Download Effect of tibia rotation on the electromyographical activity of the

Physical Therapy in Sport 6 (2005) 15–23
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Original research
Effect of tibia rotation on the electromyographical activity
of the vastus medialis oblique and vastus lateralis longus
muscles during isometric leg press
Fábio Viadanna Serrãoa,*, Cristina Maria Nunes Cabrala, Fausto Bérzinb,
Cecı́lia Candoloc, Vanessa Monteiro-Pedroa
a
Department of Physical Therapy, Federal University of São Carlos, São Paulo, Brazil
Department of Morfology, College of Dentistry of Piracicaba, State University of Campinas, Piracicaba, São Paulo, Brazil
c
Department of Statistic, Federal University of São Carlos, São Paulo, Brazil
b
Abstract
Objectives: To evaluate the electrical activity of the vastus medialis obliquus (VMO) and vastus lateralis longus (VLL) with the tibia in
neutral, medial and lateral rotation on the horizontal leg press.
Design: Repeated measures analysis of the effects of tibia rotation on VMO and VLL activity.
Setting: Evaluation and intervention in orthopaedics and traumatology laboratory.
Participants: Fifteen healthy participants, no previous musculoskeletal damage of the lower limb.
Main outcome measures: Electrical activity (Root Mean Square) of the VMO and VLL was measured during submaximal isometric
contractions (SIC) with the knee at 908 of flexion. The effect of tibia rotation in electrical activity of the VMO and VLL was measured.
Results: VLL activity was significantly higher than VMO activity with the tibia in medial rotation ðp ¼ 0:03Þ: Tibia rotation did not
influence the activity of the VMO muscle ðp ¼ 0:26Þ: VLL activity was significantly higher with medial than neutral tibia rotation
ðp ¼ 0:005Þ:
Conclusions: The results suggest that tibia rotation does not strengthen selectively the VMO muscle during isometric leg press at 908 knee
flexion.
q 2004 Elsevier Ltd. All rights reserved.
Keywords: Leg press; Femoral quadriceps; Rehabilitation
1. Introduction
The patellofemoral pain syndrome (PFPS) is among the
complaints most commonly observed in sports medicine,
usually manifesting as pain localized in the retropatellar or
peripatellar region (Doucette & Goble, 1992). This syndrome
is more common among women aged 16 –26 years but with a
high incidence among athletes (Puniello, 1993). According
to Grabiner, Koh, and Miller (1991) the PFPS occurs in 17%
of male and 33% of female knee pathology. The pain is
usually aggravated by activities involving patellofemoral
compressive forces such as remaining in the sitting position
with the knees flexed for long periods of time (movie theater
sign), climbing up and downstairs, remaining in the kneeling
position, and squatting.
* Corresponding author. Tel.: þ 55-16-260-8754; fax: þ55-16-260-2081.
E-mail address: [email protected] (F.V. Serrão).
1466-853X/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ptsp.2004.03.001
Although the exact aetiology of PFPS is unknown (Eng &
Perrynowski, 1993), investigators propose that this disorder
may be related to non-traumatic factors such as bone
abnormalities, muscle imbalance, laxity or tightness of the
ligaments or joint capsule, or to a direct traumatic injury to
the joint (Sheehy, Burdett, Irrgang, & VanSwearingen 1998).
Among non-traumatic factors, the patellar malalignment
has been pointed out as one of the major causes of
patellofemoral pain (Paulos, Rusche, Johnson, & Noyes,
1980; Fulkerson, 1983). Adequate patellar alignment
depends on the balance between static and dynamic medial
and lateral stabilizers. The static stabilizers of the patella are
the bone structures, retinaculum and ligaments (Merchant,
Mercer, Jacobsen, & Cool, 1974; Woodall & Welsh, 1990;
Ruffin & Kiningham, 1993; Sheehy et al. 1998).
