Journal of Electromyography and Kinesiology 23 (2013) 844–850

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Journal of Electromyography and Kinesiology

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Influence of the knee flexion on muscle activation and transmissibilityduring whole body vibration

1050-6411/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.jelekin.2013.03.014

⇑ Corresponding author. Address: Federal University of the Jequitinhonha andMucuri Valleys, Rodovia MGT 367 - Km 583 # 5000, Alto da Jacuba, 39100-000,Diamantina, Minas Gerais, Brazil.

E-mail address: lacerda.acr@ufvjm.edu.br (Ana Cristina R. Lacerda).

Núbia C.P. Avelar a,e, Vanessa G.C. Ribeiro a, Bruno Mezêncio b, Sueli F. Fonseca a,e,Rosalina Tossige-Gomes a,e, Sidney J. da Costa a, Leszek Szmuchrowski c, Fernando Gripp a,Cândido C. Coimbra d,e, Ana Cristina R. Lacerda a,e,⇑a Federal University of the Jequitinhonha and Mucuri Valleys, Exercise Physiology Laboratory, Brazilb University of São Paulo, Biomechanics Laboratory, Brazilc Federal University of Minas Gerais, Load Evaluation Laboratory, Brazild Federal University of Minas Gerais, Endocrinology Laboratory, Brazile Multicentric Graduate Studies Program in Physiological Sciences, Brazilian Society of Physiology, Brazil

a r t i c l e i n f o a b s t r a c t

Article history:Received 30 November 2012Received in revised form 7 March 2013Accepted 25 March 2013

Keywords:Neuromuscular functionVibration exerciseSquatting

The influence of the knee flexion on muscle activation and transmissibility during whole body vibration iscontroversially discussed in the literature. In this study, 34 individuals had electromyography activity(EMG) of the vastus lateralis and the acceleration assessed while squatting with 60� and 90� of knee flex-ion either with or without whole-body vibration (WBV). The conditions were maintained for 10 s with1 min of rest between each condition. The main findings were (1) the larger the angle of knee flexion(90� vs. 60�), the greater the EMG (p < 0.001), with no difference on acceleration transmissibility; (2)for both angles of knee flexion, the addition of WBV produced no significant difference in EMG and higheracceleration compared to without WBV (p < 0.001). These results suggest that the larger the knee flexionangle (60� vs. 90�), the greater the muscle activation without acceleration modification. However, theaddition of WBV increases the transmissibility of acceleration in the lower limbs without modificationin EMG of vastus lateralis.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Despite their having been interest for many year in the effectsof vibration on muscle capability, until today, the literature haspresented conflicting results about muscle activation/performanceafter whole-body vibration (WBV) stimulation (Bullock et al., 2008;Dabbs et al., 2010; Kelly et al., 2010; Lovell et al., 2011; Avelaret al., 2012).

EMG activity has been used because this measurement mayhelp to elucidate the neural (activation) or peripheral (contractile)mechanisms underlying any changes in function that are promotedby WBV (Hannah et al., 2013). Additionally, EMG activity can serveas an adequate parameter for estimating muscular activationintensity, thus contributing to the development of an appropriatemethodology for training. However, to develop a structured WBVtraining program, it is necessary to understand the influence ofacceleration (transmitted by the vibratory platform) and its rela-tion to muscle activation (Marín et al., 2011) because acceleration

represents the stimulus intensity during exercise (Batista et al.,2007; Rittweger, 2010).

Different positions of the subject on the platform correspond todifferent muscle mechanical stimulations for the following rea-sons: muscles and tendons are activated during WBV, and evidencesuggests that activated muscles are capable of damping themechanical waves produced by a vibratory platform (Wakelinget al., 2002). Thus, the acceleration to be transmitted by the vibrat-ing platform to the body depends on muscle stiffness (ability todampen the vibratory stimulus), which is closely related to the an-gles of flexion of the lower limb joints (especially the knee joint).Thus, to characterize the muscle response, it is important to iden-tify the actual vibratory stimulus that is delivered to a target mus-cle. Different angles of flexion of the knee can promotemodifications in muscle length, changes in the tension of the mus-cle fibers, and consequently, the sensitivity of Ia afferents to induceincreased activation of a-motor neurons and greater muscle acti-vation response (Roelants et al., 2006; Abercromby et al., 2007a).

