V0L.13.N0 2,1987
The Stress Analogy
215
by Warren K. Smith
At Issue
The At Issue section of the Schizophrenia Bulletin contains viewpoints
and arguments on controversial issues.
Articles published in this section may
not meet the strict editorial and scientific
standards that are applied to major articles in the Bulletin. In addition, the
viewpoints expressed in the following articles do not necessarily represent those
of the staff or the Editorial Advisory
Board of the Bulletin.—The Editors.
Abstract
The author calls attention to the advantages of using the engineering
meaning of stress and strain when
applying these terms to describe the
effects of social and physical forces
on people. Such an analogy opens
up the possibility of measuring the
amount of damage from excess
stresses existing in people, as well
as estimating their limits and remaining strengths. It also explains
why some people are more affected
by a given stressor than other peopie.
Today there are many articles written about the effects of stress on
people. Readers assume that stress
means some kind of mental or physical pressure endured by a person.
Social stress has long been suspected by psychiatrists as one of the
causes of mental illness, but medical
proof has been lacking. Neuroscientists study neurotransmitters and
brain chemicals which, in excess or
deficiency, are thought to be associated with mental illness. It is still
not known whether such chemical
imbalances are hereditary or also
could be caused by mental, disease,
or dietary stress. Obviously, we
need better knowledge of what
stress is, how to measure it, and
how to use those measurements.
It was apparent to me, as a former
research metallurgist, that the medi-
cal and psychological professions
could profit from using the engineering meaning of stress. This can
be done by an analogy relating
stress on metals and people. The
analogy arises because in both cases
a force is acting on a resisting body,
and the mechanics can be expected
to produce analogous changes. Such
an approach opens up the possibility of measuring the amount of
damage from stress existing in people, as well as estimating their remaining strengths.
Analogies can be useful as models
or patterns in solving similar problems. For example, Dr. Jonas Salk
(Goldberg 1984) in a recent interview said, "When one uses analogy
or metaphor, most scientists say it's
imprecise, dangerous. My mind
doesn't say that. It tells me it's fascinating." Also, "I think now of intuition as analogical thinking and
reason as analytical thinking. It's
very simple. And they're both useful and both necessary." It was just
such a thought process that led him
to the development of the polio vaccine.
Stress in Animals
Dr. Hans Selye, an Austrian-bom,
Canadian Professor of Endocrinology at McGill University, is credited
with introducing the term "stress"
in 1936 to describe mental and physical demands on animals and humans. He defined stress as the
nonspecific response of the body to
any demand made upon it. His two
books, The Stress of Life (1956) and
Stress Without Distress (1974), make
fascinating reading.
Dr. Selye spent many years experimenting with stress, physical
Reprint requests should be sent to
W.K. Smith, 16420 Avenida Eorencia,
Poway, CA 92064.
SCHIZOPHRENIA BULLETIN
216
and mental, induced in laboratory
animals. He measured the effects of
stress by the resulting inflammation
of the stomach and the actions of
the endocrine gland system, such as
adrenals, thymus, and lymph
nodes. Even substantial gland size
changes were noted. Dr. Selye then
systematically determined which
chemicals in the secretions from
those glands caused the observed
changes in various parts of the
body. To do this, he removed
glands from the test animals before
subjecting them to stress and injected synthetic hormones in some
of the animals to compare with others not injected.
Selye's most important observation by far was that excessive stress
imposed on test animals resulted in
nonspecific ailments. That is, disease or malfunction showed up almost at random within the animals'
bodies, but it did so with very positive correlation with stress.
Holmes and Rahe (1967) worked
out a list of 43 major stressors of life,
The Social Readjustment Rating
Scale. The scale has a top value of
100 = death of a spouse. Holmes
and Masuda (1973) showed that
there is definitely a greater risk of
disease to a person under severe
stress. The major health changes observed covered a wide range of psychiatric, medical, and surgical
diseases. Bloom, Lazerson, and
Hofstadter (1985) stated:
To establish a specific cause-andeffect relationship between stress
and disease requires some way to
determine in advance why some
events are more stressful to some
people than they are to others.
These issues are clearly vital to
important questions or health and
disease, but at least for the present they appear to be beyond the
reach of available research strategies.
So lef s try to add to the available
research strategies.
Stress in Engineering
When Dr. Selye borrowed the term
"stress" from engineers, he neglected to take along its definition:
stress is load divided by the crosssection area of the material specimen supporting the load. This is expressed as S = P/A, where P is load
in pounds and A is area in square
inches (in American units); thus, S
= pounds/square inch. Obviously,
the "stress" referred to by Selye and
others is really what an engineer
calls 'load." Only if we divide that
load by something equivalent to the
cross-sectional area will we have
stress (loading density) that can be
compared equally from person to
person.
