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©Journal of Sports Science and Medicine (2009) 8, 24-29
http://www.jssm.org
Received: 14 April 2008 / Accepted: 30 October 2008 / Published (online): 01 March 2009
Effect of the shoulder position on the biceps brachii EMG in different dumbbell
curls
Liliam F. Oliveira 1, Thiago T. Matta 1, Daniel S. Alves 1, Marco A.C. Garcia 1 and Taian M.M.
Vieira 1,2
1 Biomechanics Laboratory, Bioscience Department, Physical Education and Sports School, Federal University of Rio
de Janeiro, Rio de Janeiro, Brazil. 2 Laboratory for Engineering of the Neuromuscular System, Polytechnic of Turin,
Turin, Italy.
Abstract
Incline Dumbbell Curl (IDC) and Dumbbell Preacher Curl
(DPC) are two variations of the standard Dumbbell Biceps Curl
(DBC), generally applied to optimize biceps brachii contribution
for elbow flexion by fixing shoulder at a specific angle. The aim
of this study is to identify changes in the neuromuscular activity
of biceps brachii long head for IDC, DPC and DBC exercises,
by taking into account the changes in load moment arm and
muscle length elicited by each dumbbell curl protocol. A single
cycle (concentric-eccentric) of DBC, IDC and DPC, was ap-
plied to 22 subjects using a submaximal load of 40% estimated
from an isometric MVC test. The neuromuscular activity of
biceps brachii long head was compared by further partitioning
each contraction into three phases, according to individual
elbow joint range of motion. Although all protocols elicited a
considerable level of activation of the biceps brachii muscle (at
least 50% of maximum RMS), the contribution of this muscle
for elbow flexion/extension varied among exercises. The sub-
maximal elbow flexion (concentric) elicited neuro muscular
activity up to 95% of the maximum RMS value during the final
phase of IDC and DBC and 80% for DPC at the beginning of the
movement. All exercises showed significant less muscle activity
for the elbow extension (eccentric). The Incline Dumbbell Curl
and the classical Dumbbell Biceps Curl resulted in similar pat-
terns of biceps brachii activation for the whole range of motion,
whereas Dumbbell Preacher Curl elicited high muscle activation
only for a short range of elbow joint angle.
Key words: Biceps curl, EMG, biceps brachii.
Introduction
Resistance training exercises are mostly applied to over-
load the musculoskeletal system, leading to the acceler-
ated enhancement of muscle strength (Fleck and Kraemer,
1997). Equipments like dumbbells, barbells and cable
machines are often used in conditioning and strengthening
programs (Biscarini et al., 2005). However, the use of free
loads may be preferred in some occasions, since it does
not constrain the movement and different exercises can be
performed, eliciting the contribution of specific muscles
(Cotterman et al., 2005). Furthermore, free load-based
exercises mimics body movements in natural situations
and elicits joint and segments stabilization (Cotterman et
al., 2005). Many people are addicted to the benefits pro-
vided by training programs based on the use of free loads,
from experienced athletes to children and elderly
(Faigenbaum et al., 2003; Falk and Tenenbaum, 1996;
Fleck and Kraemer, 1997).
The weight of dumbbells or barbells is constantly
oriented in a vertical direction, so that the load torque
changes with joint angle and the peak of the load torque
changes for different body positions (i.e. horizontal or
inclined benches). According to a biomechanical model
for simulating Dumbbell Biceps Curl (DBC) exercise
(Biscarini et al., 2005), the force produced by elbow flex-
ors in quasi-static exercises increases with the load mo-
ment arm, which highly affects the direction and magni-
tude of joint internal forces. Moreover, the classic length-
tension relationship is critical for muscle force produc-
tion, especially during low velocity/high intensity exer-
cises (Lieber, 2002). Although such relationship holds for
isometric contractions, it can still be used to predict mus-
cle force from joint angle during low velocity contrac-
tions.
Incline Dumbbell Curl (IDC) and Dumbbell
Preacher Curl (DPC) are two variations of the standard
DBC, generally applied to optimize biceps brachii contri-
bution for elbow flexion by fixing shoulder angle at a
specific value. These different protocols for dumbbell curl
may impose different demands to the neuromuscular
system, resulting in different solutions for the load shar-
ing between elbow flexors.