The magnitude, evaluated by electromyography (EMG), of themuscle activation provided by the vibratory stimulus seems to berelated to the degree of muscle activation prior to the vibrationexercise (Roelants et al., 2006; Abercromby et al., 2007b),

http://dx.doi.org/10.1016/j.jelekin.2013.03.014mailto:lacerda.acr@ufvjm.edu.brhttp://dx.doi.org/10.1016/j.jelekin.2013.03.014http://www.sciencedirect.com/science/journal/10506411http://www.elsevier.com/locate/jelekin

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promoting greater stiffness of the muscle to absorb the accelera-tion and thereby increasing the neuromuscular response producedby the vibration. According to this theory, several studies haveinvestigated the effects of the addition of vibratory stimuli tosquatting exercises because this association appears to enhancethe neuromuscular responses (Delecluse et al., 2003; Roelantset al., 2004; Bogaerts et al., 2007; Marín et al., 2011).

Fratini et al. (2009a,b) demonstrated a positive correlation be-tween muscle activity and the acceleration transmitted duringvibratory stimulus, indicating that acceleration is one of the pointsto be checked during the exercise to quantify the overload of thevibratory stimulus. Thus, EMG and acceleration transmission anal-yses can be used to identify the conditions that maximize neuro-muscular responses and to avoid the problems of chronicexposure that have been highlighted in occupational medicine(Di Gimiane et al., 2012).

Abercromby et al. (2007b) and Di Giminiani et al. (2012) pro-vided the most comprehensive investigations of acute neuromus-cular responses to WBV in the leg muscles. However, thesestudies did not evaluate a key issue: the effects of EMG activityand of the transmission of acceleration on the two most commonpositions that are used when applying WBV (isometric squat at90� or 60� of knee flexion with the tibia perpendicular to theground) (Avelar et al., 2011b, 2012; Simão et al., 2012).

The hypothesis that EMG responses and transmission of acceler-ation to lower limbs are functions of body position is supported bythe theoretical model of Cardinale and Bosco (2003), which postu-lated that the interaction between the mechanical properties ofthe muscle–tendon unit and the tonic vibration reflex (TVR) regu-lates muscle stiffness to dampen vibratory waves. The momentabout the knee joint is greater in the half squat position, resultingin higher tension, and the knee extensors work over a longer length.Therefore, it can be assumed that the knee extensors could have agreater response at 90� of knee flexion compared to 60�, especiallyduring isometric squat exercises performed with the tibia perpen-dicular to the ground. Given the above findings, it is unknownwhether different body positions could modify muscular stiffness,influencing the transmission of vibratory stimuli to the lower limbs.

Assuming that the neuromuscular response during WBV ismediated by Ia afferents, which is the case when the vibrationstimulus is directly applied to the muscle, our hypothesis is thatthe EMG responses of the vastus lateralis, as well as transmissionof acceleration to the lower limbs, are influenced by the presenceof vibration stimuli and by the body’s position on the vibratingplate. To test this hypothesis, the effects of two body positions(squatting at 90� or 60� of knee flexion with the tibia perpendicularto the ground) and of the addition of vibration stimuli on EMG re-sponses and on the transmission of acceleration to the lower limbsunder isometric conditions were examined.

A novel aspect of the present study is that the study includedanalyses of the transmitted acceleration (considered the effectivelocal stimulus) and evaluated its relationship with EMG activity.This analysis could potentially improve the comprehension of theneuromuscular response to these types of treatments. Moreover,in this study, different squat depths (60� and 90�) that were similarto protocols used in practice were evaluated. Physical training pro-tocols and rehabilitation generally use larger knee flexion anglesduring squat exercises (Avelar et al., 2011b, 2012; Simão et al.,2012). Thus, the results may assist professionals who work inrehabilitation and sports training in developing appropriatemethodologies for prescribing a structured training program withprogressive loads that consist of squat exercises with WBV(Escamilla, 2001). Moreover, the results of the present study willprovide a better understanding of the influence of different anglesof knee flexion on neuromuscular responses and accelerationvalues (stimulus intensity during WBV exercise).

2. Methods

2.1. Subjects

The study included 34 male subjects (mean age: 26.34 ±7.07 years, height: 1.74 ± 0.04 m, body mass: 70.77 ± 7.86 kg andbody fat percentage: 12.39 ± 5.40%), aged between 18 and 35 yearswho were physically active according to a self-report. We excludedsubjects with hernia, a history of musculoskeletal diseases, diabe-tes and epilepsy. The choice of male volunteers was made tohomogenize the sample because the distribution of subcutaneousfat varies between men and women, and differences in the per-centage of fat thickness could interfere with the EMG signal (DeLuca, 1997). The study was approved by the Ethics Committee ofthe Federal University of Jequitinhonha and Mucuri Valleys.

