BIOSCIENCE V.22 N.2 2006


Original Article

95

ELECTROMYOGRAPHIC STUDY OF THE Rectus femoris AND Biceps femoris
(LONG HEAD) MUSCLES DURING BILATERAL ISOTONIC CONTRACTION IN
A 45o LEG PRESS APPARATUS

ESTUDO ELETROMIOGRÁFICO DOS MÚSCULOS Rectus femoris E Biceps femoris
(CABEÇA LONGA) DURANTE CONTRAÇÃO ISOTÔNICA NO APARELHO LEG PRESS 45º

Fernando NAZÁRIO-DE-REZENDE1; Gilmar da Cunha SOUSA2; Miguel Antônio FACURY NETO3; Roberto
BERNARDINO JÚNIOR4; Daniela Cristina de Oliveira SILVA5; Eduardo Gaspareto HADDAD6; Alexandre
GONÇALVES7; Guilherme Gulart de AGOSTINE8; Lázaro Antônio dos SANTOS9

ABSTRACT: The aim of this study was to compare the bilateral electric activity of the rectus femoris (RF)
and biceps femoris long head (BF) muscles during flexion and extension isotonic movements of the thigh and leg. Six
men and six women accomplished all movements in 45° Leg Press apparatus with 30% and 60% of the maximum
voluntary load (MVL). Electromyographic signs were captured using surface electrodes, recorded in a computerized
electromyograph and analyzed in a system of data acquisition (Alc-EMG). The results demonstrated that the RF
muscle showed greater electric activity than BF in both loads (30% and 60% MVL) and sides, regardless the sex. It
can be concluded that in spite of the RF and BF muscles are in opposite ends of the hip and knee joints and are
mentioned traditionally as antagonistic muscles, both muscles seem to act with synergism between themselves with
predominance of the activation of the RF muscle on the BF muscle in both genders and studied loads in leg press 45o
execution. In addition, the electrical activity of these muscles is directly proportional to the load, independently of
the sex.

KEYWORDS: Kinesiologic EMG. Leg Press. Rectus femoris. Biceps femoris.

INTRODUCTION

In the last years, several researchers have
contributed to the study on effects of different types of
force training in man (ALKNER; TESCH; BERG, 2000;
BERTOCHI et al., 1997; ESCAMILLA et al., 2001;
GRYZLO et al., 1994; KOMI et al., 2000; SOUSA et al.,
2000; TASSI et al., 1998; TESCH et al., 1990).

The prescription and periodicity of resisted
exercises for training, rehabilitation and improvement of

the life quality request a solid knowledge with scientific
basis to help in the development of advanced programs
of force training and in the logical development of
successive sessions of training. Therefore, techniques of
measurement and processing of data have been
contributing to the analysis of the human movement,
prescription and periodicity of the resisted exercises.

In this context, electromyography (EMG) has been
introduced to better evaluate and inform about the muscular
behavior as increases or decreases of the electric activity

1 Graduado em Educação Física - Centro Universitário do Triângulo e Professor da Universidade Presidente Antônio Carlos-UNIPAC - Uberlândia, MG.
2 Professor, Doutor, Instituto de Ciências Biomédicas, Universidade Federal de Uberlândia, Uberlândia, MG.
3 Professor, Doutor, Instituto de Ciências Biomédicas, Universidade Federal de Uberlândia, Uberlândia, MG.
4 Professor, Mestre, Instituto de Ciências Biomédicas, Universidade Federal de Uberlândia, Uberlândia, MG.
5 Professora, Mestre, Instituto de Ciências Biomédicas, Universidade Federal de Uberlândia, Uberlândia, MG.
6 Professor Especialista do Instituto de Ciências da Saúde, do Centro Universitário do Triângulo-UNITRI-Uberlândia e da Universidade Presidente Antônio