The aim of this study is to identify changes in the
neuromuscular activity of biceps brachii long head for
IDC, DPC and DBC exercises, by taking into account the
changes in load moment arm and muscle length elicited
by each dumbbell curl protocol. In the IDC protocol the
biceps brachii long head is initially lengthened, whereas
in DPC the shoulder is flexed and, thus, the biceps long
head is initially shortened. Therefore, we expect to ob-
serve greater neuromuscular activity for the beginning of
IDC and DPC exercises than for DBC, mainly due to
different postural demands.
Methods
Subject
A group of 22 male subjects (23.0 ± 3.5 years, 79.6 ± 11.6
kg and 1.8 ± 0.1 m) participated of the study after provid-
ing written consent. All participants were right handed,
did not relate any history of osteomyoarticular injuries
and were engaged in strength programs for at least one
year. This experiment was approved by the University
Ethical Committee.
Research article
Oliveira et al.
25
Figure 1. Schematics of the experimental setup. a) Body orientation for each dumbbell curl protocol and for the MVC trial
including electrodes placement; b) Time sequence of each test trial (randomized) and rest periods; c) Partition of the dumb-
bell curls cycle into concentric and eccentric contractions and further division into three phases according to elbow joint
angle.
Experimental setup
A single cycle (concentric-eccentric) of DBC and its
variations, IDC and DPC, was applied to each subject
using a submaximal load of 40%, estimated from a single
6s isometric MVC test (Kamen, 2004). Although in
practical situations most lifters may choose a different
load for each exercise, the use of a fixed load was
compulsory to compare the neuromuscular demand
elicited between DPC, IDC and DBC protocols. The 40%
MVC load was chosen on empirical basis, since with this
load all subjects could perform one or two cycles of
dumbbell curl with slow speed. Dumbbell curls were
randomly applied with two minutes (2 min) interval, after
the three minutes (3 min) rest period following the MVC
trial. A complete schematic of trials sequence is shown in
Figure 1b, whereas body orientation for each trial is out-
lined in Figure 1a and is defined as: MVC – seated posi-
tion with right elbow at 90° and forearm supinated; IDC –
seated with trunk in vertical position and right shoulder
flexed at 50°; IDC – seated with 50° of trunk hyperexten-
sion and the right arm hanging freely; DBC – standing
with a comfortable support base and the arms alongside
the body.
The display of force output was provided during
MVC trials and all subjects were allowed to track it be-
fore starting the test. Each subject performed the whole
cycle of dumbbell curls at his preferred speed, thus repro-
ducing the movement observed in practical situations.
EMG signal of biceps brachii.
26
Although the use of a metronome is important for control-
ling movement speed, it likely provides biased compari-
sons between subjects, since individual strategies may
emerge to compensate the fixed pace imposed by an
external stimulus.
Single differential surface EMG (gain = 1k, CMRR
= 106 dB, and bandwidth of 10-500 Hz) and elbow joint
angle were synchronously sampled at 1 kHz by a 16 bits
A/D converter (±10V dynamic range). Elbow joint angle
was estimated from changes in the direction of the uniax-
ial accelerometer (0-200 Hz bandwidth and 315
mVg-1 sensitivity) with respect to gravity acceleration
vector, assuming that all subjects flexed and extended the
elbow with constant velocity. The accelerometer was
fixed to the subject’s wrist with a tape and with its normal
axis orientated vertically. Two circular (20 mm diameter,
20 mm interelectrodes distance) Ag-AgCl pre-gelled
electrodes were positioned on biceps brachii long head
according to SENIAM recommendations, after skin
preparation (Freriks et al., 1999). A load cell (200 Kgf
fullscale) was used to measure the peak force during the
MVC trial.
