Research Article Muscle Activation Differs between Three...

Research ArticleMuscle Activation Differs between Three DifferentKnee Joint-Angle Positions during a Maximal IsometricBack Squat Exercise

Paulo Henrique Marchetti12 Josinaldo Jarbas da Silva1

Brad Jon Schoenfeld3 Priscyla Silva Monteiro Nardi2 Silvio Luis Pecoraro1

Julia Maria DrsquoAndreacutea Greve2 and Erin Hartigan4

1Graduate Program in Science of Human Movement College of Health Science (FACIS) Methodist University of Piracicaba13423-070 Piracicaba SP Brazil2Institute of Orthopedics and Traumatology School of Medicine University of Sao Paulo Laboratory of Kinesiology05403-000 Sao Paulo SP Brazil3Department of Health Sciences Program of Exercise Science CUNY Lehman College Bronx NY 10468 USA4Department of Physical Therapy University of New England Portland ME 04103 USA

Correspondence should be addressed to Paulo Henrique Marchetti drpmarchettigmailcom

Received 9 March 2016 Revised 2 June 2016 Accepted 26 June 2016

Academic Editor Mark Willems

Copyright copy 2016 Paulo Henrique Marchetti et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

The purpose of this study was to compare muscle activation of the lower limb muscles when performing a maximal isometricback squat exercise over three different positions Fifteen young healthy resistance-trained men performed an isometric backsquat at three knee joint angles (20∘ 90∘ and 140∘) in a randomized counterbalanced fashion Surface electromyography wasused to measure muscle activation of the vastus lateralis (VL) vastus medialis (VM) rectus femoris (RF) biceps femoris (BF)semitendinosus (ST) and gluteusmaximus (GM) In generalmuscle activitywas the highest at 90∘ for the three quadricepsmusclesyet differences in muscle activation between knee angles were muscle specific Activity of the GM was significantly greater at 20∘and 90∘ compared to 140∘ The BF and ST displayed similar activation at all joint angles In conclusion knee position alters musclesactivation of the quadriceps and gluteus maximus muscles An isometric back squat at 90∘ generates the highest overall muscleactivation yet an isometric back squat at 140∘ generates the lowest overall muscle activation of the VL and GM only

1 Introduction

The squat is one of the most frequently used exercisesin the field of strength and conditioning The squat is anexercise that increases hip and knee extensor muscle strengthwhich then indirectly improves the quality of life in athleticand nonathletic populations [1] The squat exercise utilizesmuscles with different morphology (monoarticular and biar-ticular) Muscle forces also vary depending on joint positions(moment arm length-tension relationship) whether the

muscle acts as a prime mover or stabilizer and whether thetask is dynamic or staticThough evidence suggests that archi-tecture position and function drive muscle performanceduring the squat little is known about the neuromuscularchanges that occur from a muscle activation standpointElucidating how muscle activation patterns change in themonoarticular and biarticular knee and hip extensors duringsquatting at different knee angles would thus enhance ourunderstanding of how one could capitalize on maximizingmuscle activation and the best position to specific evaluations

Hindawi Publishing CorporationJournal of Sports MedicineVolume 2016 Article ID 3846123 6 pageshttpdxdoiorg10115520163846123

2 Journal of Sports Medicine

and sEMG normalization This would be a first step tothen apply the knowledge during exercise prescription thatincludes the squat

Considering that the squat exercise is a multijoint taska large number of muscle groups can be activated simultane-ously in amore complex way Several studies have shown thatmanipulating features of the squat exercise resulted in alteredmuscle activity These manipulations include changes in footposition [2 3] barbell position [4] stability of the surfaceon which the exercise is performed [5ndash9] different levels ofintensity of load [10] range of motion [10ndash12] and differentequipment [13]

