.1 years; body
mass =77.3 �6.8 kg; stature =175.1 �5.7 cm; BMI =
25.2 �3.8 kg/m
2
), attending the necessary sample size dened a
priori (n≥15 per group) to achieve a power of 0.8 and an αof
0.05 for a moderate effect size of 0.55 in a two‐group, two‐time
point design, for improving muscle size (B. J. Schoenfeld
et al. 2017). Subjects were instructed to avoid changes in their
habitual recreational physical activities and dietary intake and
not to start taking any other nutritional supplements that could
alter their performance during the study period. Written
informed consent was obtained from all subjects after a detailed
description of study procedures was provided.
2.3
|
MT Assessment
Measures of biceps brachii and brachialis MT were obtained
using a B‐mode ultrasound machine with an 8–12 MHz linear
probe (L741; SonoScape E1 EXP, China) by the same experi-
menter, blinded to condition allocation. Subjects were instruc-
ted to show up to the laboratory in the morning hours fasting for
at least 8 h and not perform vigorous exercise for the previous
48 h. Ultrasound measurements started after subjects were lying
supine on a medical plinth for 10 min. Images were acquired at
55%, 65%, and 75% of the distance between the acromion pro-
cess of the scapula and the cubital fossa. For image acquisition,
the probe was placed perpendicular to the tissue interface,
water‐soluble transmission gel was applied over the skin on the
region of interest, so measurements were done with caution not
to depress the muscle tissue, and images were recorded at
individualized eld‐of‐view depths. Two experimenters partici-
pated in the measurement process so that one handled the
probe, and the other was responsible for freezing the images
once both considered that image quality was satisfactory. Im-
ages were stored in a ash drive and later analyzed using ImageJ
software (v. 1.50; NIH, USA). Biceps brachii MT was dened for
the three imaged regions (55%, 65%, and 75%; proximal‐distal)
as the distance between its supercial and deep aponeuroses.
Brachialis was apparent at more distal regions only (65%, 75%),
and its MT was dened as the distance between its supercial
aponeurosis and the humerus. Inter‐day test‐rest reliability
scores were satisfactory (ICC [3,1] =0.99; relative typical er-
ror =1.2%). Examples of ultrasound images of each region can
be seen in the Figure S1.
2.4
|
1RM Strength
Maximum strength was assessed via 1RM test on the respective
trained exercise for each arm, as previously done (Maeo
et al. 2021,2023; Stasinaki et al. 2018). For the pre‐training
testing session, subjects were randomly selected to start
testing for PREA or BAYE, and this was kept the same post‐
training individually. Subjects performed a warm‐up of 15 rep-
etitions with approximately 50% of their estimated load to the
rst attempt, followed by ve 1RM attempts. If an attempt was
successful or unsuccessful, weight was added or reduced,
respectively, for the next attempts by 3%–10% to the nearest
0.5 kg. Subjects were afforded 3–5 min of rest between attempts
and 5 min between exercises. Tests were performed with sub-
jects holding the cable handle with their hands supinated, and
the shoulder was positioned at about 50° in exion or extension
for PREA and BAYE, respectively. Testing started with the
elbow almost fully extended (10°), and subjects were instructed
to fully ex it (140°) to complete a valid 1RM attempt. Exercises
were performed with the same resistance proles (Figure 1); the
PREA bench and BAYE chair, as well as the pulley height of the
training machine, were adjusted individually to ensure simi-
larity between exercises for the arm‐cable starting, right, and
ending angles during execution, and the starting hand‐to‐pulley
cable distance.
2.5
|
RT Program
Training was performed twice weekly on nonconsecutive days
(≥48 h apart) in the afternoon hours for 10 weeks, with pro-
gression in the number of sets over the weeks (weeks 1–3: 3 sets;
4–7: 4 sets, weeks 8–10: 5 sets). Training intensities of load were
initially set relative to 70% 1RM and were adjusted over the
sessions so that the subjects could perform the sets in 8–12 RM
to (or very close to) failure. The rest between sets was set to
120 s. The PREA and BAYE biceps curls were performed
unilaterally, at a tempo of 1:1 s (concentric and eccentric phases,
respectively), with shoulder and arm positions and ranges of
motion the same as dened for the 1RM tests (Figure 1). The
exercise to be trained rst was alternated between sessions.