Confusing stress with load is bad
enough, and confusing stress with
strain is certainly no better. Elongation is what you get when you hang
a load from a specimen fastened at
the top. If you set a load on top of a
specimen resting on a floor, you get
compression. Dividing these length
changes by the original length of the
specimen gives strain, which in
American units is inches/inch.
Now Selye's definition can be
more accurate if you say, "Strain is
the response to any stress acting on
a body." The analogy of strain is a
measure of how far a body varies
from its homeostatic condition.
Homeostasis is a term suggested by
American physiologist Walter B.
Cannon to mean the body's undisturbed state.
Probably the most important concept in the stress analogy is the
equivalent of cross-sectional area.
One would expect it to be a composite of the capacities and maximum rates of discharge of
hormones responsible for resisting
the change of a body -from its homeostatic condition by a load. The
equivalent of cross-sectional area,
therefore, is undoubtedly the major
genetic factor in resistance to load.
A person born with a smaller than
average cross-sectional area will
have a higher density of loading
(stress) for the same load, as is evident from the equation S = P/A. As
the denominator gets smaller, S gets
larger. A larger than average crosssectional area in a person results in a
smaller stress, because the denominator in this case is larger.
For a metal or structure, load is
simply a force or weight in pounds,
but for a person, it has to be something proportional to the degree of
pain, need, and fear inflicted. At
present, the Social Readjustment
Rating Scale is useful.
Stress vs. Strain
When a test specimen of known
cross-section and length is stretched
in a testing machine until it breaks,
a graph of stress vs. strain is recorded (see figure 1). Stress is proportional to strain (a straight line)
from O to E in figure 1. Anywhere
along the line O-E the strain will return to zero if the stress is removed.
Point E is called the elastic limit of
the material, and the slope of this
line is called the modulus of
elasticity. When stress is increased
beyond E, the line bends over, indicating that stress is no longer proportional to strain. Furthermore, if
the stress is removed at Point A, for
example, strain follows the reduction of stress down the straight
dashed line from Point A to B. There
has been a permanent strain damage
imparted to the metal bar as O-B.
Now if we again increase stress,
starting from Point B this time,
217
VOL. 13, NO. 2,1987
Figure 1. Typical stress vs. strain curve
U
daily living. Isn't this the "nervous
breakdown"?
Ultimate
strength
Long-Term Stress
F Fracture
(death)
Metal: Strain, percent (inches/inch)
Human: Strain, percent deviation from homeostasis
strain will follow stress as a straight
line up to Point A, the new, higher
elastic limit, and then bend over
again to Point C. If stress is removed
at Point C, the permanent strain
damage will now be O-D, and the
new elastic limit will be at Point C,
and so on. Point U at the top of the
curve represents the ultimate
strength of that material. Beyond
that point further strain reduces the
load the test specimen will support,
because the specimen is necking
down to an hourglass shape, thus
reducing the cross-sectional area. At
Point F the specimen breaks. Most
of us have had the experience of repeatedly bending a can lid until it
suddenly bends more easily and
then breaks; it has passed Point U
and reached F in our curve illustration.
Immediately, we can see from our
analogy that one of Dr. Selye's theories needs modification. Dr. Selye
suggested that each stress, no matter how small, produces a finite
amount of permanent damage that
in a lifetime adds up to an exhausting amount and death. Rather, our
analogy says that our Creator endowed us with a liberal elastic limit,
which enables us to perform our
daily tasks and return our stress and
strain to zero. However, if the sum
of all our physical and mental
stresses is near our elastic limit, and
then an emergency stress is added,
we may pass Point E to A and sustain permanent strain damage like
O-B in figure 1. Such increments of
permanent strain damage are what
add up and finally cause us to reach
our ultimate strength. After that, we
are in trouble.
The increase in elastic limit after
each greater stress above the elastic
limit has its counterpart in the human analogy. We have often heard
that a rough, stressful experience
teaches us a lesson that enables us
to bear heavier stresses. Beyond our
ultimate strength, though, the
lessons turn to greater fear and desperation. Intuitively, we would expect from this analogy that
somewhere after we pass our ultimate strength, due to repeated overstresses, we lose our ability to handle even the ordinary stresses of
The effects of stress over long periods of time were discussed by Dr.
Selye as the "General Adaptation
Syndrome" (G.A.S.), a term he used
to describe the manner in which animals responded similarly to cold,
heat, infection, trauma, hemorrhage, nervous irritation, and many
other stimuli. The G.A.S. has the
following three stages: (1) the alarm
reaction, (2) the stage of resistance,
and (3) the stage of exhaustion. (See
figure 2.)