As a multijoint exercise the knee extensors (eg rectusfemoris RF vastus lateralis VL and vastus medialis VM)andhip extensors (eg gluteusmaximusGM biceps femorisBF and semitendinosus ST) are considered to be the primemovers during the squat exercise with other muscles actingin a secondary capacity [1 11 14] Caterisano et al [11]measured the relative contributions of GM BF VM and VLmuscles of ten experienced lifters while performing dynamicssquats at 3 depths (partial squat (the angle between the femurand the tibia was sim236 rad at the knee joint) parallel squat(the angle between the femur and the tibiawassim157 rad at theknee joint) and full-depth squat (the angle between the femurand the tibia was sim079 rad at the knee joint)) using 100ndash125 of body weight as resistance The results suggested thatthe GM was most active rather than the BF the VM or theVL during a concentric contraction as squat depth increasesOn the contrary Robertson et al [12] determined that theGM displayed a reduced activity level at maximum squatdepth Robertson et al [12] also showed that the biarticularmuscles functioned mainly as stabilizers of the ankle kneeand hip joints by working eccentrically to control descentor transferring energy among the segments during ascentWhether monoarticular and biarticular hip and knee exten-sors have different muscle activation during an isometricsquat and whether activation changes during different kneeangles are unclear Consequently the rationale of the presentstudy was to evaluate indirectly the muscle activation indifferent mechanical positions related to differences in thejoint-angle-torque diagram and the sticking region effect inall three joint angles (20∘ 90∘ and 140∘)

Finally differences in muscle activity during dynamicand isometric squat exercise have received less attentionin the physical education and rehabilitation area Othershave shown the isometric squat (90∘ and 120∘ of kneejoin position) as a reliable test to provide an indicator ofchanges in dynamic strength (1-repetition maximum barbellback squat 1RM) and power performance [15 16] howeverwhether muscle activity changes as an isometric squat ismanipulated is unknown Althoughmotor units are recruiteddifferently during dynamic movements they generate thesame relative forcetorque during a static contraction [17]Despite inherent neural and mechanical differences betweenisometric and dynamic contractions the isometric squatexercise performed in different knee joint angles may be usedto understand changes in muscle activation patterns withoutconfounding any other external effects such as the stretch-shortening cycle from dynamic movements [18] Therefore

the purpose of this study was to evaluate the maximalisometric muscle activation of the lower limbs during threedifferent knee joint-angle positions in the back squat exercise

2 Methods

21 Subjects We collected the peak amplitude of the rootmean square (RMS) from VL sEMG data during a pilotstudy to drive this power analysis Based on a statisticalpower analysis derived from these data (RMS VL EMG) itwas determined that twelve subjects would be necessary toachieve an alpha level of 005 effect size of 141 and a power(1 minus 120573) of 080 [19] Therefore we recruited fifteen younghealthy resistance-trained men (age 30 plusmn 7 years height174 plusmn 6 cm and total body mass 76 plusmn 9 kg with 5 plusmn 1 yearsof experience on the back squat exercise) to participate inthis study Subjects had no previous lower back injury nosurgery on the lower extremities and no history of injurywith residual symptoms (pain ldquogiving-awayrdquo sensations) inthe lower limbs within the last year This study was approvedby the university research ethics committee and all subjectsread and signed an informed consent document

22 Procedures Prior to data collection subjects were askedto identify their preferred leg for kicking a ball which wasthen considered their dominant leg [20] All subjects wereright-leg dominant Volunteers attended one session in thelaboratory and they reported to have refrained from per-forming any lower body exercise other than activities of dailyliving for at least 48 hours prior to testing Subjects performeda 5-minute cycle warm-up and a familiarization session withall isometric conditions The familiarization session was per-formed in all joint angles used during the experimental pro-cedure (20∘ 90∘ and 140∘) for 1 set of 3 seconds each After thewarm-up and familiarization all subjects performed threetrials of 10-second maximal isometric contractions against alocked smith machine under three different knee joint-anglepositions in a randomized counterbalanced order back squatat 20 degrees (20∘) back squat at 90 degrees (90∘) and backsquat at 140 degrees (140∘) The knee joint-angle positionswere evaluated by a goniometer (Plastic 1210158401015840 Goniometer 360Degree ISOM) and for all angles full knee extension wasconsidered the ldquozerordquo positionThe subjectsrsquo feet were alwayspositioned at hip width and vertically alignedwith the barbellposition The barbell was positioned on the shoulders (high-bar position) for all subjects and experimental conditions Arest period of 15 minutes was provided between conditionswith 3 minutes afforded between sets All measures wereperformed at the same hour of the day between 9 and 12 AMand by the same researcher

23 Measures

231 Surface Electromyography (sEMG) The subjectsrsquo hairwas shaved at the site of electrode placement and the skin wascleaned with alcohol before the sEMG electrode was affixedBipolar active disposable dual AgAgCl snap electrodes wereused which were 1 cm in diameter for each circular conduc-tive area with 2 cm center-to-center spacing Electrodes were

