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Sports 2023, 11, 39. https://doi.org/10.3390/sports11020039 www.mdpi.com/journal/sports
Article
Training in the Initial Range of Motion Promotes Greater
Muscle Adaptations Than at Final in the Arm Curl
Gustavo F. Pedrosa 1,2,†, Marina G. Simões 1,†, Marina O. C. Figueiredo 1, Lucas T. Lacerda 1,3, Brad J. Schoenfeld 4,*,
Fernando V. Lima 1, Mauro H. Chagas 1 and Rodrigo C. R. Diniz 1
1 Weight Training Laboratory, School of Physical Education, Physiotherapy and Occupational Therapy,
Federal University of Minas Gerais, Lagoa Santa 31270-901, Brazil
2 Brazilian Air Force, Aeronautical Instruction and Adaptation Center, Lagoa Santa 33400-000, Brazil
3 Department of Physical Education, State University of Minas Gerais, Divinópolis 35501-170, Brazil
4 Department of Health Sciences, CUNY Lehman College, Bronx, New York, NY 10468, USA
* Correspondence: brad.schoenfeld@lehman.cuny.edu
† These authors contributed equally to this work.
Abstract: Objective: The effects of ROM manipulation on muscle strength and hypertrophy
response remain understudied in long-term interventions. Thus, we compared the changes in
strength and regional muscle hypertrophy after training in protocols with different ranges of motion
(ROM) in the seated dumbbell preacher curl exercise using a within-participant experimental
design. Design and methods: Nineteen young women had one arm randomly assigned to train in
the initial ROM (INITIALROM: 0°–68°; 0° = extended elbow) while the contralateral arm trained in
the final ROM (FINALROM: 68°–135°), three times per week over an eight-week study period. Pre-
and post-training assessments included one repetition maximum (1RM) testing in the full ROM (0°–
135°), and measurement of biceps brachii cross-sectional area (CSA) at 50% and 70% of humerus
length. Paired t-tests were used to compare regional CSA changes between groups, the sum of CSA
changes at 50% and 70% (CSAsummed), and the strength response between the training protocols.
Results: The INITIALROM protocol displayed a greater CSA increase than FINALROM protocol at 70%
of biceps length (p = 0.001). Alternatively, we observed similar increases between the protocols for
CSA at 50% (p = 0.311) and for CSAsummed (p = 0.111). Moreover, the INITIALROM protocol displayed
a greater 1RM increase than FINALROM (p < 0.001). Conclusions: We conclude that training in the
initial angles of elbow flexion exercise promotes greater distal hypertrophy of the biceps brachii
muscle in untrained young women. Moreover, the INITIALROM condition promotes a greater
dynamic strength increase when tested at a full ROM compared to the FINALROM.
Keywords: muscle hypertrophy; partial angular; partial range of motion; partial angular
displacement; muscle strength
1. Introduction
The effects of manipulating resistance training (RT) variables on muscle hypertrophy
response has been an ongoing focus of investigation [1–3]. Among the RT variables, range
of motion (ROM) was generally overlooked in past studies targeting training prescription
recommendations [3,4]. However, its influence on neuromuscular responses is becoming
increasingly recognized as a potential area of research interest [5,6]. ROM may alter the
length at which the working muscle contracts. At the beginning of a concentric action
(INITIALROM), the muscle length is longer than at the final angles of the action (FINALROM).
Several investigations have reported greater metabolic stress and IGF-1 release after
contractions performed at longer vs. shorter muscle lengths [7–11], which have been
associated with muscle hypertrophy [12,13]. This raises the possibility that training
Citation: Pedrosa, G.F.;
Simões, M.G.; Figueiredo, M.O.C.;
Lacerda, L.T.; Schoenfeld, B.J.;
Lima, F.V.; Chagas, M.H.;
Diniz, R.C.R. Training in the Initial
Range of Motion Promotes Greater
Muscle Adaptations than at Final in
the Arm Curl. Sports 2023, 11, 39.
https://doi.org/10.3390/
sports11020039
Academic Editor: Andrew Hatchett
Received: 9 January 2023
Revised: 31 January 2023
Accepted: 1 February 2023
Published: 6 February 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license
(https://creativecommons.org/license
s/by/4.0/).
