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Komi, P. V., Rusko, H.: Quantitative evaluation of mechanical and electrical changes during fatigue. In ar re 1 , loading of eccentric and concentric work. Scand.
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European Journal of

.H.Norris

Applied

Eur. J. Appl. Physiol.42, 41-50 (1979)

Physiology and OccupationalPhysiology ~ Springer-Verlag 1979 -

. 42, 73-86 age.Copenical material.

EMG Frequency Spectrum,Muscle Structure, and Fatigue

lw-Hill1971

During Dynamic Contractions In Man

td paying the

Paavo V. Komll. and Per Tesch2

06, 689-715

I

KinesiologyLaboratory,Departmentof Biologyof physicalActivity, Universityof Jyvaskyla,

: on creatinine

SF-40 100 Jyvaskyla, Finland 1 Department of Clinical Physiology, Karolinska Hospital,

-163 (1976)

S-10401 Stockholm, Sweden

agedand older ., Hedman, R., cl and maximal .tional reference

d women in the cisePhysiol. 43,

Summary. conditioned

Fatigue

of the vastus lateralis

muscle was studied in healthy

students, who differed considerably

well-

regarding their muscle fibre type

distribution. Muscle force declineduring repeatedmaximumvoluntary knee extensions at a constant angular velocity (180° x S-l or n rad x S-l), using isokinetic equipment,was taken as the criterion for the degreeof fatigue. In an

19itudinal Study.

attempt to study quantitative as well as qualitative changes in the EMG pattern, integrated EMG (IEMG) and the frequency of the mean power (MPF), com-

cularwork.Acta

puted from the power spectraldensity function (PSDF), were analysed.It was found that individuals with musclesmade up of a high proportion of fast twitch (FT) musclefibres demonstratedhigher peak knee extensiontorque, and a greater susceptibilityto fatiguethan did individuals with musclesmainly composedof

J. Appl.Physiol.:

slow twitch (ST) muscle fibres. An IEMG decline (p

< 0.01) was demonstrated

during 100 contractionsin individuals rich in FT fibres. Only a slight, but not significant,reductionin IEMG occurredin individualswith a high percentageof ST fibres. Concomitantly,MPF decreased(p < 0.001)in individualswith a high percentageof FT fibres, while their oppositesdemonstratedonly a slight decrease(non-significant).It is suggestedthat musclecontractionfailure might also be related to qualitativechangesin the motor unit recruitmentpattern, and that thesechangesoccur more rapidly in musclescomposedof a high proportion of FT muscle fibres than in muscles composed of a high proportion of ST fibres. Key words: Electromyography

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Isokinetic contractions

-

Mean power fre-

quency - Muscle fatigue - Muscle fibre types From animal experimentsit is known that musclescomposedof slow twitch (ST) fibres possessa greaterresistanceto fatigue than musclescontainingpredominantly fast twitch (FT) fibres (e.g.,Edstrom and Kugelberg, 1968;Kugelbergand Edstrom, Offprint requests to: Per Tesch,Laboratory for Human Performance(FOA 57), Karolinska Hospital,

S-l04 01 Stockholm, Sweden

0301-5548/79/0042/0041/$02.00

"

42

P.V.KomiandP.Tesch

f'EMG Changes a

;-LumexInc.,Ne\\

1968;Baldwin and Tipton, 1972).In h~man skeletalmuscle,b.othfib~etypes ex~stin one and the same muscle. Recently, rt was found that subjects wrth a relatively;,; higher proportion of FT fibres in the quadricepsmusclewere more susceptibleto fatiguewhen performing 50 consecutivemaximal kneeextensionsthan subjectsrich

Each subject

t~ joint an~at an ! li~c~ ted °ns twas ,~ contr

.

was

in ST fibres (Thorstenssonand Karlsson, 1976; Nllsson et al., 1977; Tesch et al., 1978a).In addition,large amountsof lactatewerefound to have accumulatedpreferentially in the FT fibres after only 25 contractions (Tesch et al., 1978a, 1978b). Lactate formation and/or associatedpH changeswithin engagedmusclefibres may be responsiblefor muscle contraction failure (cf. Fitts and Holloszy, 1976). .

.'