Journal of Sports Medicine 3

placed on the dominant limb along the axes of the musclefibers according to the SENIAMISEKI protocol [21] gluteusmaximus (GM) at 50 of the distance between the sacralvertebrae and the greater trochanter vastus lateralis (VL)at 23 of the distance between the anterior spine iliac andthe superior aspect of the lateral side of the patella rectusfemoris (RF) at 50 on the line from the anterior spine iliacto the superior part of patella vastus medialis (VM) at 80on the line between the anterior spine iliac superior andthe joint space in front of the anterior border of the medialligament biceps femoris (BF) at 50 on the line between theischial tuberosity and the lateral epicondyle of the tibia andsemitendinosus (ST) at 50 on the line between the ischialtuberosity and the medial epicondyle of the tibia The sEMGsignals were recorded by an electromyographic acquisitionsystem (EMG832C EMG System do Brasil Sao Jose dosCampos Brazil) with a sampling rate of 2000Hz using acommercially designed software program (EMG System doBrasil Sao Jose dos Campos Brazil) EMGactivity was ampli-fied (bipolar differential amplifier input impedance = 2MΩcommon mode rejection ratio gt 100 dBmin (60Hz) gain times20 noise gt 5 120583V) and converted from an analog to digitalsignal (12 bits) A ground electrode was placed on the rightclavicle EMG signals collected during all conditions werenormalized to a maximum voluntary isometric contraction(MVIC) against fixed strap resistance Then two trials offive-second MVICs were performed for each muscle withone-minute rest between actions for the dominant leg Thefirst MVIC was performed to familiarize the participant withthe procedure For GM MVIC subjects were in the proneposition with their knee flexed at 90∘ and resistance placedon the distal region of the thigh with the pelvis stabilizedFor VL VM and RF MVICs subjects were seated withtheir knee flexed at 90∘ and resistance placed on the distaltibia For BF and ST MVICs subjects were seated with theirknee flexed at 90∘ and resistance placed on the distal tibiaVerbal encouragement was given during all MVICs Theorder of MVICs was counterbalanced to avoid any potentialneuromuscular fatigue

24 Data Analyses All sEMG data were analyzed withcustomized Matlab routine (MathWorks Inc USA) Thedigitized sEMG data were band-pass filtered at 20ndash400Hzusing a fourth-order Butterworth filter with zero lag Formuscle activation timedomain analysis RMS (150msmovingwindow) was calculated during the MVIC Isometric backsquat data was then normalized to the RMS peak of thetwo peak MVICs the first second was removed from RMSnormalized and the following 3 seconds of each trial wereintegrated (iEMG)

25 Statistical Analyses The normality and homogeneity ofvariances within the data were confirmed with the Shapiro-Wilk and Levenersquos tests respectively To test differences foreach muscle activity (iEMG) repeated measures ANOVAswere used Post hoc comparisons were performed withthe Bonferroni test Cohenrsquos formula for effect size (d) wascalculated and the results were based on the following

Table 1 Effect size (119889) comparisons for iEMG between knee joint-angle positions

Angle VL VM RF BF ST GM20∘ times 90∘ 099 091 098 008 020 00390∘ times 140∘ 187 087 065 027 005 18120∘ times 140∘ 095 018 050 036 024 176

VL VM RF BF ST GM0

50

100

150

200

250

20 degrees 90 degrees 140 degrees

lowast

lowast

lowast

lowast

lowast

lowast

iEM

G (

MV

IC middots)

Figure 1 Mean and standard deviation of iEMG in three differentknee joint-angle positions lowastSignificant differences 119875 lt 005

criteria lt035 trivial effect 035ndash080 small effect 080ndash150 moderate effect and gt15 large effect for recreationallytrained subjects [22] Interrater reliability was assessed forthe researcher who positioned and evaluated iEMG tracingsfor allmuscles and conditions Reliability was operationalizedusing the following criterialt04 poor 04ndashlt075 satisfactoryge075 excellent [23] The ICCs ranged between 091 and 099(excellent) for all iEMG data An alpha of 5 was used todetermine statistical significance