Sports 2023, 11, 39 2 of 12
exclusively in the INITIALROM, where the muscle is in a lengthened state, may promote a
greater hypertrophic response than training in the FINALROM.
Several studies have compared the hypertrophic response to training in the
INITIALROM and FINALROM [7,14,15]. For the quadriceps, results showed greater increases
in muscle cross-sectional area (CSA) at the distal muscle regions of the rectus femoris [14]
and vastus lateralis [7,14] for the group that performed the INITIALROM compared to the
FINALROM training group. These findings suggest that the ROM trained may influence
regional muscle growth on quadriceps muscle. Similar to results for the quadriceps, Sato
et al. [16] found a greater increase in muscle thickness of the distal biceps brachii plus
brachialis after preacher unilateral arm curl resistance training at INITIALROM compared
to FINALROM. However, the training occurred two times per week across five weeks,
raising the question as to whether differences would be maintained after a longer training
period. According to Halperin et al. [17], it is possible that the initial improvements were
due to the novel stimulus rather than an inherent superiority of the program. Conceivably,
results may have been different if the study period lasted longer. Therefore, it is necessary
to conduct further research to provide greater insight into the effect of training in various
ROMs on the muscle hypertrophic response over longer time frames.
Kassiano et al. [15] compared changes in muscle thickness of the medial and lateral
heads of the gastrocnemius across an eight-week RT program involving the calf raise
exercise when performed in the INITIALROM vs FINALROM. Results showed the
INITIALROM training elicited greater increases in muscle thickness of the medial and
lateral gastrocnemius compared to the FINALROM, providing evidence that training
exclusively at longer muscle lengths may be superior to training exclusively at shorter
muscle lengths for enhancing muscle hypertrophy of the plantar flexors. However, these
authors assessed hypertrophy at a single point along the muscle, and it is known that
resistance training in different ROM configuration may induce non-homogeneous
hypertrophic adaptations across the length of the muscle [14,18]. Furthermore, the change
in muscle volume analyzed via magnetic resonance imaging (MRI) is considered the gold
standard for estimating muscle hypertrophy [19]. However, this procedure is expensive
[19]. A more economical alternative to analyzing muscle volume by MRI is to assess
muscle CSA by B-mode ultrasound [19], with measurements taken at different sites along
the length of the muscle [14,20]. This approach provides a proxy for muscle volume,
imparting a better comprehension of the influence of ROM manipulation on muscle
hypertrophy.
In addition to its effects on muscle hypertrophy, RT also promotes increases in
maximal strength. Research generally shows that strength increases are specific to the
given ROM trained [21,22]. Accordingly, training in the INITIALROM and FINALROM could
lead to a greater strength increase in the specific angles trained [23]. Taking into account
that the sticking point is a primary determinant of performance in the 1RM test [24], it can
be expected that training in the INITIALROM, which promotes greater strength increases in
this region, would also cause greater increases in the 1RM test performed in full ROM in
comparison to training in the FINALROM. In line with this reasoning, Pedrosa et al. [14]
found that 12 weeks training in the INITIALROM promoted a greater 1RM increase at full
ROM than training in the FINALROM using the knee extension machine. Werkhausen et al.
[2] compared the isokinetic strength after training in the INITIALROM and the full ROM in
the leg press exercise. Results showed similar changes between training in the INITIALROM
and a full ROM, suggesting the strength adaptations across a full ROM are influenced by
the initial training angle. These findings further the rationale that training in the
INITIALROM could be superior to training in the FINALROM in a full ROM strength test.
However, this hypothesis has not yet been objectively tested in other muscles such as the
elbow flexors.
Therefore, this study aimed to compare dynamic strength and regional muscle
hypertrophy changes of the elbow flexors in young women after performing the arm curl
exercise for eight weeks while training in INITIALROM and FINALROM. We hypothesized
Sports 2023, 11, 39 3 of 12
that the INITIALROM protocol would elicit greater increases in dynamic strength and distal
muscle hypertrophy than FINALROM protocol.
