The Regulation Of Muscular Strength
By ERICH A. MULLER, M.D.
What you are about to read is the original work on isometrics from the researchers that started it all. Although it can be some what difficult to understand at times... rest assured that if you are interested in building muscle size, muscle strength and mass.
Then this is the one article you should read on isometric training
Introduction To Isometrics
our investigations on the physiology of muscular strength and training
were first undertaken, little knowledge was available either from
experimentation or from practical experience in this field. Isometrics and Isometric training were too new.
attention had been given to problems such as whether common muscular
strength is an equilibrium between activity and inactivity, whether
it is regulated by inherent conditions and whether it is possible
to alter the regulated level of strength.
An excellent review of
the last half century of research in this field was given by Steinhaus
in this Journal in 1955.
What was clearly established by the work
of Petow and Siebert (1925)² and Siebert (1928) is the fact
that nothing but an increase in intensity of work above that previously
demanded of a muscle is the stimulus for an increase of muscular
How Strong Can You Get
With Isometrics Training
An answer for the fundamental question how strong,
how long, and how often this stimulus must operate to get an increase
of strength and how weak or how seldom, on the other hand, in order
to get an atrophic decrease, was never investigated.
advantage of using Isometric contraction for the measuring and training
of muscular strength.
our training was done with isometric contraction for the
1.The maximal strength possible in a certain position during a moment
is much lower than the strength in the same position reached with
a static contraction.
2. Due to the influence of mass and speed it is not possible to get
strictly isotonic contractions in man, except with very low speed.
It is therefore difficult to determine the identity of the stimulus
exerted on the muscle fibers during dynamic training.
is even more difficult to measure strength and its increase or decrease
by measuring maximal dynamic work. Maximal dynamic work depends
as much on the blood supply to a muscle as on muscular strength.
Whereas maximal work increases roughly proportionally to muscular
strength, it rises in a hyperbolic curve with a steady increase
in blood supply.
Speed Of Movement
As we know from the work of A. V. Hill, maximal
work is moreover influenced by the speed of movement.
have to date obscured and confounded interpretations of results
from training experiments with dynamic work whereas training with
isometric static contractions has permitted the drawing of valid
Dynamometry And Isometrics Training
used types of dynamometers, usually heavy springs, that were extended
no more than a couple of millimeters, enlarged sufficiently on a
scale that permitted readings with as error no greater than 5%.
(similar to the Bully Xtreme)
These dynamometers served for both training and the measuring of
maximal strength. (A very similar and
fantastic way to use the principles in this report is by using the
Bully Xtreme. It combines the features of a Dynamometer, but with
increased comfort and resistance.)
The Truth about Isometrics Training
For Isometric training, the subject had to contract according
to a given pattern, e.g. a prescribed number of kg's: for a prescribed
number of seconds. In measuring maximal strength the subject had
to make one short maximal contraction. The maximal position on the
scale was recorded automatically for later reading.
is very important in dynamometric studies that the position of the
subject be fixed in an exactly duplicable way for each reading in
a series that may extend over months, and that the equipment be
adaptable to the size of different persons.
strong isometrics contraction is the stimulus which makes a muscle increase
it mass and strength.
no difference whether the contraction happens at home, at work,
or is a gymnasium... whether one contracts muscles with the special
aim to increase muscular strength, or just casually.
In order to
determine the relationship between muscular activity and increase
or decrease in strength, on should, therefore, be able to control
all activities of a person.
The stimulus giving on the dynamometer
is therefore not the only one responsible for the observed training.
All of the other uncontrolled contractions made in the course of
the day should be added.
This Cannot Be Done!
We experimented on
members of our staff and on a number of students and asked them
merely to avoid excessive work with the muscles that we were observing.
To get quantitative and reliable results under such conditions seems
at first impossible. It will, however, become clear why the daily
activities did little or nothing to disturb the results.
threshold of muscular tension necessary to get a training effect
(Hettinger and Muller) In
normal life muscular strength usually holds at a constant level.
This means obviously that out daily activities do not act as a training
stimulus-at least not beyond that of maintaining our strength.
the first series of experiments the subject made one single static
contraction daily with each arm, the right arm at one fraction of
maximal strength, and the left to another, e.g., the right arm to
1/3, the left arm to 2/3.
We call this the training strength. Once
a week the maximal strength was measured, and the training strength
adjusted progressively to the increasing maximal strength in order
to keep the traction of 1/3, 2/3, etc.
How To Get Maximum Strength
Using Isometrics Training
We found that the training
stimulus need not be a contraction of maximal strength. In fact,
2/3 of maximal has the same training effect whereas 1/3 or less
is not effective. The threshold lies between 3/10 and 4/10 of maximal.
is difficult to determine the threshold with greater exactness since
the lower the fraction of maximal strength that is used for training,
the more it equals the strength used in daily life.