Carlos-UNIPAC-Araguari, MG.
7 Professor Mestre, Centro Universitário do Triângulo-UNITRI-Uberlândia-MG e do Centro Universitário do Planalto do Araxá-MG.
8 Professor, Mestre, Faculdade de Educação Física, Universidade Federal de Uberlândia, Uberlândia, MG.
9 Graduando em Educação Física, Universidade Federal de Uberlândia-UFU e Técnico Laboratório de Anatomia Humana do Instituto de Ciências Biomédicas-

UFU.
Received: 08/12/05 Accept:09/06/06

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in resisted exercises and identification of the individual
and concomitant muscular actions during the exercises.
Such evaluations can be obtained through the analysis of
the performance degree of agonist and antagonist muscles
during different modalities of exercises (ALKNER;
TESCH; BERG, 2000; GRYZLO et al., 1994; MARKOS,
1979; MURPHEY; BLANTON; BIGGS, et al., 1971;
SODERBERG et al., 1987; SODERBERG; COOK, 1983;
SOUSA et al., 2000; TASSI et al., 1998).

The contraction of agonist muscles can be
associated with the simultaneous contraction of its
antagonists. The co-contraction of antagonists may be
seen as contra-productive, particularly in a force task,
because the opposite torque developed by the antagonists
would decrease the production of net force in the direction
intended in the movement, harming the ability in
completely activating agonists by reciprocal inhibition
(ALKNER; TESCH; BERG, 2000; SALE, 1988). Co-
activation of the antagonist muscles is a phenomenon
often observed when high levels of force are needed,
being sometimes activated at a level closer to a movement
in which they would be agonists. It has also been reported
that practice and training would reduce the amount of
co-contraction, what would allow larger agonists
activation and a greater production of net force in the
direction of the intended movement (ALKNER; TESCH;
BERG, 2000).

Alkner, Tesch and Berg (2000) compared the
electromyographic activity and the isometric force of the
quadriceps femoris and biceps femoris (BF) muscles in
the single-joint knee extension and the multi-joint Leg
Press exercises. Their results demonstrated that the electric
activity of the rectus femoris (RF) muscle was significantly
greater than that of the BF muscle in all loads tested, having
this latter an activity increased linearly with increased
loads. Soderberg et al. (1987) compared the electric activity
of the vastus medialis, gluteus medius, RF and BF muscles
in exercises of lifting the maximally extended leg and
exercises of quadriceps contraction at 0°. They found that
RF was more active than the other muscles in exercises of
lifting the extended leg.

Some considerations on the performance of the
RF muscle in Leg Press exercises have been suggesting
that additional muscles, including hip and ankle
extensors, are brought into action and this might affect
the EMG/force relationship (ALKNER; TESCH; BERG,
2000). Schantz et al. (1989) reported lower levels of force
in the leg extension (Leg Press) when compared to the
knee extension. On the other hand, the results found by
Alkner, Tesch and Berg (2000) provide no evidence of
failure of RF and the entire quadriceps muscle to be

maximally activated because no differences were
observed in the maximal EMG/force relationship between
the single-joint knee extension and multi-joint Leg Press
exercises. In addition, the antagonistic co-contraction of
BF muscle could increase with a progressive increase of
the load to stabilize the knee articulation.

Another important aspect concerning the
prescription and periodicity of resisted exercises is the
different performance between dominant and non-
dominant limbs that can be found during the
accomplishment of bilateral movements of lower limb
(TASSI et al., 1998) in both maximum load and potency
(SIMÃO, 2001; SIMÃO; MONTEIRO; ARAÚJO, 2001;
SIMÃO et al., 2003).

The purpose of this study was to compare the
bilateral simultaneous action of the RF and BF (long
head) muscles during the leg press 45o exercise execution
with different loads and genders.