Data analysis
The neuromuscular activity of biceps brachii long head
was compared by dividing a curl cycle into concentric and
eccentric contractions, and by further partitioning each
contraction into three phases, according to individual
elbow joint range of motion (Figure 1c; i.e. phase 1 = 0 –
33%; phase 2 = 34 – 67% and phase 3 = 68 – 100% of
ROM). The sEMG root mean square (RMS) was esti-
mated for each phase and contraction according to the
following equation:
∑
=
+−
=
pe
psn
pc nx
pspe
RMS ][
1
12
, (1)
where x[n] is the raw sEMG, c and p stands for contraction type
(concentric or eccentric) and contraction phase (1, 2 or 3), re-
spectively, and n is the sample number ranging from phase start
(ps) to phase end (pe), for each one within each contraction
type. To avoid the effect of geometrical and physiological factor
on sEMG data, the RMS amplitude was normalized for the
maximum RMS value estimated from the MVC trial, by using
equation 1 with n ranging from 1000 (1s) to 5000 (5s).
Statistical analysis
A multifactorial ANOVA design 3x2x3 (exercises x con-
traction types x contraction phases) was applied to com-
pare changes in RMS amplitude according to different
contraction types and phases, within and between the
dumbbell curl protocols. Significant changes in the size or
duration of the elbow flexion/extension cycles between
exercises were assessed by applying the one-way
ANOVA design. The Tukey Post Hoc test was applied to
identify significant difference between means with p
value set to 0.05 (Statistica 6.0 - StatSoft, Inc.).
Results
The maximal force achieved during the MVC trial was
34.4 ± 5.0 Kg. The load corresponding to 40% of the
MVC score, which was applied in this study for the
dumbbell curl exercises, represented about 43.6 % of
individual body mass.
Figure 2. Mean and SD of RMS values for all phases of
concentric contractions, divided according to each exercise
(DBC, IDC and DPC). * p < 0.05 between exercises, † p < 0.05
between phases.
When comparing RMS values for the concentric
contractions between IDC and DBC exercises, no statisti-
cal differences were observed, even when considering
each phase independently (Figure 2). On the other hand,
the sEMG amplitude increased for both IDC and DBC
protocols from the beginning to the end of concentric
contraction, reaching statistical significance (p <0.05) at
phase 3. Interestingly, for DPC protocol the RMS mean
values showed an opposite trend throughout the three
phases, decreasing from phase 1 to phase 3 (p < 0.05). In
addition, statistical difference was observed between DPC
and the other two exercises. RMS amplitude was higher
and lower for DPC at phase 1 and 3, respectively, when
compared to RMS values for IDC and DBC, suggesting
that shoulder flexion angle affects biceps brachii activa-
tion.
Figure 3. Mean and SD (whiskers) of RMS values for all
phases of eccentric contractions, divided according to each
exercise (DBC, IDC and DPC). * p < 0.05 between exercises, † p <
0.05 between phases.
Oliveira et al.
27
Figure 3 shows the RMS values for all phases of
the eccentric contraction. Even for the eccentric contrac-
tion, IDC and DBC presented no differences for the
muscle activation between the three phases. The RMS
value for the initial phase of DPC was significantly lower
when compared to that measured for DBC and IDC.
Table 1 shows the amplitude and time duration
(mean values and standard deviation) of both concentric
and eccentric contractions. A significant increase of curl
duration was observed for the eccentric contraction, inde-
pendent of the exercise. IDC protocol was performed
within a statistical smaller ROM of the elbow joint, with
respect to the other two dumbbell curl exercises.
Table 1. Mean (SD) of duration and range of motion (ROM)
of the concentric end eccentric phases of each exercise.
Exercise Duration (sec) ROM (degrees)
Concentric Eccentric
DBC 3.59 (.91) * 4.05 (.93) 131.9 (18.3)
IDC 3.81 (1.13)* 4.67 (1.57) 134.3 (19.5)
DPC 4.47 (1.60)† 4.65 (1.68) 115.5 (11.2) *
* p < 0.05 between phases, † p < 0.05 between exercises.
Discussion
By dividing elbow flexion and extension in three different
phases, according to joint ROM, we expected to observe
changes in modulation of neuromuscular activity for the
three dumbbell curl protocols. Dumbbell Biceps Curl and
Inclined Dumbbell Curl elicited similar pattern of increas-
ing and decreasing muscle activation along the three
phases, for the concentric and eccentric contractions re-
spectively, whereas an opposite trend of sEMG RMS
amplitude was observed for the Dumbbell Preacher Curl.