2.2. Procedures

The study design consisted of a preliminary session followed bythe experimental conditions. The preliminary session consisted ofverification of the anthropometric measurements (weight andheight) and measurements of the skinfold thickness at three sites(chest, abdomen and thigh) to evaluate the percentage of body fat(Jackson and Pollock, 1978). In the same session, the volunteers par-ticipated in a familiarization procedure on the vibratory platform tolearn the exercise that would be performed during the experimentaltesting.

2.3. Experimental conditions

Seven days after the preliminary session, the volunteers re-turned to the laboratory to perform the experimental tests, whichconsisted of four isometric sets without or with WBV (30 Hz,4 mm) (Cardinale and Lim, 2003; Abercromby et al., 2007b;Ritzmann et al., 2010) at angles of 60� or 90� of knee flexion fora duration of 10 s (Sousa et al., 2007; Ritzmann et al., 2010; Marínet al., 2011). There was 1 min of rest between each test (Cardinaleand Lim, 2003; Abercromby et al., 2007a; Fratini et al., 2009a,b;Marín et al., 2011). The sessions were balanced to control for anypossible effects of fatigue or adaptation to the vibration stimulus(Fig. 1).

The squat exercise was performed using a commercial modelvibratory platform (FitVibe, GymnaUniphy NV, Bilzen, Belgium),which produces vertical sinusoidal vibrations in both legs whilethe platform moves predominantly in the vertical direction.

For this exercise, the volunteers were positioned on the platformwith their feet 28 cm apart. The squat exercise was performed iso-metrically at angles 60� and 90� of knee flexion for 10 s with vibra-tory stimulation (frequency 30 Hz and 4 mm extend), performedwith the tibia perpendicular to the floor (Fig. 2). These vibrationparameters were chosen because Cardinale and Lim (2003) sug-gested that these parameters could induce a greater reflex responseof the VL during exercise associated with WBV (Cardinale and Lim,2003).

To perform the squat exercise without WBV, the vibratory stim-ulus was not applied, but the individual remained on the vibratoryplatform with the power off. For temporal control of each exercise,an examiner was instructed to indicate the maintenance of eachpredetermined angle. In addition, the participants were instructedon proper body positioning (i.e., the correct positioning of the feet,spine, arms and head) while performing the squat exercises in eachexperimental situation.

During the tests, the subjects were barefoot to avoid any effectof dampening due to different footwear (Marín et al., 2009). During

Fig. 2. Squat exercise at angles 60� and 90� of knee flexion.

Fig. 1. Study flow chart.

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and after the testing protocol, the subjects were instructed toreport any discomfort to the study’s investigators.

2.4. EMG activation

Muscle activity was measured in the VL of the dominant limb(Cardinale and Lim, 2003; Abercromby et al., 2007b; Sousa et al.,2007) for a duration of 10 s (Abercromby et al., 2007b) of squatwith or without WBV. This muscle was chosen because the VLmuscle produces 40–50% more muscle activity than the rectusfemoris muscle during the squat exercise (Escamilla et al., 1998),and it produces a greater activation of the muscles of the kneeextensor group during vibration exercise (Roelants et al., 2006).

For the acquisition of the electromyographic signals from the VLmuscle, we used circular surface electrodes that were 30 mm indiameter, Ag/AgCl (MedTrace, Sao Paulo, Brazil) with a distanceof 20 mm between the electrodes. The site of attachment for eachelectrode was prepared by shaving and cleaning with rubbing alco-hol (Hermens et al., 2000). The electrodes were secured with elas-tic straps to prevent them from releasing during vibration and toprevent movement of the cable (Cardinale and Lim, 2003).

The placement of the electrodes was followed the recommenda-tions of SENIAM (Surface Electromyography for the Non-InvasiveAssessment of Muscles). The location of the electrodes for captur-ing the activation of the VL was at a site 2/3 of the length of a lineconnecting the anterior superior iliac spine to the patella, and thereference electrode was positioned on the spinous process of C7.