MATERIAL AND METHODS

Subjects

Twelve volunteers, six men and six women, 20-
25 years old, height of 1.77 ± 0.10 m (men) and 1.62 ±
0.04 m (women), weigh of 73 ± 5 kg (men) and 54 ± 4 kg
(women) were enrolled in a study to analyze the bilateral
electric activity of the RF and BF muscles through the
kinesiologic EMG. All volunteers were students of the
Physical Education Course of the Universidade Federal
de Uberlândia (UFU) and Centro Universitário do
Triângulo (UNITRI), Uberlândia, MG, with training in
resisted exercises for at least three months and with no
history of joint or muscular diseases that could influence
the results.

EMG
Electrodes - In order to capture the electric

activity of the RF and BF muscles, simple differential
active surface electrodes were used with two parallel
metallic bars and common mode rejection ratio (CMRR)
at 93dB, value considered minimum for surface EMG
(PORTNEY, 1993; MATHIASSEN; WINKEL; HÄGG,
1995). A ground electrode of reference common to all
channels was used to eliminate external interferences (DE
LUCA, 1997) and it was positioned on the tuberosity of
the volunteers’ tibia. The first electrode pair was placed
on the medium point of the RF muscle, in the anterior
face of the thigh at 22 ± 2 cm between the patella superior
border and the anterior superior iliac spine, according to
Bertochi et al. (1997) and Leis; Trapani (2000). The



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second electrode pair was placed on the medium point of
the BF muscle through an imaginary line between the
ischial tuberosity and the fibula head at 22 ± 2 cm (LEIS;
TRAPANI, 2000). The medium point of both muscles
was chosen according De Luca (1997), who reports that
the probability of detecting an interference sign can be
considerably reduced placing the electrode on the medium
line of the muscular belly.

The precision of the electrode position on the RF
muscle was confirmed using maneuvers of activation as
described by Leis and Trapani (2000), in which the
volunteer sat down in a stretcher, executed the movement
of leg extension against a resistance accomplished by
the researcher, what evidenced the RF muscle (primary
motor in this movement). For the BF muscle, movements
of leg flexion were carried out with the volunteer in the
ortostatic position, in which it was evidenced the BF
muscle.

Electromyograph – The electromyographic
signals were recorded using a computerized
electromyograph developed in the Biomedical Engineer
Laboratory, Faculdade de Engenharia Elétrica, UFU,
Uberlândia, MG, with the following characteristics:
simultaneous acquisition of up to 8 differential channels
with 10 GΩ input impedance in differential mode; 12
resolution bits; filters set at 20 Hz (low pass) and 1 kHz
(high pass); input range from –10 V to +10 V; ground
electrode common to all channels; adjustable
amplification stage, making possible gains between 100
and 4960 times; galvanic isolation (1.5 kV at 60 Hz)
between the electronic circuit and the stage that is in
contact with the volunteer.

An acquisition system of data (Alc-EMG) was
used to quantify the electromyographic sign, transforming
the action potential in numeric data of RMS (root mean
square), expressed in microvolts (µV), with sample
number of 8.000 and frequency of 2000 Hz, resulting in
a total acquisition time of 4 seconds.

 Leg Press – The exercises were carried out using
an apparatus of muscular activity denominated 45o Leg
Press (Righetto, São Paulo, SP, Brasil) consisting of a
platform measuring 30 cm of width and 45 cm of length,
and gently given by the Laboratory of Muscular Activity
and Human Performance of the Centro Universitário do
Triângulo (UNITRI), Uberlândia, MG. The volunteers
positioned the feet in the center of the platform at a
distance individually obtained by the correspondent
distance between the left and right anterior superior iliac
spines.

General procedures - Before the collection of data
the volunteers received information on the research and

an informed consent was obtained from all participants
of the study according to the Ethical Committee of the
UNITRI. The volunteers were submitted to explanations
and simulations on the adequate posture for the execution
of the exercises, the initial and final position of each
movement, and the speed of execution of the exercises.
A pilot test was accomplished with a short training period
so that the volunteers acquired the kinesiologic sense of
the movement in agreement with the proposed angle.

