Different Shoulder Exercises Affect the Activation of Deltoid Portions in Resistance-Trained Individuals

Abstract

The aims of this study were to compare muscle activity of the anterior deltoid, medial deltoid, and posterior deltoid in the bench press, dumbbell fly, shoulder press, and lateral raise exercises. Thirteen men experienced in strength training volunteered for the study. Muscle activation was recorded during maximum isometric voluntary contraction (MVIC) for data normalization, and during one set of 12 repetitions with the load of 60% 1RM in all exercises proposed. One-way repeated-measures ANOVA with Bonferroni's posthoc was applied using a 5% significance level. For anterior deltoid, the shoulder press (33.3% MVIC) presented a significantly higher level of activation when compared to other exercises. Also, no significant difference was found between the bench press (21.4% MVIC), lateral raise (21.2% MVIC), and dumbbell fly (18.8% MVIC). For the medial deltoid, the lateral raise (30.3% MVIC) and shoulder press (27.9% MVIC) presented a significantly higher level of activity than the bench press (5% MVIC) and dumbbell fly (3.4% MVIC). Besides, no significant difference was found between the bench press and the dumbbell fly. For the posterior deltoid, the lateral raise (24% MVIC) presented a significantly higher level of activation when compared to other exercises. For the posterior deltoid portion, the shoulder press (11.4% MVIC) was significantly more active than the bench press (3.5% MVIC) and dumbbell fly (2.5% MVIC). Moreover, no significant difference was found between the bench press and the dumbbell fly. In conclusion, the shoulder press and lateral raise exercises showed a higher level of muscle activation in the anterior deltoid and medial deltoid when compared to the bench press and dumbbell fly exercises.

Full text

Journal of Human Kinetics volume 75/2020, 5-14 DOI: 10.2478/hukin-2020-0033 5
Section I – Kinesiology
1 - Studies Research Group in Neuromuscular Responses, University of Lavras, Lavras, Brazil.
2 - Postgraduate Program of the Faculty of Physical Education and Sports of the University of Juiz de fora, University of Juiz de
Fora, Juiz de Fora, Brazil.
3 - Postgraduate in Human Movement and Rehabilitation Sciences,University of São Paulo, Santos, Brazil.
4 - Department of Physical Activity Sciences, University of Los Lagos, Puerto Montt, Chile.
5 - AFSYE research group, Adventist University of Chile, Chile.
6 - Department of Kinesiology, California State University, Northridge, CA, USA.
.
Authors submitted their contribution to the article to the editorial board.
Accepted for printing in the Journal of Human Kinetics vol. 75/2020 in October 2020.
Different Shoulder Exercises Affect the Activation
of Deltoid Portions in Resistance-Trained Individuals
by
Yuri A. C. Campos1,2, Jeferson M. Vianna2, Miller P. Guimarães1,3,
Jorge L. D. Oliveira2, Claudio Hernández-Mosqueira4,5, Sandro F. da Silva1,
Paulo H. Marchetti6
The aims of this study were to compare muscle activity of the anterior deltoid, medial deltoid, and posterior
deltoid in the bench press, dumbbell fly, shoulder press, and lateral raise exercises. Thirteen men experienced in
strength training volunteered for the study. Muscle activation was recorded during maximum isometric voluntary
contraction (MVIC) for data normalization, and during one set of 12 repetitions with the load of 60% 1RM in all
exercises proposed. One-way repeated-measures ANOVA with Bonferroni’s posthoc was applied using a 5%
significance level. For anterior deltoid, the shoulder press (33.3% MVIC) presented a significantly higher level of
activation when compared to other exercises. Also, no significant difference was found between the bench press (21.4%
MVIC), lateral raise (21.2% MVIC), and dumbbell fly (18.8% MVIC). For the medial deltoid, the lateral raise (30.3%
MVIC) and shoulder press (27.9% MVIC) presented a significantly higher level of activity than the bench press (5%
MVIC) and dumbbell fly (3.4% MVIC). Besides, no significant difference was found between the bench press and the
dumbbell fly. For the posterior deltoid, the lateral raise (24% MVIC) presented a significantly higher level of activation
when compared to other exercises. For the posterior deltoid portion, the shoulder press (11.4% MVIC) was significantly
more active than the bench press (3.5% MVIC) and dumbbell fly (2.5% MVIC). Moreover, no significant difference
was found between the bench press and the dumbbell fly. In conclusion, the shoulder press and lateral raise exercises
showed a higher level of muscle activation in the anterior deltoid and medial deltoid when compared to the bench press
and dumbbell fly exercises.
