Quadriceps Concentric EMC Activity
I s Greater Than Eccentric EMC Activity
During the Lateral Step-Up Exercise
Angie Selseth, Marilyn Dayton, Mitchell 1. Cordova, Christopher D.
lngersoll, and Mark A. Merrick
Purpose:To analyze vastus medialis obliquus (VMO) and vastus lateralis (VL) muscle
activity during the concentric and eccentric phases of a lateral step-up exercise.
Design: Repeated-measures. Dependent variable: the integrated electromyogram measured as a percentage of the maximal voluntary isometric contraction of the VMO
and VL muscles. Independent variable: muscle contraction with 2 levels (concentric
and eccentric).
Subjeds:Twenty-three volunteers with no previous history of knee surgery or anterior
knee pain.
Methods:Surface electrodes were positioned over the VMO and VL, and electromyographic data were collected during the exercise.
Results: The 2 muscle phases of contraction were different when both dependent
variables were considered simultaneously (F,,,, = 33.2, P < .001). Concentric contractions produced greater muscle activity for VL (P< .05) and VMO (P< .05).
Conclusions: Because concentric contractions produce greater activity than eccentric
contractions do during the lateral step-up exercise, they provide a stronger stimulus
for muscle activation, which might result in greater muscle strength gains.
Key Words: concentric muscle contraction, eccentric muscle contraction, I-EMG
analysis
Selseth A, Dayton M, Cordova ML, lngersoll CD, Merrick MA. Quadriceps concentric EMC activity is greater
than eccentric EMG activity during the lateral step-up exercise. J Sport Rehabil. 2000;9:124-134. O 2000
Human Kinetics Publishers, Inc.
Knee rehabilitation has traditionally focused on the use of open kinetic
chain (OKC) exercises such as straight-leg raises and knee-flexion/kneeextension exercises in which the distal segment of the extremity is nonweight-bearing and free to m o ~ e . lClosed
,~
kinetic chain (CKC) exercises
are advocated more often in rehabilitation settings because they offer distinct advantages over OKC exercises by providing cocontraction of the
quadriceps and hamstring muscles and by providing functional muscle
recruitment patterns through which integrated multijoint movement is
The authors are with the Sports Injury Research Laboratory, Athletic Training Department, at Indiana State University, Terre Haute, IN 47809.
Quadriceps EMG Activity During the Lateral Step-Up
125
p r ~ d u c e d .Furthermore,
~,~
contemporary lower extremity rehabilitation
regimes include CKC exercises because of enhanced stability caused by
increased joint compressive forces and decreased shear forces.
The lateral step-up is a common CKC exercise used in lower extremity
rehabilitation. This exercise has been found to reduce shear forces at the
knee5and is important because it activates both the vastus medialis obliquus
(VMO) and vastus lateralis (VL) muscles. Worrell and colleagues6demonstrated that VMO and VL activation during the lateral step-up was more
than that of the hamstrings and gluteus maximus muscles, which supports
the use of the lateral step-up exercise for improving quadriceps activation
during knee rehabilitati~n.~-lO
Recently, the eccentric phase of muscle contraction during training has
received attention because of the fact that most activities of daily living
and sport incorporate an eccentric loading phase." Hortobagyi et all2found
that ipsilateral, eccentric exercise training increased contralateral strength
of the homologous muscle group more than ipsilateral concentric exercise
did. Furthermore, it has been shown that eccentric training provides as
much as a 3-fold increase in muscle-activation stimulus for improving eccentric strength compared with concentric training for improving concentric ~trength.'~
Electromyographic(EMG)analysis of the thigh musculature during the
lateral step-up exercisehas been well inve~tigated."~~-~~
These studies, however, have failed to take into consideration the height of the subject when
establishingthe range of motion of the knee when performing the exercise.
Not standardizing the range of motion of the knee can change the EMG
activity of the involved musculature. The purpose of this study was to analyze the VMO and VL muscle activity independently during the concentric
and eccentric muscle-contraction phases while subjects performed the lateral step-up exercise using a constant external resistance and consistent
knee range of motion.
