Bulletin of Prosthetics ResearchBPR 10-35 (Vol 18 No. 1) Spring 1981Pages 5-14

RICHARD SHIAVI, Ph. D. b

Research Service

SHERRY CHAMPION, RPTResearch Service

FRANK FREEMAN, M.D.Neurology Service

PAUL GRIFFIN, M.D.Orthopedics and Rehabilitation Service

Veterans Administration Medical Center1310 24th Avenue SouthNashville. Tennessee 37203

and

Vanderbilt University HospitalNashville. Tennessee 37203

a This research was supported by theRehabilitative Engineering Researchand Development Service. VeteransAdministration.b Correspondence should be addressed

to Dr. Shiavi.

5

Variability of ElectromyographicPatterns for Level-Surface Walkingthrough a Rangeof Self-Selected Speeds a

ABSTRACT-The surface electromyographic patterns of eightmuscles and the foot-contact patterns exhibited by 25 normalpersons between the ages of 20 and 40, were measured andstudied. These persons were walking indoors on a level surfacewithout shoes at several different self-selected walking speeds.The electromyographic patterns demonstrated a considerableamount of interindividual variability at each speed. There weredefinite trends in the number of individuals exhibiting each patterntype as walking speed increased. The foot-contact patternsshowed a consistent sequencing of foot events at all speeds withthe double-limb support stages and stance phase comprising asmaller percentage of the gait cycle as speed increased.

INTRODUCTION

Many investigations have been undertaken to study electro­myographic (EMG) patterns during level walking. The majoremphasis has been directed toward finding commonalities inpatterns. The concepts and results have been summarized byEberhart. et al. (1). Basmajian (2). and Perry (3). A partialcompilation of the classical results is shown in Figure 1, which isan excerpt from Eberhart (1).

Population variabilities in EMG patterns have been noted (4,5).but more recently attention has been directed toward this fact(6,7,8,9). Paul has compiled the results of several reportedinvestigations and demonstrated some significant disagreementson the phasings of particular major muscle groups including thequadriceps and hamstrings (7). The apparent disagreements maybe attributed either to differences in investigatory protocol andEMG processing techniques or to actual interindividual (popula­tion) variations. The wearing of shoes, the type of walking, andthe attempts to control speed or stride time are all experimentalvariables which can affect walking conditions. Walking speed isan experimental parameter which is critical and must be welldefined or controlled. Several investigators have shown in small­sample studies that the phasing of activity in some muscles doeschange with walking speed (10,11,12). This can be expectedsince floor reaction forces and center of gravity dynamics are afunction of walking speed (13,14,15).

Knowledge of the population variability of EMG patterns andhow they are affected by walking speed is important. Thesenormative data can provide a comparative basis for evaluatingpatients having locomotor disabilities (4,16). This leads to twomajor questions: What are the EMG patterns that can result innormal locomotion? How are these patterns affected by speed ofprogression? The need for answering these questions has been

6

SHIAVI et al. ELECTROMYOGRAPHIC PATTERNS for WALKING

9080

INCONSISTENTACTIVITY

,"

30 40 ~O 60 70TIME, PERCENT OF CYCLE

20

HAMSTRING GROUP

too

~::::> 1OOl)ft~---,.----r--""T""--r----,r--~+--"""",--~---'r---,~

X~

~

b~>-•.­:>.­u~

w...JU(J')~

~

FIGURE 1.Electromyographic Gait Patterns. The average EM G patterns of several muscle groups is plotted as a function 01normalized time. This data is from Eberhart (1 I.

METHODS

TABLE 1.Average and Standard Deviation of Subjects' Height (HT) and Weight(WT)

discussed at conferences and workshops (17.18).The object of the investigation reported herein

was to study the population variability of electro­myographic patterns in the normal adult populationand to ascertain any changes that occurred as afunction of different self-selected walking speeds.