Key words: EMG, strength training, glenohumeral joint, deltoid muscle, upper body.
Introduction
The deltoid is considered a primary motor
muscle in many upper body strength training (ST)
exercises (Andersen et al., 2014; Botton et al., 2013;
Franke et al., 2015; Welsch et al., 2005; Wilk et al.,
2019). Due to its triangular shape, the deltoid
muscle is commonly subdivided into anterior,
medial and posterior portions (Botton et al., 2013)
being responsible for several movements of the
glenohumeral joint such as shoulder abduction
(medial deltoid, anterior and posterior) (Hall,
2006; Houglum and Bertoti, 2011), shoulder
flexion and horizontal adduction

6 Different shoulder exercises affect the activation of deltoid portions in resistance-trained individuals
Journal of Human Kinetics - volume 75/2020 http://www.johk.pl
(anterior deltoid) (Hall, 2006; Houglum and
Bertoti, 2011), as well as shoulder extension and
horizontal abduction (posterior deltoid) (Hall,
2006; Houglum and Bertoti, 2011).
The use of different exercises with
different mechanical strains has been highly
recommended for the complete development of
different deltoid portions. In this sense, priority
exercises such as the bench press (McCaw and
Friday, 1994; Schick et al., 2010; Welsch et al.,
2005; Wilk et al., 2019), lat pulldown (Andersen et
al., 2014; Vilaça-Alves et al., 2014), seated row
(Botton et al., 2013; Franke et al., 2015), and
complementary exercises such as the lateral raise
(Botton et al., 2013), shoulder press (Saeterbakken
and Fimland, 2013), and reverse pec deck fly
(Botton et al., 2013; Franke et al., 2015) can be
used. However, the importance of including
complementary exercises in ST routines, as well as
how these different exercises affect the muscle
recruitment of the deltoid portions remain still
unclear.
Some studies using surface
electromyography (sEMG) have been proposed to
verify differences in muscle activity during
priority and complementary exercises for the
upper (Botton et al., 2013; Franke et al., 2015) and
lower (Ema et al., 2016; Wright et al., 1999) limbs.
Wright et al. (1999) found greater muscle
activation in the semitendinosus and biceps
femoris muscles during knee flexion when
compared to squats. Ema et al. (2016) found
greater muscle activity in the rectus femoris
during knee extension compared to the leg press.
As for the medial portion of the deltoid, Botton et
al. (2013) reported higher muscle activity during
the lateral raise exercise with a cable/dumbbell
than the shoulder press. Regarding the posterior
portion of the deltoid, Botton et al. (2013) and
Franke et al. (2015) reported higher muscle
activation of this muscle portion by the reverse
pec deck fly exercise than a seated row or inclined
pulldown. Additionally, for the anterior portion
of the deltoid, Botton et al. (2013) did not observe
differences in muscle activation between the
smith machine shoulder press and the bench
press.
Therefore, considering that exercise
selection is one of the important variables to
maximize acute responses and chronic
adaptations (Grgic et al., 2018) and that muscle
involvement plays a key role in your choice
(Stastny et al., 2017), the objective of this study
was to compare the muscle activity of anterior,
medial, and posterior portions of the deltoid in
the bench press, dumbbell fly, shoulder press, and
lateral raise. A thorough understanding of how
each portion of the deltoid is involved in each
exercise might assist coaches and physiotherapists
in choosing and using the most appropriate
exercise in ST and rehabilitation programs.