2. Methods
We employed a within-participant experimental design whereby the right and left
arms of 21 untrained women trained in INITIALROM or FINALROM for eight weeks. We
chose the seated dumbbell preacher curl exercise to ensure that participants maintained
strict form throughout exercise performance. Pre- and post-study strength was assessed
by the 1RM test in the arm curl, and B-mode ultrasound was employed to assess CSA
changes in the mid- and distal regions of the biceps.
The sample size was estimated a priori following the recommendations of Beck [25]
using the software G*Power (version 3.1.9.2; Heinrich Heine Universität Düsseldorf, DE,
Germany). We used the t-statistic with an alpha of 0.05, power of 0.8, and a relatively
moderate Cohen’s d effect size (ES) of 0.7 and determined that 19 subjects were required
for adequate statistical power. We recruited two additional subjects to account for the
possibility of dropouts, expected to be ~10% of the sample.
Participants were untrained women who had not performed any physical activity for
at least six months prior to the onset of the study. Two participants withdrew for personal
reasons; therefore, 19 women completed the study (mean age = 22.8 ± 10.5 years; mean
body mass = 64.5 ± 8.05 kg; mean height = 164.1 ± 4.7 cm). Each participant’s upper limb
was allocated in a randomized fashion according to upper limb dominance. The order of
training was counterbalanced whereby half of the participants performed the INITIALROM
protocol with their preferred limb, while the other half performed the FINALROM protocol
with their preferred limb. Before participation, written consent was obtained from each
participant after being informed of the procedures, risks, and benefits of the investigation.
The study followed the standards established in the Declaration of Helsinki and was
approved by the ethics committee of the Federal University of Minas Gerais (approval
#CAAE 91438418.4.0000.5149).
In the first pre-training session, after the anthropometric data assessment, we
obtained measures of biceps brachii CSA at 50% and 70% of the distance from the
acromion to the lateral epicondyle of each humerus via B-mode ultrasound (MindRay®
DC-7, Shenzhen, China). It should be noted that muscle hypertrophy assessed by B-mode
ultrasound imaging is highly correlated with MRI, which is considered the gold standard
for measuring changes in muscle mass [26]. Images were acquired at a frequency of 21
frames/s, using a 4–10 MHz linear transducer with a depth ranging from 1 to 6 cm and
gain between 50 and 64 db. The settings were individually adjusted to produce a clear
image of the entire muscle for extended field-of-view, and replication at post-training. The
same trained technician performed all ultrasound scans, moving the transducer in a line
parallel to the humeral epicondyles at a relatively constant speed for approximately 7s at
each site. The images were saved to hard drive and coded for blinded CSA calculation
using the Horos® software. We averaged the two CSA measurements in each region to
obtain the final values used for analyses. Moreover, we summed the CSA at 50%, and 70%
of biceps length (CSAsummed) to produce an estimate of overall biceps hypertrophy.
Previous studies have employed similar formulas in an attempt to produce a hypertrophy
measure more representative of the whole muscle in comparison to a single muscle region
[1,20]. The intraclass correlation coefficients (ICC3,1) in our laboratory for CSA at 50% and
70% of biceps length were 0.94 and 0.92, respectively.
After ultrasound imaging, we assessed participants 1RM in the seated dumbbell
preacher curl exercise. The 1RM test was performed alternately on each arm throughout
a full ROM, with a 3-min recovery interval between the limbs and between attempts. A
final value was obtained within 5 attempts on each arm. Each attempt started with the
elbow fully extended (0°), and the shoulder angle (humerus and trunk) fixed at 45°. The
dumbbell was handed to the participant in this initial position, who then performed a
concentric muscle action until 135° of elbow flexion (forearm perpendicular to the
Sports 2023, 11, 39 4 of 12
ground). The attempt was considered successful if the participant was able to perform the
full range of elbow flexion (0° to 135°) without assistance from auxiliary movements. The
dumbbell load was progressively increased (minimum of 0.5 kg) until the participant was
unable to perform the concentric action with proper form. Hence, the 1RM value corre-
sponded to the weight lifted in the previous successful attempt. This initial test was con-
sidered a familiarization session to the 1RM assessment. The 1RM test was repeated 48h
later (pre-training session 2) and the value obtained in this session was used for statistical
analysis. Between 48 h and 72 h after the last training session, the ultrasound imaging and
the 1RM test in a full ROM were repeated using the procedures previously described.