Methods
A 1x 2 factorial design was implemented for this study. The single withinsubject factor was muscle contraction with 2 levels: eccentric and concentric. The dependent variable was integrated electromyogram (I-EMG)measured as the percentage of maximum voluntary isometric contraction of
the VMO and VL.
Subjects
+
Twenty-three healthy subjects (23.26 1.7years, 170.5It 4.2 cm, 72.3 f 12.5
kg) with no history of knee surgery or anterior knee pathology volunteered
for this study. Subjects had to be able to hold 25% of their body weight while
performing the lateral step-up exercise, and they were asked to refrain from
126 Selseth et al
exercisingon the day of testing. All participants were accepted after giving
written informed consent and completing a medical history questionnaire.
Subjects reported to the laboratory on 1 occasion, which consisted of an
orientation session and the testing procedures. This study was approved
by the School of Health and Human Performance Human SubjectsReview
Committee.
Instrumentation
A4-channel telemetered physiological measurement system (MP 100WSW,
BIOPAC Systems, Santa Barbara, Cal) was used to measure the I-EMG activity of the VMO and VL muscles. Ten-millimeter Ag-AgC1 adhesive, disposable surface electrodes were placed in a bipolar configuration over the
muscle bellies of the VMO and the VL. The raw data were digitally converted at 500 Hz and stored for processing. Acqknowledge 3 . 5 ~
software
(BIOPAC Systems, Santa Barbara, Cal) was used to full-wave rectify the
raw signal and smooth it using the root mean square with a time constant
of 100 milliseconds. The concentric and eccentric phases of the processed
signal were integrated to evaluate the area during each trial.
A metronome (model S006P 9V, Qwik Time, Woodburn, Ind) was used
to maintain a standardized cadence during the lateral step-up exercise. An
adjustable step (Reebok International) was used to perform the exercise
and was adjusted according to the height of each subject so that he or she
would not exceed 60" of knee flexion.
Testing Procedures
Subjects were first asked to sign and date the medical history questionnaires and informed consent forms. They were then familiarized with the
testing procedures used in the study. Surface electrodes were positioned in
a bipolar configuration over the muscle bellies of the VMO and VL muscles
as previously described.16The VMO electrode was positioned 4 finger
breadths proximal to the supermedial angle of the patella, and the VL electrode was positioned 1 handbreadth over the lateral aspect of the thigh
above the patella.16The ulnar styloid process served as the site for the ground
electrode. After the muscles were marked, a 2-cm2area around each mark
was shaved, debrided, and cleansed with an isopropyl alcohol solution.
Once the electrodes were positioned on the subject, a maximum voluntary isometric contraction (MVIC) was performed. This was done by positioning the subject in a seat with the knee in 60' of knee flexion. A manual
muscle test was then performed for 6 seconds, while the EMG activity of
the VMO and VL was being sampled. The average I-EMG data for each
muscle were taken for 6 seconds and used for normalization procedures.
Subjects then performed a warm-up, which consisted of going through
the correct lateral step-up and step-down technique using their dominant
leg. Warm-up repetitions varied with each subject, and they were contin-
Quadriceps EMG Activity During the Lateral Step-Up 127
ued until the investigators and the subjects were comfortablewith the performance of the exercise.
The standardized technique for performing the lateral step-up exercise
involved stepping down from the step and steppingup onto the step while
keeping time with a metronome set at 55 beats/min. The lateral step-up
exercise was performed in a 6-phase series using the beat of the metronome as a guide. During the first beat, the subject stepped down from the
step onto the floor, impactingfirst with the forefoot, then the rnidfoot. They
completed this phase of the exercise by the time the second beat started.
Subjects were instructed to place the foot at touchdown in plane (level)
with the opposite leg. Furthermore, the involved foot remained neutral
throughout and was monitored to ensure that no adduction or abduction
occurred. During the second beat, the subject transferred his or her body
weight to the non-weight-bearing leg and stayed there for 1full count. On
the next beat, the subject paused and stood on the floor with equal weight
on both legs. On the fourth beat, the subject stepped up onto the step with
the dominant leg. The subject completed the step-up phase by the fifth
beat and stood with both feet on the step for the sixth beat. Subjects performed a warm-up to delineate the concentric and eccentric phase of the
exercise by practicing the technique of the lateral step-up exercise. They
performed 5 repetitions while holding an external resistance of 25%of their
body weight with dumbbells. The 5 repetitions were adequate for the data
analysis because this study was not designed to analyze muscle strength.