Measurements

The electromyographic and foot-contact patternsof 25 normal subjects ranging between 20 and 40years of age were measured and studied. None hadany history of neuro-musculo-skeletal disorders andall were active wage-earners or students. There were13 females and 12 males in the group and theirheight and weight statistics appear in Table 1.

The electromyograms of the eight muscles listedbelow were measured using miniature Beckmansurface electrodes in a bipolar arrangement. Theelectrodes were connected to the differential ampli­fiers of an eight-channel Bio-Sentry telemetry sys­tem. The amplifiers have an input impedance of 500kD and a common mode rejection ratio of 58 dB.Each output channel was filtered to remove motionartifact and high-frequency noise. using bandpassfilters with cutoff frequencies of 40 Hz and 400 Hz.In addition. for each channel the integrated EMGwas formed using a full-wave rectifier and Paynterfilter with an integration period of 6 ms (19).

The electrode sites were found by palpating themuscle during a voluntary contraction and locatingthe portion of muscle presenting the largest surfacearea. The exception was the soleus; the electrodeswere placed over the distal one-third of the muscle.The skin was always cleaned thoroughly with alcoholbefore electrode placement. The placements weretested for accuracy. "cross talk," bad connections.etc. by requesting the subject to perform severaltest movements (e.g.. voluntary contractions of aselected muscle vs. neighboring muscles) and a testwalk. If any apparent malfunction was found. cor­rective action was taken and the test repeated. Bycareful placement of miniature electrodes. tests forcross-talk. and rejection of suspicious dat~, e~e~troimyographic patterns were obtained on Indlvlduamuscles.

WT (kg)

55.8 ± 5.372.8 ± 9.9

HT (em)

160 ± 8.2174 ± 6.9

FemalesMales

7

Bulletin of Prosthetics Research. BPR 10-35 (Vol. 18 No.1) Spring 1981

The foot-contact patterns were measured withoutshoes using footcovers and a B&L Engineering Foot­Pattern Telemetry System c. The footcovers consistof elastic stockings worn over the subjects' barefeet. Conductive rubber soles are glued to thestockings, and metal contacts are fastened at theappropriate points on the bottom of the sole usingdouble-sided adhesive tape. (The tape not only holdsthe contact in place but also insulates it from theconducting sole; a circuit terminating in a contactis activated when the conducting surface of thewalkway electrically connects that metal contactand the rubber sole.) The footcovers fit securely andcomfortably, and subjects did not perceive any riskof slipping (20).

The subjects walked indoors on a metal-coveredwalkway which is 8 meters long. An electric eyesystem demarcated the middle 5 meters of thewalkway; only the data recorded within that middlesection was studied. (The electric eye system placedan impulse on the chart recorder whenever one ofits two beams was transgressed.) The time of travelbetween the two beams was used to calculatewalking speed.

All measurements were recorded on a 14-channelHewlett-Packard analog magnetic tape recorder anda Consolidated Electronics oscillographic recorder.

The specific protocol was:1. Electromyograms of the following muscles on

the right lower extremity were measured: tibialisanterior (TA). peroneus longus (PL). gastrocnemius(GAS). soleus (SOL). rectus femoris (RF). vastuslateralis (VL). medial hamstring (MH). and gluteusmedius (GM).

2. Foot-contact patterns of both feet were meas­ured simultaneously.

3. Each subject. after being fully instrumented,made several traverses of the walkway in order tobecome acclimated to the experimental setting.

4. Each subject was requested to walk at hispreferred free, fast. slow and very-slow walkingspeeds on the walkway. (A specific subject repro­duced each of his or her chosen speeds very closely.)Several traverses of the walkway at each speedwere required in order to ensure that measurementsof all signals were made for a minimum of 10 fullgait cycles, i.e., 10 strides. Two sets of measure­ments were made at each speed because the Bio­Sentry System has only five EMG channels. TheEMG from the tibialis anterior and gastrocnemiusmuscles were recorded during both sets to checkthat the subject was walking with consistent pat­terns.