One has also
to consider that the determination of the maximal strength once
a week itself acts as will be shown later, as a training stimulus
sufficient to increase muscular strength.
At present we can at least
be sure that about 40% of the maximal strength does enough to get
the quickest possible training effect.
next series of experiments dealt with the question as to whether
a longer unstained contraction, especially one sustained until complete
exhaustion, would lead to a greater training speed.
the question of whether or not highly anaerobic conditions and the
accompanying accumulation of metabolites are a necessary accessory
stimulus for the increase of muscular strength during training.
In this series we found that the increase of strength gained in
the course of several weeks by one daily contraction is not influenced
by the length of contraction time.
Even the shortest contraction
of more than 40% of maximal strength has a maximal effect. Fatigue
and exhaustion do not influence the training effect.
This has been
confirmed by further experiments of Hettinger that compared the
training effect of the same training strength under conditions of
good and poor blood supply.
third series of experiments pursued the question of what happens
if more or less than one contraction per day is performed for training.
The intervals were varied from a fortnight down to fractions of
the frequency of the training stimulus ranged from one every 14
days to 7 per day. One can see that more than one contraction per
day gives no better results than just one per day. Contracting a
muscle less often than once a day, on the other hand, reduces the
spread of increase in strength.
After an interval of 14 days no
increase in strength is detectable. This is due to the course of
increase and decrease of strength. Following a single contraction
strength rises at the highest rate of speed during the day and then
more slowly from day to day for seven days.
Thereafter in the days
of the second week it drops back to its initial value. That is why
after two weeks no effect is found.
the results reported thus far... one can say that there is no better
way to increase muscular strength than one short, about half-maximal,
isometrics training contraction, once a day.
Contracting the muscle for a longer
time, more strongly or oftener does not improve the resulting increase
in strength. In ordinary practice one would not use a half-maximal
but a maximal contraction.
This Has 3 Distinct Advantages
1. One needs no dynamometer to measure the training strength . It can
be exerted against any resistance at hand.
The training stimulus increases progressively with the increase
If a dynamometer is used each maximal training contraction is at
once also a measurement of maximal strength.
application of these findings permits large savings in training
time and apparatus.
They will permit the strengthening of muscles
without burdening metabolic, respiratory and circulatory functions
since a short one-second contraction does not increase these functions
Discussion of Possible Errors
are now able to assess the errors that could be introduced in our
experiments by the training effect of uncontrolled contractions
in daily life.
If a man keeps his daily activities nearly constant
before and during training experiments, one can be sure that from
this stimulus his maximal muscular strength has about three times
the force exerted in his daily activities.
No further training stimulus
is to be expected from the latter. If perchance during a training
experiment force applied in daily life surpasses the normal limits,
it would not influence the course of daily isometrics training with maximal
strength. Since a second daily contraction does not increase the
Only if sub maximal training strength is used or
if the training stimulus is not given each day could a quicker increase
of strength follow from super-normal uncontrolled contraction of
the subject's routine activities of daily life.
would disappear in a fortnight if the surpassing stimulus were not
authors have claimed that training muscles of one side of the body
has a marked influence on the muscular strength of the other. (Hellebrandt,
Parrish and Houtz; Slater-Hammel; Darcus and Salter).
We never observed
such an effect in our experiments. Even the most marked increases
in muscular strength of the trained muscle were absolutely one-sided.
What Could Be the Reason
for This Striking Difference ?
reason for this difference may be found in the fact that all the
authors who found crossover training effects have measured strength
by judging maximal dynamic work. Whereas we took a maximal status
contraction as the measure of strength involves not only the strength
of muscles but also the blood supply, as already mentioned.
training itself was also done by long-lasting dynamic work and not,
as in our case, by a single static contraction, there are good reasons
to believe that the training had worked on heart and circulation
An increased power of the circulation to supply muscles
with blood obviously helps the muscles of both sides and even the
other muscles such as the abdominal's.
is another explanation for the reported results with cross training.
In order to compare the extremities of both sides of the body before
and after training, one measures the maximal strength at the beginning
and at intervals during the course of training.
If one trains only
one side but controls the results on both sides, this control of
maximal work is in itself a training stimulus. Before we ere able
to verify this fact, we were ourselves misinterpreting our results.
third, but probably less likely, reason might be that doing dynamic
work involves a much more complicated pattern of innervations than
a mere static contraction.
Different parts of muscles have to contract
one after the other during shortening, with changing force adjusted
to the changing resistance.
That means "nervous learning"
and we know that such "nervous learning" does cross over.