Training sessions consisted of the seated dumbbell preacher curl performed in a spe-
cific ROM for each limb. The shoulder angle was fixed at 45° (as in the 1RM test). The
INITIALROM protocol was trained from 0° to 68° of elbow flexion, and the FINALROM pro-
tocol was trained from 68° to 135° of elbow flexion (Figure 1). The ROMs were individu-
ally checked by a manual goniometer (axis fixed in the elbow, and the rules fixed in the
arm and forearm) at the beginning of each training session. An elastic cord was placed in
front of the machine to serve as a mechanical stop ensuring training was limited to the
prescribed ROMs (Figure 1). In the INITIALROM, participants began the eccentric muscle
action when their forearm touched the string (68° of elbow flexion) and they continued
lowering the load until full extension. In the FINALROM protocol, the participants began
the concentric action when their forearm touched the string (68° of elbow flexion) and
they continued raising the load until their forearm was perpendicular to the ground (135°
of elbow flexion).
Figure 1. Training protocols range of motion. (A1,A2) = starting and finishing the concentric action
of INITIALROM protocol (0°–68° of elbow flexion), respectively. (B1,B2) = starting and finishing the
concentric action of FINALROM protocol (68°–135° of elbow flexion), respectively.
Each protocol was trained three times per week, in the same session, separated by
48–72 hours over the eight-week study period. We alternated the session-to-session order
in which the training protocols were performed: i.e., if the INITIALROM protocol was the
first to be performed in a given training session, the FINALROM protocol would be trained
first in the next session. If the participant was assigned to start with INITIALROM protocol,
after completing each set, 1 minute interval was allowed before initiating the FINALROM
Sports 2023, 11, 39 5 of 12
protocol with the contra lateral limb. The next set for the starting protocol was only initi-
ated after 3 minutes of the completion of the previous set of the INITIALROM; all recovery
periods were timed with a stopwatch to ensure accuracy.
Participants performed four sets per session in both the INITIALROM and the FI-
NALROM protocols. In an effort to standardize the training stimulus for the development
of hypertrophy and muscle strength, all sets were carried out until volitional failure
[27,28]. When the last set was performed with more than 10 or less than 8 repetitions, the
load was increased or reduced diminished in 1 kg at the next training session, respectively.
Each repetition was performed with a 2s concentric action and a 2s eccentric action (timed
by metronome). Five sets were performed from the fifth week on, following the same pre-
viously described procedures.
The Shapiro–Wilk test confirmed the normality of data distribution, and all variables
presented similar baseline values between training protocols. We analyzed the absolute
difference values (post–pre-values) between training protocols by paired t-test for all var-
iables of interest. We reported 95% confidence intervals (CI) around the point estimate.
Cohen’s d effect sizes (ES) were calculated (post-pre/pooled standard deviation) with the
following interpretation: trivial: <0.20; small: 0.20–0.60; moderate: 0.61–1.20; large: 1.21–
2.0; very large: >2.0) [29]. All statistical procedures were performed using JASP statistics
packages, version 0.14 (Wagenmakers, Amsterdam). We considered statistical signifi-
cance when α < 0.05.
3. Results
When comparing regional CSA between the training protocols, analysis showed the
INITIALROM protocol displayed a greater CSA increase than the FINALROM protocol at 70%
of biceps brachii length (p = 0.001; 95% CI = 0.18 to 0.59 cm2; ES = 0.89), and a relatively
similar CSA increase at 50% (p = 0.331; 95% CI = −0.10 to 0.34 cm2; ES = 0.23). Analysis
showed the CSAsummed increase was not statistically different between the training proto-
cols (p = 0.111; 95% CI = −0.08 to 0.67 cm2; ES = 0.39), as shown in Figure 2. Regarding the
1RM test, analysis showed the INITIALROM protocol presented a statistically greater in-
crease than the FINALROM protocol (p < 0.001; 95% CI = 0.39 to 1.06 kg; ES = 1.05), as shown
in Figure 3.