The volunteers were positioned in the 45o Leg
Press apparatus, with the gluteal region on the seat, the
trunk and head supported on the apparatus back, the feet
on the platform according to pre-established measures
and the two hands holding a metallic support, with the
arm and forearm parallel to the trunk.

The exercise consisted of two phases of isotonic
movements: (1) eccentric phase, in which the volunteer
was initially positioned with total extension of the leg
(180o) and then accomplished a simultaneous bilateral
flexion of the thigh and leg for 2 seconds, until reaching
90o of leg flexion, what was indicated by a demarcation
done in the apparatus and then a verbal command was
expressed to determine the end of this phase; (2)
concentric phase, in which the volunteer accomplished
total extension of the leg and thigh, until reaching 180o
for 2 seconds too. For the measurement of the 90o angle
of leg flexion of each volunteer, a universal goniometer
(Carci, Indústria e Comércio de Aparelhos Cirúrgicos e
Ortopédicos Ltda., São Paulo, Brasil) was used. The
screw of the goniometer was placed on the lateral condyle
of femur and laterally aligned along the femur from the
greater trochanter to the lateral condyle of femur and from
the head of fibula to the lateral malleolus (GARY;
HARRELSON, 2000).

Prior the exercise a test of maximum voluntary
load (MVL) of assay-mistake in one maximum repetition
was accomplished in 45o Leg Press, as suggested by
Dantas (1998) in order to determine the loads to be
worked (30% and 60% of MVL). Immediately before
the test, a series of three active stretching with 30 second-
duration and 1 minute-interval was accomplished for the
quadriceps femoris, hamstrings and triceps surae
muscles.

After the test of MVL, a series of three repetitions
was accomplished with loads of 30% and 60% of MVL,
with 3 minute-interval in order to restore the energy
sources and to minimize the effects of fatigue. In this
interval period, the volunteers removed the feet of the
platform leaving them down on the soil, maintaining the
relaxed lower limb.



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Statistical analysis

In order to verify the differences among the
electric activities obtained from the four muscles with
loads of 30% and 60% of MVL in both masculine and
feminine groups, the test of Friedman and Wilcoxon was
used (SIEGEL, 1975), with a significance level
established at p < 0.05 in a bilateral test.

RESULTS

In the total group of 12 volunteers, the electric
activity of the left RF muscle was significantly greater
than that obtained for the right BF muscle (p < 0.05)
with 30% of MVL. When using 60% of MVL, significant
differences were found between right BF and right RF,
right BF and left RF, left BF and right RF, left BF and
left RF, with the RF muscle showing greater electric
activity than BF muscle in all cases (p < 0.05).

In the masculine group, the electric activity of
the left RF was significantly greater than that of the right
RF muscle in both loads (30% and 60% of MVL). For
the feminine group with 30% of MVL, the left BF was
significantly more active than the right BF muscle, and
this latter was significantly less active than the right RF
muscle. On the other hand, with 60% of MVL, the electric
activity of the RF was significantly greater than that of
the BF muscle in both sides (Table 1 and 2).

When comparing the results obtained with 30%
and 60% of MVL, significant differences were found for
the right BF, right RF and left RF muscles, with the RF
muscle always showing the greatest electric activity. In
addition, all muscles exhibited greater electric activity
with 60% than 30% of MVL (Figure 1).

A comparison between the masculine and
feminine groups revealed significant differences for the
left RF muscle, which showed greater electric activity in
the masculine group (Tables 1 and 2).

Table 1. RMS mean values of electric activity of the right (RFr) and left (RFl) Rectus Femoris, right (BFr) and left
(BFl) Biceps Femoris muscles at 30% of the maximum voluntary load (MVL) during bilateral isotonic
contraction in a 45o leg press apparatus.