Alarm Reaction. The body shows
the changes characteristic of the first
exposure to a stressor. At the same
time, its resistance is diminished
and, if the stressor is sufficiently
strong (e.g., severe bums or extremes of temperature), death may
result.
Stage of Resistance. Resistance ensues if continued exposure to the
stressor is compatible with adaptation.
Stage of Exhaustion. Following
long-continued exposure to the
same stressor, to which the body
has become adjusted, eventually adaptation energy is exhausted. The
signs of the alarm reaction reappear,
but now they are irreversible, and
the individual dies.
The metal analogy of the G.A.S. is
known as "creep" (see figure 3). In
general, it only works when the
metal is above one-half of its absolute melting temperature. For an
analogy, high temperature promotes
plastic flow. At low stress and temperature, a metal specimen may
never break. However, the second-
SCHIZOPHRENIA BULLETIN
218
Figure 2. The 3 stages of the General Adaptation Syndrome (Selye)
(Adaptation)
(Alarm)
Figure 4. Effect of small tensile
stress on steel
(Exhaustion)
/
Normal level
\
of resistance
Death
Time
ary stage of creep practically disappears at the upper limits of stress
and temperature. It appears that an
analogy of the metal creep curve
would give a better expression of
the G.A.S. than that by Dr. Selye,
because it gives a quantitative measure of strain and strain rate.
It is interesting that the G.A.S.
theory states that the body has a
finite store of resisting or adaptative
energy for which there is no known
measure or source of replacement.
The metal analogy indicates that the
total available resisting energy is
equal to the area under the curve
bounded by O-E-F-H-O in figure 1.
Of course, the useful potential energy, up to the ultimate strength,
would be the area bounded by O-EFigure 3. Creep test of a metal
Fracture
/
c
Primary
55 creep
^—
s
Secondary
creep
A
—-—/V
Long time
/
J/
Tertiary
creep
U-G-O. Perhaps, with the correct
human units, one could measure the
total useful resisting energy and
even the fractions used up or remaining in people.
Stress During Internal Changes
Research on metals undergoing a
crystalline phase change—for example, from body-centered cubic to
face-centered cubic structure, or the
reverse—revealed (see figure 4) that
while such a change is in progress
the metal can be plastically deformed by a very small external
stress (Feuerstein and Smith 1954).
This was later termed "superplasticity" by other investigators.
In the stress analogy, this phenomenon would imply that while
neural changes (Haracz 1985) are in
progress, a person with low crosssectional area equivalent is vulnerable to damage by stressors so small
that ordinarily they would be considered negligible. For example, if a
child with unusually small crosssectional area equivalent is subjected
to certain small but sufficient
Temperature
*•
The effect Is shewn of small tensile stress on
steel specimen heated and cooled through the
critical temperature range.
stressors at the time he is learning to
speak, it is conceivable that autism
might occur. Likewise, this may offer an explanation of why schizophrenia strikes young adults at an
age when great emotional changes
and new learning are in progress.
Additional research on this subject
is needed.
Fuel for Researchers
As is frequently true in research,
more questions are raised than answered. Some questions that come
to mind here are the following:
• What is the modulus of
elasticity for a human, and is it the
same for all humans as it is for each
of the various kinds of metals?
• How can we safely measure a
person's elastic limit and ultimate
strength?
• Does a person's elastic limit
start near zero at birth and increase
during learning until maturity and
beyond?
• What are all the medical factors
that compose strain in humans, and
219
VOL 13, NO. 2,1987
how do you measure and express
them as units of strain?
• What are all the factors that
compose the "cross-sectional area"
of humans, and how do you measure and express them as units of
area?
Some measurement approaches
are suggested. In making stress and
strain measurements on any person,
we have to realize that he already
has residual elastic and plastic strain
of an unknown amount. It would be
risky to add a large amount of load
for an experiment. Therefore, let's
start with a person under at least
one known serious stress that he is
able to handle. After measuring his
total strain medically, remove the
stress from him (pay his debts?),
and measure his total strain again.
This would yield the slope of the
elastic line (modulus of elasticity)
and its intercept on the horizontal
axis. That intercept would be the total strain damage borne by the person.
Suppose we have established the
modulus of elasticity for people.
Then if we obtain a medical measurement of a person's strain below
his elastic limit, the corresponding
stress he is bearing can be calculated
from the modulus of elasticity. With
a knowledge of the load causing the
stress, we can use the equation A =
P/S (transposed from S = P/A) to
obtain a value of A for that person.
Such values of A (cross-sectional
area) can serve as indices with
which to compare the resistance to
loads among people.