Analysis

The kinetic parameters of speed, stride length,and stride frequency (strides / second) were calcu­lated for men and for women and compared withparameter values in the existing literature. Sinceheight has been shown to be an important factor,these parameters will be presented mainly in termsof relative speed (speed / height) and relative stridelength (stride length / height) (21).

A normal person walking at a constant speeddemonstrates a very consistent gait pattern withonly slight stride time variations. The typical rangeof variations is 3 percent of a person's average. Afew persons had a 5-percent range but only whilewalking at very-slow speeds. Because of this, thedata from the cycle whose stride time was closestto the subject's average was selected to representthat person's pattern.

A muscle was considered to be active when itsintegrated EMG exceeded a threshold level. Thisthreshold was chosen as that level which is 10percent greater than the peak magnitude of thebackground noise. Any EMG measurement whichwas contaminated with 60 Hz noise or with "cros­stalk" from another EMG was eliminated from thestudy. (This mostly happened with the thigh EMG.)Nevertheless, for each muscle there remained aminimum of 20 eligible patterns from the 25 sub­jects. The foot-contact patterns and the times ofonset and cessation of all muscle activities weremeasured from the time of initial contact and nor­malized by the stride time.

The population averages for each speed desig­nation were achieved by averaging the normalizedevent times from the individual gait patterns. Forinstance, the average time of initial contact of thefifth metatarsal was calculated by averaging thenormalized times of initial contact for all subjects.The population EMG patterns were calculated in thesame manner except that the individual patternswere first classified according to their general char­acteristics. Characteristics used to classify the pat­terns were features such as monophasicity, biphas­icity, duration of activity, etc.

c The system measures when the heel. head of 5th metatarsal. headof 1st metatarsal and large toe make contact with the walkingsurface. These are encoded as deflections of 1. 2 and 4 units. andoscillation of 1 unit, respectively. Several parts in contact result ina simple sum of units.

8SL

0'----'------'----'--------"---'------'-----'---.- v (S-I)2 .4 .6 .8 1.0 1.2 14

FIGURE 2.Relative Stride Length (SL) vs. Relative Speed (V). The relative stridelengths for males (0) and females (X) are plotted as functions ofrelative speed. The smooth curve is the average results from Grieve'sstudy (26). without shoes. The brackets delimit one standard deviationfrom the average.

Terminology

There is a standard nomenclature which dividesthe gait cycle into stance and swing phases of thereference lower extremity and further describesthese phases. The stance phase is described by thetimes of specific events. These are: initial-contact.foot-flat. midstance. heel-off and toe-off. The swingphase is divided into time spans which denoteacceleration (early-swing). mid-swing. and deceler­ation (late-swing) of the limb (22). Using this no­menclature to describe the muscular synergy pat­terns is cumbersome because of the mixed style;event descriptors are usually used in stance phasewhereas time spans are used in swing phase. It ismore convenient to utilize time spans for describingpatterns. therefore the stance phase is subdividedinto time spans bounded by event times. (Dubo. et.al.. (23) also found this necessary. and a revisedterminology was adopted during a recent workshopon Gait Analysis (24).) The stance phase consistsof:

1. A loading stage. which extends from initial­contact to the end of double-limb support (DLS);

2. An initial midstance stage. which extends fromthe beginning of single-limb support (SLS) to thetime when the body is over the supporting limb;

3. A terminal mid-stance stage. which enduresfor the remainder of SLS; and

4. An unloading or preswing stage. which coin­cides with the second DLS stage.

1.0

8

rtfri.6

4

.2

1.2

1.0

~i.8

,i)I/.6

.4

.2

'---_-=-_---':__-':-_---'-__L.-_-I..-_---'__ V (S-I).2 1.0 1.2

FIGURE 3.Stride Frquency (f) vs. Relative Speed (V). The stride frequencies ininverse seconds for males (0) and females (X) are plotted as afunction of relative speed. The smooth curve is calculated from Dean'sformula using the average height of the subjects (32). Dean's subjectswore shoes. The brackets delimit one standard deviation from theaverage stride frequency.