Dynamically, the major stabilizers are the four components of the femoral quadriceps muscle-vastus medialis
(VM), vastus lateralis (VL), vastus intermedius, and rectus
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F.V. Serrão / Physical Therapy in Sport 6 (2005) 15–23
femoris (Blackburn & Craig, 1980). Lieb and Perry (1968)
observed that the fibers of the VM muscle present different
orientations. Besides, in one of the cadavers studied, it was
observed the presence of an areolar fascial plane. Thus, a
portion of long fibers was recognized and denoted vastus
medialis longus (VML), and an oblique portion was denoted
vastus medialis obliquus (VMO), the latter being the only
dynamic medial stabilizer of the patella. The fibers of the
VMO muscle originate from the femur and from the tendon
of the adductor longus and adductor magnus muscles, with
an inclination angle of 50– 558 in relation to the longitudinal
axis of the femur, described by Lieb and Perry (1968).
This inclination angle favours an advantageous line of
action for medial patella traction (Bose, Kanagasuntherum,
& Osman, 1980).
Similarly, other studies (Scharf, Weinstabl, & Firbas,
1986; Hallisey, Doherty, Bennet, & Fulkerson, 1987;
Weinstabl, Scharf, & Firbas 1989; Javadpour, Finegan, &
OBrien, 1991; Bevilaqua-Grosso, Monteiro-Pedro, & Berzin, 1997) have shown that the VL muscle is also divided
into two portions. In an anatomical study, Bevilaqua-Grosso
et al. (1997) reported that the the VL muscle has a long and
proximal portion denoted vastus lateralis longus (VLL), and
an oblique and distal portion denoted vastus lateralis
obliquus (VLO), separated by a fascia in the distal portion.
The fibers of the VLL muscle originate from the femur and
are inserted into the middle of the quadriceps tendon
(Javadpour et al., 1991), while the fibers of the VLO
originate from the rough line of the femur and from the
lateral intermuscular septum and are inserted through their
own tendon that runs inferiorly and laterally to the VLL
tendon, joining the latter in a common tendon in the
superolateral margin of the patella (Bevilaqua-Grosso et al.,
1997). Bevilaqua-Grosso et al. (1997) also reported that the
long fibers of the VL have an inclination of approximately
13.68 and the oblique fibers have an inclination of 50.48 in
relation to the longitudinal axis of the femur.
Some investigators (Hanten and Schulthies, 1990;
McConnell, 1986) have reported that adequate patellar
alignment is obtained by balance between the VMO and VL
muscles and that muscular imbalance caused by weakness
of the VMO muscle may result in lateral subluxation and
pain in the patellofemoral joint.
It is thought that isolated insufficiency of the VMO
muscle or in combination with other factors such as bone
abnormalities and malalignment of the lower limb, may
result in improper tracking of the patella in the femoral
groove and an abnormal distribution of loads in the
patellofemoral joint.
On this basis, selective strengthening of the VMO muscle
has been indicated by several authors (Insall, 1982;
Sczepanski, Gross, Duncan, & Chandler, 1991; Doucette
& Goble, 1992) to be of fundamental importance for the
treatment of PFPS. Hanten and Schulthies (1990) stated
that, for an effective patellar realignment, emphasis should
be placed not only on increased VMO activity, but also on
decreased VL activity.
The pattern of VMO and VL muscle recruitment has
been studied during various exercises in the open kinetic
chain (OKC) and closed kinetic chain (CKC) used for knee
rehabilitation. However, there are contradictions in the
definition of kinetic chain terminology (Ellenbecker &
Davies, 2001). Thus, recognizing the contradictions in the
definition of kinetic chain terminology, we opted not to use
it in the present study. The term leg press will be used
throughout the manuscript, but without defining exercise as
OKC or CKC.
A topic that has attracted great interest and that requires
further study is the influence of tibia or hip rotation on the
pattern of recruitment of the VMO and VL muscles. Some
studies (Slocum & Larson, 1968; Engle, 1987; Gough &
Ladley, 1971) showed that the tibia or hip rotation changed
the recruitment pattern of the VMO and VL muscles. On the
other hand, other studies (Hanten & Schulthies, 1990; Cerny,
1995) didn’t find any difference in the electrical activity of
the VMO and VLL muscles with lower limb rotation.