An external resistance of 25% of a subject's body weight has been previously described in the literatureas an acceptable amount of resistance while
performing this e~ercise.~
Statistical Analysis
A Hotelling F test was used to determine whether there were differences
between concentric and eccentric phases on VMO I-EMG activity and VL IEMG activity. Two dependent t tests were used post hoc to determine whether
concentric and eccentric contractions differon VMO and VL percent MVIC IEMG activity. The P I .05 level of sigrufrcance was used for all tests.
Results
The percentage of MVIC I-EMG values for muscle contraction (concentric,
eccentric) for VMO and VL are shown in Table 1. There was an overall
multivariate effect of contraction type on the linear combination of the dependent variables (Hotelling F;F,,,, = 33.2, P < .001). When considered
separately, there was an effectof contraction on VMO (F,,l, = 8.3, P < .001)
and VL (F,,, = 46.4, P < .001). Concentric contractions produced greater
muscle activity than eccentric contractions did for VL (P < .05; see Figure 1)
and VMO (P < .05; see Figure 2).
128 Selseth et al
Table 1 I-EMG (% MVIC) for VL and VMO During Concentric and
Eccentric Muscle Contraction
Minimum
Maximum
Mean f SD
concentric
5.81
35.81
20.50 f 1.86*
eccentric
3.31
22.32
1 1.80
concentric
2.03
27.00
13.16 f 1.36*
eccentric
0.84
20.52
9.73 f 1.33
Variable
Vastus lateralis
+ 1.28
Vastus medialis obliquus
*Concentric activity greater than eccentric activity for both the vastus lateralis and vastus
rnedialis oblique, P < .05.
Concentric
Eccentric
Figure 1 Vastus lateralis activity by condition. Values represent mean f SD.
* P < .05 compared with eccentric.
Discussion
Dynamic contractions can affect the EMGtensionrelationshipbecause muscle
length varies during the course of contraction. Furthermore, because the
muscle length varies over some interval of time, the rate of the muscle shortening must concurrentlybe taken into account. Bigland and Lippold17evaluated the effect of contractionby maintaining a constant shortening or lengthening velocity in an open kinetic chain. They noted that EMG values from
concentric contractions always exceeded values from eccentric contractions
produced during similar levels of tension. Additionally, when velocity was
Quadriceps EMG Activity During the Lateral Step-Up
Concentric
129
Eccentric
Figure 2 Vastus medialis obliquus activity by condition. Values represent mean rt SD.
* P < .05 compared with eccentric.
held constant and the same tensions were required, the shortening contraction reproduced greater EMG thanthe lengtheningcontraction did. With this
in mind, they suggested that the number of motor units and frequency of
activation of those motor units is less for eccentric contraction than for concentric contraction at equivalent power levels. In our study it is possible that
fewer motor units were recruited in the VMO and VL during the eccentric
phase of the lateral step-up, thus resulting in a greater amount of activity per
muscle unit in those recruited motor units.The critical stimulus for muscle
hypertrophy might be the amount of tension produced by a contractingmuscle
fiberx8or increased relative use of a m~scle.'~
For this reason, we used a constant external resistance of 25% of body weight throughout the exercise, but
the eccentricphase produced less motor unit recruitment.This result is mainly
attributed to the metabolic cost it takes to step up against gravity (concentric
phase) with an externalresistancethanit does to step down (eccentricphase)?O
It is well known that skeletalmuscle can generate greater levels of tension
during eccentric contractions than during either concentric or isometric contraction~?~-~~
Mayhew et alZ4found differences in the change of muscle fiber
area after concentric and eccentric isokinetic exercise programs that were attributed to specific fiber type. The postexercise areas of type 11 fibers of the
group that trained concentrically were sigruficantly greater than in the group
that trained eccentrically There have been many criteria associated with the
types of motor units in any muscle. The slow-twitchmotor units are smaller
(type I), have fibers rich in mitochondria, are highly capillarized, and have a
high capacity for aerobic metabolism. Mechanically, they produce twitches
with a low peak tension and a long time to peak (60-120 milliseconds). The
larger, fast-twitch motor units (type 11) have less mitochondria, are poorly
capillarized, and therefore rely on anaerobic metabolism. They alsohave peak
tensions in a shorter time (10-50 millisecond^).^^
130 Selseth et al
Our results could also be related to greater efficiency of eccentric contractions compared with concentric contractions performed at equivalent
power levels. Abbott et a120,26
demonstrated that a subject performing concentric contractions consumed more oxygen than did a subject performing
an equal amount of work with eccentric contractions. They hypothesized
that fewer fibers were active per unit of force during eccentric contractions. Bigland et alz7confirmed this finding while providing EMG evidence
that fewer muscle fibers were necessary to provide a given amount of force
during eccentric contractions.In another study, by Infante and c0lleagues,2~
frog sartorius muscles' eccentric contractions required 1/13th the amount
of adenosine triphosphate required during concentric contractions.