RMS* at 30% MVL

Volunteers Gender Muscles

RFr BFr RFl BFl

1 Female 198 ± 6 139 ± 32 211 ± 39 168 ± 39
2 Female 315 ± 12 151 ± 26 112 ± 33 290 ± 109
3 Female 323 ± 160 194 ± 54 236 ± 71 449 ± 70
4 Male 113 ± 7 203 ± 48 315 ± 26 344 ± 24
5 Male 321 ± 21 126 ± 21 517 ± 64 113 ± 17
6 Male 863 ± 29 296 ± 57 665 ± 31 150 ± 26
7 Male 189 ± 7 116 ± 10 221 ± 11 183 ± 23
8 Male 250 ± 35 391 ± 63 351 ± 39 281 ± 37
9 Male 244 ± 35 203 ± 69 447 ± 18 304 ± 223

10 Female 140 ± 2 116 ± 4 211 ± 16 173 ± 13
11 Female 413 ± 23 148 ± 4 404 ± 29 124 ± 6
12 Female 131 ± 14 096 ± 24 133 ± 06 138 ± 34

Mean ±±±±± SD 292 ±±±±± 193 182 ±±±±± 82 319 ±±±±± 158 226 ±±±±± 101
*RMS expressed in µV; SD: standard deviation.



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Table 2. RMS mean values of electric activity of the right (RFr) and left (RFl) Rectus Femoris, right (BFr) and left
(BFl) Biceps Femoris muscles at 60% of the maximum voluntary load (MVL) during bilateral isotonic
contraction in a 45o leg press apparatus.

RMS at 60% MVL

Volunteers Gender Muscles

RFr BFr RFl BFl

1 Female 360 ± 22 192 ± 12 316 ± 06 379 ± 147
2 Female 589 ± 51 180 ± 7 440 ± 21 139 ± 2
3 Female 471 ± 35 367 ± 21 405 ± 08 138 ±30
4 Male 493 ± 17 466 ± 41 591 ± 59 312 ± 75
5 Male 874 ± 63 217 ± 8 852 ± 09 149 ± 6
6 Male 1620 ± 69 182 ± 65 1373 ± 60 132 ± 14
7 Male 462 ± 34 160 ± 4 475 ± 32 224 ± 83
8 Male 634 ± 39 226 ± 38 651 ± 34 313 ± 182
9 Male 588 ± 18 681 ± 108 908 ± 11 503 ± 73

10 Female 346 ± 11 165 ± 1 352 ± 03 201 ± 9
11 Female 798 ± 41 224 ± 1 783 ± 43 169 ± 17
12 Female 232 ± 25 134 ± 18 228 ± 02 181 ± 28

Mean ±±±±± SD 622 ±±±±±  348 266 ±±±±± 155 615 ±±±±± 309 237 ±±±±± 112
*RMS expressed in µV; SD: standard deviation.

Figure 1. RMS mean values (expressed in µV) of electric activity of the right (RFr) and left (RFl) Rectus Femoris,
right (BFr) and left (BFl) Biceps Femoris muscles at 30% and 60% of the maximum voluntary load
(MVL) during bilateral isotonic contraction in a 45o leg press apparatus.

 

0

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

6 0 0

7 0 0

R
M

S 
(u

v)

R F r B F r R F l B F l R F r B F r R F l B F l
M u s c l e s

30% MVL 60% MVL 



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DISCUSSION

Differently of previous studies, the present study
shows data on the dominant and non-dominant action of
limbs during isotonic contractions. Concerning the
isotonic exercises of flexion and extension of thigh and
leg, one of the limitations was the observation of the RF
and BF muscles only, making not possible to take
conclusions on the global activation of the quadriceps
femoris and hamstrings muscles.

In this study, the biarticular action of the RF and
BF muscles was verified, thus confirming the anatomic
and kinesiologic data previously reported (FURLANI;
VITTI; BÉRZIN, 1973; JOSE; FURLANI, 1984;
YAMASHITA, 1988; GONÇALVES, 1996; BERTOCHI
et al., 1997; ESCAMILLA et al., 1998; GONÇALVES;
BÉRZIN, 2000).

