109
J.
Physiol.
(I955)
I30,
I09-II3
THE
EFFECT
ON
MUSCLE
STRENGTH
OF
MAXIMUM
ISOMETRIC
AND
ISOTONIC
CONTRACTIONS
AT
DIFFERENT
REPETITION
RATES
By
NANCY
SALTER
From
the
Unit
for
Research
on
Climate
and
Working
Efficiency
of
the
Medical
Research
Council,
Department
of
Anatomy,
University
of
Oxford
(Received
10
March
1955)
There
is
some
controversy
concerning
the
most
efficient
method
of
producing
a
rapid
improvement
in
muscle
strength
(Delorme,
1945;
Asmussen,
1949;
Ionesco,
1949;
MacQueen,
1954;
McMorris
&
Elkins,
1954),
many
clinical
exercise
routines
having
an
empirical
rather
than
an
experimental
basis.
Since
there
is
no
generally
accepted
routine,
it
might
be
assumed
that
the
optimum
method
is
still
to
be
formulated.
In
outlining
an
exercise
schedule,
the
following
variables
have
to
be
considered:
whether
the
contractions
should
be
isometric
or
isotonic;
whether
they
should
be
maximal
or
submaximal;
the
duration
of
each
contraction;
the
repetition
rate
and
the
total
number
of
contractions
per
session,
and
the
total
number
and
spacing
of
sessions.
Following
the
initial
investigation
into
the
relative
importance
of
certain
of
these
factors
(Darcus
&
Salter,
1955),
the
present
experiment
was
carried
out
on
normal
individuals
to
compare
the
effect
of
training
by
repeated
sessions
of
isometric
contractions,
made
at
a
repetition
rate
of
either
2
or
15/min,
with
the
effect
of
comparable
'doses'
of
exercise
by
isotonic
contractions.
METHODS
A
strain
gauge
dynamometer
(Darcus,
1953)
was
used
for
the
measurement
of
isometric
contrac-
tions,
and
a
modification
of
this
apparatus
(Darcus
&
Salter,
1955)
for
isotonic
contractions.
In
the
isometric
contractions,
subjects
applied
a
gradually
increasing
force
to
the
maximum
possible
over
about
4
sec,
and
then
relaxed.
The
contractions
resulted
in
virtually
no
movement
of
the
joint
on
which
the
muscles
were
acting.
Isotonic
contractions
involved
lifting
a
load
equivalent
to
approximately
75%
of the
maximum
isometric
tension
as
far
as
possible,
also
over
about
4
sec,
and
returning
it
to
its
resting
position.
These
contractions
were
accompanied
by
movement
and
marked
shortening
of
the
muscles.
The
movement
trained
was
supination
of
the
left
hand,
and
exertions
were
made
at
-
300
(isometric)
or
from
-
300
(isotonic):
the
zero
position
being
with
the
handle
of
the
apparatus
vertical
(thumb
uppermost)
and
negative
angular
deviations
being
in
the
direction
of
pronation.
Twelve
male
and
eight
female
subjects
between
the
ages
of
17
and
48
yr
110
NANCY
SALTER
were
used.
All
were
of
apparently
normal
physical
development
and
all
except
one
right-handed.
No
subject
had
been
previously
trained
in
either
pronation
or supination,
although
several
of
them
were
familiar
with
the
apparatus
and
technique.
While
using
the
apparatus,
the
subject
was
com-
fortably
seated
with
the
left
arm
adducted
to
the
side
of
the
body
and
the
elbow
flexed
to
a
right
angle.
The
height
of
the
apparatus
was
recorded
for
each
subject
on
the
first
day,
so
that
the
same
position
could
be
adopted
on
subsequent
occasions.
Subjects
were
allowed
to
watch
the
galvano-
meter
deflexion
in
isometric
contraction.
On
the
basis
of
previous
work
(Darcus
&
Salter,
1955),
thirty
contractions
were
made
in
each
training
session.
One
session
was
carried
out
on
each
of
4 days
a
week
(usually
Monday
to
Thursday)
for
4
weeks.
The
total
length
of
the
experiment
was
limited
by
the
availability
of
the
experimental
subjects.
Exertions,
either
isometric
or
isotonic,
were
made
at
a
repetition
rate
of
either
2 or
15/min.
Each
subject
followed
only
one
training
procedure
throughout
the
training
period.
In
order
to
assess
accurately
the
improvement
in
muscle
strength
resulting
from
training,
a
test
consisting
of
five
maximum
isometric
supination
contractions
at
half-minute
intervals
was
made
once
on
each
of
4
consecutive
days
in
the
week
preceding
the
beginning
of
the
training.