3 Results

There was a significant main effect of VL (119875 lt 0001) VM(119875 = 0030) RF (119875 = 0018) and GM (119875 lt 0001) for muscleactivity during three different knee joint-angle positions (20∘90∘ and 140∘) in the isometric back squat

TheVL activity was significantly less in 140∘ than 20∘ (119875 =0027 Δ = 244) and 90∘ (119875 lt 0001 Δ = 375) TheVM activity was significantly less in 140∘ than 90∘ (119875 = 0036Δ = 30) The RF activity was significantly less in 20∘ than90∘ (119875 = 0015 Δ = 36) The GM activity was significantlyless in 140∘ than 90∘ (119875 lt 0001 Δ = 804) and 20∘ (119875 lt0001 Δ = 80) (Table 1 and Figure 1)

4 Discussion

The purpose of this study was to evaluate the maximalisometric muscle activation of the lower limbs during three


different knee joint-angle positions in the back squat exerciseThe architecture position and function influence muscleforces during the squat however little is known about theneuromuscular changes that occur from a muscle activationstandpointTheprimary finding of this investigationwas thatduring isometric squatting a position of 90∘ of knee jointangle demonstrated the overall highest muscle activation ofthe quadriceps and gluteus maximus whereas the 140∘ kneejoint-angle position presented the lowest muscle activationvalues for almost all muscles that act as prime moversInterestingly the activation of the hamstring did not differamong knee joint-angle positions and the three quadricepsmuscles responded differently as the knee went from arelatively extended position to a more flexed position

Given the close chain nature of the squat as the knee jointchanges position the hip joint angles also change positionsConsequently the squat exercise simultaneously utilizes sev-eral muscles with different morphologies (monoarticular andbiarticular) in amanner that produces ldquomuscle coordinationrdquo[24] A multijoint task to strengthen the knee and hipextensors is more complex for the neuromuscular system astwo joints work in concert to achieve the task [12] Alsosince somemuscles crossmore than one joint the complexityincreases compared to open chain terminal knee extension orisolated hip extension exercise [12] During the squat exercisethere are several biarticular muscles interacting including thehamstrings and RF [1] Biarticular muscles such as RF BFand ST have intermediate activation when the muscles haveagonistic action at one joint and antagonistic action at theother joint this is in contrast with the high activation seenwhen a biarticular muscle works as an agonist for both jointssimultaneously [24] Lombard [25] suggested that biarticularmuscles of the lower extremity act in a ldquoparadoxicalrdquo fashionwhen the movement is constrained or controlled (namedLombardrsquos paradox) it is observed when RF BF and STcontract concurrentlywhen rising froma chairThe extensionseen from both the hip and the knee is the result of thedifferentialmoment arms of the twomuscles at each jointThepresent results showed lowmuscle activation for BF and ST inall knee positions probably because these muscles act morelike a joint stabilizer at the knee and a prime mover at thehip Both BF and ST have the longer moment arm at the hipthereby creating a hip extensor momentThus the BF and STmuscles allow for the extension of both the knee and the hip[12] Since the RF has a greater moment arm across the kneedue to the patella it creates an extensor moment at the kneejoint Considering the present results the RF showed highermuscle activation at 90∘ when compared to 20∘ however itwas similar to 140∘ of knee angleThis may represent a highereffect on muscle activation during the initial phase of thesquat movement (between 20∘ and 90∘) than after 90∘ sincethe muscle activation did not change

On the other hand monoarticular muscles act on onespecific joint During the squat exercise several monoartic-ular muscles contribute to movement including the soleusvasti (lateralis medialis and intermedius) and GM [1]The present results showed that muscle activation for allmonoarticular muscles (eg VM VL and GM) did notdiffer between 20∘ and 90∘ Additionally the highest muscle

activation was observed at 90∘ when compared to 20∘ and140∘ on the other hand 140∘ presented the lowest activationfor VL and GM muscles Interestingly the VM behaveddifferently from the other monoarticular muscles even theVL as themuscle activation of the VMdid not differ betweenthe 20- and 140-degree knee joint angles

