Effect of maximal grip strength and initial grip strength on contraction time and on areas under force-time curves during isometric contractions


Byrd, R.; Jenness, M.E.

Ergonomics 25(5): 387-392

1982


Subjects (30) volunteered for a study designed to investigate the usefulness of force-time curve areas as determinants of endurance. With the termination point being 50% of maximum voluntary contraction, the effect of varying the initial strength of contraction was studied. Correlations among maximum grip strength, area under force-time curves and time of sustained isometric contractions were examined. No significant difference were found in force-time curve areas across test conditions, while means for time were different. Strongest correlations were found among the force-time curve areas. Because of the greater consistency of force-time curve areas over time alone, force-time curve areas should be considered as a useful alternative tool for those researchers dealing with handgrip endurance.

ERGONOMICS,
1982,
voL.
25,
NO.
5,
387-392
Effect
of
maximal
grip
strength
and
initial
grip
strength
on
contraction
time
and
on
areas
under
force—time
curves
during
isometric
contractions
By
RONALD
BYRD
School
of
Health,
Physical
Education,
Recreation,
and
Dance,
Louisiana
State
University,
Baton
Rouge,
Louisiana
70803,
U.S.A.
and
MARTIN
E.
JENNESS
677
Ala
Moana
Boulevard,
Suite
408,
Honolulu,
Hawaii
968
I
3,
U.S.A.
Thirty
subjects
volunteered
for
a
study
designed
to
investigate
the
usefulness
of
force—time
curve
areas
as
determinants
of
endurance.
With
the
termination
point
being
50%
of
maximum
voluntary
contraction,
the
effect
of
varying
the
initial
strength
of
contraction
was
studied.
In
addition,
correlations
among
maximum
grip
strength,
area
under
force—time
curves,
and
time
of
sustained
isometric
contractions
were
examined.
No
significant
differences
were
found
in
force—time
curve
areas
across
test
conditions,
while
means
for
time
were
different.
Strongest
correlations
were
found
among
the
force—time
curve
areas.
Thus,
because
of
the
greater
consistency
of
force—time
curve
areas
over
time
alone,
it
was
concluded
that
force—time
curve
areas
should
be
considered
as
a
useful
alternative
tool
for
those
researchers
dealing
with
handgrip
endurance.
1.
Introduction
In
reviews
of
the
literature,
it
has
been
reported
that
correlations
between
strength
and
endurance
ranged
from
0.91
to
—0.63
(Shaver
1971,
Smith
and
Edwards
1968).
While
strength
is
a
clear-cut
concept,
endurance
is
not,
and
this
is
partially
the
explanation
for
the
extreme
ranges
of
correlations.
Endurance
is
usually
expressed
as
a
function
of
time
and
can
be
defined
in
absolute
or
in
relative
terms.
It
is
generally
accepted
that
maximum
grip
strength
(MGS)
is
positively
related
to
absolute
grip
endurance
(McGlynn
1968,
Start
and
Graham
1964).
However,
the
relationship
of
grip
strength
to
relative
grip
endurance
is
not
so
clear,
one
group
claiming
that
the
two
are
negatively
related
(Heyward
1975,
Kroll
1968;
Tuttle
et
al.
1950),
another
stating
that
relative
endurance
is
independent
of
strength
(Caldwell
1964,
Heyward
and
McCreary
1977,
Rohmert
1960,
Shaver
1971),
and
a
third
reporting
positive
relationships
(Shaver
1971,
Shaver
1972).
Smith
and
Edwards
(1968)
cited
differences
in
methods
and
equipment
as
being
primarily
responsible
for
the
controversy.
While
this
might
be
at
the
root
of
some
of
the
apparent
disagreement,
it
was
felt
that
a
more
pertinent
problem
might
have
been
that
created
by
the
possible
inconsistency
of
subjects
in
obtaining
true
maximum
contractions
upon
request.
The
purposes
of
this
investigation
were:
(1)
to
determine
the
effect
of
varying
the
initial
per
cent
of
maximum
grip
strength
(with
the
termination
per
cent
held
constant)
on
the
areas
generated
by
force—time
curves
and
on
the
length
of
time
that
isometric
contractions
could
be
sustained,
and
(2)
to
0014-0139/82/2505
0387 503.00
1982
Taylor
&
Francis
Ltd
388
R.
Byrd
and
M.
E.
Jenness
examine
relationships
between
maximum-
grip
strength,
areas
under
force—time
curves,
and
time
of
sustained
isometric
contractions.
2.
Methods
2.1.