TA -PL

GASO

T ~.Rt. Ft.

0 20 40 60 80 100 0/0FIGURE 4.Gait Pattern for Subject HW. The EMG patterns of four muscles and the right foot-fall pattern areshown for very-slow speed walking. The characters (H.5.1.T) indicate the event times for thevarious foot contact points.

...---....-:::r-----rr------, 0

RESULTS

r

tvo

eno

eno

tvo

<Xlo

o

:::0r

L---1111..----..L.....-----()---l8

(5L-_--Jloj __'__ ~ 0

,---...,...-----rr--------,or

(5L-__~ __'__ ....J 0

,..----cr-----....--------,o

~OJ::JC.

-l~

Cl>

-mCl>

­OJ

~

~OJ

7<'S'

<0(Jl

'CCl>Cl>C.(Jl

Fast

.80 ± .16

.81±.11

Fast1.39 ± .291.31 ± .17

Free

.56 ± .13

.61 ± .10

Free.98±.21.98 ± .14

.39 ± .07

.41 ± .10

Slow.68 ± .13.66 ± .16

.25 ± .08

.23 ±08

RELATIVE SPEED (SEC-I)Very-Slow Slow

MalesFemales

ACTUAL SPEED (MIS)

Very-SlowMales .43±.14Females .37 ± .12

TABLE 2.Averages and Standard Deviations of Speeds for Males and Females

Kinematic Parameters

The statistics for the speeds of walking for thefour self-selected speeds are listed in Table 2. Therelative stride lengths and stride frequencies aregraphed in Figures 2 and 3. respectively. Note thatthe range of self-selected speeds used by the sub­jects does not extend to the full range of relativespeeds of which people are capable (26}.

Foot-Contact Patterns

The foot-contact patterns for 23 of the 25 sub­jects had identical sequencing at all walking speeds.The onset sequence was heel. fifth metatarsal. firstmetatarsal. and toe. The offset sequence followedthe same order. (In Figure 4 is shown one of thesepatterns.)

The two exceptions were subjects DB and RS.DB had a bilateral equinus gait and as a result hadthe fifth metatarsal contacting before the heel at allspeeds. RS had a valgus right foot; the first andfifth metatarsal onset events were simultaneous atall speeds. These latter patterns were grouped withthe predominant patterns (or statistical calculation.Since these two subjects had neither abnormalmedical histories nor conspicuously different EMGpatterns.

The population averages of the bilateral foot­contact patterns for all subjects while walking atvery-slow. free. and fast speeds are shown in Figure5. (All patterns for slow speeds were omitted fromthe figure for the sake of conciseness.) Males andfemales are not treated separately since their statis­tics are the same. The variability of event times forthe right foot IS depicted by the double-headedarrow centered around and located below the eventOCcurrences. Most of the events have a small vari­ation. The exceptions are the toe-contact and heel­off events.

10

SHIAVI et al. ELECTROMYOGRAPHIC PATTERNS for WALKING

a.100

There is a great amount of interindividual varia­bility at each speed as well as changes in the patterntypes as speed changes. Thus, the main character­istics of each muscle's activity are classified intoprimary and secondary major patterns. The percent­age of subjects having a particular major pattern atthe designated speed is denoted by the numberlocated to the right of that pattern. The primarypatterns are plotted above the secondary ones. Notall subjects in a particular primary or secondarygroup demonstrated that ~roup's entire pattern ex­actly. Such a variation, typically in the form of anadditional period of EMG activity, is plotted in Figure7 as a dashed line: the number printed directly

. above or below the dashed line indicates the per­centage of subjects (relative to the number in thegroup) who demonstrated that variation. Note thatpercentages for the patterns equal 100 percentexcept for those of the leg muscles in Figure 7a. Atvery slow speed, two subjects had very conspicu­ously different patterns, as will be described below.