(Hellebrandt, Vetter and Muller).
experience also does not support the cross training theory. Why
should an unused limb or a lesser used limb lose strength and mass
if the parallel limb has a normal or even abnormal strength as is
usually the case in patients with a one-sided inactivity, e.g. in
The Threshold of Muscular Tension
Necessary to Avoid Atrophy
is well known that absolute inactivity of a muscle is followed by
atrophy, i.e. a loss of mass and strength. We investigated if this
loss occurs at the same rate of speed as the loss observed following
the close of training period. (Muller and Hettinger)
We put one
arm in plaster and kept it inactive for periods from one day to
one week. This procedure should give the maximal speed of loss in
strength by atrophy.
We found that the loss of strength in strict
inactivity is at least four times as rapid as the loss from a trained
muscle after the end of training.
Since, one cannot be sure that
all static contractions inside the plaster cast are avoided, the
actual speed might even be greater.
We can therefore say that the
condition in an atrophic muscle are different in principle from
those in a trained muscle. It is not the same state as two different
levels of strength.
This is confirmed by the fact that the speed
of regaining strength after a period of inactivity and atrophy is
also about four times the speed of the increase in strength in training
a normal muscle.
next step was to measure the threshold of the stimulus necessary
to prevent atrophy. This was done by Hettinger who made a cast of
plaster for the forearm and divided it into two halves which were
screwed together (Fig. 3).
The cast was opened once a day carefully
avoiding any load by gravity on the flexors and extensors. The elbow
joint axis was brought in a vertical position and one contraction
of 1/5, 1/10, 1/20 etc. of the maximal strength was exerted. The
arm was put back in the cast again.
It could be shown that a contraction
equal to 1/5 of maximal strength one per day was just sufficient
to prevent atrophy, 1/20 was equal to full inactivity while fractions
between had a tropical effects of various speed.
Definition of Normal Strength
stimulus of any muscular contraction has therefore two different
effects: the one prevents atrophy, the other induces increase in
These effects have different thresholds. The maximal effect
of one is reached with a contraction of 20% of the maximal strength,
the other with a contraction of 35% of the maximal strength.
between the 20% and the 35% do not induce training yet they are
sufficient to prevent atrophy. The maximal strength that we found
when stimuli did not exceed these limits we designated as normal
The two stimulating effects of a contraction differ according
to the speed of their action as already shown. They differ also
in the frequency necessary to make them effective.
We found that
the isometrics training effect is secured even by one contraction per week.
The atrophy-preventing effect, however, needs more frequent contractions
per week. We are now trying to determine this frequency. Finally,
the atrophy-preventing effect persists in older people whereas the
training effect is lost.
proof for the existence of a normal strength is given by the distribution
curve of the strength of a group of 56 men and 58 women (Fig. 4).
80% of the men have a flexor- torque on the forearm in a right angle
position in the narrow range from 5.5 to 6.7 kgs.; 80% of the women
from 3.5 to 4.6 keg. There is a different maximum for each sex and
practically no overlapping of the curves.
of Normal Strength
mentioned above that strength which was increased by daily isometrics training
is lost in about the same time that was required to build it up.
We know ,however, from experience that strength gained in youth
by over-normal activity persists for life even when activity no
more surpasses normal limits.
To reconcile these divergent findings
the follow experiments are condensed in Fig. 5. Curve A shows the
increase in strength of a person trained with daily contractions
of maximal strength.
Strength is doubled in 20 weeks and lost after
the end of training in 30 weeks.
In Curve B, which belongs to the
same person, daily training lasted merely 11 weeks. Strength increased
during this time 66% of 6% per week. Training was then continued
for another 12 weeks with only one maximal static contraction per
The slow drop of strength following the end of training in
Curve B compared with the quick fall in Curve A is very striking.
To avoid any training effect from the testing for maximal strength,
these measurements were taken at long intervals of several weeks.
C gives the average results of an experiment where training with
one maximal static contraction per week was done on 11 different
muscle groups of another person.
They increased in strength 72%
in 46 weeks, i.e. 1.6% per week. The fall of strength after the
end of training is again very slow. 70 weeks after the end of training
it is still 42% higher than before the beginning of training.
have already established in unpublished experiments that fortnightly
training after daily training maintains an increased level of muscular
strength for longer than one year.
It looks like a permanent increase
of the normal strength. We don't know yet the reason for this fixation
of strength gained by slow training.
Isometric Training, Exercise and Nutrition
could ask, why does not every muscle keep a constant strength big
enough for the necessary activities of the individual? Why has selection
developed the possibility of training?
One could try to answer these
questions in the light of our results.
seems that nature has very carefully provided for reducing muscular
mass to as little as possible. This is seen in the sparing of muscle
mass on children, on women, in sparing it during winter.
It is also
seen in the quick drop of mass after the end of intensive daily
training. Only if again and again muscles are forced to strong contractions
for months does the body allow a lasting increase of muscle substance.