Sports 2023, 11, 39 6 of 12
Figure 2. The paired mean difference for cross-sectional area in INITIALROM and FINALROM at (a)
50% humeral length; (b) 70% humeral length; and (c) summed values of 50% and 70% humeral
length [30]. The raw data are plotted on the upper axes; each paired set of observations is connected
by a line. On the lower axes, each paired mean difference is plotted as a bootstrap sampling distri-
bution. Mean differences are depicted as dots; 95% confidence intervals are indicated by the ends of
the vertical error bars. ES = effect size. * Significant differences compared with FINALROM protocol.
Sports 2023, 11, 39 7 of 12
Figure 3. The paired mean difference for 1 repetition maximum in INITIALROM and FINALROM [30].
The raw data are plotted on the upper axes; each paired set of observations is connected by a line.
On the lower axes, each paired mean difference is plotted as a bootstrap sampling distribution.
Mean differences are depicted as dots; 95% confidence intervals are indicated by the ends of the
vertical error bars. ES = effect size. * Significant differences compared with FINALROM protocol.
4. Discussion
A primary finding of our study was that training in the INITIALROM elicited greater
increases in CSA at 70% of biceps brachii length and in the 1RM test than the FINALROM
protocol. These results are consistent with our initial hypothesis and provide further evi-
dence that ROM manipulation impacts regional muscular adaptations across a variety of
different muscles and exercises.
To our knowledge, only three previous studies compared regional hypertrophic
changes after training in INITIALROM and FINALROM. McMahon et al. [7] found that the
INITIALROM group achieved greater vastus lateralis hypertrophy than the FINALROM
group only at the distal region after 8 weeks of knee extension training. Similarly, Pedrosa
Sports 2023, 11, 39 8 of 12
et al. [14] showed the INITIALROM group presented greater distal muscle growth of the
rectus femoris and the vastus lateralis muscles than the FINALROM group after 12 weeks
of knee extension training. Moreover, Sato et al. [16] demonstrated the INITIALROM train-
ing elicited greater distal biceps brachii plus brachialis muscle hypertrophy after only five
weeks resistance training. These results corroborate our findings, which suggest that
training in INITIALROM promotes greater distal hypertrophy of the biceps than training in
FINALROM, and a similar hypertrophy response between conditions at the middle region
in young, untrained women. Moreover, our study expands on the findings of McMahon
et al. [7] and Pedrosa et al. [14] and supports those of Sato et al. [16] by providing evidence
that training a muscle at long muscle length has a beneficial effect on muscular adapta-
tions in the upper extremities.
Some other studies have investigated regional muscle hypertrophy between the FI-
NALROM and the FULLROM protocols [14,18,31]. Bloomquist et al. [18] reported greater hy-
pertrophy in the middle and distal regions of the anterior quadriceps femoris in a group
of young men performing the back squat for 12 weeks in a FULLROM group compared to
the FINALROM group. Similarly, McMahon et al. [31] reported greater distal vastus lateralis
hypertrophy in a group of young men and women performing a variety of lower limb
exercises in a FULLROM versus a FINALROM over an 8-week training period. Pedrosa et al.
[14] showed greater distal muscle hypertrophy of rectus femoris and vastus lateralis mus-
cles after training in FULLROM compared to FINALROM. Given that the main difference be-
tween training in FINALROM and FULLROM is that the FULLROM excurses the INITIALROM,
it can be speculated that the greater muscle hypertrophy after training in a FULLROM re-
sults from training at longer muscle lengths.
Although speculative, a possible mechanistic explanation for the heightened regional
hypertrophic response is related to the production of higher amounts of metabolic stress
[10], and insulin-like growth factor (IGF)-1 release [7] when training at longer muscle
lengths in comparison to training at shorter muscle lengths, which in turn may confer
anabolic effects [32]. Additionally, there is evidence suggesting that both metabolic stress
[33] and IGF-1 [34] concentrations may vary between muscle regions after mechanical
overload, and that greater regional muscle hypertrophy occurs in regions demonstrating
greater metabolic stress [35] and IGF-1 concentrations [34]. Thus, we hypothesize that
training in the INITIALROM promotes a heightened physiological response at the distal
portion of the muscle, thereby leading to greater muscle protein increase in this region.
Previous research supports our findings [7,14,18,31]; however, no attempts were made to
explore mechanisms involved, which requires further investigation.