However, the literature has no data about the demonstration of the effect of tibia rotation during isometric leg
press on the pattern of the femoral quadriceps muscle. On
this basis, the purpose of this study was to evaluate the
electrical activity of the VMO and VLL muscles during
submaximal isometric contraction (SIC) of the femoral
quadriceps muscle with the knee joint in 908 flexion and the
tibia in a neutral, medial or lateral position, on the horizontal
leg press.
2. Methods
2.1. Subjects
The study was conducted on 15 healthy participants
(10 women and 5 men) aged 18 – 25 years ðX ¼ 21:9;
SD ¼ 1.57) who undertook physical activity at a frequency
of twice a week or more. The participants reported no
previous musculoskeletal damage to the hip, knee or ankle
joints. To verify this statement, the participants were
submitted to physical evaluation consisting of specific
tests for these joints. Before the beginning of the
experimental procedure, the participants signed a formal
term of agreement, and the study was conducted according
to the guidelines of the National Health Council, Resolution
196/96. This research was carried out with approval from
the Human Ethics Committee of the Federal University of
Sao Carlos, Brazil.
2.2. Instruments
The electrical activity of the VMO and VLL muscles was
determined using simple active differential surface electrodes (Delsys Inc.) and a 16-channel signal conditioning
F.V. Serrão / Physical Therapy in Sport 6 (2005) 15–23
module (MCS 1000-V2-Lynx Electronics Technologies).
The simple active differential surface electrode (Delsys
Inc.) housing is constructed with a waterproof polycarbonate plastic case, which is internally shielded to reject
ambient electrical noise. The electrode contacts are made
from 99.9% pure silver bars measuring 10 mm in length,
1 mm in diameter and spaced 10 mm apart. The electrode
has a Common Mode Rejection Ratio (CMRR) higher than
80 dB, an internal gain (V/V) of 10 times, an input
impedance higher than 100 MV and a noise of 1.2 mV.
The signal conditioning module (MCS 1000-V2) was
interfaced with a computer and has a digital analogue A/D
converter (CAD 12/32-60K- LYNX Electronics Technologies) with a resolution of 12 bits, an acquisition frequency
of 1000 Hz per channel and a data acquisition program
Aqdados version 4.6 (Lynx Electronics Technologies).
Besides, this equipment has a filter Butterworth type with
bandpass of 10.6 – 509 Hz and a gain of 100 times. The
electromyographic signals were sampled in a synchronous
manner and stored for later processing.
SIC was performed on a horizontal leg press, Top Line
model (Vitally-Industry of Gymnastics Equipment). A
universal goniometer was used to measure the flexion
angle of the knee joint and the inclination angle of the VMO
and VLL muscles.
2.3. Procedures
Before the recording of the electrical potential of the
muscles studied, the skin was shaved and cleaned with 70%
alcohol and the electrodes were fixed to the skin with
micropore adhesive tape. A line joining the anterosuperior
iliac spine to the center of the patella was traced with a
dermographic pen to guide electrode placement at the
different angles of insertion of the portions of the femoral
quadriceps muscle. For the recording of the electrical
activity of the VMO muscle, the electrode was positioned
4 cm from the superomedial border of the patella (Hanten &
Schulthies, 1990; Laprade, Culham, & Brouwer, 1998), at
an inclination angle of 50– 558 in relation to the reference
line (Lieb & Perry, 1968). For the VLL muscle the electrode
was fixed 15 cm from the superolateral border of the patella,
with an inclination angle of approximately 13.68, according
to the anatomical study of Bevilaqua-Grosso et al. (1997). A
universal goniometer was used to position the electrodes on
the muscle belly. To achieve this, the goniometer axis was
aligned to the centre of the patella, the fixed arm was aligned
to the reference line (line joining the anterosuperior iliac
spine to the centre of the patella) and the mobile arm moved
up to the inclination angle desired. In addition, palpation of
the muscle belly with the subject in the testing position was
also used to confirm electrode placement. The electrodes
were fixed to the midline of the muscle belly with the
detection surface perpendicular to the muscle fibers, as
suggested by DeLuca (1997). A reference electrode was
17
fixed to left wrist of the participant with Velcro tape in order
to eliminate possible external interferences.