Concerning the choice of an appropriate load rep-
resenting 40% of individual maximum, the mean MVC
score observed in this study (43.6 ± 7.7% of individual
body mass) was far higher than that reported by Kasprisin
and Grabiner (2000) (30.6 ± 4.7% for 10 healthy adults).
This difference likely results from the elbow joint angle
considered for the MVC trial, since at 90° of elbow flex-
ion the biceps brachii fibers may be closer to optimal
length for isometric force production (Hay, 1991; Inman
et al., 1982; Langenderfer et al., 2005; Oliveira, 2004),
with respect to the 75° elbow flexion considered by
Kasprisin and Grabiner (2000).
The submaximal elbow flexion elicited neuromus-
cular activity up to 95% of the maximum RMS value
during the phase 3 of the concentric contraction for the
IDC and DBC protocols. This relatively high neuromus-
cular activity suggests that the 40% MVC load was suffi-
cient to elicit high modulation of sEMG amplitude.
The mean duration and size of either concentric or
eccentric contractions ranged from 3.59 ± 0.91 to 4.65 ±
1.68 s and from 115.50 ± 11.20 to 131.91 ± 18.25°, re-
spectively, therefore characterizing a quasi-isometric
movement (Siff, 2004). Since force production is criti-
cally affected by muscle tension-length relationship, only
for movements performed at low velocities (Lieber,
2002), the neuromuscular activity for all protocols was
expected to be highly dependent on muscle length.
Furthermore, Prilutsky (2004) observed a similar level of
neuromuscular activity of biceps brachii muscle for
eccentric contractions with constant speed, corroborating
the almost constant RMS values (Figure 3) observed for
the eccentric contractions performed in this study. This
evidence supports the effect of muscle length on the
muscle force production, since dumbbell curls may have
been performed with minimal changes at movement
velocity.
Although subjects were instructed to start from
full elbow extension, their movements started from a
slightly flexed position (around 20°), suggesting a com-
pensation mechanism to optimize the contribution of
elbow flexors and passive tension. Some studies reported
similar strategy for starting the movement, with elbow
joint angle ranging from 15° to 48° (Hansen et al., 2003;
Keeler et al., 2001; Uchiyama et al., 1998).
During isometric contractions, the increase of
muscle force heavily relies on both motor unit firing rate
and recruitment, according to the size principle (Henne-
man, 1985). However, the use of these strategies seems to
be reweighted in a different way during dynamic contrac-
tion, with the recruitment of additional motor units play-
ing a critical role in muscle force production (Sbriccoli et
al. 2003; Søgaard et al., 1998). Such changes in motor
unit recruitment pattern, in addition to different load shar-
ing strategies, may have contributed to the high variability
of RMS values between subjects (coefficient of variation
ranged from 31 to 69 %, for all phases and contractions).
Regarding the changes in sEMG amplitude for dif-
ferent dumbbell curl protocols, it was expected an in-
crease of neuromuscular activity during IDC, especially
when elbow joint was close to full extension. The shoul-
der hyperextension, elicited by the IDC protocol, stretches
the long head of biceps brachii muscle beyond its optimal
length, leading to an inefficient actin-myosin coupling.
On the other hand, the similar RMS values between IDC
and DBC (Figure 2) indicates an increased contribution of
other elbow flexors, besides the contribution of passive
tension from muscle and soft tissues, at the beginning of
concentric and at the end of eccentric contraction. The
low values of sEMG amplitude observed for the begin-
ning of concentric contractions, independent of the dumb-
bell curl protocol, may be explained by the reduced load
moment arm and/or the right shift of muscle length value
with respect to the muscle tension-length relationship
(Falk and Tenenbaum, 1996). Although at about 90o of
elbow flexion the moment arm of biceps brachii is close
to its highest value (Murray et al., 1995; 2002), such posi-
tion was not sufficient to compensate the increment of the
resistance torque, which is maximal for this joint angle,
and thus resulting in high RMS values.