Methods
Experimental Approach to the Problem
To investigate muscle activity of the
anterior deltoid (AD), medial deltoid (MD), and
posterior deltoid (PD) during the bench press
(BP), dumbbell fly (DF), shoulder press (SP), and
lateral raise (LR), five sessions were conducted
separated by a 48-hour interval. During the first
session, participants were evaluated for body
mass, height, and body fat and were informed
about all procedures that would involve data
collection. During the second and third sessions,
participants performed the test and retest of one-
repetition maximum (1RM) in the proposed
exercises. During the fourth session, data of
muscle activation during the proposed exercises
were collected. After a 15-min rest interval,
participants performed a maximum voluntary
isometric contraction (MVIC) in each exercise for
subsequent normalization of the EMG signal. The
evaluated exercises were performed randomly in
the second, third, and fourth sessions.
Participants
This study included 13 healthy male
volunteers (age 24.50 ± 4.46 years, fat content
13.80 ± 4.92%, body height 1.76 ± 0.06 m, body
mass 78.40 ± 15.30 kg, 1RM testing – BP 111.50 ±
7.12 kgf, DF 70.38 ± 5.18 kgf, SP 55.53 ± 4.63 kgf,
and LR 34.90 ± 2.98 kgf) with 3.58 ± 2.90 years of
ST experience, who performed the proposed
exercises regularly in their training programs. The
exclusion criteria were the presence of any type of
bone, joint or muscle injuries that compromised
the total or partial performance of the movements,
or participants who were not familiar with the
proposed exercises. All procedures were
approved by the local ethics committee (protocol:
#0068/2010) following the Declaration of Helsinki.
All participants signed a consent form for their
participation in the study.

by Yuri A. C. Campos et al. 7
© Editorial Committee of Journal of Human Kinetics
Evaluation
Anthropometric evaluation
A stadiometer (110 FF, Welmy®, Santa
Bárbara d’Oeste, Brazil) was used for
anthropometric evaluation and a four-pole
bioimpedance device (Quantum BIA-II, RJL
Systems®, Clinton Township, USA) was used to
estimate body fat composition.
One-repetition maximum (1RM) testing
The 1RM protocol followed
recommendations proposed by the National
Strength and Conditioning Association (Baechle
and Earle, 2008). Some precautions were followed
to reduce the possibility of errors in the
determination of 1RM for each exercise: 1)
participants were instructed to execute BP, DF, SP,
and LR exercises according to the National
Strength and Conditioning Association manual
(NCSA, 2008); 2) the correct technique was
monitored during the execution of all exercises; 3)
researchers gave feedback to participants on each
exercise technique; 4) researchers encouraged
participants during all exercises; and 5) exercises
were interrupted if there was any modification in
the execution technique. Participants warmed up
with mild cardiovascular exercises for
approximately five to 10 minutes. Subsequently,
from the load reported by participants to perform
sets of 8 to 12 maximum repetitions, the warm-up
loads were calculated by an equation (Brzycki,
1993). Then, all participants executed a set of five
repetitions of each exercise at 50% 1RM, followed
by two to three repetitions with a load
corresponding to 60 and 80% 1RM as a specific
warm-up. Participants executed a set of single
repetitions with increasing weight to determine
1RM, and a 5-min rest interval between attempts.
The 1RM was tested using maximally five
attempts. These procedures were followed for all
exercises proposed (Schoenfeld et al., 2016). A 30-
min recovery interval was used between
exercises.
Measurements
Participants had their skin shaved, wiped,
and cleaned using a cotton ball and isopropyl
alcohol. Then, disk-shaped self-adhesive sEMG
surface electrodes (2223 BR, 3M®, Campinas,
Brazil) with a one-centimeter diameter AgCl
capture surface were placed using the conductive
gel in the presumable underlying muscle fiber
direction at a center-to-center distance of
approximately 2 cm. Surface electrodes were
placed on the evaluated muscles according to the
SENIAM recommendations (Hermens et al., 1999)
on the dominant side of each participant (Behm et
al., 2005). For AD, electrodes were fixed at one
finger width distal and anterior to the acromion in
the direction of the line between the acromion and
the thumb. For MD, the electrodes were fixed
from the acromion to the lateral epicondyle of the
elbow in the direction of the line between the
acromion and the hand. For PD, the electrodes
were centered in the area about two finger breaths
behind the angle of the acromion in the direction
of the line between the acromion and the little
finger. Reference electrodes were properly placed
on the bony process of the elbow. After electrodes
fixation, participants' skin was marked with a
special pen to avoid mistakes in electrode
positioning between the fourth and fifth sessions.