Loads were adjusted set by set when concentric failure occurred
outside the repetition maximum zone and progressed individ-
ually over the weeks to the nearest 0.5 kg. The number of rep-
etitions and the weight used in the rst set of every session were
recorded to adjust the training load and represent training
volume.
2.6
|
Statistical Analyses
Data normality was assessed using the Shapiro–Wilk test, and
homogeneity of variances was evaluated with Levene's test.
Analyses of variance were used to compare the groups for
training measures. For both MT and 1RM, analyses of covari-
ance were performed, with the pre‐to‐post training difference as
dependent variables, baseline values as covariates, and group as
xed factors, with adjusted marginal pre‐post mean differences
tested against zero to determine training effects relative to
baseline. For MT changes, analyses of covariance were per-
formed to compare the groups, whereas analyses of variance
were performed to compare percentage changes in MT between
muscle regions to examine whether each exercise elicited
regional hypertrophy. Bonferroni correction was applied to
multiple‐comparison tests. For 1RM changes, given it was hy-
pothesized that improvements would be equivalent between
conditions, two one‐sided tests (TOST) for equivalence were
performed to compare the groups, standardizing with Hedges' g
effect size (ES). The standardized equivalence bounds were set
at �0.20. ESs were calculated as post‐training mean minus
4 of 9 European Journal of Sport Science, 2025
pre‐training mean, divided by pooled pre‐training standard de-
viation, with Hedges' g correction factor for small samples
(Borenstein et al. 2009). An ES of 0.00–0.19 was considered as
trivial, 0.20–0.49 as small, 0.50–0.79 as moderate, and ≥0.80 as
large (Borenstein et al. 2009). A p<0.05 was accepted as sta-
tistically signicant. The data were expressed as mean, standard
deviation, 95% condence intervals (CIs), average percentage
changes, and ESs. Analyses were conducted using JASP v.0.16.2
(JASP Team, Netherlands).
3
|
Results
Subjects completed all the training sessions. No injuries
occurred during the intervention. Training stimuli were
matched between conditions, as reected by the similar average
repetitions per set (PREA: 9.5 �0.5 repetitions; BAYE: 9.6 �0.5
repetitions; p=0.392), the average load (PREA: 18.2 �5.0 kg;
BAYE: 18.3 �4.5 kg; p=0.970), and the weekly progression in
load (PREA: 0.5 �0.3 kg/wk; BAYE: 0.7 �0.4 kg/wk; p=
0.252). For 1RM strength, signicant (p<0.05) large increases
were observed for both conditions (PREA: pre =21.9 �6.7 kg,
post =27.1 �6.6 kg; BAYE: pre =20.7 �5.0 kg, post =
28.1 �5.9 kg), with equivalent improvements observed between
them (PREA: 28% [ES: 0.85], BAYE: 37% [ES: 1.22]; ES differ-
ence: 0.37 [95%CIs = −0.33, 1.08]; TOST for equivalence, p‐
values =0.061, 0.637). Figure 2presents the progression in
training load by the exercise condition.