a. Tibialis anterior. The tibialis anterior is act1iveboth during the stance-to-swing and the swing-to­stance transitional stages. In approximately 25 per­cent of the subjects it was also active during aportion of midstance. During very-slow speed walk­ing the TAwas monophasic while during fasterspeeds it could be multiphasic.

b. Peroneus longus. The peroneus longus isprimarily active during stance phase. Transitionalstage activity is variable but becomes more prevalentas walking speed increases.

c. Gastrocnemius. The gastrocnemius is mainrya stance phase muscle. As walking speed increasesit tends to become active earlier during stancephase, and actually becomes active during the late­swing at fast speeds. Stance-to-swing transitionalstage activity accompanies the earlier onset of ac­tivity and when it is present it forms a second periodof activity.

d. Soleus. The qualitative behavior of the soleusis the same as that of the gastrocnemius except thatthere is no stance-to-swing transitional activity.

e. Hamstring. The hamstring is mainly activeduring the late-swing, loading, and initial midstancestages. In some subjects there is a second period ofactivity during the stance-to-swing transitionalstage. A trend exists toward a shorter period (orabsence) of activity during late-swing at slowerwalking speeds.

f. Rectus femoris. The rectus femoris is alwaysactive during the late-swing, loading, and initialmidstance stages. In approximately 25 percent ofthe subjects this period continues throughout midst­ance. Among another 50 percent of all subjects, asecond period of activity occurs during the stance-

b.

STANCE

SWING

DLS

SWING

DLS

~STANCE

'-------'---'--_--'-_----J'---_...J.....~V (5-1).4 .6 .8 1.0

PD (s)

.4

.8

1.2

20

40

1.6

'----=---L--'--.l.--...:...L__L.-J!~V (5 -)). 2 .4 .6 .8 1.0

FIGURE 6.Phase Durations vs. Relative Speed. The phase durations (PO) inrelative time (a) and in actual time (b) are plotted as a function ofrelative speed (V).

80

PD(%)

As walking speed increases, there are certaintrends in the different phases of the gait. Figure 6summarizes these trends.

Electromyographic Gait Patterns

The subject population averages for the EMGpatterns measured at very-slow, free, and fast walk­ing speeds are shown in Figure 7. The averagespeeds (S) and stride times (ST) for each speed areprinted on the bottom of the graphs. The double­limb (DLS) and single-limb (SLS) support of stancephase (and the swing phase) are shown on the sameline which designates percentages of the gait cycle.

60

IG> < ::0 l>s:: r " s::

(f) G>o l> "1) --ir (f) r l>

<(f) 0r - r0 (f):E -(f)

~- -"1)I'Tl -I'Tl (f)0 r.. - (f)(f)II

0 ~- -~

s:: - 0 IU, r I I(f)1 I ~ll.. I- I til I~ II I~(J) - 1-1> I til I 100

--l I- I Itil III - (J) I IN :E I

~-

I-~I I

(f)

~ III

to-swing transitional stage.g. Vastus lateralis. The vastus lateralis is also

mainly active during the late-swing. loading. andinitial midstance stages. In a minority of subjectsthere is also activity during the stance-to-swingtransitional stage. At very-slow and free walkingspeeds this is observed as two separate periods ofactivity. However, at fast speeds the two periods aremerged and one long period of activity is observed.

h. Gluteus medius. The gluteus medius is mainlya loading and midstance stage muscle. This periodof activity extends into the late-swing stage forsome subjects. As walking speed increases thislengthened period is more prevalent. A secondperiod of activity during the stance-to-swing transi­tional stage occurs in a minority of subjects. Itsprevalence also increases with walking speed.

u;~ g ~~ ~~

IG> < ::0 l>s:: r " s::

N(j)01 CD

(f)

or

G>l> "1) --i(f) r l>

TABLE 3.