Before testing, the participants were submitted to a
period of training for familiarization with all the test
procedures.
During the week before the recording of the electromyographic signal the participants were submitted to a test for
the determination of maximal repetition (MR) based on the
load addition method of De Lorme and Walkins (1948). The
proposed protocol was as follows: with the thoracic and
lumbar regions in contact with the seat of the equipment and
the left foot sole in contact with a vertical support platform
of the leg press, the participant was instructed to extend the
knee joint from 1208 of flexion to complete extension and
then to return to the initial 1208 position with an initial load
of 15 kg. The participant repeated this procedure ten times
and 10 kg was then added to the load. The 10 MR was
considered to be that observed before the participant started
to present symptoms of fatigue and/or pain or was unable to
achieve the full amplitude of movement. In the actual study,
the contractions performed against this load were called SIC.
Initially, the electrical activity of the VMO and VLL
muscles was recorded during maximal isometric contraction
(MIC), which was used only for the normalization of the
electromyographic recordings obtained during SIC. The
MIC was performed with the hip and knee joints at 908
flexion and with the tibia in neutral rotation. Three 4-s MIC
were performed, with a 30-s resting interval between
contractions. During MIC, the investigator encouraged the
participant with the following verbal commands: Prepare!
Go! Pull! Pull! Relax!
For SIC, the load was first adjusted according to the
previously established 10 MR. The participant was then
positioned with the knee joint in 908 flexion and the tibia
randomly positioned in neutral, lateral or medial rotation
(Figs. 1 and 2). Three SIC were performed for each tibia
rotation and maintained for a period of 4 s. A 30-s resting
interval was established between contractions and a 2-min
interval was established between the various tibia rotations
to prevent possible fatigue. During SIC the participant was
verbally encouraged as follows: Hold it! Hold it! Relax! The
electrical activity of the muscles under study started to be
recorded 2 s after the beginning of muscle contraction
according to the protocol of Hanten and Schulthies (1990).
The Root Mean Square (RMS) of the electromyographic
signal was used to evaluate the pattern of muscle electrical
activity during each contraction. The RMS is representative
of the number of active motor units during contraction and
is commonly used as a measurement of muscle activity
(Basmajian & De Luca, 1985). The data obtained during
SIC at the different tibia rotations were normalized as a
function of the recordings obtained during MIC. Mean RMS
values (in mV) obtained during MIC were first calculated for
the VMO and VLL muscles, followed by the calculation of
mean RMS values for the same muscles during SIC. On this
basis, the mean RMS values obtained during SIC were
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F.V. Serrão / Physical Therapy in Sport 6 (2005) 15–23
Fig. 1. Positioning of the participant on the horizontal leg press.
expressed as percentage of the mean RMS values obtained
during MIC considering the muscle studied (mean RMS
during SIC/mean RMS during MIC £ 100).
2.4. Statistical analysis
The differences between the two muscles and between
the three tibia rotations were analyzed statistically by 2 £ 3
(muscles by tibia rotations) two-way repeated measures
analysis of variance. When the effects were found to be
significant, the data were submitted to contrast analysis and
one-way repeated measures analysis of variance considering
separately tibia rotations for each muscle and, conversely,
considering separately the muscles for each tibia rotation.
The level of significance was set at p , 0:05 in all analyses.
Prior to statistical analysis, tests for normality of descriptive
analysis were performed. All calculations were performed
with the S-PLUS statistical software (S-PLUS 2000, Lucent
Technologies, Inc.).