When summing the CSA results of the two regional sites (CSAsummed), hypertrophic
increases were statistically similar between training protocols. This value provides a gen-
eral proxy for hypertrophy of the muscle as a whole. Our findings in this regard are con-
sistent with previous studies on the topic [1,20]. However, although the study lasted eight
weeks and is in line with previous research that aimed to measure muscle hypertrophy
over this time period [7,31], we cannot necessarily infer that results would hold true over
longer-term interventions nor rule out the possibility that other factors may have influ-
enced changes [36]. Therefore, further investigation on topic using longer interventional
period is recommended to confirm or refute the present findings.
In regard to the 1RM results, our study shows that training in the INITIALROM elicits
greater dynamic strength improvements in a full ROM test compared to training in the
FINALROM; these results were observed despite the use of heavier absolute loads when
training in the FINALROM. To our knowledge, only one study to date has compared
changes in dynamic strength at a FULLROM after training in the INITIALROM versus FI-
NALROM. Pedrosa et al. [14] reported the INITIALROM group showed greater 1RM test in-
crease at a FULLROM compared to the FINALROM after 12 weeks of knee extension training,
lending support to our results.
Several studies indicate a ROM-specific strength increase after training in a FULLROM,
FINALROM [18,21,22], and INITIALROM [14]. Bloomquist et al. [18] found that the training
Sports 2023, 11, 39 9 of 12
groups (FULLROM and FINALROM) presented greater 1RM increases in the trained ROM.
Similarly, Martínez-Cava et al. [21] reported ROM-specific strength adaptations after 10
weeks of training in the bench press exercise at a full ROM, two-thirds ROM, and one-
third-ROM). In addition, Pedrosa et al. [14] showed the INITIALROM and FINALROM groups
presented greater 1RM increases in the ROM trained. Although the present study did not
compare the strength performance in different ROMs, previous findings [14,18,21–23]
support the rationale that a ROM-specific strength increase may also have occurred in the
present study, and therefore influenced the results of the 1RM test in a full ROM. Accord-
ingly, the INITIALROM training would allow a greater strength enhancement at the begin-
ning of the concentric action of a full ROM compared to training in the FINALROM [14]. We
speculate that this specific joint-angle strength adaptation (from the INITIALROM protocol)
was fundamental to overcoming the sticking point and thus resulted in a superior increase
in 1RM.
Changes in muscle morphology may help to provide a mechanistic explanation for
the observed angular specific differences in strength increase between conditions [37]. Ev-
idence indicates a positive association between greater increases in distal muscle CSA re-
gions and increases in torque angles where the muscle is elongated [37]. Thus, the greater
muscle hypertrophy response at 70% in the INITIALROM condition may have enhanced
strength performance in a full ROM 1RM test to a greater extent than training in FI-
NALROM. This hypothesis needs further investigation.
Additionally, it is known that the increase in maximum dynamic strength is related
to alterations in neural factors, such as an increase in the number of activated motor units,
improvement in inter and intra muscular synchronization, and a reduction in the activa-
tion of the antagonist muscles during exercise performance [38]. Thepaut-Mathieu et al.
[39] reported that resistance training performed exclusively at a short muscle length pro-
moted greater neural adaptations (as assessed by surface electromyography) near or at
the trained angles, and this adaptation coincided with the greater observed increases in
muscle strength near or at the trained angles; the response did not occur in the group that
trained in long muscle length. This finding is supported by Noorkoiv et al. [37], who
demonstrated a positive and significant correlation between the force increase at short
muscle length angles and the increase of the surface electromyographic signal only in the
group that trained at the short muscle length compared to the long length group. It there-
fore could be hypothesized that the contribution from the improvement of neural factors
to increase the performance of the 1RM test was smaller in the FINALROM group compared
to INITIALROM group. The present study did not attempt to assess neural factors; hence,
further investigations are needed to better elucidate the mechanisms of strength increases
associated with ROM manipulation.