Subjects.
Thirty-two
Caucasian
physical
education
students
volunteered
for
this
study.
Two
were
eliminated
because
of
injuries
unrelated
to
the
experiment.
The
remaining
30
(mean
.
age
20.1
years)
consisted
of
14
males
and
16
females.
All
subjects
had
prior
experience
with
strength
and
endurance
tasks
with
the
hand
dynamometer
and
were
therefore
familiar
with
the
general
procedures.
2.2.
Testing
procedures.
Each
subject
reported
to
the
laboratory
for
testing
on
three
separate
days,
with
a
minimum
of
three
days
between
visits.
Maximum
grip
strength
(MGS)
was
designated
as
the
highest
of
three
values
taken
on
the
first
test
day.
MGS
was
checked
by
the
same
procedure
on
subsequent
visits.
Treatments
were
randomly
assigned
in
a
Latin
square
design
to
counterbalance
any
order
effect.
The
assigned
tasks
were:
(1)
to
hold
a
100%
MGS
contraction
until
a
decrement
to
50%
MGS
was
observed,
(2)
to
hold
an
80%
MGS
contraction
until
a
decrement
to
50%
MGS
was
observed,
and
(3)
to
hold
a
60%
MGS
contraction
until
a
decrement
to
50%
MGS
was
observed.
Tests
were
conducted
with
the
subject
seated,
gripping
a
Stoelting
hand
dynamometer
with
the
dominant
hand,
with
a
90°
angle
at
the
elbow.
An
adjustable
stop
was
fixed
at
the
elbow
so
that
the
exertion
could
only
be
a
squeezing;
pulling
was
rendered
impossible.
The
subject
was
allowed
to
see
the
dynamometer
scale
and
was
given
verbal
encouragement
prior
to
and
throughout
the
bout
with
special
attention
to
motivation
towards
termination.
The
dynamometer
was
mechanically
connected
to
a
pen
so
that
deflections
proportional
to
grip
strength
were
recorded
on
a
Gorrell
and
Gorell
Type
S
Monodrum
which
was
set
to
rotate
at
13.27
cm/min.
Areas
under
the
generated
force—time
curves
(FTA)
were
measured
with
an
Ott
Type
30
Planimeter,
duplicates
being
required
to
agree
within
0.1
cm
2
.
Force
exerted
was
measured
to
the
nearest
kilogram
and
time
of
contraction
(7)
to
the
nearest
second.
2.3.
Data
analysis.
Differences
between
means
for
each
of
the
dependent
variables,
FTA
and
7',
were
tested
for
significance
using
1-tests.
Fisher's
modified
least
significant
differences
was
used
to
control
type
1
error.
Correlations
were
determined
between
FTA,
T
and
MGS.
Finally,
sex
differences
for
FTA,
T,
and
MGS
were
determined
by
analysis
of
variance.
3.
Results
Analysis
revealed
no
significant
differences
between
FTA
means
across
test
conditions
(table
1).
Comparisons
of
isometric
contraction
time
(7)
means
for
the
three
conditions
revealed
significant
differences
between
the
100-60
.
and
the
80-60
initial
load
level
comparisons
(table
1).
Significant
sex
differences
were
detected
in
MGS,
FTA,
and
T
(table
2).
Males
were
stronger
and
generated
larger
FTA
values,
but
the
females
exhibited
superior
endurance
time.
An
examination
of
the
correlations
among
FTA,
T,
and
MGS
(table
3)
revealed
:
Grip
strength
and
force—time
curve
areas
389
(1)
The
strongest
correlations
were
among
the
FTA
conditions.
Those
for
T
comparisons
were
also
all
positive
and
significant,
but
of
less
magnitude
and
thus
less
meaning.
(2)
Substantial
to
strong
significant
positive
correlations
existed
between
MGS
and
the
measures
of
FTA
for
all
three
treatments.
(3)
Of
the
remaining
twelve
correlations,
only
three
were
statistically
significant.
None
were
of
importance,
the
strongest
accounting
for
only
18.5%
of
the
variance.
4.
Discussion
Grip
time
has
been
criticized
as
an
endurance
measure
because
of
the
lack
of
reliability
(Bowie
and
Cumming
1972).
It
was
the
authors'
hypothesis
that
some
of
this
variability
springs
from
inconsistency
in
eliciting
truly
maximum
contractions.
Resultant
differences
in
intramuscular
tension
and
in
local
metabolic
rate
would
certainly
contribute
to
the
observed
variance
in
endurance.