For muscle thickness (MT), signicant (p<0.05) moderate‐to‐
large increases were observed at all sites analyzed for both
conditions. No signicant difference was observed between
PREA and BAYE in any muscle regions (pvalues =0.205–
0.662), nor between regions of the biceps brachii for either
PREA (p=0.908) or BAYE (p=0.964). Similar responses were
observed between conditions for the overall response (sum of
the three regions) of the biceps brachii (PREA: 7% [ES: 0.53],
BAYE: 9% [ES: 0.68]; p=0.314), and brachialis (PREA: 10% [ES:
0.72], BAYE: 8% [ES: 0.65]; p=0.911), as well as the proximal
region (only biceps brachii; PREA: 6% [ES: 0.51], BAYE: 9% [ES:
0.73]; p=0.205), and overall middle (PREA: 8% [ES: 0.65],
BAYE: 10% [ES: 0.79]; p=0.374) and distal (PREA: 7% [ES:
0.65], BAYE: 8% [ES: 0.67]; p=0.946) regions, or the sum of all
measured regions (PREA: 8% [ES: 0.66], BAYE: 9% [ES: 0.77];
p=0.416). While comparing relative changes between muscles,
no signicant difference was detected between biceps brachii
and brachialis for PREA (7% [ES: 0.53] vs. 10% [ES: 0.72];
p=0.325) or BAYE (9% [ES: 0.68] vs. 8% [ES: 0.65]; p=0.895).
Table 1displays the results of pre‐ and post‐training data and
Figure 3presents the individual relative changes, according to
conditions, muscles, and regions.
4
|
Discussion
In the present study, the effects of RT on regional hypertrophy
and maximum strength of the elbow exor muscles were
compared between elbow exion exercises performed with
different shoulder positions (exion [PREA] vs. extension
[BAYE]). It was hypothesized that biceps brachii hypertrophy
would be greater for BAYE than PREA, but changes in strength
would be equivalent between conditions. After the intervention,
similar adaptations were observed following PREA and BAYE
biceps curls, rejecting the hypothesis for hypertrophy, but sup-
porting the hypothesis on the strength gains.
Altering shoulder position may have shortened the biceps bra-
chii bers in PREA and lengthened them in BAYE, potentially
shifting the sarcomere operating length along the force–length
curve, with BAYE operating more on optimal lengths for force
production (Koo et al. 2002; Murray et al. 2000; Newham
et al. 1988). However, it seems that such an advantage for BAYE
did not occur since the exercises were performed with similar
weights throughout the intervention (Figure 2), resulting in
similar torques between conditions (assuming: (i) the exercises
were matched in torque‐angle proles, as shown in Figure 1; and
(ii) the exercises were performed at similar execution velocities).
The post hoc elaboration of the force–length relationship model
(Figure 1) supports the idea that such a variation in shoulder
position likely elicited only small changes in biceps ber
FIGURE 2
|Progression in training load during Preacher (PREA) and Bayesian (BAYE) curl conditions. The horizontal lines are mean and 95%
CIs. No difference was detected between groups (comparison of slopes; p=0.252).
5 of 9
operating lengths during training, and this may explain the lack
of differential biceps growth between exercises. Moreover,
changes in tendon properties after a few training sessions may
impact tendon slack length, an effect that is inuenced by the
muscle‐length training position (Lambrianides et al. 2024),
thereby affecting muscle–tendon behavior during exercise,
deviating from the predicted models. Additionally, there was no
emphasis on the lengthening phase of the contraction. Per-
forming the eccentric phase at a slower tempo (e.g., 4 s) could
have allowed BAYE to experience more time under higher loads
in longer lengths, potentially providing an advantage over PREA.
It remains to be explored whether manipulating execution tempo
inuences the effects of longer‐length RT on muscle growth.
Korta et al. (2023) and others (Kassiano et al. 2025; Kobayashi
et al. 2024; Vendruscolo et al. 2024) have recently compared
exercises similar to the ones used herein, where they used bi-
ceps dumbbell curls that have opposite resistance proles: one
emphasizing torque at the end of the eccentric phase but pre‐
shortening the biceps by shoulder exion (a similar version of
“PREA” used here, but done with dumbbells), and the other
emphasizing torque at the end of the concentric phase but pre‐
lengthening the biceps by shoulder extension (“BAYE” done
with dumbbells [incline curl]). Therefore, inferences on the ef-
fects of longer versus shorter muscle length training could not
be made from such comparisons as two factors distinguished
their exercises: resistance exercise proles and shoulder posi-
tions. Moreover, hypertrophy measures were often taken for the
“elbow exors”; whether the observed differential results
stemmed from biceps or brachialis hypertrophy could not be
established. In addition, Nunes et al. (2020) compared exercises
emphasizing greater torques at shorter or longer muscle lengths
with the same shoulder position (exed; cable vs. dumbbell
PREA) and found that no difference in biceps brachii MT in-
creases; however, the biceps was measured only at the mid‐
segment region. In this regard, the inuence of training at
shorter versus longer biceps brachii lengths on regional changes
in biceps size was unclear, and the present study is the rst
where biceps brachii MT changes were measured regionally
while isolating differences in muscle length as a factor to be
compared between exercises, revealing no signicant difference
between conditions.