The only good reason for this economic principle is obviously the
fact that muscles are made of protein, and need a daily intake of
protein to maintain it. The 30 kgs. muscles of a normal man ask
for about the same amount of meat to be eaten in a year.
between basal metabolism and biceps strength was +0,79 +0,04 in
a group of 56 men and 58 women between 16 and 50 years of age.
aimed to enlighten the relation between muscular strength and protein
intake have been done by Kraut and Muller, Kraut, Muller and Muller-Wecker.
The Role of Protein in Isometrics Training
Summarizing their work, one can say that the eating of plenty of
meat in order to assimilate muscular substance is only necessary
for a man after a long period of insufficient protein intake.
such conditions other organs, the big glands, the heart and the
brain have first rights on the protein. They take most of the protein
given after starvation, not leaving much for an increase in muscular
In a state of normal and sufficient food intake with enough
protein however, there is so much protein stored in the body that
an increase in muscular tissue by training is possible without any
protein intake over the normal rate of 1 gram per kg. per day.
Special experiments have shown that the training effect cannot be
speeded up by increasing the protein intake over the normal limits
under normal conditions.
As little as 0.8 rams of protein per kg.
per day when only 14% is of animal origin stop any training effect
(Kraut, Muller and Muller- Wecker-unpublished).
The Need for Protein In An Isometrics Training Diet
Intake of sufficient
protein is therefore a necessary condition but not a stimulus necessary
to prevent atrophy nor to allow training.
is possible that besides protein other factors in nutrition influence
training-e.g. vitamins. The annual variation of the training effect
showing a maximum in August-September and a minimum in January is
possibly due to this influence (Hettinger and Muller).
however, be due as well to a more direct influence of ultraviolet
radiation (Hettinger and Seidl).
Sex and Age in Isometrics Training
strength and train ability of muscles depends on other factors.
Sex and age have a marked influence, as several authors have shown.
As far as strength is concerned, the difference
between sexes varies with the muscle group tested. The selection
of man as the stronger, fighting individual compared with the weaker
woman charged with bearing and nursing the young does not concern
all muscles equally.
Ufland found a very small difference (about
20%) in the chewing muscles, where as the strength relation of men
to women for the biceps group was 1:0-.5.
muscles answer to training stimuli less than do those of men. Training
a group of men and women changed the strength relation from 1:0.6
to about 1:0.5 in experiments of Hettinger. Whereas sex differences
in strength and trainability are correlated in middle aged people,
this is not the case in older people.
It is well known that strength
does not drop with age, the gift however to increase strength by
training is lost in the course of aging.
Static Work Training in Rehabilitation
a few cases we trained patients with one single static contraction
per day to see if our findings on normal persons were applicable
in rehabilitation. (Muller and Hettinger; Hettinger).
had lost one hand. They were fitted with artificial hands (Huffer-Hand),
where supination on the forearm closed the hand between thumb and
forefinger. Fig. 6 shows the increase in strength following one
2/3 maximal contraction per day. Fig. 5 in its lower curve shows
the increase in stump cross-section of a thigh which was trained
by static contractions against a circular compressing air pressure
of 100 mm., Hg.
Noack, had great success regaining strength of the
abdominal muscles of women after childbirth by contracting them
against a suitable resistance.
Advantages of Isometrics Training
are several great advantages of Isometrics training compared with dynamic
Much money and time is saved. One contraction per day or even one
week can be done at home in many cases. There is no need to drive
to a center to spend time there and to use the time of others.
No fatigue is necessarily involved in training muscles since one
single contraction does not lead to fatigue.
May prevent diseases. In diseases where metabolic rate has to be kept low (diabetes),
a muscular atrophy due to little activity can easily be presented
by static training.
Heart and circulation are not stressed by static training. Atrophy
is therefore unnecessary in hear cases.
Isometrics Training and Endurance
and Muller found that the time which a static contraction with given
strength can be held until exhaustion remains unaltered in spite
of an increased maximal strength of 64% to 97%.
This means that
in spite of a lower tension (strength per cross-section) blood supply
is not remarkably better. One cannot deduce any knowledge on vascularization
from these findings since blood supply and endurance in static work
are mainly a function of the uninterrupted compression of blood
vessels (Muller, Barcrof and Swan).
One should know the maximal endurance of a trained muscle for prolonged dynamic work in order
to learn about the relation between improvement of increased strength
A better vascularization might follow other
laws than the ones found improving strength.
strong muscle, however, does not mean better performance in practice
whether in sports or in daily work. Skill and an appropriate adaptation
of ventilation and circulation to the increased muscular power must
be acquired by other ways than by static muscular training.
results do not claim to cover more than one page of the book to
be written about the training of all physiological functions.
In summary the benefits of isometrics training are numerous. for the individuals that do not have much time or the money to purchase expensive gym equipment isometric exercises using an isometric exerciser is a great solution.
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