CHANGES IN ELASTIC CHARACTERISTICS OF HUMAN MUSCLE INDUCED BY ECCENTRIC EXERCISE MICHEL

POUSSON,*

JACQUES

VAN

and FRANCIS

HOECKE’

CoLieELt

de Biomkanique, INSEP. I I Avenue du Tremblay. 75012 Paris. France and de GEnie Biologique. UA CNRS 858. UTC. BP 649. 60206 Compiegne. France

l Laboratoire t Departement

Abstract-The effect of an eccentric strength training programme on the muscular series elastic component (SEC) was studled on the flexors of the human elbow. The characteristics of the SEC were determined using an in siru technique derived from methods commonly used on isolated muscles. The results wereexpressed in terms of compliance-force and tension+zxtension relationships. These relationships indicate a sharp increase in compliance when tension decreases. Furthermore. for a given value of tension. the SEC compliance of the trained muscles is found 10 be lower than that of the untrained muscles. These results are discussed in relation to the active and passive parts of the SEC.

IXTRODCCTIOS

the training nique

During

eccentric

muscles are stretched while

exercises.

active. As a result of this muscular increase in force production hancemcnt

of force

lengthening,

is observed.

has been

studied

an

This

in

period by means of a quick-release

(Goubel

classical

and

methods

experiments

Pertuzon,

used in isolated

(Jewcll and Wilkie.

tech-

1972) derived animal

from muscle

1958).

en-

isolated

muscles and single fibres during tetanic contractions (Katz,

193‘); Edman

Crowc,

et (II., IY7H; Van Atteveldt

1980). According

to IIill’s

classical

and

model

(193X). much more potential energy is stored in the socalled series elastic component force production. very

This

inexpensive

and

during

a subsequent

total

Davies.

IY75)

and

cncrgy

energy

it can

shortening

efliciency.

positive work

produced

is

cost

be released

which

and energy expended a

of human muscle is its use of such

stretch-shortening

cycles (Thys et 01.. 1972; Asmussen

Bonde-Petersen,

1987). Moreover,

1974;

Bosco,

this connection,

Komi

and Buskirk

that an eccentric conditioning

(1972)

During a

was 45 ‘. The exercise con-

of the elbow

i.e. an eccentric

of the flexors from a 30 to a 160’ flcxion

angle with a bar-bell held in the hand. Each movement 8 s, the limb being returned

position

by the experimenter.

to

Thirty

movements were performed during one session but the loads

eccentric In

used were

progressively

decreased. Each training

increased

in-

maximal

and

then

load was expressed in per-

centage of one-repetition-maximum

reported

caused a greater

contraction

lasted approximately

19112; Goubel.

exercises during their strength training programme.

eccentric exercise training.

training session, the subject was seated on ;I stool and

the starting

high level athletes such as jumpers

and throwers are accustomed to performing

served as scdontary controls whcrcas the other

sisted in an extension

typical behaviour and

(n ‘4)

(n = 6) underwent

between arm and trunk

between

exercise conditions,

in

his right arm was fastened to a wood surface; the angle

improves

i.e., the ratio

1977). In rwtural

(Cavagna,

potential

terms of chemical

in

(Curtin

muscle mechanical

additional

Ton sodcntary malts (age: 2Y + 5 yr) participated

this study and wcrc divided in two groups. One group

(SEC) due to the extra

(I RM),

i.e. the

load the subject could lift in one concentric

crease in muscle strength than did a concentric condi-

all-out elTort (Johnson C’L01.. 1976). A training session

tioning.

was done twice a week for a period of six weeks. In

Despite

formance

the

produced

cycles is believed characteristics

fact

In

the

to be ascribed

(Komi.

enhanced

pcr-

order

training

study,

precisely determine training programme

have not been

during

an attempt

was made

to

identical

Then a progression

on the characteristics a six-week

(optimal

E.qwrimcntal

period.

et

ul..

was relatively

during

the first two weeks.

was adopted (see Table

a load corresponding conditions

1986; limited

I) which

during the

to 125%

for an eccentric

of

condi-

procedure

The subjects were tested before and soon after (i.e. about

2-3 days) the training

has been detailed injinoljtirm

(FridL:n

tioning; see Jones. 1973).

of the SEC.

conditioning

sixth week with I RM

the erects of an eccentric strength

The SEC properties were established before and after

Receid

soreness

allowed the subject to perform contractions

The subjects trained their elbow flexors using eccentric contractions

prevent

1988). the overload

and remained

investigated.

the present

to

Newham.

to muscle elastic

lY84). changes in SEC behavi-

our as a result of eccentric thoroughly

that

by the use of stretch-shortening

I9 October 1989.

previously

period.

The ergometer

(Goubel

and Pertuzon,

1973). In short, the subjects were seated with the right 343

M. POUSSON.J. VAN HOECKE and F. GOUBEL

Table 1. Training programme Training week

Session contents* (repetitions x loads)?