TABLE 1 |Training effects on regional muscle thickness (mm) after
Preacher (PREA) and Bayesian (BAYE) biceps cable curls.
PREA (n=15) BAYE (n=15)
Proximal—Biceps brachii
Pre 28.2 �3.2 28.5 �3.7
Post 30.0 �3.2
*
31.0 �3.3
*
ES 0.51 (0.14, 0.88) 0.73 (0.34, 1.13)
Middle—Biceps brachii
Pre 24.5 �3.6 24.2 �3.3
Post 26.2 �3.2
*
26.4 �2.9
*
ES 0.49 (0.13, 0.86) 0.62 (0.24, 1.00)
Distal—Biceps brachii
Pre 23.5 �3.3 23.0 �3.0
Post 25.2 �3.0
*
25.0 �2.8
*
ES 0.53 (0.16, 0.90) 0.62 (0.24, 1.00)
Middle—Brachialis
Pre 5.7 �0.7 6.0 �1.0
Post 6.5 �0.8
*
6.8 �1.2
*
ES 0.84 (0.44, 1.24) 0.94 (0.52, 1.36)
Distal—Brachialis
Pre 11.1 �1.5 11.5 �1.6
Post 11.9 �1.7
*
12.1 �1.6
*
ES 0.57 (0.19, 0.94) 0.42 (0.06, 0.78)
Notes: Data are mean �standard deviation. Effect sizes (ES) are presented as
mean and 95% condence intervals (upper, lower bounds).
*
p<0.05 versus Pre. No signicant difference was detected between groups.
FIGURE 3
|Individual percentage changes from pre‐ to post‐training in muscle thickness (MT) of biceps brachii (BB) and brachialis (Br) for more
proximal (55%), middle (65%), and more distal (75%) regions after Preacher (PREA) and Bayesian (BAYE) biceps curls. The horizontal lines are mean
and 95% CIs. All measures increased pre‐ to post‐training, but no signicant difference was detected between regions or conditions (pvalues =0.205–
0.662).
6 of 9 European Journal of Sport Science, 2025
Interestingly, other studies have reported greater distal arm
muscle growth after dumbbell PREA curls but did not measure
biceps brachii size isolated from the brachialis (Kassiano
et al. 2025; Korta et al. 2023; Sato et al. 2021). Therefore, the
increased growth in more distal regions might be attributed to
enhanced brachialis development, not to a biceps regional hy-
pertrophy. In the present study, a post hoc analysis of the biceps
brachii “net hypertrophy”, calculated as the biceps relative
change minus brachialis relative changes, revealed a small dif-
ference (ES =0.38) favoring BAYE (biceps–brachialis; PREA:
7%–10%, BAYE: 9%–8%), suggesting a shift in muscle recruit-
ment preference for the biceps in BAYE compared to PREA.
Supporting this idea, BAYE resulted in next to no negative
changes in MT across all three biceps regions, as can be seen in
individual results presented in Figure 3. Moreover, in a recent
nonpeer‐reviewed work presented as a conference abstract
(Kobayashi et al. 2024), authors reported that dumbbell PREA
induced greater increases in brachialis size, whereas dumbbell
BAYE induced greater increases in biceps brachii size.