A
similar
test
series
was
carried
out
in
the
week
following
the
end
of
the
training
period.
In
addition,
one
test
was
made
at
the
beginning
of
each
'training'
week,
immediately
before
the
training
seasion,
so
that
five
tests
in
all
were
made
before
any
training
was
started.
In
isotonic
training,
the
best
of
the
five
mean
values
obtained
was
used
to
calculate
the
load
to
be
lifted
by
the
subjects.
The
load
was
increased
each
week
in
accordance
with
the
isometric
tension
recorded
in
the
test,
but
if
the
tension
remained
the
same
as
in
the
preceding
week,
or
decreased,
the
load
was
not
changed.
A
control
series
was
carried
out
to
determine
the
effect
of
the
tests
alone.
The
decision
to
use
only
isometric
tests
was
based
on
the
results
of
a
preliminary
experiment
in
which
both
isometric
and
isotonic
tests
were
used
to
assess
the
effects
of
training.
Isotonic
tests
were
found
to
have
various
disadvantages;
for
instance,
the
speed
with
which
an
isotonic
contrac-
tion
is
made
greatly
influences
the
distance
through
which
a
given
load
can
be
moved,
and
it
is
difficult
to
control
this
speed
accurately.
Also,
although
the
load
used
is
a
definite
percentage
of
the
maximum
isometric
tension,
it
is
not
known
how
this
compares
with
the
optimum
load,
and
the
same
load
must
therefore
be
used
in
the
'before'
and
'after'
tests.
The
improvement
due
to
training
may
therefore
be
underestimated.
as
the
subject
may
be
able
to
lift
the
load
easily
through
the
full
range
of
movement
in
the
'after'
test.
The
isotonic
test
may
indicate
a
greater
training
effect
than
the
isometric
test,
probably
because
a
much
larger
proportion
of
the
improvement
is
due
to
the
acquisition
of'
knack'
rather
than
an
actual
increase
in
muscle
strength.
An
advantage
of
the
isometric
test
is
that
the
five
consecutive
readings
are
usually
much
less
variable
than
five
'isotonic'
readings.
A
possible
objection
to
using
isometric
tests
as
the
only
criterion
of
changes
in
muscle
strength
is
that
they
may
indicate
a
greater
improvement
in
isometric
than
in
isotonic
training,
because
of
the
greater
practice
the
subject
has
in
using
the
apparatus
and
in
developing
maximum
isometric
torques.
However,
the
results
of
the
preliminary
experiment
showed
that
in
the
ten
subjects
there
was
no
significant
difference
between
the
relative
amounts
of
improvement
measured
isotonically
and
isometrically
following
the
two
methods
of
training.
Thus
the
test
routine
used
in
the
present
series
can
be
taken
as
producing
a
reliable
criterion
of
improvement
in
muscle
strength
irrespective
of
the
training
method.
RESULTS
The
results
are
shown
in
Table
1.
All
training
procedures
resulted
in
a
signifi-
cant
improvement
in
muscle
strength,
but
it
was
demonstrated,
using
the
ana-
lysis
of
co-variance,
that
there
is
no
significant
difference
between
the
different
methods.
The
apparent
differences
which
are
found
when
percentage
improve-
ment
or
absolute
increment
are
studied
may
be
accounted
for
by
initial
differences
between
the
groups
of
subjects.
The
results
of
the
control
series
MUSCLE
TRAINING
111
indicate
that
the
amount
of
exercise
provided
by
the
test
contractions
alone
is
insufficient
to
produce
any
significant
increase
in
muscle
strength.
An
assessment
of
the
decrement
in
applied
force
during
each
training
session
was
made
by
calculating
the
percentage
difference
between
the
mean
of
the
first
five
and
the
mean
of
the
last
five
readings.
This,
of
course,
is
not
necessarily
a
reliable
indication
of
the
general
trend
throughout
the
session,
but
provides
a
rough
value
for
the
degree
of
'fatigue'.
It
can
be
seen
from
these
figures
that
isometric
training
in
each
group
generally
results
in
a
greater
falling
off
in
strength
throughout
a
session
than
does
isotonic
training.
With
rapid
isotonic
contraction
the
falling
off
is
extremely
variable
from
subject
to
subject.
TABLE
1.
Summary
of
the
results
Average
%
Initial
Final
Absolute
change
Training
Subject
strength
strength
increase
Significance
%
through
procedure
no.