1.2 3 4 5 6

(6 x 90) (6 x 90) (6 x 90) (6 x 100) (6 x 100)

(5 x 95) (5 x 95) (5 x 100) (5 x 105) (5 x I IO)

(4 x 100) (4 X 1 IO) (4 x 110) (4 x 120) (4 x 125)

(5 X 95) (5 x 100) (5 x 105) (5 x 110) (5 x 120)

(5 x 90) (5 x 105) (5 x 105) (5 x I IO) (5 x 110)

(5 X 90) (5 x 901 (5 x 100) (5 x 105)

(5 x 105)

*Twice a week. tln % of I RM.

upper limb horizontal

and flexed at 75”. The forearm

increased as the flexors shortened.

was tightly fixed in a light frame whose vertical axis of

ations

rotation

was aligned

variations

angular

displacement

with

that

of the elbow.

(0) and acceleration

measured by means of a potentiometer ometer,

respectively.

The

frame

means of an electromagnet

The

(0’) were

and an acceler-

was connected

by

to a force transducer which

measured the initial torque(T).

The surface EMGs

of

in 0 and

0’ allowed

Recording

of vari-

the calculation

of the

in force (AF) and length (A/) of the equival-

ent flexor according to the above formulae. In contrast to experiments

on isolated

simultaneously.

However,

decrease in acceleration

muscles, F and I varied the early beginning

of the

was ascribed to an SEC recoil

that is suddenly unloaded (Cnockaert

et ul.. 1978). The

biceps brachii and triceps brachii were continuously

ratio AI/AF

was then used as a measure of the SEC

recorded

compliance

(C’) since AF values were small with re-

using bipolar

performed

electrodes.

The subject

first

an isometric flcxion torque: as soon as the

torque was constant cut offwithout

the electromagnetic

the knowledge

quick-relcasc

(QR)

was

isometric force(F)

developed by the subject through a

of the subject, causing a

C-F relationship.

In order to depict the evolution

movement.

current

Seven initial

values were used four times. They comprised 30 and 60% contraction

of a prcdctermincd

maximal

torque bctwecn

voluntary

(MVC).

SEC

characteristics

muscle

of the elbow

as in experiments

tension-extension

relationships

in

on isolated were also es-

tablished. The SEC negative extension was calculated from the C-F

relationship

using the equations given in

the Appendix.

Compliunce meusurements Flexion

spect to the initial value of F. C was then related to the

results from

the combined RWIJLTS

action of five flexor muscles. The force and the length of each muscle cannot easily be measured. The problem is solved satisfactorily equivalent

1973). The equivalent biceps brachii. l=J(cl*

with the utilization

flexor concept (Pertuzon.

flexor has the dimensions of the

Its length (I) is given by the formula

+h2+20hcos0)

where (I and b are the dis-

tances between the axis of rotation the insertion

of the

1972; Bouisset,

and origin,

of the elbow and

respectively,

brachii,

0 being measured

from

force(F)

is given by the formula

of the biceps

full extension.

The

F = fD’l/ub sin 9 where

I is the moment of inertia of the whole mobile system. For each subject, I was calculated

according

to the

Figure EMG

I shows a QR

movement

of flexion.

The

of the biceps brachii is quite constant during the

initial isometriccontraction

while the triceps brachii is

silent. The start of the QR movement the abrupt

increasing

release of the forearm

in angular

is expressed by

acceleration.

involves a shortening

The of the

elbow flexors that are suddenly unloaded.

inducing a

decrease in acceleration.

the triceps

Simultaneously,

brachii is stretched and a reflex burst ofactivity on that muscle. The SEC

compliance

occurs

is calculated

between the beginning of the decrease in acceleration

method proposed by Bouisset and Pertuzon (1968). In

and the stretch reflex appearance:

short, at the beginning

ponds to the beginning of the recoil of the previously

angular maximal

acceleration

rotation

reaches

value (amax);

point of application

of the QR

movement,

at the first onset

if the distance

(d) from

is known,

I is easily calculated

from

the

For each subject, three initial

forces (80, I IO and 140 N) were considered. measures

were made.

showed very slight inter-test

The

For each

values of f

ditTerences (3 and 1.5%)

which were in no way significant. The measurement the SEC compliance

its the

of the isometric force to the axis of

formula: I = T-@max. force, three

the

of the equivalent

at the start of the QR movement

of

flexor was made

i.e., when o’began to

decrease. At the same time, the angle of the elbow

this period corres-

stretched SEC that is suddenly allowed initial

length

(Wilkie.

1956; Goubel

to recover its and

Pcrtuzon.

1973). Figure 2 shows that constant

but is related

curvilinear

the SEC

compliance

is not

to the tension (F) through

a

relation. The shape of the C-F relationship

of the trained muscles is similar to that of the controls, indicating

a sharp increase in compliance

sion decreases: a power curve (C=nF’) fit to the data

(O.S5 crc0.96).

given value of tension. trained

when tcn-

gives the best

Furthermore.

for a

the SEC compliance

of the

muscles is found to be lower than that of the

34s

Eccentric exercise-induced changes in human muscle elastic characterrstrcs ru

I-

i

-30

I

I

I

30

45

60

Force

EMG

fl

EMG

f

I 80

( 7’.MVC 1

level

Fig. 3. Differences tn compliance between pre- and posttraining in control subjects and exercised subjects. DtR‘erences (AC) are calculated born the power (uncttons and expressed rn percentage of the initial value. Results for all subjects and four force levels (normalized with respect to MVC). r: Student-Fischer I significant at p