ðp ¼ 0:28Þ: Analysis of variance of contrast variables for
tibia rotation showed significantly higher electrical activity
for medial rotation of the tibia compared with neutral
rotation ðp ¼ 0:03Þ; whereas no significant difference was
observed between medial and lateral rotation ðp ¼ 0:15Þ or
between neutral and lateral rotation ðp ¼ 0:37; Table 1).
One-way repeated measures analysis of variance considering separately muscles for each tibia rotation showed
significantly greater electrical activity for medial rotation of
the tibia compared with neutral rotation ðp ¼ 0:005Þ in the
case of the VLL muscle. In addition, there was no significant
difference between neutral and lateral rotation ðp ¼ 0:58Þ;
or between medial and lateral rotation ðp ¼ 0:080Þ: The
electrical activity of the VMO muscle was not significantly
changed by tibia rotation ðp ¼ 0:260; Table 2 and Fig. 3).
When tibia rotation was analyzed separately for each
muscle, the electrical activity of VLL was found to be
significantly higher than that of VMO in medial tibia
rotation ðp ¼ 0:007Þ; however, did not differ in neutral ðp ¼
0:100Þ or lateral ðp ¼ 0:150Þ tibia rotation (Table 3 and
Fig. 4).
3. Results
The effects of muscle and tibia rotations were both close
to significance ðp ¼ 0:04 and 0.06, respectively) with
greater electrical activity for the VLL muscle. However,
two-way repeated measure analysis of variance revealed a
no significant interaction between muscles and tibia rotation
4. Discussion
The present study was an initial one carried out to
determine the pattern of VMO and VLL muscle recruitment
during isometric leg press with variation of tibia rotation.
F.V. Serrão / Physical Therapy in Sport 6 (2005) 15–23
Fig. 2. Tibia in neutral (A), maximal lateral (B) and maximal medial (C) rotation.
19
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F.V. Serrão / Physical Therapy in Sport 6 (2005) 15–23
Table 1
Two-way repeated measure analysis of variance
Source of variation
p
Internal comparison
for tibia rotation effect
p
Muscles
Rotations
Muscles £ rotations
0.04*
0.06
0.28
Medial–neutral
Medial–lateral
Neutral– lateral
0.03*
0.15
0.37
*Significant difference.
Table 2
One-way repeated measure analysis of variance for each tibia rotation
Source of
variation (VLL)
p
Source of
variation (VMO)
p
Rotations
Medial–neutral
Medial–lateral
Neutral–lateral
0.020
0.005*
0.080
0.58
Rotations
0.260
VMO, Vastus Medialis Obliquus; VLL, Vastus Lateralis Longus.
*Medial rotation significantly higher than neutral rotation for VLL muscle.
In order to obtain a more homogeneous sample for our
protocol, we studied healthy individuals. However, caution
should be exercised when extrapolating these results to
individuals with patellofemoral dysfunction. Thus, the same
protocol will be applied to subjects with this dysfunction in
future studies.
It is important to point out that many of the electromyographic studies of the VMO and VL muscles did not
describe the placement of the electrodes in a precise
manner. In the present study, the placement of the electrode
on the belly of the VMO muscle was based on the classical
anatomical study of Lieb and Perry (1968) and on the
electromyographic study of Hanten and Schulthies (1990),
and the placement of the electrode on the VLL muscle was
based on the anatomical study of Bevilaqua-Grosso (1997).
Observation of the force vector of the oblique portion of
the VL muscle suggests that it may play a more important
role in patellar alignment than the long fibers. This was
previously observed by Morrish and Woledge (1997), who
reported that the oblique fibers of the VL muscle can control
the position of the patella by acting in opposition to the
VMO. However, when the different portions of the VL are
considered, the long portion is found to be much greater
than the oblique one (Hallisey et al., 1987). Thus, although
the orientation of the oblique fibers of VL represents an
advantageous line of action for lateral patellar traction, it is
questionable whether it is the major factor responsible for
this action, since the long portion has a greater dimension.