It has been reported that acute eccentric muscle actions induce more severe muscle soreness, microtrauma, and edema than concentric-only contractions do.29-31
Many researcher^^^-^^ and clinicians,however, use concentric-only
training for prepubescent children, older individuals, or patients recovering from surgery or injury. A common rationale for this approach is that
concentric-only exercises are less likely to cause acute muscle soreness
and microtrauma and thus are presumed to be safer for some patients. It
is unknown, however, what effect concentric training has on susceptibility to eccentric muscle damage. Ploutz-Snyder and colleagues35reported
that concentric-only training predisposes muscle to eccentric dysfunction
and injury, even when compared with an untrained muscle performing
eccentric exercise at the same relative load. E n ~ k has
a ~ speculated
~
that the
nervous system might not be capable of commanding a muscle to activate
eccentrically; whether or not the length of an activated muscle changes depends on the magnitude of the torque generated by the resistance relative
to the torque exerted by the muscle. Perhaps exercising a specific muscle to
the point of concentric fatigue is sufficient to elicit similar increases in concentric and eccentric strength, regardless of the action of the muscle at the
time of stimulus. It appears that both concentric and eccentric phases of
exercise are important and that clinicians should customize each program
to the athlete's individual needs.
Care should be taken when interpreting EMG results, so as to not directly relate EMG activity to muscle and joint forces, because these relationships have been shown to depend on a variety of factors. Some of
these factors include muscle firing rate, cross talk, recruitment patterns,
muscle type (fast vs slow), muscle length, and contraction type. In order
for a muscle to perform positive or negative work it must undergo length
changes while creating tension.37K ~ m reported
i ~ ~ that EMG amplitude
remained fairly constant in spite of decreased tension during shortening
and increased tension during eccentric contractions. He also demonstrated
increases with eccentric contractions during maximal exertions for elbow
flexion.
Comparing the results of our study with those of others was difficult
for a few reasons. First, our study used a CKC exercise, whereas most
Quadriceps EMC Activity During the Lateral Step-Up 131
studieshave compared OKC exercises.Recently, this has started to change,
and more research is being done with CKC exercises. The lateral step-up
is one CKC exercise that has gained popularity and has been studied before. In most studies, an 8-in step was used. Although this height is also
commonly used in the clinical setting,13,14clinicians often employ a progressive gradual program of increasing step height. Because of the amount
of muscle shortening and lengthening in different subjects, we felt that
the step height needed to be controlled because a 5-ft individual would
produce more muscle activity on an 8-in step than a 6-ft individual would.
Therefore, we adjusted the step height according to each individual's height
so that the range of motion was 0-60". We also chose 25% of body weight
as the external resistance, with the hypothesis that there would be more
muscle activity.Worrell and colleagues6confirmed this hypothesis, reporting that there was an increase in EMG activity in the VMO (71% to 98%)
and VL (54%to 82%)with weight compared with no weight, which only
produced 49% to 82%VL and 63% to 80%VMO. They also reported more
muscle activity in the VMO and VL muscles than in the hamstring and
gluteus muscles with weight than without weight. It should be noted that
their subjects performed the lateral step-up exercise with an 8-in step.