In addition, no study has reported that the biceps brachii exhibit
inhomogeneous regional hypertrophy, despite presenting
regional strains during shortening (Blemker et al. 2005; Pappas
et al. 2002). Different strains across regions of the fascicles could
cause different regions of the muscle to experience varying
mechanical work and, thus, receive different stimuli for growth
(Jorgenson et al. 2020). However, different strains alone may not
explain potential inhomogeneous regional hypertrophy. It is
known that skeletal muscles exhibit regional variations in
resting sarcomere lengths across muscle regions and even
within the same ber, and sarcomeres in different muscle re-
gions have their own operating lengths (Jorgenson et al. 2020;
Pappas et al. 2002; Purslow 2010). Of note, sarcomeres experi-
encing greater strain but operating in regions of lower tension
on the force–length curve might experience reduced stimuli for
growth. Due to the pre‐shortening state in PREA, the more
proximal regions of the biceps were expected to be insufciently
active and then receive less tension stimulus for growth than the
distal regions, and then BAYE for the same region. However,
these were not observed herein. It is possible that the biceps
brachii architecture permits homogeneous force production and
transmission across its ber bundles, and altering shoulder
position does not affect how stimuli are set to it during
maximum elbow exion exercises. It is important to note that
the present study lasted 10 weeks, and a potential difference
might emerge over a longer timeframe, warranting further
investigation.
Similar results between conditions were also observed for 1RM
strength gains. These ndings can be attributed to the compa-
rable loads used and their relatively similar progression across
sessions. Since 1RM testing was conducted only for the specic
exercise each arm performed, the inuence of training‐test
specicity limits inferences about the muscle's overall force
production capacity (Buckner et al. 2017). Nonetheless, this
testing design followed previous works, which also showed
similar relative increases in strength between different exercises
trained at shorter versus longer lengths (Maeo et al. 2021,2023;
Stasinaki et al. 2018). The effects on nonspecic strength tests
remain unknown. Results from Sato et al. (2021) suggest greater
“global” strength increases (as evaluated by varied testing
modes) with longer‐length training. Further investigations are
warranted exploring these aspects as well as the neuroplasticity
of the strength adaptation (Škarabot et al. 2021). Of additional
note, any potential cross‐education interference effect on
maximum strength (i.e., improvements in the contralateral,
traditionally nontrained, and arm) appears negligible in this
context, as it is unlikely to occur when both limbs are trained,
particularly with similar loads (Song et al. 2024).
The present study has some limitations. Although muscle
thickness was assessed in two distinct regions of the limb, as
recommended (Nunes et al. 2024), measuring cross‐sectional
area at sites closer to the arm extremities (Drummond
et al. 2016) or evaluating each biceps brachii head separately
could have provided additional insights, particularly given their
distinct force–length relationships (Koo et al. 2002). Addition-
ally, although participants were carefully instructed and su-
pervised to maintain the specied shoulder positions (visually
veried after extensive piloting using mobile device‐based go-
niometers) and to perform exercises with consistent ranges of
motion and tempos, continuous monitoring with specialized
devices (e.g., electrogoniometers and metronomes) was not
implemented.
5
|
Conclusion
In conclusion, biceps cable curl training with the shoulder
exed (PREA) or extended (BAYE) resulted in similar increases
in muscle size and strength. Altering shoulder position does not
appear to inuence the effects of biceps cable curls after
10 weeks of RT in untrained young men. There is no evidence
that the biceps brachii benet from longer‐length RT or exhibit
regional hypertrophy.
Author Contributions
P.A. was involved with conceptualization, methodology, and data
collection. J.P.N. analyzed the data, generated the gures, and drafted
the rst version of the manuscript. S.K., S.N., A.G., H.N., S.N., S.M., and
R.S. participated in the data collection and provided critical revisions to
the writing. K.N. provided critical revisions to the manuscript. All au-
thors read, revised critically, and approved the nal version of the
manuscript.
Acknowledgments
The authors thank all subjects for their engagement in the study.
Ethics Statement
The present study was conducted according to the Declaration of Hel-
sinki. The present study was approved by the University of Tehran
Ethics Review Board Committee.
Conicts of Interest
The authors declare no conicts of interest.
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