One of the limitations of the present study was the fact
that VLO and VML activity was not evaluated. Thus, in
order to elucidate the efficiency of VLO and VML on
patellar alignment and to determine whether rotation of the
lower limb affects its activity, future studies evaluating this
portion are needed.
With respect to the knee flexion angle used in the present
study, it is known that during the support phase of the gait
cycle, 908 knee flexion is not used, a fact that leads us to
believe that the position studied here is not functional.
However, 908 flexion is used in other activities such as
sitting on a chair, and in this case the angle is functional. In
addition, this angle was chosen for this study because it is
frequently used for knee rehabilitation, and previous studies
(Wilk et al., 1996; Escamilla et al., 1998) have demonstrated
a greatest mean amplitude of the electric signal of
the femoral quadriceps muscle during exercise on the leg
press at this angle.
Selective strengthening of the VMO muscle has been
extensively studied in investigations about knee rehabilitation. Several exercises are used in clinical practice in order
Fig. 3. Mean and standard deviation (SD) of normalized electrical activity readings (as percentage of maximal isometric contraction) of the vastus medialis
obliquus (VMO) and vastus lateralis longus (VLL) considering muscles for each tibia rotation.
F.V. Serrão / Physical Therapy in Sport 6 (2005) 15–23
Table 3
One-way repeated measure analysis of variance for each muscle
Source of variation
Tibia rotation
Medial rotation
Lateral rotation
Neutral rotation
VMO £ VLL
0.007*
0.150
0.100
VMO, Vastus Medialis Obliquus; VLL, Vastus Lateralis Longus.
*Electrical activity for the VLL significantly higher than that of the VMO.
to selectively strengthen this muscle. However, electromyographic studies have not confirmed this theory, with
several controversies still persisting. For example, for many
years there was a belief that the VM muscle was active only
at the last degrees of knee extension (Mariane & Caruso
1979). Thus, this exercise has been extensively used in
clinical practice to selectively strengthen the VM muscle.
However, more recent studies (Boucher, King, Lefebvre, &
Pepin, 1992; Worrell, Connelly, & Hilvert, 1995; Isear,
Erickson, & Worrell, 1996) have demonstrated that this
muscle is activated throughout the amplitude of knee
extension, including 908 flexion.
Similarly, tibia rotation was proposed as another form of
selective VMO strengthening, since Slocum and Larson
(1968) stated that the VMO is inserted into the anteromedial
aspect of the tibia through a medial extensor aponeurosis
and can resist lateral tibia rotation during the first 608 of
knee flexion. On this basis, it was suggested that medial tibia
rotation exercise may selectively strengthen the VMO.
However, Hanten and Schulthies (1990) did not detect a
significant difference between the activity of the VMO and
VL muscle during resisted medial rotation at 308 knee
flexion in healthy individuals. On the other hand, the results
obtained by Laprade et al. (1998) support the statement
made by Slocum and Larson (1968). These investigators
detected a greater VMO/VL ratio during resisted medial
21
tibia rotation combined with knee joint extension at 708 of
flexion compared to other exercises, both for healthy
individuals and for patients with patellofemoral pain.
Based on their results, Laprade et al. (1998) suggested
that exercises involving knee extension in combination with
resisted medial tibia rotation could be used for selective
strengthening of the VMO muscle. We observed some
contradictions in the findings related to the effect of tibia
rotation on VMO recruitment. Powers (1998) reported that
these studies applied different methods and procedures to
evaluate the electromyographic recordings, thus preventing
direct comparisons between them. Perhaps these differences
are the major reason why no definitive conclusions have
been reached thus far with respect to the effect of tibia
rotation on VMO activity.