Frequency of Occurrence of Loading Stage Activity in Soleus duringFree Speed Walking

--ll>

"1)r

(f)

or

~O'Io ON-..I-CDo OUlUl","O'I

IG> < ::0 l>s:: r " s::

"0r

l> =- (f)(f) ~

--l(f) -"1)I'Tl (J) II'Tl - r I0 (J) I",(f) - 100

II Ic- I().J

~- f-- IU1 0 I

~r I 101 1-1> I

Q2-~ I 1-1> 101 I

I~ I I I(J) - I 10l--l (f) I

:E III I I

9 - - 'Illz<D G>

II

U1 - II I I I(f)

A II I

0 I IIr

" - (f)::0 ::; -f'TIf'TI -(J) (J)lJI'Tl - rI'Tl (J)

0.. -

I(J) I• I0 ~- -

101(0 0 I-.jI(Xl - ~II I I1-1>s:: I I

U, ~ - ~II", 1-1> I'"II'" 101 I I.. -II I

(J) (f)' I:i>

--l - :E I ,•:-- Z I ,- - G>

I I II li~~(f)

~

619

2513

112

Female

57

12

MaleActivity

YesNo

FI G U RE 7 (right) Population Electromyographic Patterns. Theaverage EMG patterns for subjects walking at very-slow (al. free (bl.and fast (c) speeds are plotted as a function of relative time.

Two subjects, RW and MS, had EMG pat­terns that were vastly different from thosepresented for the legs during very-slow speedwalking. These patterns showed reciprocal burstsof activity between the plantarflexor and the dorsi­flexor muscles. (Figure 4 shows the pattern forsubject RW.) Even though the peroneus longus isactive during the 55 percent to 60 percent periodof the gait cycle. its intensity was greatly reduced.

Because of the diversity and trends in the EMGpatterns. it was decided to test the correlation ofany pattern type with sex. A 2 X 2 contingencytable was made for every pattern type at eachwalking speed.

Table 3 shows the frequency of occurrence datafor the soleus muscle at free speed. This table istesting whether or not males are more prone toexhibit activity during the loading stage. A modifiedchi-squared test was used to test the statisticalsignificance of any correlation (25). None of thecorrelations were statistically significant at the 5percent level.

12

SHIAVI et al: ELECTROMYOGRAPHIC PATTERNS for WALKING

DISCUSSION

Kinematic Parameters

Examination of the statistics listed in Table 2show that there is a dispersion of relative speeds foreach self-selected speed category. Notice from thestandard deviations that the values overlap cate­gories; that is, one person's free speed can beanother person's fast speed, etc. For all categoriesexcept very-slow, the female's relative speed isslightly greater. When the actual speeds are calcu­lated, the female's walking speed is less in mostcategories, though equal at free speed. Comparisonof these speed statistics with results from otherlaboratory studies with barefooted subjects showsgood agreement (22,26,27). As Drillis has remarked,a laboratory setting induces shorter step lengths.thus causing slower speeds (28). Another indicationof this fact can be obtained by comparing the datafrom two studies of Finley et al. (29.30). The freewalking speed of women was 33 percent lower inthe laboratory than in an urban setting.

As has been shown in other studies, the increasein walking speed is accomplished by an increase inboth stride frequency and stride length d (13,26.31).These results are corroborated in Figures 2 and 3.Figure 2 shows the relative stride length vs. relativevelocity statistics with a superimposed averagecurve from Grieve (26). These are in good agree­ment. Figure 3 shows the stride frequency vs.relative velocity statistics with a superimposed av­erage curve from Dean (32). For a given relativevelocity the subjects exhibited a greater averagestride frequency. This is consistent with other ob­servations and data summarized by Dean becausethe curve is based on walking with subjects wearingregular heeled shoes~the wearing of shoes de­creases cadence for a given walking speed.

Foot-Contact Patterns

The foot-contact patterns demonstrate a bilateralsymmetry and no change in the sequencing of footevents with respect to speed. In the two subjectswho exhibited different patterns, there seemed tobe no clear correlation between these exceptionsand the electromyographic patterns. For instance,subject RS. who has a valgus right foot. was alwaysin the group which has peroneus longus activityduring late swing or early stance; however. so wereseveral other subjects who had the predominantfoot-fall pattern.