The shoulder flexed position in the DPC exercise
elicited a particular pattern of muscle activation, which
significantly decreased and increased from the initial to
the final phases of the concentric and eccentric contrac-
tions, respectively. Although the early phase of the con-
centric contraction elicited high muscle activity to over-
come the load torque, the neuromuscular demand de-
creased rapidly for the biceps brachii throughout the mid-
dle and late phases. The main reason for this pattern of
activation is likely linked to the initial moment arm of the
load, resulting from the shoulder flexion at the starting
EMG signal of biceps brachii.
28
position (phase 1), and the inefficient length of elbow
flexors. As the elbow flexes the load torque reduces, until
the hand crosses elbow line, thus shifting the force pro-
duction from elbow flexors to extensors (phase 3). There-
fore, DPC exercise seems to have elicited high myoelec-
tric activity only within a short range of elbow joint angle
(i.e. the beginning of concentric and ending of eccentric
contractions), which may be disadvantageous for training
programs focused on the improvement biceps brachii
ability to produce force.
The use of a couple of electrodes could have been
a limiting factor in this study. The shift of the innervation
zone (IZ), inherent to dynamic contractions, attenuates or
enlarges sEMG amplitude as the IZ gets closer or farer
from the electrodes (Farina et al., 2001). However, the IZ
effect on the RMS values estimated in this study was
minimized by positioning the electrodes on the location
recommended by SENIAM, since this location is close to
half way between the biceps brachii IZ and the distal
tendon (Merletti and Parker, 2004).
Conclusion
Although all protocols elicited a considerable level of
activation of the biceps brachii muscle (at least 50% of
maximum RMS), the contribution of this muscle for el-
bow flexion depended of the dumbbell curl protocol. For
the Dumbbell Preacher Curl cycle, the activation of bi-
ceps brachii long head was maximal, only for elbow joint
angles close to full extension, and the elbow joint range of
motion was shorter. The Incline Dumbbell Curl and the
Dumbbell Biceps Curl resulted in a considerable neuro-
muscular effort throughout the whole elbow range of
motion and, thus, may be preferable for the improvement
of biceps brachii force in training programs.
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Key points
• The Incline Dumbbell Curl and the Dumbbell Bi-
ceps Curl resulted in a considerable neuromuscular
effort throughout the whole elbow range of motion.
• The Incline Dumbbell Curl and the Dumbbell Bi-
ceps Curl may be preferable for the improvement of
biceps brachii force in training programs.
Oliveira et al.
29
AUTHORS BIOGRAPHY
Liliam F. DE OLIVEIRA
Employment
Biomechanics Laboratory, Bioscience De-
partment, Physical Education and Sports
School, Federal University of Rio de Janeiro,
Rio de Janeiro, Brazil.
Degree
D.Sc. in Bioengineering
Research interests
Biomechanics, muscle modelling, EMG
E-mail: liliam@eefd.ufrj.br
Thiago T. DA MATTA
Employment
Biomechanics Laboratory, Bioscience Department, Physical
Education and Sports School, Federal University of Rio de
Janeiro, Rio de Janeiro, Brazil.
Degree
Ms.C. student in Biomechanics
Research interests
Biomechanics.
E-mail: ttmatta@yahoo.com.br
Daniel DE SOUZA ALVES
Employment
Biomechanics Laboratory, Bioscience Department, Physical
Education and Sports School, Federal University of Rio de
Janeiro, Rio de Janeiro, Brazil.
Degree
M.Sc. student in Biomedical Engineering
Research interests
Biomechanics.
E-mail: danielves@ig.com.br
Marco A.C. GARCIA
Employment
Biomechanics Laboratory, Bioscience De-
partment, Physical Education and Sports
School, Federal University of Rio de Janeiro,
Rio de Janeiro, Brazil.
Degree
D.Sc. student in Biomedical Engineering
Research interests
EMG, mechanomyography, spasticity.
E-mail: marcoacg@unisys.com.br
Taian M.M. VIEIRA
Employment
Laboratory for Engineering of the Neuro-
muscular System, Polytechnic of Turin,
Turin, Italy
Degree
Ph.D. candidate in Biomedical Engineering
Research interests
Electromyography, postural balance
E-mail: taian.vierira@polito.it
Liliam Fernandes De Oliveira
Rua Lauro Muller 96 apt 105, RJ, Brasil. CEP 22290-160