The present results demonstrate a significantly higher
activity of the VLL muscle than of the VMO muscle on
medial rotation, whereas no significant difference was
observed in lateral or neutral rotation. Thus, on the basis
of these results, we may suggest that medial rotation should
not be used to strengthen selectively the VMO muscle, as
pointed out by Laprade et al. (1998). However, the present
study was carried out under an axial load which was not
present in the study by Laprade et al. (1998). Another
difference is that Laprade et al. (1998) performed medial
tibia rotation under resistance, whereas in our study the tibia
was only positioned in medial rotation. Some literature
reports evaluated the effect of lower limb rotation during
exercises under an axial load. Ninos et al. (1997) concluded
that rotation of the lower extremity does not affect the
pattern of activity of the VM and VL muscles during the
descent and ascent phases of the Olympic squat. Similarly,
Willett et al. (1998) reported that there was no significant
difference in the VMO/VL ratio between neutral, medial
and lateral rotation of the lower extremity during knee
extension with support of body weight against elastic
Fig. 4. Mean and standard deviation (SD) of normalized electrical activity readings (as percentage of maximal isometric contraction) of the vastus medialis
obliquus (VMO) and vastus lateralis longus (VLL) considering tibia rotation for each muscle.
22
F.V. Serrão / Physical Therapy in Sport 6 (2005) 15–23
resistance in the popliteal region (also referred to as the
‘stove-pipe’ or ‘walk-stance’ exercise). However, these
studies detected the influence of rotation of the lower limb
on quadriceps activity, whereas in the present study we only
investigated the influence of tibia rotation. The results of the
present study suggest that medial tibia rotation with the knee
in 908 flexion causes preferential activation of the VLL, and
could therefore be used to strengthen this muscle.
One-way repeated measures analysis of variance considering the muscles separately for each rotation demonstrated that tibia rotation does not influence the pattern of
VMO recruitment. Thus, it is not possible to strengthen
selectively the VMO muscle with a variation of tibia rotation
during isometric leg press with the knee in 908 flexion. These
results differ from those reported by Signorile et al. (1995a,
b), who stated that the VMO muscle produced a significantly
higher activity in neutral rotation than in medial rotation at
908 knee flexion.
On the other hand, the electrical activity of the VLL was
significantly higher with the tibia in medial rotation than in
neutral rotation. However, there was no significant difference
between medial and lateral rotation or between neutral and
lateral rotation. These results also disagree with those reported
by Signorile et al. (1995a,b), who detected a significantly
higher activity of the VL muscle in neutral rotation than in
medial rotation, but no significant difference between neutral
and lateral rotation at 908 knee flexion. However, these
divergent results may be related to the methodological
differences between the two studies. The results obtained
here for the VLL (higher activity in medial than in neutral
rotation) support those reported previously in the analysis of
tibia rotation with respect to the muscles, with medial rotation
resulting in higher activity in the VLL than in the VMO.
When evaluating other knee flexion angles (5 and 308
flexion), Signorile et al. (1995a,b) noted that the pattern of
VM and VL recruitment was different from that observed at
908. Thus, another limitation of the present study was the fact
that other knee angles were not analyzed, since results
differing from those obtained at 908 might have been
observed. Thus, other angles will be explored on future
studies on the leg press, which may lead to conclusions
differing from those reached in the present study about the
selective strengthening of the VMO.
5. Conclusions
The results of the present study obtained under the
experimental conditions used permit us to reach the
following conclusions:
1. The electrical activity of the VLL muscle was significantly higher in medial rotation than in neutral rotation,
with no significant difference between medial and lateral
rotation or between lateral and neutral rotation.
2. Tibia rotation does not affect the pattern of VMO muscle
recruitment. Thus, it is not possible to strengthen
selectively the VMO muscle during isometric leg press
at 908 knee flexion by varying tibia rotation.
3. The electrical activity of the VLL muscle was significantly higher than that of the VMO muscle with the tibia in
medial rotation, but the difference was not significant
when neutral or lateral rotation was used.
Acknowledgements
We are grateful to Vitally (São José do Rio Preto, São
Paulo, Brazil) for donating the leg press equipment used in
the present study.
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