Usually when monoarticular muscles perform as ago-nists the activation increases as the joint moment increases[24] Additionally monoarticular muscles are affected bythe sticking region which is considered a poor mechanicalforce position in which the mechanical advantage of themuscles involved is such that their capacity to exert forceis reduced and where the lifter experiences difficulty inexerting force against the external load [26ndash30] Cardinaleet al [31] displayed that the higher muscle activation duringthe squat exercise occurs at 90∘ of knee joint-angle positionwhich is considered the sticking region The present resultssupport this finding for all monoarticular muscles analyzed(VL VM and GM) Our findings support this theory as allmonoarticular muscles presented lower values of activationat 140∘ of knee joint-angle position when compared to 90∘In this specific position (at 140∘) it is feasible to speculatethat changes inmuscle lengthmodifymuscle contractile abil-ities and in turn modify sEMG-force and sEMG-momentrelationships [18 24] Alternatively afferent signals frommuscles could decrease motoneuronal firing frequency (ieGolgi tendon reflex) during isometric contractions when themuscle fibers are in an elongated position [17]

Others have also investigated muscle activation duringthe squat by comparing different knee joint angles yetprevious studies compared knee positions during a dynamicsquat not an isometric squat Caterisano et al [11] measuredthe relative contributions of GM BF VM and VL musclesof ten experienced lifters while performing dynamics squatsat 3 depths (partial squat (the angle between the femur andthe tibia was sim236 rad at the knee joint) parallel squat(the angle between the femur and the tibia was sim157 radat the knee joint) and full-depth squat (the angle betweenthe femur and the tibia was sim079 rad at the knee joint))using 100ndash125 of body weight as resistance Caterisanoet al [11] found that during the concentric phase of thedynamic squat the GM activation was higher during full-depth (354) squat compared to the partial (169) andparallel (280) squat exercise and that the BF the VMand the VL did not change The results suggested that theGM rather than the BF the VM or the VL becomes moreactive in concentric contraction as squat depth increasesOthers have also shown superiormuscular hypertrophywhensquatting throughout a full versus a partial range of motion[32 33] Our findings of less muscle activation at 140∘ donot support Bloomquist and colleaguesrsquo findings The greatercross-sectional area of the muscles found by Bloomquist etal [32] may be more related to time under tension than themuscle activation However without muscle activation datathis remains speculative In opposition when our subjectsperformed an isometric squat in different positions the GMactivity was the highest in the 90-degree position not thedeeper knee flexion position Perhaps the change in 100ndash125 body weight load during the dynamic trials and our


maximum isometric load in all three conditions influencethe lack of agreement between the studies Similar to ourresults Robertson et al [12] reported that the GM muscleactivity level was reduced at maximum full (deep-knee) squatdepth Robertson et al [12] also concluded that the biarticularmuscles (BF ST and RF) functioned mainly as stabilizers ofthe knee and hip joints during the eccentric and concentricphases of a dynamic squat The authors presumed that thereduced GM activity level at maximum squat depth wasbecause the GM was not needed to maintain stability orperhaps it permitted an extra degree of hip flexion thatcreated a deeper countermovement immediately before theascent phase From an activation standpoint our findingssuggest a diminished benefit from squatting beyond 90∘ Thereason for these seemingly contradictory findings amongstudies remains to be elucidated Investigations comparingmuscle activity during isometric and dynamic squatting areneeded

A limitation of this study includes the use of healthywell-trained men only and therefore our findings are notgeneralizable to other conditions populations or womenWe also have a small sample size thus this study may beunderpowered to identify differences between knee jointpositions We did not control for hip angles to create a morerealistic squat performance

5 Conclusion

Knee position alters muscles activation of the quadricepsand gluteus maximus muscles An isometric back squat at90∘ generates the highest overall muscle activation yet anisometric back squat at 140∘ generates the lowest overallmuscle activation of the VL and GM only Knee angledid not affect muscle activation of the hamstrings Thuswe recommend performing an isometric squat at 90∘ tomaximize neuromuscular recruitment of the knee and hipextensors

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

References

[1] B J Schoenfeld ldquoSquatting kinematics and kinetics and theirapplication to exercise performancerdquo Journal of Strength andConditioning Research vol 24 no 12 pp 3497ndash3506 2010

[2] S T McCaw and D R Melrose ldquoStance width and bar loadeffects on legmuscle activity during the parallel squatrdquoMedicineamp Science in Sports amp Exercise vol 31 no 3 pp 428ndash436 1999

[3] A Paoli G Marcolin and N Petrone ldquoThe effect of stancewidth on the electromyographical activity of eight superficialthigh muscles during back squat with different bar loadsrdquoJournal of Strength and Conditioning Research vol 23 no 1 pp246ndash250 2009