In experimentsusing electromyographic(EMG) techmques,rt has been suggested

that

the

shift

in

EMG

spectral

density

function

towards

lower

frequency

componentsis associatedwith reductionin muscleaction potentialconductionvelocity

(Mortimer

et al.,

1970).

In

addition,

the

shift

in

EMG

frequency

. . " . d. . h b h t b I t d t h lsometnclatlgue con ltions as een~. own 0 ere a e. 0 tel "'

tion

of

the

muscle

(Larsson,

1978;

Vlltasalo

and

Koffil,

spectrum

fib

1978).

under

The

" r:i ;,~ :1

I

I

present

study

'

t I

Results

-

Eleven

male

ments,

all subjects

~hysical

mental.p~oc~ures.

"",.!

were diVIded

:';1,'

":"' !:'f':,1

ed~cation

students

were Informed After

Into two

muscle

about

volunte.ered the possible

biopsy

groups,

.s~~ling

in.the

histochemical

muscle

study:

and nsks

Prior

associated

~aI~sis.(see

fibre

type

.to theexpe~With the expen-

below),

distribution.

the

Table

I

occupied

subj~cts

area.

The

knee

extensioJ

II)

Nm

1 summanzes

theirphysical characteristics withrespect to age,weight, height, percentdistribution, andrelative area of fast twitch

(FT)

were

fibres in the vastus

biopsies

!j,~

Classificati.on

i "j

based on histochelDlcal

staining

Herman,

1962). Muscle

taken

from

of the, fibres

1955; Engel,

M.

vastus

lateralis

muscle,

lateralis

prior

~n~o slow twitch

for myofibnllar fibre

transverse muscle sections stained for NADH area occupied

fibres

to experiments

ATPase

was calculated

dynamic

according

according

strength.

to Bergstrom

at pH

to Thorstensson

When the I

(1962).

t

and

~

greater

I

experiments

10.3 (Padykula (1976)

and

con

(Tab!,

Muscle

~FT or type II) fibre types was

after preincubation

area was measured

;:

by FT

as well as maximum

(~T or type 1) and fast ~witch

~ 1';1 1 I~;

~o participate discomforts

and

based on indiVIdual

i\-!!

)1

area

averagevalue

I'~~

i~

wa

latedfor the bar

Methods

!'~I

'!T - (ill

'".

d.

Thetwo groul

;\~; : ;t.lf!

-:':;.,

spectral

power (MPF) I

~

n-

The data pr( 2116 C labol

Piersol(1971). T

4~

~

range

of knee extensioJ

power ~

~

~

requency

(PhilipsAnalog 7

~P

.

t

was undertakento investigateEMG spectral changesunder maximal dynamic fatigue conditionswherelactateformation is likely to occur preferentiallyin FT fibres (Tesch et al., 1978a, 1978b).

c,

ficnstaillaca.EM!

I

re ype composl-

0 th

IDl

Electromyog entireexperiment placed overthev; aI~ay~ ~verthet

the knee exten lb.

Both in

gro h

from

diaphorase activity (Novikofif et aI., 1961). The relative' according

to Tesch

et aI. (1978a).

01

..:. :;' \ :.. '. i 1:: ,

"","

..

ili:

TableI. Physical characteristics (mean:t SE)of thetwo subjectgroups.Percentdistribution and relative

'I ii.

':1,:: "" ,:

area of fast twitch

(FT)

fibres were obtained

r---

--.

Group

I

Group

:,.f ,

< 50% FT

I:'\]"' i\: il rl

(n = 5)

I

( ,,/

biopsy

.

...", "c..'

.:\,

muscle

sample

of M. vastus lateralis.

Thepeaktorqueexpresses themaximum torqueof theunilateral kneeextension

-, -»), ",-~.;

from

area

> 50%

1'50 ~

~

-.Difference

II FT

m

area

(n = 6) 50

Age (year) Weight (kg)

27.8:t 74.0:t

2.8 3.4

23.1:t 1.1 69.6 :t 2.0

t 0

, 2.

Height

(cm)

180.4 :t 1.8

;:: ii,'!