(kg-m)
(kg-m)
(kg-m)
of
difference
increase
session
Isometric
15/min
1
1-68
2-86
1-18
0-001
69-9
-18-5
2
2-22
4-18
1-96
0-001
88-4
-
16-4
3
1-54
2-35
0-81
0-001
52-3
-23-7
4
3-64
5-60
1-96
0
001
53-8
-
17-8
Isotonic
15/min
5
1-70
2-22
0-52
0.001
30-6
-
1-2
6
2-46
2-89
0-43
0-01-0-001
17-3
-40-1
7
1-60
1-93
0-33
0-001
20-6
-32-4
8
3-75
5-92
2-17
0.001
58-0
-
6-7
Isometric
2/min
9
3-92
6-45
2-53
0-001
64-2
-
10-6
10
2-83
4-48
1-65
0-001
58-4
-
1-8
11
4-51
7-89
3-38
0-001
74-9
-
1-1
Isotonic
2/min
12
4-02
6-27
2-25
0-001
55-7
+
2-3
13
4-74
9-26
4-52
0-001
95-4
+
4-4
14
3-80
8-87 5-07
0-001
133-4
-
0-5
15
2-81
4-82
2-01
0-001
71-7
+
1-4
16
3-41
5-54
2-13
0-001
62-4
-
0-5
Control
17
3-54
3-61
0-07
N.S.
18
1-90
2-22
0-32
N.S.
19
1-80
1-88
0-08
N.S.
20
4-35
4-81
0-46
N.S.
-
The
initial
and
final
strength
have
been
calculated
from
the
average
of
the
tests
made
before
and
after
the
training
period.
The
last
column
indicates
the
effect
of
the
exercise
in
each
session,
calculated
from
the
difference
between
the
average
of
the
first
five
and
the
last
five
readinigs
in
each
of
the
sixteen
training
sessions.
DISCUSSION
The
results
of
these
experiments
indicate
that
there
is
no
significant
difference
between
the
four
methods
of
training
in
their
effect
on
muscle
strength
of
the
movement
tested.
Previous
work
(Darcus
&
Salter,
1955)
suggested
that
there
was
little
difference
in
the
amount
of
improvement
in
muscle
strength
resulting
from
comparable
'doses'
of
isometric
and
isotonic
activity
when
the
contrac-
tions
were
made
at
one-minute
intervals,
but
no
record
of
investigations
has
been
found
comparing
the
effect
of
exercising
at
different
repetition
rates,
i.e.
varying
the
amount
of
decrement
in
muscle
strength
produced
by
a
standard
number
of
contractions.
Part
of
the
improvement
measured
may
be
due
to
the
acquisition
of
'knack',
every
co-ordinated
muscular
activity
being
partly
dependent
on
the
develop-
ment
of
this.
However,
there
was
no
training
effect
in
the
five
'pre-training'
test
runs,
and
no
improvement
in
the
control
series.
In
the
earlier
study
(Darcus
&
Salter,
1955),
subjects
making
repeated
isometric
contractions
were
not
allowed
to
see
the
results
of
their
efforts
on
the
galvanometer,
although
subjects
exercising
by
isotonic
contractions
were
able
to
assess
the
increase
in
the
distance
the
load
could
be
moved
on
successive
occasions.
It
was
thought
that
the
tendency
for
isometric
training
to
produce
less
improvement
in
muscle
strength
might
have
been
due
to
the
fact
that
exercise
without
knowledge
of
results
is
a
monotonous
process.
In
the
present
series,
however,
where
all
subjects
received
a
comparable
indication
of
their
progress,
there
was
still
no
significant
difference
between
the
two
methods.
The
fact
that,
despite
knowledge
of
results,
isometric
contractions
may
not
be
accompanied
by
the
same
sense
of
achievement
as
the
isotonic
contractions
might
be
partly
responsible
for
the
relatively
greater
'fatigue'
effect
in
the
former
type
of
activity.
However,
subjects
did
experience
a
greater
feeling
of
tiredness
following
a
session
of
thirty
isometric
contractions
than
after
weight
lifting,
and
despite
the
considerable
static
component
provided
by
the load
in
isotonic
contractions,
isometric
activity
appeared
to
the
observer
to
require
more
effort
on
the
part
of
the
subject.
The
following
comments
on
these
findings
apply
mainly
to
the
'two-per-minute'
routine.
In
making
an
isometric
con-
traction,
a
subject,
having
reached
what
proved
to
be
his
maximum
torque
in
3-4
sec,
maintained
this
for
a
further
1-2
sec
in
an
attempt
to
increase
the
galvanometer
reading.
On
the
other
hand,
it
was
difficult
to
make
a
subject
take
as
long
as
4
sec
lifting
a
weight
because
he
soon
found
out
that
he
could
produce
better
results
by
moving
the
weight
rapidly.