[4] J C Gullett M D Tillman G M Gutierrez and J W ChowldquoA biomechanical comparison of back and front squats in

healthy trained individualsrdquo Journal of Strength and Condition-ing Research vol 23 no 1 pp 284ndash292 2009

[5] K Anderson and D G Behm ldquoTrunk muscle activity increaseswith unstable squat movementsrdquo Canadian Journal of AppliedPhysiology vol 30 no 1 pp 33ndash45 2005

[6] E J Drinkwater E J Pritchett and D G Behm ldquoEffect ofinstability and resistance on unintentional squat-lifting kinet-icsrdquo International Journal of Sports Physiology and Performancevol 2 no 4 pp 400ndash413 2007

[7] J M Kohler S P Flanagan andW CWhiting ldquoMuscle activa-tion patterns while lifting stable and unstable loads on stableand unstable surfacesrdquo Journal of Strength and ConditioningResearch vol 24 no 2 pp 313ndash321 2010

[8] JMMcBride P Cormie and J RDeane ldquoIsometric squat forceoutput and muscle activity in stable and unstable conditionsrdquoJournal of Strength and Conditioning Research vol 20 no 4 pp915ndash918 2006

[9] J M McBride T R Larkin A M Dayne T L Haines and T JKirby ldquoEffect of absolute and relative loading onmuscle activityduring stable and unstable squattingrdquo International Journal ofSports Physiology and Performance vol 5 no 2 pp 177ndash1832010

[10] R R Aspe and P A Swinton ldquoElectromyographic and kineticcomparison of the back squat and overhead squatrdquo Journal ofStrength and Conditioning Research vol 28 no 10 pp 2827ndash2836 2014

[11] A Caterisano R F Moss T K Pellinger et al ldquoThe effect ofback squat depth on the EMG activity of 4 superficial hip andthigh musclesrdquo Journal of Strength and Conditioning Researchvol 16 no 3 pp 428ndash432 2002

[12] D G E Robertson J-M J Wilson and T A St PierreldquoLower extremity muscle functions during full squatsrdquo Journalof Applied Biomechanics vol 24 no 4 pp 333ndash339 2008

[13] A H Saeterbakken V Andersen and R van den TillaarldquoComparison of kinematics and muscle activation in free-weight back squat with and without elastic bandsrdquo Journal ofStrength and Conditioning Research vol 30 no 4 pp 945ndash9522016

[14] P H Marchetti W A Gomes W A Da Luz Junior et alldquoAspectos neuromecanicos do exercıcio agachamentordquo RevistaCentro de Pesquisas Avancadas emQualidade de Vida vol 5 no2 pp 1ndash16 2013

[15] A J Blazevich N Gill and R U Newton ldquoReliability andvalidity of two isometric squat testsrdquo Journal of Strength andConditioning Research vol 16 no 2 pp 298ndash304 2002

[16] S Demura K Miyaguchi S Shin and Y Uchida ldquoEffectivenessof the 1RM estimation method based on isometric squat usinga back-dynamometerrdquo Journal of Strength and ConditioningResearch vol 24 no 10 pp 2742ndash2748 2010

[17] P F Gardiner Advanced Neuromuscular Exercise PhysiologyHuman Kinetics Champaign Ill USA 2011

[18] T W Worrell G Karst D Adamczyk et al ldquoInfluence of jointposition on electromyographic and torque generation duringmaximal voluntary isometric contractions of the hamstringsand gluteus maximus musclesrdquo Journal of Orthopaedic andSports Physical Therapy vol 31 no 12 pp 730ndash740 2001

[19] J Eng ldquoSample size estimation how many individuals shouldbe studiedrdquo Radiology vol 227 no 2 pp 309ndash313 2003

[20] P Maulder and J Cronin ldquoHorizontal and vertical jumpassessment reliability symmetry discriminative and predictiveabilityrdquo Physical Therapy in Sport vol 6 no 2 pp 74ndash82 2005


[21] H J Hermens B Freriks C Disselhorst-Klug and G RauldquoDevelopment of recommendations for SEMG sensors andsensor placement proceduresrdquo Journal of Electromyography andKinesiology vol 10 no 5 pp 361ndash374 2000