The electromyographic signal was obtained with a system offour channels (Miotool400, MIOTEC, Porto Alegre, Brazil) with a

sampling rate of 2000 Hz, a gain of 500 and a common moderejection >110 dB. The data from the EMG signals were storedusing Miograph software. All EMG signals were digitally filteredusing a 4th-order Butterworth band-pass filter with a cut-off of20–450 Hz and a notch filter of 60 Hz. The movement artifacts gen-erated by the vibration stimulus were filtered with a 4th-orderButterworth band-stop filter with a cut-off frequency of 30 Hzand harmonics (Fratini et al., 2009a,b).

To obtain the amplitudes of the EMG data, we discarded the first2 s and the last 2 s of the registered signal. The average of the rec-tified signal over 6 s was calculated (Sousa et al., 2007; Marín et al.,2011).

The amplitude of the estimated EMG by the RMS (root meansquare) reflects the pattern of recruitment or activation of motorunits that control a particular muscle. Therefore, there is a linearrelationship between the EMG and the force generated by the mus-cle, especially in isometric contractions (Sousa et al., 2007). Nor-malization relative to the maximum voluntary contraction wasnot performed (Abercromby et al., 2007b; Marín et al., 2009) be-cause, according to Soderberg and Knutson (2000), in an experi-mental procedure such this, the individual is his own control;when comparisons are made on the same day and in the samemuscle, normalization of the signal becomes unnecessary(Soderberg and Knutson, 2000).

Before beginning the study, the intra-examiner reliability wascalculated for the EMG activity. For this, a pilot study with 30 vol-unteers was conducted on two separate days with 24 h betweenthe tests. The intra-correlation coefficient (ICC) was 0.814 (95% CI0.1760-0958).

Fig. 3. Electromyographic activity (EMG) of the vastus lateralis muscle (RMS) atdifferent angles of knee flexion with and without whole-body vibration (WBV). Thedata are presented as the mean and standard deviation. ⁄P 6 0.05.

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2.5. Evaluation of the transmissibility of the vibratory stimulus

To assess the transmissibility of the vibration stimulus, twoaccelerometers (10 g and 3 cm in length each) (Mega, Finland)were placed on the knee and hip of the dominant limb, accordingto the following measures: knee – the distance from the lateralmalleolus to the joint line; hip – the ipsilateral distance from thelateral malleolus to the anterior superior iliac spine. These mea-surements were performed to minimize the influence of the sizeof the lower limbs on the accelerations. The positions of the accel-erometers were: knee – 41.12 ± 2.61 cm; hip – 93.41 ± 8.89 cm.

The accelerometers were connected to the receiver ME-6000(Mega, Finland) and configured for the acquisition and the mea-surement range of 2000 Hz and approximately 6 g. Evaluations ofthe accelerations in the Y and Z axes correspond to the accelera-tions in the vertical and medio-lateral plane, respectively. It isworth mentioning that the vibratory platform used in this studyproduces a vertical synchronous vibration, in which both legs aresimultaneously vibrated while the vibratory platform moves pre-dominantly in the vertical direction (Y axis) during exposure tothe vibratory stimulus (Cochrane, 2011). Moreover, the model ofthe synchronous vibration platform is more popular in clinicalpractice, and thus it is used in most studies that evaluate the effec-tiveness of WBV training (Cardinale and Lim, 2003; Roelants et al.,2006; Avelar et al., 2011a,b, 2012; Marín et al., 2011; Hannah et al.,2013; Simão et al., 2012).

After data collection, the data were transferred to the Megawinsoftware (Mega, Finland) and analyzed in Matlab 2009b (Math-works, USA). We discarded the first and the last 2 s of data acqui-sition and therefore analyzed the interval between 3 and 8 s of datacollection.

A spectral analysis of the data was performed to determinethe frequency of the occurrence of movement artifacts. A spec-tral analysis of the accelerometer data was performed by divid-ing each signal into overlapping segments, which were thensegmented using a 1024-sample Hanning window. The short-term frequency content of each segment was computed usinga 8192-sample Fast Fourier Transform (FFT) with the sectionsoverlapping by 1000 samples. Inspection of the resulting spec-trograms revealed the presence of significant motion artifactsnot only at the fundamental excitation frequency (30 Hz) butalso, to a lesser degree, at integer multiples of the excitationfrequency. With these results, it was possible to determinethe parameters for the Notch filter used to remove the influ-ence of motion artifacts of the EMG signal (Fratini et al.,2009a,b).

The RMS acceleration for each accelerometer was calculated toassess the transmissibility of acceleration produced by the vibra-tion platform.