We chose to not compute VM0:VL ratios but to treat them as independent muscles with their own separate functions. Other researchers2J5have
reported computed ratios of these 2 muscles, but we feel that 2 different
muscles should not be compared with each other. In studies similar in
design and analysis to ours,"15 interpretation of the calculated VM0:VL
ratio suggests that the VL produced more muscle activity than the VMO
did. Care should be taken when considering these results because these
ratios cannot clearly define whether the VMO muscle activity decreased
while the VL increased or vice versa. In our study, we found that the VL
and VMO produced less muscle activity during the eccentric contraction
phase than during the concentric contraction phase. These results were
clear because each muscle was analyzed independently.
Conclusions
Muscle activity is greater during concentric contraction than during eccentric contraction for both the VL and the VMO during a lateral step-up
exercise with a constant load (bodyweight + 25%).This suggests that each
of these muscles is performing more work during the concentric phase
than during the eccentric phase of muscle loading. It appears from these
data that the concentric contraction, or shortening phase, during this movement provides a greater stimulus for VL and VMO activation. In reestablishing activation of the quadriceps musculature after knee injury, clinicians might want to initially focus on the concentric phase when using the
lateral step-up exercise while progressively increasing the height of the
step.
132 Selseth et al
References
1. Palmitier RA, An K, Scott SG, Chao YS. Kinetic chain exercise in knee rehabilitation. Sport Med. 1991;11:402-413.
2. Worrell TW, Crisp EA, Larosa CN. Electromyographic reliability and analysis
of selected lower extremity muscles during lateral step-up conditions. J Athl
Training. 1998;33:156-162.
3. Bynum EB, Barrack RL, Alexander AH. Open versus closed chain kinetic exercises after anterior cruciate ligament reconstruction. A prospective randomized study [see comments]. A m J Sports Med. 1995;23:401-406.
4. Brossmann J, Muhle C, Schroder C, et al. Patellar tracking patterns during active and passive knee extension: evaluation with motion-triggered cine MR
imaging. Radiology. 1993;187:205-212.
5. Lutz GE, Palmitier RA, An KN, Chao EY. Comparison of tibiofemoral joint
forces during open-kinetic-chainand closed-kinetic-chain exercises.J Bone Joint
Surg [Am].1993;75:732-739.
6. Worrell TW, Borchert B, Erner K, Fritz J, Leerar P. Effect of a lateral step-up
exercise protocol on quadriceps and lower extremity performance. J Orthop
Sports Phys Ther. 1993;18:646-653.
7. Westfall DC, Worrell TW.Anterior knee pain syndrome: role of the vastus medialis oblique. J Sport Rehabil. 1992;1:317-325.
8. Reynolds L, Levin TA, Medeiros JM, Adler NS, Hallum A. EMG activity of the
vastus medialis oblique and the vastus lateralis in their role in patellar alignment. Am J Phys Med. 1983;62:61-70.
9. Antich TJ, Brewster CE. Rehabilitation of the nonreconstructed anterior cruciate ligament-deficient knee. Clin Sports Med. 1988;7:813-826.
10. Huegel M, Indelicato PA. Trends in rehabilitation following anterior cruciate
ligament reconstruction. Clin Sports Med. 1988;7:801-811.
11. Tmdell-Jackson E, Meske N, Highgenboten C, Jackson A. Eccentric/concentric torque deficits in the quadriceps muscle. J Orthop Sport Phys Ther.
1989;11:142-145.
12. Hortobagyi T, Lambert NJ,Hill JP. Greater cross education following training
with muscle lengthening than shortening.Med Sci Sports Exerc. 1997;29:107-112.
13. Cook TM, Zimmemann CL, Lux KM, Neubrand CM, Nicholson TD. EMG comparison of lateral step-up and stepping machine exercise. J Orthop Sports Phys
Ther. 1992;16:108-113.
14. Brask B, Lueke RH, Soderberg GL. Electromyographic analysis of selected
muscles during the lateral step-up exercise. Phys Ther. 1984;64:324-329.
15. Sheehy P, Burdett RG, Irrgang JJ, VanSwearingenJ. An electromyographicstudy
of vastus medialis oblique and vastus lateralis activity while ascending and
descending steps. J Orthop Sports Phys Ther. 1998;27:423-429.