[22] M R Rhea ldquoDetermining the magnitude of treatment effectsin strength training research through the use of the effect sizerdquoJournal of Strength and Conditioning Research vol 18 no 4 pp918ndash920 2004

[23] B Rosner Fundamentals of Biostatistics Cengage LearningBoston Mass USA 7th edition 2010

[24] B I Prilutsky ldquoCoordination of two- and one-joint musclesfunctional consequences and implications for motor controlrdquoMotor Control vol 4 no 1 pp 1ndash44 2000

[25] W P Lombard ldquoThe action of two-joint musclesrdquo AmericanJournal of Physics Education vol 9 pp 141ndash145 1903

[26] B C Elliott G J Wilson and G K Kerr ldquoA biomechanicalanalysis of the sticking region in the bench pressrdquo Medicine ampScience in Sports amp Exercise vol 21 no 4 pp 450ndash462 1989

[27] R van den Tillaar and A H Saeterbakken ldquoFatigue effectsupon sticking region and electromyography in a six-repetitionmaximum bench pressrdquo Journal of Sports Sciences vol 31 no16 pp 1823ndash1830 2013

[28] R van den Tillaar ldquoKinematics and muscle activation aroundthe sticking region in free weight barbell back squatrdquo Kinesiolo-gia Slovenica vol 21 no 1 pp 15ndash25 2015

[29] R van den Tillaar V Andersen and A H Saeterbakken ldquoTheexistence of a sticking region in free weight squatsrdquo Journal ofHuman Kinetics vol 42 no 1 pp 63ndash71 2014

[30] R Van den Tillaar and A Saeligterbakken ldquoThe sticking region inthree chest-press exercises with increasing degrees of freedomrdquoJournal of Strength and Conditioning Research vol 26 no 11 pp2962ndash2969 2012

[31] M Cardinale R Newton and K Nosaka Strength andConditioningmdashBiological Principles and Practical ApplicationsJohn Wiley amp Sons Chichester UK 2011

[32] K Bloomquist H Langberg S Karlsen S Madsgaard MBoesen and T Raastad ldquoEffect of range ofmotion in heavy loadsquatting onmuscle and tendon adaptationsrdquo European Journalof Applied Physiology vol 113 no 8 pp 2133ndash2142 2013

[33] G E McMahon C I Morse A Burden K Winwood and GL Onambele ldquoImpact of range of motion during ecologicallyvalid resistance training protocols onmuscle size subcutaneousfat and strengthrdquo Journal of Strength andConditioning Researchvol 28 no 1 pp 245ndash255 2014

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and sEMG normalization This would be a first step tothen apply the knowledge during exercise prescription thatincludes the squat

Considering that the squat exercise is a multijoint taska large number of muscle groups can be activated simultane-ously in amore complex way Several studies have shown thatmanipulating features of the squat exercise resulted in alteredmuscle activity These manipulations include changes in footposition [2 3] barbell position [4] stability of the surfaceon which the exercise is performed [5ndash9] different levels ofintensity of load [10] range of motion [10ndash12] and differentequipment [13]

As a multijoint exercise the knee extensors (eg rectusfemoris RF vastus lateralis VL and vastus medialis VM)andhip extensors (eg gluteusmaximusGM biceps femorisBF and semitendinosus ST) are considered to be the primemovers during the squat exercise with other muscles actingin a secondary capacity [1 11 14] Caterisano et al [11]measured the relative contributions of GM BF VM and VLmuscles of ten experienced lifters while performing dynamicssquats at 3 depths (partial squat (the angle between the femurand the tibia was sim236 rad at the knee joint) parallel squat(the angle between the femur and the tibiawassim157 rad at theknee joint) and full-depth squat (the angle between the femurand the tibia was sim079 rad at the knee joint)) using 100ndash125 of body weight as resistance The results suggested thatthe GM was most active rather than the BF the VM or theVL during a concentric contraction as squat depth increasesOn the contrary Robertson et al [12] determined that theGM displayed a reduced activity level at maximum squatdepth Robertson et al [12] also showed that the biarticularmuscles functioned mainly as stabilizers of the ankle kneeand hip joints by working eccentrically to control descentor transferring energy among the segments during ascentWhether monoarticular and biarticular hip and knee exten-sors have different muscle activation during an isometricsquat and whether activation changes during different kneeangles are unclear Consequently the rationale of the presentstudy was to evaluate indirectly the muscle activation indifferent mechanical positions related to differences in thejoint-angle-torque diagram and the sticking region effect inall three joint angles (20∘ 90∘ and 140∘)