Electromyography (Miotool 400, Miotec®, Porto
Alegre, Brazil) with four input channels, 14 bits
resolution, and the acquisition rate per channel of
2000 samples/s and an SDS-500 sensor with a
maximum gain of 1000 times were used to collect
electromyographic signals. The common-mode
rejection ratio was 106 dB and impedance
between each electrode pair was < 1012 Ω. All
electromyograph channels were properly
calibrated prior to data collection. The concentric
and eccentric phases were evaluated during a set
of 12 repetitions. Then the first two and last two
repetitions were excluded on the signal (RAW) to
avoid mechanical failure or neuromuscular
fatigue. The remaining eight repetitions of the
sEMG signal were filtered with a fourth-order
Butterworth bandpass filter with zero phase delay
and cut-off frequency between 20 and 500 Hz, and
the amplitude was calculated using the root mean
square (RMS) with a 100 ms moving window.
Specialized Miograph 2.0 Alpha 9 Build 5
software (Miotec® Equipamentos Biomédicos
Ltda, Porto Alegre, Brazil) was used for data
analysis and processing. The sEMG RMS was
normalized by the MVIC peak previously
obtained for each muscle portion of the deltoid
muscle. Finally, normalized sEMG RMS signal
(RMSn) means were used for subsequent analysis.
Procedures
Participants were instructed to abstain
from strenuous exercise and to avoid alcohol and
caffeine for 48 hours before the evaluations. Soon

8 Different shoulder exercises affect the activation of deltoid portions in resistance-trained individuals
Journal of Human Kinetics - volume 75/2020 http://www.johk.pl
after the anthropometric assessments, at the
beginning of the experimental session, all
participants performed 20 repetitions of each
exercise as a warm-up, with loads adjusted to 30%
1RM. After a three-minute rest interval, they
executed one set of 12 repetitions of each
proposed exercise with loads adjusted to 60%
1RM (Muyor et al., 2019) to collect muscle activity
(sEMG) data. During all exercises, movement
speed (cadence) was maintained at (2/0/1/0), i.e. a
2-s eccentric phase, 0-s i.e., no break in the
transition phase, a 1-s concentric phase, and 0-s
i.e., no rest before the next repetition (Schoenfeld
et al., 2015; Wilk et al., 2018) using a digital
metronome (DM90, Seiko®, Tokyo, Japan).
Exercises were performed as follows: for the BP
and DF exercises, participants remained supine in
the specific bank. During the SP and LR,
participants remained seated, with their backs
resting on a specific bench set at 90°, and their feet
flat on the floor. In the initial BP and DF
positioning, the shoulders were horizontally
abducted according to each participant's footprint,
using 165% and 100% of the bi-acromial distance,
respectively, with the elbows extended. In both,
participants were instructed to lower the barbell
and dumbbells until the shoulders reached a
horizontal abduction of approximately 45º below
the trunk line (Van den Tillaar and Ettema, 2009).
For the SP exercise, participants used a barbell
and started with the shoulders abducted at 180º
(from the anatomical position) and the elbows
extended. Thus, they were instructed to perform
shoulder adduction along with an elbow flexion
in eccentric action until approximately 135°
shoulder adduction was reached. Finally, for the
LR exercise, participants were instructed to
perform 90º of shoulder abduction from the
anatomical position. A 15-min recovery interval
was used between exercises. For the exercises, the
following materials and equipment were used: (a)
a 1.30-m and 10 kg barbell was used for the BP, (b)
two 40-cm and 2 kg dumbbells were used for the
DF and LR, (c) a 1.10-m and 8 kg barbell was used
for the SP. An adjustable bench and bumper
plates were used for all exercises. All equipment
used was produced by Physicus® (Auriflama,
Brazil).