2.6. Statistical analysis

The SPSS� (IBM�, Chicago, IL, USA) version 18.0 software pro-gram was used for statistical analysis. The data are expressed asthe means and standard deviations. The significance level wasp 6 0.05. The mean EMGrms (measured from the vastus lateralis)and the transmissibility of acceleration were used for the analy-sis (the dependent variables of this study). Initially, the Kol-mogorov–Smirnov test was used to assess the normality of thedata. A 2 � 2 two-way repeated-measures ANOVA was calculatedwith Bonferroni-corrected post hoc tests for the mean EMGrms(measured from the vastus lateralis) and the transmissibility ofacceleration, with the following factors: (1) the knee angle and(2) squat exercise with or without WBV. To verify the size ofthe difference between the conditions, the magnitude and statis-tical power were analyzed.

3. Results

3.1. Influence of different angles of knee flexion on the EMG activity

We observed a greater EMG activation of the VL at 90� of kneeflexion compared to 60� during the squat exercise performed with-out WBV and in combination with WBV (p < 0.001, effect size:0.214, power: 1.00) (Fig. 3).

3.2. Influence of the addition of WBV to squatting exercises on the EMGactivity

The addition of the vibratory stimulus to the squat exercise didnot alter the EMG activation of the VL at 60� of knee flexion and at90� of knee flexion (p < 0.704, effect size: 0.001, power: 0.067)(Fig. 3).

3.3. Interaction

The interaction between different angles of knee flexion andaddition of WBV on EMG was not significant (p: 0.938, effect size:0.00, power: 0.051).

3.4. Transmissibility of acceleration

3.4.1. Knee jointWe observed that the addition of WBV to squat exercises pro-

duced more vertical (Y) (p < 0.001, effect size: 0.969, power:1.000) and medio-lateral (Z) (p < 0.001, effect size: 0.735, power:1.000) acceleration in the lower limbs during the squat exerciseindependent of the angle (Y – p: 0.435, effect size: 0.005, power:0.122 and Z – p: 0.204, effect size: 0.014, power: 0.244) (Table 1).

3.4.2. Hip jointWe observed that the addition of WBV to squat exercises pro-

duced more vertical (Y) (p < 0.001, effect size: 0.720, power:1.000) and medio-lateral (Z) (p < 0.001, effect size: 0.481, power:1.000) acceleration in the lower limbs during the squat exerciseindependent of the angle (Y – p: 0.687, effect size: 0.001, power:0.069 and Z – p: 0.921, effect size: 0.000, power: 0.051) (Table 1).

Table 1Values of acceleration (Root Mean Square, Mean+SD) at different angles of knee flexion with and without the addition of whole-body vibration (WBV) to squatting exercises.

Joint 60� 90� p

With WBV Without WBV With WBV Without WBV Angle Vibration Interaction

Hip Z 0.240 ± 0.116 0.014 ± 0.007 0.231 ± 0.200 0.020 ± 0.010 0.921

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electromyographic response (Roelants et al., 2006). However, inthe aforementioned study, the authors did not present the positionof the tibia, and the control of this variable is extremely importantbecause it interferes with the activation of the quadriceps muscle.

The hypothesis of the EMG responses and of the transmission ofacceleration to the lower limbs as a function of body position issupported by the theoretical model of Cardinale and Bosco(2003), which postulated that the interaction between themechanical properties of the muscle–tendon unit and the tonicvibration reflex (TVR) regulates muscle stiffness to dampen vibra-tory waves. Thus, the presence of the potentiation of muscle acti-vation could improve muscle stiffness and consequently thetransmission of acceleration to the lower limbs. Furthermore, thissupposition was supported by Fratini et al. (2009a,b), who demon-strated a positive correlation between muscle activity and theacceleration transmitted during vibratory stimulation, indicatingthat the transmissibility of acceleration to the lower limbs can con-tribute to determining the conditions that maximize neuromuscu-lar responses and can avoid the problems of chronic exposure thathave been highlighted in occupational medicine.

The results of the present study disproved the aforementionedhypothesis because 90� of knee flexion resulted in an enhancementof the isometric muscular contraction of the vastus lateralis com-pared to 60� of knee flexion, without modification of the accelera-tion transmission.

Despite the relevance of this study, it had some limitations with re-gard to the selected sample and the experimental protocol adopted.Regarding the sample, the subjects having been healthy and the ab-sence of an objective assessment of the strength of the subjects indi-cate that caution should be taken regarding the generalization ofthese results. With regard to the experimental protocol, the tests wereconducted in a static position during a single session and evaluation.Therefore, the results might have been different if a dynamic protocolwas applied or after a training protocol with WBV. Furthermore, itshould be noted that different types of vibration can produce differentmuscle activation responses (Abercromby et al., 2007b; Ritzmannet al., 2013), and the results should be interpreted considering theuse of synchronous, vertical, and sinusoidal vibration.