The relative timing for most of the foot events is

d The term "stride," employed by the authors in such expressions asstride length, stride time and its inverse, stride frequency, refers tothe complete gait cycle of two consecutive steps-not to a singlestep.

fairly consistent as indicated by the small standarddeviations. Only two foot events, toe-contact andheel-off, have a large range of times. In severalsubjects the toe did not contact the walking surfaceuntil the middle of stance phase. This was usually,but not always, concomitant with the prolongedactivity of the tibialis anterior muscle. There was nonoticeable correlation between heel-off and any ofthe other kinematic parameters or EMG patterns.

As walking speed increases, the stance and dou­ble-limb support phases decrease in relative andactual time. In contradistinction, the swing phaseduration increases in relative time though it. too,decreases somewhat in actual time. The reductionin stance phase duration is about five times greaterthan that of swing phase. These population averages,which are graphed in Figure 6, are in agreementwith the results of other investigations (33,34).

On the average, some of the events on oppositefeet occur concurrently. During very-slow speedwalking, heel-off on one foot occurs at heel-on ofthe contralateral foot. During free speed walking theipsilateral first metatarsal head onset and contralat­eral first metatarsal head offset are concurrelilt.Whereas, at fast walking speed, a person will makecontact of the fifth metatarsal concurrently with theoffset of the opposite first metatarsal.

Given the consistency in the sequencing and therelatively small standard deviations of time of mostof the foot events, the foot-fall pattern of themajority of normal individuals is a stereotyped pat­tern.

Muscle Synergy Patterns

The EMG patterns found at various walkingspeeds will be discussed with respect to the classi­cally accepted patterns as exemplified in Figure 1.

a. Tibialis Anterior Most of the subjects studieddisplayed the classical patterns of the tibialis anteriormuscle at all speeds. The exception was that 24percent to 28 percent of the subjects had someactivity during midstance with 19 percent havinghad midstance activity at all speeds. Midstanceactivity during free speed walking has been observed(23).

b. Peroneus Longus The peroneus longus musclewas found to be extremely variable in its activity.This variability was also observed by Walmsley (5).As walking speed increases. the percentage of sub­jects exhibiting swing-to-stance stage activity in­creases from 14 percent at very slow. to 26 percentat free speed, to 68 percent at fast speed. Thosesubjects incorporating late-swing stage activity ~t

one speed also utilized it at a faster speed. ThIStrend was not observed for the other transitionalstage,

13

Bulletin of Prosthetics Research, BPR 10-35 (Vol. 18 No.1) Spring 1981.

In some subjects the peroneus longus had apattern similar to the tibialis anterior, but in othersubjects its pattern was more like the plantarflexormuscles. Perhaps more insight could be gainedabout the function of the peroneus longus if theEMG of tibialis posterior were recorded simultane­ously. The tibialis posterior is more of a true antag­onist of the peroneus longus than any of the othermuscles recorded. .

c. Gastrocnemius The EMG of the gastrocnemiusmuscle during very-slow speed walking is consistentwith the classical descriptions. However, as a personwalks faster there is a trend for the gastrocnemiusto become active earlier in stance and even duringlate-swing. Several other investigators have shownthis type of activity at free or fast speeds(10,12,23,35). At free speed, 21 percent of thesubjects displayed this early activity. At fast speed,this is more conspicuous with 58 percent of thesubjects displaying such activity.

d. Soleus The soleus muscle is active withinstance phase except at fast walking speeds. At very­slow speed most of the subjects have the classicalperiod of activity whereas 23 percent of them havea shortened period. As walking speed increases, thesoleus commences activity earlier in the gait cycle.At fast speed, late-swing stage activity is exhibited.The early onset of soleus activity in some subjectswalking at free speed has been previously reported(12,35,36).