Maximum voluntary isometric contraction (MVIC)
Fifteen minutes after the main session,
participants performed MVIC in all proposed
exercises (Golas et al., 2017a, 2017b). For the
MVIC in the bench press, dumbbell fly, shoulder
press, and lateral raise, a barbell and/or apparatus
for performing the lateral raise and fly on the
pulley, a specific bank with adjustable inclination,
and chains that used to secure the barbell to the
ground at the specific angles of each exercise,
were used. To measure the MVIC, the participant
held the barbell or apparatus in the following
positions: (a) BP - the barbell grip width was 165%
of the biacromial distance with 90° horizontal
shoulder abduction and approximately 90° elbow
flexion; (b) DF - 90° horizontal abduction and
approximately 90° elbow flexion (the reference
position for both abovementioned exercises was
complete horizontal shoulder adduction with the
trunk in dorsal decubitus); (c) SP - 90° shoulder
abduction (in conjunction with external shoulder
rotation) and 110° elbow flexion; and (d) LR - 90°
shoulder abduction. All positions were defined
using a goniometer (Konex®, São Paulo, Brazil).
Participants performed three sets of 5-s
contractions with a recovery time of 30 s between
sets and exercises. The value attributed to
normalization was the highest value found during
the MVIC for each of the muscles analyzed among
the four exercises evaluated (Castelein et al.,
2016).
Statistical Analysis
Shapiro-Wilk and Levene’s tests were
used for analyses of variance normality and
homogeneity, and data were reported using mean
and standard deviation. If the assumptions of
normality and homogeneity of variance were
fulfilled, a one-way ANOVA with repeated
measures and a Bonferroni’s posthoc were used to
compare AD, MD, and PD muscle activity (RMSn)
among BP, DF, SP, and LR exercises. The effect
size was calculated according to the Cohen’s test
(d) using the following formula: d = (group 1 mean
- group 2 mean)/standard deviation. Effect size (d)
was evaluated using the following criteria: <0.35
trivial; 0.35-0.80 small; 0.80-1.50 moderate; and
>1.5 large, according to the classification of
recreationally trained individuals proposed by
Rhea (2004). To verify reproducibility for the 1RM
test-retest the intraclass correlation coefficient
(ICC) was applied. A significance level (α) of 5%
was used as statistical evidence and SPSS
software (20.0, IBM, Armonk, USA) was used for
statistical analysis.

by Yuri A. C. Campos et al. 9
© Editorial Committee of Journal of Human Kinetics
Results
ICCs for the 1RM test-retest were between
0.930 and 0.950. For the anterior deltoid muscle
activity (RMSn) significant differences were
observed between the SP and DF (p = 0.001, d =
1.41 [moderate], Δ% = 14.5); the SP and BP (p =
0.002, d = 1.14 [moderate], Δ% = 11.9); and the SP
and LR (p = 0.003, d = 1.25 [moderate], Δ% = 12.1).
However, no significant difference was found
between the BP and DF (p = 0.091, d = 0.31 [trivial],
Δ% = 2.6); the BP and LR (p = 0.738, d = 0.03
[trivial], Δ% = 0.2); and the LR and DF (p = 0.698, d
= 0.33 [trivial], Δ% = 2.4) (Figure 1).
For the medial deltoid muscle activation
(RMSn) significant differences were observed
between the LR and DF (p = 0.001, d = 3.48 [large],
Δ% = 26.9); the LR and BP (p = 0.001, d = 3.23
[large], Δ% = 25.3); the SP and DF (p = 0.001, d =
2.90 [large], Δ% = 24.5); and the SP and DF (p =
0.001, d = 2.68 [large], Δ% = 22.9). However, no
significant difference was found between the LR
and SP (p = 0.596, d = 0.22 [trivial], Δ% = 1.6) and
the BP and DF (p = 0.484, d = 0.79 [small], Δ% =
2.4) (Figure 2).
For the posterior deltoid muscle activity
(RMSn) significant differences were observed
between the LR and DF (p = 0.001, d = 3.95 [large],
Δ% = 21.5); the LR and BP (p = 0.001, d = 3.67
[large], Δ% = 20.5); the LR and SP (p = 0.014, d =
2.12 [large], Δ% = 12.6); the SP and DF (p = 0.001, d
= 3.43 [large], Δ% = 8.9); and the SP and BP (p =
0.001, d = 2.73 [large], Δ% = 7.9). However, no
significant difference was found between the BP
and DF (p = 0.667, d = 0.59 [small], Δ% = 1.0)
(Figure 3).
