Effects of Combat"
Physiology of Close Combat
An understanding of the stress of close combat begins with
an understanding of the physiological response to close-range
interpersonal aggression. The traditional view of combat
stress is most often associated with combat fatigue and
Post-Traumatic Stress Disorder, which are actually manifestations
that occur after, and as a result of, combat stress. Bruce
Siddle has defined combat stress as the perception of an
imminent threat of serious personal injury or death, or
the stress of being tasked with the responsibility to protect
another party from imminent serious injury or death, under
conditions where response time is minimal.
debilitating effects of combat stress have been recognized
for centuries. Phenomenon such as tunnel vision, auditory
exclusion, the loss of fine and complex motor control, irrational
behavior, and the inability to think clearly have all been
observed as byproducts of combat stress. Even though these
phenomena have been observed and documented for hundreds
of years, very little research has been conducted to understand
why combat stress deteriorates performance.
The key characteristic which distinguishes combat stress
is the activation of the SNS. The SNS is activated when
the brain perceives a threat to survival, resulting in a
immediate discharge of stress hormones. This "mass discharge"
is designed to prepare the body for fight-or-flight. The
response is characterized by increasing arterial pressure
and blood flow to large muscle mass (resulting in increased
strength capabilities and enhanced gross motor skills--such
as running from or charging into an opponent), vasoconstriction
of minor blood vessels at the end of appendages (which serves
to reduce bleeding from wounds), pupil dilation, cessation
of digestive processes, and muscle tremors. Figure 2(below)
presents a schematic representation of the effects of hormone
induced heart rate increase resulting from SNS activation.
activation of the SNS is automatic and virtually uncontrollable.
It is a reflex triggered by the perception of a threat.
Once initiated, the SNS will dominate all voluntary and
involuntary systems until the perceived threat has been
eliminated or escaped, performance deteriorates, or the
parasympathetic nervous system activates to reestablish
The degree of SNS activation centers around the level of
perceived threat. For example, low-level SNS activation
may result from the anticipation of combat. This is especially
common with police officers or soldiers minutes before they
make a tactical assault into a potential deadly force environment.
Under these conditions combatants will generally experience
increases in heart rates and respiration, muscle tremors,
and a sense of anxiety.
contrast, high-level SNS activation occurs when combatants
are confronted with an unanticipated deadly force threat
and the time to respond is minimal. Under these conditions
the extreme effects of the SNS will cause catastrophic failure
of the visual, cognitive, and motor control systems. Although
there are endless variables that may trigger the SNS, there
are six key variables that have an immediate impact of the
level of SNS activation. These are the degree of malevolent,
human intent behind the threat; the perceived level of threat,
ranging from risk of injury to the potential for death;
the time available to response; the level of confidence
in personal skills and training; the level of experience
in dealing with the specific threat; and the degree of physical
fatigue that is combined with the anxiety.
activated, the SNS causes immediate physiological changes,
of which the most noticeable and easily monitored is increased
heart rate. SNS activation will drive the heart rate from
an average of 70 beats per minute (BPM) to more than 200
BPM in less than a second. As combat stress increases, heart
rate and respiration will increase until catastrophic failure
or until the parasympathetic nervous system is triggered.
In 1950, S.L.A. Marshall's The Soldier's Load and the
Mobility of a Nation was one of the first studies to
identify how combat performance deteriorates when soldiers
are exposed to combat stress. Marshall concluded that we
must reject the superstition that under danger men can be
expected to have more than their normal powers, and that
they will outdo their best efforts simply because their
lives are in danger. Indeed, in many ways the reality is
just the opposite, and individuals under stress are far
less capable of doing anything other than blindly running
from or charging toward a threat. Humans have three primary
survival systems: vision, cognitive processing, and motor
skill performance. Under stress, all three break down.
Bruce K. Siddle's landmark research at PPCT involved monitoring
the heart rate responses of law enforcement officers in
interpersonal conflict simulations using paintball-type
simulation weapons. This research has consistently recorded
heart rate increases to well over 200 beats per minute,
with some peak heart rates of up to 300 beats per minute.
These were simulations in which the combatants knew that
their life was not in danger. The combatant,in a true life-and-death
situation (whether soldier or law enforcement officer),
faces the ultimate universal human phobia of interpersonal
aggression and will certainly experience a physiological
reaction even greater than that of Siddle's subjects. The
fundamental truth of modern combat is that the stress of
facing close-range interpersonal aggression is so great
that, if endured for months on end without any other means
of respite or escape, the combatant will inevitably become
a psychiatric casualty.
Even greater than the resistance to being the victim of
close-range aggression is the combatant's powerful aversion
to inflicting aggression on fellow human beings. At the
heart of this dread is the average healthy person's resistance
to killing one's own kind.
of Violence, Peace, and Conflict, Volume 3, p.159
1999 by Academic Press. All rights of reproduction in any