Finally differences in muscle activity during dynamicand isometric squat exercise have received less attentionin the physical education and rehabilitation area Othershave shown the isometric squat (90∘ and 120∘ of kneejoin position) as a reliable test to provide an indicator ofchanges in dynamic strength (1-repetition maximum barbellback squat 1RM) and power performance [15 16] howeverwhether muscle activity changes as an isometric squat ismanipulated is unknown Althoughmotor units are recruiteddifferently during dynamic movements they generate thesame relative forcetorque during a static contraction [17]Despite inherent neural and mechanical differences betweenisometric and dynamic contractions the isometric squatexercise performed in different knee joint angles may be usedto understand changes in muscle activation patterns withoutconfounding any other external effects such as the stretch-shortening cycle from dynamic movements [18] Therefore

the purpose of this study was to evaluate the maximalisometric muscle activation of the lower limbs during threedifferent knee joint-angle positions in the back squat exercise

2 Methods

21 Subjects We collected the peak amplitude of the rootmean square (RMS) from VL sEMG data during a pilotstudy to drive this power analysis Based on a statisticalpower analysis derived from these data (RMS VL EMG) itwas determined that twelve subjects would be necessary toachieve an alpha level of 005 effect size of 141 and a power(1 minus 120573) of 080 [19] Therefore we recruited fifteen younghealthy resistance-trained men (age 30 plusmn 7 years height174 plusmn 6 cm and total body mass 76 plusmn 9 kg with 5 plusmn 1 yearsof experience on the back squat exercise) to participate inthis study Subjects had no previous lower back injury nosurgery on the lower extremities and no history of injurywith residual symptoms (pain ldquogiving-awayrdquo sensations) inthe lower limbs within the last year This study was approvedby the university research ethics committee and all subjectsread and signed an informed consent document

22 Procedures Prior to data collection subjects were askedto identify their preferred leg for kicking a ball which wasthen considered their dominant leg [20] All subjects wereright-leg dominant Volunteers attended one session in thelaboratory and they reported to have refrained from per-forming any lower body exercise other than activities of dailyliving for at least 48 hours prior to testing Subjects performeda 5-minute cycle warm-up and a familiarization session withall isometric conditions The familiarization session was per-formed in all joint angles used during the experimental pro-cedure (20∘ 90∘ and 140∘) for 1 set of 3 seconds each After thewarm-up and familiarization all subjects performed threetrials of 10-second maximal isometric contractions against alocked smith machine under three different knee joint-anglepositions in a randomized counterbalanced order back squatat 20 degrees (20∘) back squat at 90 degrees (90∘) and backsquat at 140 degrees (140∘) The knee joint-angle positionswere evaluated by a goniometer (Plastic 1210158401015840 Goniometer 360Degree ISOM) and for all angles full knee extension wasconsidered the ldquozerordquo positionThe subjectsrsquo feet were alwayspositioned at hip width and vertically alignedwith the barbellposition The barbell was positioned on the shoulders (high-bar position) for all subjects and experimental conditions Arest period of 15 minutes was provided between conditionswith 3 minutes afforded between sets All measures wereperformed at the same hour of the day between 9 and 12 AMand by the same researcher

23 Measures

231 Surface Electromyography (sEMG) The subjectsrsquo hairwas shaved at the site of electrode placement and the skin wascleaned with alcohol before the sEMG electrode was affixedBipolar active disposable dual AgAgCl snap electrodes wereused which were 1 cm in diameter for each circular conduc-tive area with 2 cm center-to-center spacing Electrodes were







VL VM RF BF ST GM0

50

100

150

200

250


lowast

lowast

lowast

lowast

lowast

lowast

iEM

G (

MV

IC middots)



3 Results



4 Discussion












5 Conclusion


Competing Interests


References









































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of






















VL VM RF BF ST GM0

50

100

150

200

250


lowast

lowast

lowast

lowast

lowast

lowast

iEM

G (

MV

IC middots)



3 Results



4 Discussion












5 Conclusion


Competing Interests


References









































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of


























5 Conclusion


Competing Interests


References









































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of



































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of
















Research Article Muscle Activation Differs between Three...

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