The
prime
focus
of
this
project
was
to
determine
whether
FTA
values
might
serve
as
alternative
measures
of
endurance
that
would
be
less
variable
and
so
more
valid.
Some
attention
has
been
given
to
similar
combinative
treatments
of
strength
and
endurance
(Caldwell
1964,
Start
and
Graham
1964),
but
the
results
have
been
inconclusive.
Through
examination
of
FTA
and
T
means
during
manipulation
of
the
initial
load
(constant
termination
point
of
50%
MGS),
it
was
found
that
FTA
yields
more
consistent
data
(table
1).
There
were
no
significant
differences
in
FTA
and
there
was
only
a
4%
difference
between
the
highest
and
lowest
mean.
Two
of
the
three
possible
Table
1.
Force—time
areas
(FTA)
and
contraction
time
(T)
means,
standard
deviations
and
locations
of
significant
differences.
Initial
load
(%
MGS)
Significant
100
80
60
differences
(0.05)
FTA
(cm
2
)
71
±29
74±25
73
±
25
None
T
(s)
60±16
66±23
80±18
100
and
60
80
and
60
comparisons
of
means
for
T
were
significantly
different,
with
a
33%
difference
between
high
and
low
values.
Practically,
this
means
that
once
MGS
is
established,
if
a
subject
fails
to
exert
a
true
maximum
contraction
on
subsequent
tests,
it
would
have
little
or
no
effect
on
the
area
under
the
force—time
curve,
but
his
endurance
will
be
extended.
If
one
can
accept
the
hypothesis
that
females
might
be
generally
less
well
motivated
and
thus
might
often
fail
to
go
all-out
on
strength
tests,
the
apparent
endurance
disadvantage
of
males
(table
2)
is
explained.
Extrapolation
of
this
line
of
reasoning
to
subgroups
of
strong
and
weak
subjects
within
each
sex
would
be
interesting,
but
not
supportable
on
the
basis
of
these
data.
Two
of
the
three
negative
correlations
between
MGS
and
T
were
found
to
be
significant
in
this
study,
supporting
several
previous
investigations
(Heyward
1975,
Kroll
1968,
Tuttle
et
al.
1950).
It
has
been
hypothesized
that
these
inverse
relationships
might
be
attributed
to
relative
difficulty
of
larger
muscles
in
dissipating
heat
(Bowie
and
Cumming
1972),
to
impairment
of
blood
flow
being
more
dependent
on
absolute
tension
rather
than
on
the
percentage
the
tension
is
of
390
R.
Byrd
and
M.
E.
Jenness
Table
2.
Sex
differences
for
means
of
maximum
grip
strength
(MGS),
contraction
time
(T),
and
force—time
area
(FTA).
MGS*
(kg)
FTA*
(cm
2
)
T*
(s)
Males
59-3
90.0
63.1
Females
35.5
56.3
73.9
*
Significant
at
the
0.05
level.
maximum
strength
(Bowie
and
Cumming
1972),
and
to
more
accumulation
of
waste
'
products
in
the
stronger
muscle'
(Start
and
Graham
1964).
Rohmert
(1960)
and
Caldwell
(1964)
found
no
such
relationships
and
suggested
that
motivation,
or
willingness
to
assume
and
maintain
greater
relative
loads,
might
be
an
important
factor
involved
in
those
studies
that
did.
Motivation
and
psychological
adjustments
to
the
extreme
discomfort
experienced
during
sustained
isometric
contractions
were
credited
as
a
partial
cause
of
endurance
changes
observed
in
an
isometric
training
program
(Byrd
and
Hills
1971).
Greater
consistency
of
FTA
over
T
in
the
present
data
suggest
that
FTA
might
be
less
susceptible
to
such
differences
in
motivation.
The
significant
correlations
among
the
FTA
measures
and
among
the
T
measures
for
all
three
treatments
indicated
that
a
subject's
position
within
each
of
the
three
initial
load
conditions
for
both
area
under
the
force—time
curve
and
for
length
of
time
of
the
isometric
contraction
remained
relatively
stable
(table
3).
However,
there
was
little
relationship
between
FTA
and
T
since
only
one
of
the
nine
correlations
between
the
two
was
found
to
be
significant
o
Table
3.
Force—time
areas
(FTA),
isometric
contraction
time
(T)
and
maximal
grip
strength
(MGS)
intercorrelations
for
the
three
initial
load
conditions.