This study has several limitations that should be taken into account when attempting
to draw practical conclusions. First, although performing sets to volitional fatigue helps
to ensure that all individuals receive a comparable hypertrophic stimulus [27], its imple-
mentation influences other variables, such as the number of repetitions performed. Future
studies should seek to study ROM-induced muscular adaptations with different configu-
rations of RT variables. Second, we only tested dynamic strength in a full ROM using the
knee extension machine and thus cannot extrapolate findings to specific partial ROMs,
isometric strength at different joint-angles or the transfer of these results to the activities
of everyday life. Third, the findings are specific to dynamic elbow flexion exercise and
thus cannot necessarily be generalized to other exercises or muscle groups. Fourth, we
measured hypertrophy at only two points along the length of the biceps brachii; it would
be interesting to analyze other regions or even the muscle volume to obtain a more robust
perspective of hypertrophic changes. Fifth, our findings are specific to young, healthy,
untrained women and thus cannot necessarily be generalized to other populations.
Finally, we chose to employ a within-participant design, which affords the benefit of
enhancing statistical power by reducing the amount of between-participant variability
[40]. While this experimental model can provide keen insights into skeletal muscle
Sports 2023, 11, 39 10 of 12
adaptations in longitudinal RT investigations [40], a potential limitation of this design is
the possibility of a cross-education effect. There is evidence indicating that the cross-edu-
cation effect, if it indeed occurs, would be restricted to neural parameters and muscle
strength gains; morphological changes (e.g., CSA) are not materially influenced by this
effect [41]. Hence, any muscle strength gains achieved in the contralateral limb should
conceivably evolve from an increase in motor neuron activation without contribution
from morphological adaptations. Moreover, previous studies investigating the cross-ed-
ucation effect for EMG amplitude have shown inconclusive results [42,43]. For example,
Hortobágyi, et al. [42] found that changes in the EMG amplitude of the untrained limb
depend on the training mode performed (e.g., type of muscle action). The neuromuscular
changes were similar to the changes in muscle strength. Moreover, other researchers
found that the cross-education effect contributes to approximately 7.8% of the muscle
strength gain of the contralateral limb [44]. In the present study, the mean relative increase
in the INITIALROM and FINALROM groups was 42.8 ± 14.8% and 19.0 ± 10.3%, respectively;
these differences would be outside of any potential confounding from cross-education.
Furthermore, it has been argued that, when both limbs of an individual are trained with
different protocols, the cross-education effect is minimal or non-existent [44,45]. Thus,
based on the magnitude of influence presented by Munn et al. [44], it seems likely that
any difference in the strength responses between limbs would be due to training protocols
with minimal confounding from cross-education.
5. Conclusions
In conclusion, the seated dumbbell preacher curl performed in the INITIALROM elic-
ited greater biceps brachii hypertrophy at 70% length, but not at 50% nor for the CSAsummed
in untrained women. Moreover, the INITIALROM protocol promoted a greater increase in
the 1RM test in full ROM compared with training in the FINALROM. These findings add to
the body of literature indicating that training at long muscle lengths promotes increases
in hypertrophy at the distal muscle region, and these findings occur in both the upper and
lower extremity musculature.
Author Contributions: Conceptualization, R.C.R.D., F.V.L. and M.H.C.; methodology, R.C.R.D.,
L.T.L. and M.G.S.; formal analysis, G.F.P., M.O.C.F., B.J.S. and M.G.S.; writing—original draft prep-
aration, G.F.P., M.G.S. and R.C.R.D.; writing—review and editing, G.F.P., B.J.S. and R.C.R.D. All
authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: The study was conducted in accordance with the Declara-
tion of Helsinki, and approved by the Ethics Committee of Federal University of Minas Gerais (pro-
tocol code CAAE - 91438418.4.0000.5149 and august 09, 2018)
Informed Consent Statement: Informed consent was obtained from all subjects involved in the
study. Written informed consent has been obtained from the patient(s) to publish this paper.
Data Availability Statement: All data generated or analyzed during this study will are included in
the published article as Table(s) and Figure(s). Any other data requirement can be directed to the
corresponding author upon reasonable request
Acknowledgments: Supported by the FAPEMIG; CAPES (Brazil); and PRPq of Universidade Fed-
eral de Minas Gerais.
Conflicts of Interest: B.J.S. serves on the scientific advisory board for Tonal Corporation, a manu-
facturer of fitness equipment. The other authors declare no conflicts of interests, financial or other-
wise.
Sports 2023, 11, 39 11 of 12
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