Conflict of interest

None declared.

Acknowledgements

This study was supported by FAPEMIG, CNPq, and CAPES.

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graphy and Kinesiology 23 (2013) 844–850

Núbia Carelli Pereira de Avelar earned a degree inPhysiotherapy in 2008 and a Master’s degree in Bio-

logical Sciences (Physiology) in 2010, both at the Fed-eral University of the Jequitinhonha and Mucuri Valleys,Brazil. She is currently working on her Ph.D., investi-gating the acute and chronic effects of whole-bodyvibration exercise. Her major research interests arerelated to physical activity and exercise physiology.

850 N.C.P. Avelar et al. / Journal of Electromyo

Vanessa Goncalves César Ribeiro is a graduate studentin physiotherapy at the Federal University of theJequitinhonha and Mucuri Valleys. She works in thestudent undergraduate research lab for exercise physi-ology.

Bruno Mezêncio earned a degree in Physical Educationand a Master’s degree in mechanical engineering in2010 from the Federal University of Minas Gerais. Heworks at the University of São Paulo in the Laboratory ofBiomechanics. His major research interest is researchmethods in biomechanics.

Sueli Ferreira Fonseca earned a bachelor’s degree inphysiotherapy in 2011 from the Federal University ofthe Jequitinhonha and Mucuri Valleys, Brazil. She iscurrently working on her Master’s degree, investigatingthe thermoregulatory response in hypertensivehumans.

Rosalina Tossige-Gomes earned a bachelor’s degree inPhysiotherapy from the Federal University of the Val-leys Jequitinhonha and Mucuri in 2011. She is currentlyworking on her Master’s, evaluating the effect of exer-cise on the immune system.

Sidney José Costa earned a degree as a Physical Edu-cation teacher in 2011 at the Federal University of theJequitinhonha and Mucuri Valleys. He is currentlyundertaking research in the areas of sports training,physical activity and health. His major research inter-ests are related to physical activity and exercise physi-ology.

Leszek Szmuchrowski earned a doctoral degree inSports Training Sciences at the Warsaw Academy in1995. He is the coordinator of the Load EvaluationLaboratory at the Sports Excellence Center of the FederalUniversity of Minas Gerais, Brazil. He is also supervisorof the Athletics Sports Training Center of Federal Uni-versity of Minas Gerais. His major research interests arein the planning, registration and control of load trainingand mechanical vibration.

Fernando Gripp earned the degree of Physical Educa-tion Teacher in 1996 and a Master’s degree in PhysicalEducation in 2001, both at the Federal University ofMinas Gerais. He is currently working on research in theareas of sports training, physical activity and health atthe Federal University of the Jequitinhonha and MucuriValleys, Brazil.

Cândido Celso Coimbra earned his Ph.D. in Physiologyfrom the University of São Paulo (1982). Currently, he isa professor at the Federal University of Minas Gerais. Hehas experience in physiology with an emphases onautonomic regulation, intermediary metabolism, bodytemperature, and the metabolic response to stress. Heperforms research on the following topics: exercisephysiology and regulation of autonomic glucose; insulinsecretion mobilization; and free fatty acids in adiposetissue.

Ana Cristina R. Lacerda earned her Ph.D. in BiologicalSciences (Physiology) in 2006 and works as a full pro-fessor in the Department of Physiotherapy, Faculty ofHealthy and Biological Sciences, Federal University ofJequitinhonha and Mucuri Valleys, Brazil. Her majorresearch focus is in the field of exercise physiology.

Influence of the knee flexion on muscle activation and transmissibility during whole body vibration1 Introduction2 Methods2.1 Subjects2.2 Procedures2.3 Experimental conditions2.4 EMG activation2.5 Evaluation of the transmissibility of the vibratory stimulus2.6 Statistical analysis

3 Results3.1 Influence of different angles of knee flexion on the EMG activity3.2 Influence of the addition of WBV to squatting exercises on the EMG activity3.3 Interaction3.4 Transmissibility of acceleration3.4.1 Knee joint3.4.2 Hip joint

3.5 Interaction

4 DiscussionConflict of interestAcknowledgementsReferences