Figure 1. Mean and standard deviation of the anterior deltoid muscle activity (RMSn)
for each exercise: the bench press (BP), dumbbell fly (DF), shoulder press (SP),
and lateral raise (LR) exercises.
a, b, cp ≤ 0.05, significant difference between the SP and DF, SP and BP and, SP and LR.

10 Different shoulder exercises affect the activation of deltoid portions in resistance-trained individuals
Journal of Human Kinetics - volume 75/2020 http://www.johk.pl
Figure 2. Mean and standard deviation of the medial deltoid muscle activity (RMSn) for each
exercise: bench press (BP), dumbbell fly (DF), shoulder press (SP), and lateral raise (LR) exercises.
a, b, c ,dp ≤ 0.05, significant difference between the LR and DF, LR and BP, SP and DF,
and SP and BP.
Figure 3. Mean and standard deviation of the posterior deltoid muscle activity (RMSn) for each
exercise: the bench press (BP), dumbbell fly (DF), shoulder press (SP), and lateral raise (LR)
exercises.
a, b, c, d, ep ≤ 0.05, significant difference between the LR and DF, LR and BP, LR and SP, SP and DF,
and SP and BP.

by Yuri A. C. Campos et al. 11
© Editorial Committee of Journal of Human Kinetics
Discussion
The objective of this study was to
compare the muscle activity of different deltoid
portions (anterior [AD], medial [MD], and
posterior [PD] for the BP, DF, SP, and LR
exercises. The main finding of the present study
indicated that the shoulder press (SP) and lateral
raise (LR) exercises presented a higher muscle
activity for AD, MD, and PD when compared to
the bench press (BP) and dumbbell fly (DF)
exercises.
Exercises such as the BP and DF are
frequently included in ST routines due to their
large AD activation (Muyor et al., 2019; Welsch et
al., 2005). Welsh et al. (2005) and Júnior et al.
(2007) compared AD muscle activity response in
the BP and DF exercises; however, they found no
difference between them. Due to the magnitude
and similarity of the AD muscle response when
compared to the pectoralis major muscle, Júnior et
al. (2007) suggested that specific exercises such as
the SP are not necessary for the AD. In contrast,
for the AD the present study showed higher
muscle activation in the SP (33.3% MVIC), BP
(21.4% MVIC), LR (21.2% MVIC), and DF (18.8%
MVIC). In a similar study, Botton et al. (2013)
found no significant difference in AD muscle
activation between the Smith machine shoulder
press, bench press, and peck deck exercises using
10RM workloads. However, the present study
showed a significant difference between the SP
and BP, and between the SP and DF (Figure 1),
which might be partially explained by the use of
free weights instead of a machine. Similarly,
sEMG-based studies have shown greater muscle
activation in free weight exercises when
compared to machines in the AD muscle (McCaw
and Friday, 1994; Schick et al., 2010; Schwanbeck
et al., 2009). Thus, the SP can also be an effective
exercise for the activation of the AD based on the
movement of the shoulder (abduction associated
with external rotation of the glenohumeral joint)
(Liu et al., 1997), favoring the AD and MD
activation, as shown in Figures 1 and 3.
As for the MD, the present study showed
higher muscle activation in the LR (30.3% MVIC),
SP (27.9% MVIC), BP (5% MVIC), and DF (3.4%
MVIC). Based on the results of the present study,
no significant difference between LR and SP
exercises was observed. However, there was a
significant difference between these exercises
when compared to the BP and DF (Figure 2).
Although this portion of the deltoid is considered
the main glenohumeral abductor (Don Lehmkuhl
and Smith, 1983; Hall, 1999) a similar muscle
recruitment between the SP and LR may be
related to high indices of muscular synergism
between 50 and 90 degrees (Liu et al., 1997)
reaching its maximum peak at 100 degrees of
glenohumeral abduction (Wickham et al., 2010).
Contrary to the results of the present study,
Botton et al. (2013) reported higher MD muscle
activity during cable/free weight LR compared to
SP executed on a Smith machine. This difference
may be related to the type of equipment used
(free weight vs. machine) where greater activation
is observed in primary motor and stabilizer
muscles (McCaw and Friday, 1994; Schwanbeck et
al., 2009). Thus, the use of the Smith machine in
the SP (Botton et al., 2013) may have affected
muscle activation by promoting greater stability
during exercise execution.