Alkner, Tesch and Berg (2000) found increased
activity patterns for the BF and RF muscles in the Leg
Press exercise with 20%, 40%, 60%, 80% and 100% of
MVL. Although we did not use relatively high loads (30%
and 60% of MVL) in this study, the significant increase
of myoelectric activation in both analyzed muscles (RF
and BF) was evident when the load was doubled from
30% to 60% of MVL. This might be due to some
protecting mechanism that is capable to help the ligaments
in the maintenance of the articular stability (BARATTA
et al., 1988).

Carnaval (2001) and Delavier (2002) reported
that RF and BF constitute the muscles that will be act in
the 45° Leg Press exercise, what it is in agreement with
the findings of this study since there was a significant
electric activity of the RF and BF muscles regardless of
the load and sex. In addition, studies reported by Tassi et
al. (1998) also confirmed the participation of the BF
muscle in both concentric and eccentric movements in
the 45o Leg Press exercise. On the other hand, our findings
disagree with the reports of Tesch (2000) that showed no
activity of the RF ad BF muscles of subjects trained in
45° Leg Press apparatus with the feet positioned in both
high and low part of the platform, although he has used
the magnetic resonance instead of EMG.

Previous studies have also shown that the entire
quadriceps muscle in leg extension and squat movements
presents simultaneous contraction and increased activity
proportional to the increase of the load (DUARTE-
CINTRA; FURLANI, 1981). Such an increase might have
led to the intensification of the capacity of the motor
centers in mobilizing a great number of motor neurons
previously still which increased the number of motor units
that participated in the muscular contraction

(VERKHOSHANSKI, 2001). This result is in agreement
with the theory of graduation of muscular force, which
affirms that a simultaneous activation of a larger number
of motor units occurs with the increase of the force, as
reported in other studies (ALKNER; TESCH; BERG,
2000; BILODEAU et al., 1992; SOUSA et al., 2000;)
and evidenced in the present study, when 60% of MVL
was used. For training such conditions are favorable due
to the fact that the muscle should be submitted to the
tension change in order to obtain force. According to
Fleck and Kraemer (1999) the muscle should act against
a resistance that usually does not exist for the physiologic
changes to take place resulting in required training effects.

Escamilla et al. (2001) analyzed the dynamic
unilateral activity of the quadriceps, biceps femoris long
head, semitendinosus, semimembranosus, and
gastrocnemius muscles in squat and Leg Press exercises
and found significant activity of the BF and RF muscles,
what is in agreement with our findings.

Tassi et al. (1998) investigated the bilateral
behavior of the biceps femoris muscle during flexion and
extension movements of the leg and thigh in the horizontal
Leg Press apparatus and verified strong potentials of the
dominant limb on the non-dominant one. These results
are not in agreement with our findings since that no
differences in the bilateral electric activity of the BF and
RF muscles were found between dominant and non-
dominant limbs in both loads and sexes, in spite of all
volunteers were skillful. Although some studies have not
used EMG (SIMÃO, 2001; SIMÃO; MONTEIRO;
ARAÚJO, 2001; SIMÃO et al., 2003), their findings were
similar to ours for both maximum load and muscular
potency.

The exercise chosen for our study was part of the
training program of the volunteers. Thus, our results can
be related to the fact that these volunteers already
presented a great level of inter- and intra-muscular
adaptation to the analyzed exercise, favoring their motor
performance.

Bilodeau et al. (1992) analyzed the EMG signs
of homologous flexors and extensors of the elbow with
10%, 40% and 80% of MVL in dominant and non-
dominant limbs and verified no significant differences
between the right and left sides. Although the levels of
force analyzed were not similar to the ones of our study,
we also found minor but not significant differences
between the right and left sides. These minor differences
might have occurred due to a higher level of concentration
in the muscles that possess lower expression of force to
win the proposed resistances. It is possible that with the
progress of training and the improvement of the



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recruitment pattern of motor units, the differences among
the contralateral muscular contractions become less
evident due to the transfer or crossed effect, as reported
by Moritani and De Vries (1979), Sale (1988), Zhou
(2000), and Munn, Herbert and Gandevia (2004).