Against
this,
however,
is
the
fact
that,
following
an
isotonic
contraction,
some
work
was
done
by
the
muscles
in
controlling
the
return
of
the
load
to
its
resting
position,
whereas
following
an
isometric
contraction,
the
subject
could
immediately
relax.
As
might
be
anticipated,
the
'fifteen-per-minute'
routine
was
more
tiring
than
the
'two-per-minute'
routine,
although
there
was
a
tendency,
particularly
with
isotonic
contraction,
to
cut
down
on
the
contraction
time
so
as
to
leave
1-2
sec
rest
between
successive
contractions.
Subjects
appeared
to
derive
a
certain
amount
of
advantage
by
getting
into
a
definite
rhythm,
and
of
course
the
'fifteen-per-minute'
routine
was
much
less
tedious
than
the
longer
session.
An
advantage
of
the
rapid
repetition
rate
in
the
practical
situation
is
its
obvious
economy
of
time.
Since
neither
the
type
of
muscle
activity
nor,
within
the
described
limits,
the
amount
of
'fatigue'
resulting
from
it,
appears
to
affect
significantly
the
amount
of
improvement
which
can
be
expected
in
normal
muscles
of
the
human
fore-
arm,
it
is
suggested
that
the
type
of
remedial
exercise
chosen
might
be
con-
112
NANCY
SALTER
MUSCLE
TRAINING
sidered
on
the
merits
of
what
other
effects
it
produces.
For
example,
isotonic
contractions
might
help
to
maintain
or
increase
the
range
of
joint
movement,
whereas
isometric
contractions
might
be
useful
where
movement
is
contra-
indicated.
The
effects
of
different
types
of
muscle
activity
on
muscle
strength
may
well
vary
in
abnormal
conditions,
for
example,
following
acute
poliomyelitis.
It
is
suggested
that
a
further
series
of
experiments
on
normal
subjects
should
investigate
the
effects
of
different
amounts
of
activity
on
the
improvement
in
muscle
strength.
It
would
be
interesting
to
know,
for
instance,
whether
the
degree
of
improvement
found
in
this
experiment
could
be
achieved
by
a
smaller
number
of
contractions
in
each
training
session
or
by
fewer
sessions
each
week.
SUMMARY
1.
Training
of
supination
of
the
left
hand
was
studied
in
twenty
normal
subjects
to
compare
the
effect
of
repeated
sessions
of
thirty
maximum
isometric
exertions
made
at
a
repetition
rate
of
either
2
or
15/min
with
the
effect
of
comparable
doses
of
exercise
by
isotonic
contractions.
2.
Sixteen
training
sessions
were
carried
out
over
a
period
of
4
weeks,
the
effect
of
these
being
assessed
by
the
difference
between
two
groups
of
four
tests
made
in
the
weeks
immediately
preceding
and
following
the
training
period.
3.
A
test
consisted
of
five
maximum
isometric
supination
contractions
made
at
half-minute
intervals.
The
reliability
of
isometric
test
contractions
as
criteria
of
improvement
in
strength
following
different
methods
of
training
is
con-
sidered.
4.
All
training
procedures
resulted
in
an
improvement
in
muscle
strength,
but
no
significant
difference
was
found
between
the
four
different
methods
used.
5.
No
correlation
was
found
between
the
amount
of
improvement
in
muscle
strength
and
the
degree
of
'fatigue'
resulting
from
the
training
sessions.
The
author
would
like
to
thank
Mr
R.
M.
Jones
for
his
advice
on
statistical
matters.
REFERENCES
ASMUSSEN,
E.
(1949).
Training
of
muscular
strength
by
static
and
dynamic
muscle
activity.
2.
Lingiaden
Stockholm
Kongre8sen
F6redrag,
ia,
20-22.
DAR,uus,
H.
D.
(1953).
A
strain
gauge
dynamometer
for
measuring
the
strength
of
muscle
contrac-
tion
and
for
re-educating
muscles.
Ann.
phy8.
Med.
1,
163-176.
DiARCus,
H.
D.
&
SALTER,
N.
(1955).
The
effect
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on
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strength.
J.
Physiol.
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DELORME,
T.
L.
(1945).
Restoration
of
muscle
power
by
heavy
resistance
exercises.
J.
Bone
Jt.
Surg.
27,
645-667.
IONEsco,
A.
(1949).
Muscular
training
by
means
of
dynamic
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static
labour.
2.
Lingiaden
Stockholm
Kongressen
F6redrag,
iI,
83-84.
McMoRRIs,
R.
0.
&
ELKINS,
E.
C.
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8
PHYSIO.
CXXX
113