PD muscle showed greater activation in
the LR (24% MVIC), SP (11.4% MVIC), BP (3.5%
MVIC), and DF (2.5% MVIC). The results of our
study showed a significant difference for the LR
compared to the BP, DF, and SP. Additionally, a
significant difference was found for the SP
compared to the BP, and DF (Figure 3). The
increased PD muscle recruitment during the LR
observed in the present study might be explained
by its secondary and stabilizing function during
glenohumeral joint abduction (Botton et al., 2013).
Some studies suggested the use of more specific
exercises, such as reverse the pec deck fly for a
greater PD participation (Botton et al., 2013;
Franke et al., 2015), but this exercise was not
analyzed in the present study. In this sense,
Botton et al. (2013) reported higher PD muscle
activity during the reverse pec deck exercise
compared to the LR.
A limitation of the study is the difficulty
in comparing the workload (60% 1RM) used in
the present investigation to collect the sEMG
signal with workloads used in other studies
(Botton et al., 2013; Franke et al., 2015; McCaw
and Friday, 1994; Schick et al., 2010; Schwanbeck
et al., 2009). Although classic (McCaw and Friday,
1994) and current (Muyor et al., 2019) studies
have used 60% 1RM workloads for sEMG signal
collection, these results should be interpreted with
caution as exercise intensity may modify the

12 Different shoulder exercises affect the activation of deltoid portions in resistance-trained individuals
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pattern of muscle recruitment (McCaw and
Friday, 1994; Schick et al., 2010; Stastny et al.,
2017). Besides, limitations regarding the use of
sEMG signals during dynamic contractions
(Stastny et al., 2017) and their comparisons
between different exercises (Vigotsky et al., 2018)
should be considered. Moreover, not evaluating
the percentage of body fat in the specific regions
where the surface electrodes were placed, which
could affect electromyographic signal levels due
to its low-pass filter characteristic, is another
limitation. To reduce this problem,
electromyographic signals were normalized by
positioning electrodes on the same collection sites.
In addition, there is a possibility that the data
normalization process adopted in our study did
not allow reaching the maximum contraction
value for all studied muscles (Golas et al., 2018).
Complementary exercises for the anterior
portion of the deltoid, such as the shoulder press,
should be included in the ST routines to offer
greater variability to the training program and to
present greater muscle activation when compared
to priority exercises such as the bench press and
dumbbell fly. However, the inclusion of many sets
of complementary exercises for this muscle
portion should be viewed with caution, as it is
often requested during priority exercises such as
the bench press and dumbbell fly. Also,
complementary exercises such as the lateral raise
and shoulder press should be included in ST
routines, because they have greater muscle
activation in the medial portion of the deltoid
when compared to priority exercises such as the
bench press and dumbbell fly. Additionally, the
inclusion of these exercises in the ST programs
would be important to maintain muscle activation
of the medial deltoid portion, which has an
important stabilizing function of the
glenohumeral joint in priority exercises such as
the bench press and dumbbell fly.
Conclusion
Finally, the use of SP exercise increased
AD muscle activity when compared to the BP and
DF. As for the MD, both the SP and LR exercises
resulted in greater muscle activity, although the
LR resulted in slightly superior muscle activity
when compared to the SP. As for the PD, LR
exercise presented higher muscle activity
compared to the SP. Both the BP and DF resulted
in low muscle recruitment in medial and posterior
portions of the deltoid, possibly due to their
stabilizing function in these exercises. In addition,
further studies should include an analysis of the
external kinematics structure to verify all the
characteristics of the movements involved in the
exercises evaluated (Król and Golas, 2017).
Acknowledgements
We would like to thank all the participants who selflessly participated in the study.
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Corresponding author:
Yuri de Almeida Costa Campos.
Department of Physical Education, University of Lavras. Zip Code: 37200-000, PO BOX 3037, Lavras, Brazil.
Phone Number: +55(35) 3829-5132.
Email: reiclauy@hotmail.com