Discussion
When we can determine if a person
is carrying total physical and mental
stress and strain close to his limits,
we may be able to prevent the onset
of schizophrenia, if indeed it is
proved that stress is an important
part of its etiology. The stress analogy, taken together with the works
of Selye and others, does appear to
implicate accumulated physical and/
or mental over-stress as the origin of
mental illness. A point to be remembered from Selye is that the effect of
over-stress on a person can be nonspecific on his body, including that
part of his body called brain. It may
turn out to be the part of the brain
system responsible for schizophrenia, depression, acute anxiety,
phobias, or whatever. The most vulnerable part at that time may receive
the damage.
The measurement methods indicated by the stress analogy can be
useful in psychiatry for evaluating
the patient's resistance to stress and
what his limits are. Medical (biological) measurements of strain magnitude are necessary, and these
should be included in the duties of a
psychiatrist, since he is an M.D. as
well as a psychologist.
Currently much attention is directed to stress management, which
consists of teaching patients consciously to force themselves to relax.
This in itself is a stressor requiring
effort, but it is a negative stressor
that results in reduced harmful
stress. The measurements suggested
by the stress analogy can help the
psychiatrist or psychologist evaluate
the results of his stress management
program.
Since it has been well established
that a person's own mind can direct
the reduction of stress, then it follows that the mind—imagination—
can generate unreasonable fears,
which can become a large component of the total unwanted stress.
Herein may lie the reason for surprise suicides in youth. Preventive
psychiatry, consisting of confidencebuilding and allaying the common
fears of the unknown in children via
school programs, can also be aided
by the stress analogy concept in
evaluations.
Once a person's stress and strain
have been carried beyond his ultimate strength, his usefulness has
been damaged beyond present-day
psychiatric repair, and he only can
be provided with drug crutches yet.
Rehabilitation by retraining is notoriously ineffective, because the patient cannot tolerate stress well
enough to be competitive in employment. The same is true in the metal
analogy without first reconstructing
the metal crystals, which requires a
high temperature annealing treatment. Such a treatment, of course, is
not in the psychiatrist's book, and
the metaphor is of no use.
It is encouraging to read of the
proposed research on "neural plasticity" by Haracz (1985). Perhaps
this work may someday lead to the
ability to repair or rebuild neural
connections in the brain. If that happens, the metaphor of an "annealing" treatment may not seem so
farfetched after all.
References
Bloom, F.E.; Lazerson, A.; and
Hofstadter, L. Brain, Mind, and Behavior. New York: W.H. Freeman &
Co., 1985. p. 294.
Feuerstein, W.J., and Smith, W.K.
Elevation of critical temperatures in
steel by high heating rates. Transactions of American Society for Metals,
46:1280, 1954.
Goldberg, J.R. An interview: Jonas
Salk. Science Digest, 92:50, 1984.
Haracz, J.L. Neural plasticity in
schizophrenia. Schizophrenia Bulletin,
11:191-229, 1985.
Holmes, T.H., and Masuda, M. Life
change and illness susceptibility.
Separation and Depression. (Publica-
SCHIZOPHRENIA BULLETIN
tion No. 94) Washington, DC:
AAAS, 1973. pp. 161-186.
Holmes, T.H., and Rahe, R.H. The
Social Readjustment Scale, journal of
Psychosomatic Research, 11:213-218,
1967.
Selye, H. The Stress of Life. Philadelphia: J.B. Lappincott Co., 1956.
Selye, H. Stress Without Distress.
Philadelphia: J.B. Lippincott Co.,
1974.
An Invitation
to Readers
Providing a forum for a lively
exchange of ideas ranks high among
the Schizophrenia Bulletin's objectives. In the section At Issue, readers
are asked to comment on specific
controversial subjects that merit wide
discussion. But remarks need not be
confined to the issues we have identified. At Issue is open to any schizophrenia-related topic that needs
airing. It is a place for readers to
discuss articles that appear in the
Bulletin or elsewhere in the professional literature, to report informally
on experiences in the clinic, labo-
The Author
Warren K. Smith, B.S., Ch. E., is a
retired Research Metallurgist and
currently Chairman, Research and
MIRA Fund, San Diego, and California Alliances for the Mentally 111, 450
Olive St., San Diego, CA.
ratory, or community, and
ideas—including those that
seem to be radical notions.
come all comments. — The
to share
might
We welEditors.
Send your remarks to:
At Issue
Schizophrenia Research Branch
National Institute of Mental Health
Alcohol, Drug Abuse, and Mental
Health Administration
5600 Fishers Lane, Rm. 10C-16
Rockville, MD 20857