%FT % FT

area

41.2:t3.2 43.2:t 1.0

60.3:t3.0 67.0:t 3.4

p

6

40

-1 ()1 15

~

~ ~5 s'o ;!5 '100 ~ s'o ;!5 ~100 a _oIC(Xrtr8Ct;,"," b _",c actionS Fig. 1aandb. Mean(:I: SE)torqueexpressed asNm (a) andpercentof initial value(b), respectively, during 100 repeatedkneeextensionsat an angularvelocity of 1800x S-I. Filled and open dots represent groupsof subjectswith a relativeareaof 67%(n = 6) and41%(n = 5) fast twitch fibres,

respectively

'~

~EMG Changes "'

"'C~

.

~\~ ~ ""

~~!;,

110 '.

GI ~

~> ~ ~ '2 .-

90

"0

~ 0

-

u:

Do

~

I

100

300

400

~

Fig. 2. Power spectrum density function (PSDF) recorded for one subject (65% FT area) initially ("non-fatigued") and at end of exercise("fatigued")

110

I

,;%

L'

" \,\ \ \

'

,

\~"",

-

'f

1

\\ \\\\\

1 .1 1

_-1,

"

'"

---

" Fig. 4. Relatio

(n= II)

T

~

,Ii .~

.5 '0 ~

L~!

*

*

.

tively. If the

*

weig ht

' meal

kg-I, respect lated positivI and lb, the j :!i~tions. EMG t (IEMG) dec, ,,~An increase slightly, but T 0

, 25

, 50

I 75

I 100

.,'"

Numberof contractions Fig. 3. Meanvalues(:t SE)of meanpowerfrequency(MPF)expressed aspercentage of initialvaluefor the two groups studied during 100 contractions. Differences between groups are denoted with

p < 0.05 and

..= p < 0.01.For furtherexplanationseeFig. 1

-~-

.=

!C:..shiP. was est. decline (r = f

1!!loading (Fig, .1.i,12 ::!:4% (n. f;. Differences '" 25-30 cont

45

.

. . . .

u: Q.

.

2 .rea)

.

initially

r = 0.73 P< 0.01

Y = 0.81x

+ 32.77

. . L~---sQ

TORQUE, 6t % of initial ~ value

~

Fig. 4. Relationshipbetweenrelativechangesin peak torque and MPF after 25-30 contractions (n= 11) tively. If the torque decline during the 100 contractions was expressed per kg body weight, mean (::t SE) reductions were 1.1 ::t 0.1 Nm x kg-1 and 1.7 ::t 0.1 Nm x kg-1, respectively, for groupS I and II (p < 0.001). The decline in torque was correlated positively to the % FT area (r = 0.73,p < 0.01). Moreover, as shown in Fig. 1a and 1b, the initial torque decline in group I was delayed until the 7th-10th contracEMG measurements revealed that integrated electromyographic activity tions. (IEMG) declined as follows: group I, 4 ::t 3% (n.s.); group II, 15 ::t 3% (p < 0.01). An increase in IEMG/torque ratio occurred with fatigue (p < 0.01), and it was slightly, but not significantly, more pronounced in group II. Furthermore, a relationship was established between the relative increase in IEMG/torque ratio and torque decline (r = 0.88, p < 0.00 1). PSDF changed considerably in group II during fatigue loading (Fig. 2). For instance, mean power frequency (MPF) declined 13 ::t 4 Hz or 12 ::t 4% (n.s.) (group I) and 26 ::t 3 Hz or 25 ::t 3% (p < 0.001) (group II) (Fig. 3). Differences in the PSDF change between the two groups were observed after only 25-30 contractions (p < 0.01).

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46

24-48Hz .1%

:' c~:

,

+100 ,,' T

1' 1 """

*

movements. ,,- J(1 ",

",'i'

Y

'

I

Integrated decreas~ng

,"7'

,1

The decrease

:.~ IEMG activity ir The increase in I cles of the fast tv et al. (1977), wh gastrocnemius a

**

*

and Karlsson, IS sessedby the dec FT muscle fibre:

i E

in so

(e.g., NIlsson et

1'

1

b---l> *

6

&---l>o---~-

* -

t

!

-

136-400 Hz .1 %

T .J, ~o-* ""

I

partially explain

I

muscle to anotht

~

muscles)but al! pold (1955), (1976).

an,

) The changes crease in MPF