e. Hamstring Muscle Group The hamstringgroup EMG patterns exhibited at free speed are inagreement with the classical patterns. Some inves­tigators do not report finding any stance-to-swingtransitional stage activity (7,10). The activity duringthe late-swing stage becomes less prevalent aswalking speed decreases. Those who did not havethis activity at free speed also did not have it atvery-slow speed walking.

f. Rectus Femoris The primary pattern of therectus femoris agrees with the classical quadricepspattern except that the second period of activityoccurring during the stance-to-swing transitionalstage is not exhibited by everyone. The secondarypattern has a very prolonged single period of activitywhich extends through midstance and sometimesthrough the unloading stage. There are not anyspeed trends in patterns used by anyone subject.

g. Vastus Lateralis The vastus lateralis patternof activity at free speed agrees with the morerecently published results (8,12). The main trendexhibited was that the subjects exhibiting biphasicpatte~n at free speed tended to exhibit the longerduration monophasic pattern at fast speed.. h. Gluteus Medius Classically the gluteus mediusIS l' f .ac Ive rom late-swing stage through midstance.

This period of activity is exhibited by a majority ofsubjects at free and fast walking speeds. However,many subjects also demonstrated a second periodof activity during the stance-to-swing transitionalstage or lacked activity during late-swing stage. Ingeneral. activity during the stance-to-swing transi­tion did not seem to be a function of speed and wasconsistent for an individual. The activity during thelate-swing period tended to become less prevalentat the slower walking speeds.

The two subjects who displayed the reciprocalbursting of antagonistic muscular activity, RW andMS, were walking with relative speeds of 0.15s- 1

and 0.20s -1, respectively. This reciprocity is dem­onstrative of hesitancy in motion. This hesitancy isindicative of the instability of motion that cali occurat such slow speeds (25).

Although there were no statistically significantcorrelations between pattern types and sex, a fewtrends did develop. The significance level for thesetrends was between 10 and 20 percent. Males havea greater tendency to have: biphasic hamstringpatterns at all speeds of walking, biphasic gluteusmedius patterns at slower speeds of walking, andloading stage activity of the soleus at free speed.Actually these trends may also be an effect ofstature, since the females were shorter than themales.

CONCLUSIONS

The electromyographic gait patterns of eight mus­cles in 25 normal subjects were studied. The resultsshow that there is an intersubject variability andthat the pattern types change with the speed ofprogression. The apparent disagreements among theresults of several investigations of normal EMG gaitpatterns are a reflection of these variations.

Several nonclassical electromyographic synergypatterns were exhibited that emphasize the impor­tance of speed of progression. During very-slowspeed walking, two subjects exhibited the reciprocalactivity between plantarflexor and dorsiflexor mus­cles. This phenomenon is often observed in hemi­plegic gait. Also, in fast speed walking there is anoverlap in time of activity between the plantarflexorand dorsiflexor muscles. This is often observed inthe gait of persons with a spastic lower extremity.

The range of average relative speeds observedwas between 0.24s- 1 and 0.8s- 1·Since people arecapable of walking at relative speeds of 1.5s -1, anyfuture studies concerning speed dependence shouldinclude an expanded speed range. An effect oflaboratory conditions seems to be a reduced stridelength-perhaps another technique worth consid­eration is to measure the stride frequencies andstride lengths of potential subjects in an uncon-

14

SHIAVI et al. ELECTROMYOGRAPHIC PATTERNS for WALKING

strained environment-and then have them replicatethem during any laboratory measurement sessions.

A weak correlation between EMG pattern typesin some muscles and sex seems to be occurring.However, a study using a much larger subjectpopulation is needed to test its significance,

The gait patterns were analyzed in a fairly quali­tative manner in order to determine general trendsand variabilities. Expansion of this kind of studynecessitates computerized data acquisition and pro­cessing systems and objective analytical techniquesbecause of the volume of data involved. It is plannedto continue this study with such systems and toincorporate the techniques of multivariate analysisand pattern recognition for data reduction and clas­sification.

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