16. Delagi EF, Perotto A. Anatomic Guidefor the Electromyographer:The Limbs. Springfield, Ill: Charles C Thomas; 1980.
17. Bigland B, Lippold OCJ. The relation between force, velocity and integrated
electrical artiviwin R m a f i muscles. J Physiol (Zond). 1954;123:214-224.
Quadriceps EMG Activity During the Lateral Step-Up 133
18. Booth FW, Nicholson WF, Watson PA. Influence of muscle use on protein synthesis and degradation. Exerc Sport Sci Rev. 1982;10:27-48.
19. Goldberg AL, Etlinger JD, Goldspink DF, Jablecki C. Mechanism of workinduced hypertrophy of skeletal muscle. Med Sci Sports. 1975;7:185-198.
20. Abbott BC, Bigland B, Ritchie JM. The physiological cost of negative work. J
Physiol (Lond). 1952;117:380-390.
21. Doss WS, Karpovich PV. A comparison of concentric, eccentric and isometric
strength of elbow flexors. J Appl Physiol. 1965;20:351-353.
22. Olson VL, Smidt GL, Johnston RC. The maximum torque generated by the
eccentric, isometric, and concentric contractions of the hip abductor muscles.
Phys Ther. 1972;52:149-158.
23. Singh M, Karpovich PV. Isotonic and isometric forces of forearm flexors and
extensors.J Appl Physiol. 1966;21:1435-1437.
24. Mayhew TP, Rothstein JM, Finucane SD, Lamb RL. Muscular adaptation to
concentric and eccentric exercise at equal power levels. Med Sci Sports Exerc.
1995;27:868-873.
25. Winter DA. Biomechanics and Motor Control of Human Movement. 2nd ed. New
York, NY: John Wdey & Sons; 1990.
26. Abbott BC, Bigland B. The effects of force and speed changes on the rate of
oxygen consumption during negative work. J Physiol (Lond). 1953;118:319-325.
27. Bigland B, Ritchie JM, Woods JJ. Integrated EMG and oxygen uptake during
dynamic contractions of human muscles. J Appl Physiol. 1974;36:475-479.
28. Infante AA, Klaupik SD, Davies RE. Adenosine triphosphate: changes in
muscles during negative work. Science. 1964;144:1577-1578.
29. Rians CB, Weltman A, Cahill BR, Janney CA, Tippett SR, Katch FI. Strength
training for prepubescent males: is it safe? A m J Sports Med. 1987;15:483-489.
30. Rice CL, Cunningham DA, Paterson DH, Dickinson JR. Strength training alters contractile properties of the triceps brachii in men aged 65-78 years. Eur J
Appl Physiol. 1993;66:275-280.
31. Weltrnan A, Janney C, Rians CB, et al. The effects of hydraulic resistance strength
training in pre-pubertal males. Med Sci Sports Exerc. 1986;18:629-638.
32. Gibala MJ, MacDougaU p,Tarnopolsky MA, Stauber WT, Elorriaga A. Changes
in human skeletal muscle ultrastructure and force production after acute resistance exercise. J Appl Physiol. 1995;78:702-708.
33. Golden CL, Dudley GA. Strength after bouts of eccentric or concentricactions.
Med Sci Sports Exerc. 1992;24:926-933.
34. Jones DA, Newham DJ, Round JM, Tolfree SE. Experimental human muscle
damage:morphologicalchanges in relation to other indices of damage.JPhysiol
(Lond). 1986;375:435-448.
35. Ploutz-Snyder LL, Tesch PA, Dudley GA. Increased vulnerability to eccentric
exercise-induced dysfunctionand muscle injury after concentric training. Arch
Phys Med Rehabil. 1998;79:58-61.
36. Enoka RM. Neuromechanical Basis of Kinesiology. 2nd ed. Champaign, Ill: Human Kinetics; 1994.
134 Selseth et al
37. Solomonow M, Baratta R, Shoji H, D'Ambrosia R. The EMG-force relationships of skeletal muscle; dependence on contraction rate, and motor units control strategy. Electromyogr Clin Neurophysiol. 1990;30:141-152.
38. Korni PV. Relationship between muscle tension, EMG, velocity of contraction
under concentric and eccentric work. New Dev Electromogr Clin Neurol.
1973;1:596-606.