According to Fuglsang-Frederiksen (1987),
differences in the unilateral maximum force between
dominant and non-dominant limbs are mainly due to the
heterogeneity in the diameter of muscular fibers or in
the number of fibers by motor unit or in both diameter
and number of muscular fibers. For these authors a weaker
muscle activates more motor units to exercise a 2 kg force
than a stronger muscle, what could explain the differences
found between the right and left limbs in our study. De
Luca, Sabbahi and Roy (1986) also report that
electromyographic differences between right and left
limbs in skillful individuals provide an indication of
modifications in the metabolic properties of the muscular
fibers induced for a lifetime in consequence of the favorite
functional use (law of the use and disuse).

Our results, although in a indirect comparison,
were similar to those found by Gryzlo et al. (1994) who
verified that the rectum femoris, vastus lateralis oblique
and vastus medialis muscles were significantly more
active than the biceps femoris and semimembranosus
muscles during the squat in both concentric and eccentric
phases of the movement.

Based on the results obtained in the present study
that showed the predominant electric activity of RF on
BF muscles, it can be suggested that the employment of
multi-joint exercises such as 45° Leg Press should not

RESUMO: O objetivo deste estudo é comparar a atividade elétrica bilateral dos músculos rectus femoris
(RF) e cabeça longa do biceps femoris (BF) durante movimentos isotônicos de flexão e extensão da coxa e perna.
Seis homens e seis mulheres realizaram todos os movimentos em um aparelho Leg Press 45o com 30% e 60% da
carga voluntária máxima (CVM). Os sinais eletromiográficos foram captados usando eletrodos de superfície, registrados
em um eletromiógrafo computadorizado e analisados em um sistema de aquisição de dados (Alc-EMG). Os resultados
demonstram que o músculo RF mostra atividade elétrica maior em relação ao músculo BF em ambas as cargas (30%
e 60% CVM) e lados, independente do sexo. Pode ser concluído que apesar dos músculos RF e BF estarem em
extremidades opostas das articulações do quadril e joelho e serem mencionados como músculos antagônicos, ambos
músculos parecem agir com sinergismo entres si, com predominância de ativação do músculo RF sobre o BF em
ambos gêneros e cargas estudadas na execução do leg press 45o. Além disso, a atividade elétrica destes músculos é
diretamente proporcional à carga, independente do sexo.

PALAVRAS-CHAVE: EMG cinesiológica. Leg Press. Rectus femoris. Biceps femoris.

be indicated as single training form with loads for the
phase of anatomical adaptation of the thigh muscles
related to the resisted training of athletes and non athletes,
since these exercises make stronger muscles in
disadvantage to the other ones. On the other hand, such
multi-joint exercises might be indicated only when the
feet are supported on the superior portion of the platform,
as proposed by Tassi et.al. (1998) and Escamilla et.al.
(2001). In addition, single-joint exercises should be
indicated because they provide a larger strengthening and
recruitment of hamstring muscles, which possess smaller
electric activity and consequently poorer anatomical
adaptation.

These findings could provide valuable
information on the prescription of physical exercises to
the sport professionals, establishing the importance of
the aggregation of specific exercises for strengthening
of the hamstring muscles in the basic phase of the
periodicity of the sport training, in both single-joint and
multi-joint characters.

CONCLUSION

According to the obtained results and the
proposed methodology, it can be concluded that in spite
of the RF and BF muscles are in opposite ends of the hip
and knee joints and are mentioned traditionally as
antagonistic muscles, both muscles seem to act with
synergism between themselves with predominance of the
activation of the RF muscle on the BF muscle in both
genders and studied loads in leg press 45o execution.



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