FTA-80
FTA-60
T-100
T-80 T-60
MGS
FTA-100
0.87*
080*
037*
—0-02
0-12
0.71*
FTA-80
0.86*
0.30
0.24
0.20
0.68*
FTA-60
0.06
—0
,
07
0.09
0.78*
T-100
0-45
0.65*
—0-27
T-80
0.72*
—0.43*
T-60
—042*
*
Significant
at
the
0-05
level.
Since
FTA
is
by
definition
a
function
of
MGS,
the
highly
significant
correlations
between
MGS
and
FTA
for
all
load
conditions
were
not
unexpected.
However,
MGS
contributes
to
only
about
half
of
the
variance;
the
remainder
can
be
assumed
to
be
largely
an
endurance
factor.
The
greater
consistency
of
FTA
and
its
independence
of
initial
loading
were
suggested
earlier
in
the
discussion
to
minimize
the
effect
of
lack
of
motivation
and
failure
to
attain
a
true
initial
MGS
contraction.
Further,
if
the
termination
point
is
set
at
70%
MGS,
then
according
to
Caldwell
(1963)
the
contraction
should
last
no
more
than
about
20-25
s,
further
reducing
the
contribution
of
pain
tolerance
and
motivation.
On
this
basis,
it
is
suggested
that
with
standardized
isometric
bouts
in
which
the
initial
contraction
is
approximately
100%
MGS
and
the
termination
Grip
strength
and
force—time
curve
areas
391
criterion
a
decrement
to
70%
MGS,
metabolic
factors
become
paramount
in
determining
endurance.
Alterations
in
the
amount
of
force
exerted,
whatever
the
reason,
would
be
inversely
compensated
by
time,
the
area
under
the
force—time
curve
remaining
relatively
constant.
Thus,
FTA
should
be
considered
as
an
alternative for
researchers
in
need
of
a
more
consistent
measure
than
time
for
endurance
in
isometric
bouts,
recognizing
that
approximately
equal
contributions
will
be
made
by
strength
and
by
endurance.
Trente
sujets
ont
participes
a
une
etude
ayant
pour
objectif
d'etudier
l'utilite
des
aires
delimitees
par
des
courbes
force-duree
pour
determiner
l'endurance.
Pour
le
point
terminal
qui
represente
50
%
de
la
contraction
volontaire
maximum,
on
a
etudie
l'effet
de
la
variation
de
Ia
force
initiate
de
contraction.
En
outre,
on
a
etudie
les
correlations
entre
la
force
de
poignet
maximale,
I'aire
delimitee
par
les
courbes
force—duree
et
la
duree
d'application
des
contractions
isometriques.
On
n'a
pas
observe
de
differences
significatives
entre
les
aires
force—duree
pour
les
diverses
conditions
etudiees,
alors
que
les
moyennes
etaient
differentes.
Commit
it
y
avait
une
forte
consistence
dans
les
aires
en
fonction
du
temps,
on
en
a
conclu
que
ces
aires
peuvent
etre
utilisees
valablement
pour
les
etudes
qui
portent
sur
l'endurance
dynamometrique.
30
VPn
nahmen
freiwillig
an
Untersuchungen
zur
Anwendbarkeit
der
Flachen
unterhalb
der
Kraftverlaufe
uber
der
Zeit
(d.h.
Integrate
der
Zeitdynamogramme)
zur
Bestimmung
der
Ausdauer
tell.
Untersucht
wurden
die
Auswirkungen
unterschiedlicher
Anfangskrafte,
als
Bezugswert
dienten
50%
des
maximalen
isometrischen
Kraftvermagens.
Dariiberhinaus
wurden
die
Korrelationen
zwischen
den
maximalen
Griffkraften,
den
Integralen
der
Zeitdynamogramme
and
der
maximalen
Ausdauer
getestet.
Signifikante
Auswirkungen
der
Versuchsbedingungen
auf
die
Integrale
der
Zeitdynamogramme
wurden
nicht
gestgestellt,
wahrend
die
zeitbezogenen
Mittelwerte
unterschiedlich
waren.
Am
starksten
ausgepragt
waren
die
Korrelationen
zwischen
den
Integralen
der
Zeitdynamogramme.
Damit
kann
bereits
im
Hinblick
auf
die
groflere
Ubereinstimmung
der
Integrate
der
Zeitdynamogramme
festgestellt
werden,
dal?,
diese
als
ein
nfitzliches
Instrument
fur
die
Untersuchung
der
Ausdauer
bei
Handgriffbetatigung
betrachtet
werden
konnen.
References
BOWIE,
W.,
and
CUMMING,
G.
R.,
1972,
Sustained
handgrip
in
boys
and
girls:
variation
and
correlation
with
performance
and
motivation
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