ACCLIMATIZATION TO DIVING IN
by Dr. Jolie Bookspan
All Rights Reserved
(c) JOLIE BOOKSPAN
Who gets cold when diving in cold water, and why?
Is cold something you can get used to? How?
BRIEF OVERVIEW OF SUSCEPTIBILITY TO COLD
Just as the "dose" of nitrogen or oxygen, meaning partial pressure
and time exposed, are main factors in decompression sickness and oxygen
toxicity respectively, major factors in cold stress are temperature and
length of exposure. As with dosage of any drug or substance, several
and competing mechanisms, in addition to the dosage, determine if you
be affected, and by how much.
You generate heat in many ways, lose heat in many ways, and have
anatomical structures and physiologic schemes to block heat loss and
Thermal scientists can put all the figures for heat generation, heat
and resistance to heat loss into mathematical models to estimate what
final temperature might be. But it is more involved than just saying
young or old, or big or small people have any one characteristic and
Losing body heat, by itself, does not mean that you are chilling.
lose heat all the time. Your body generates heat in the process of
alive. If you didn't lose heat, your body would cook (sometimes it
and that will be covered in another article on overheating).
Losing heat doesn't necessarily mean you are in danger of
or any other injury from cold. You need to lose some heat. Whether you
stay comfortable or get cold depends on how much heat you keep and how
much you lose.
You lose heat in several ways. You also generate heat and store
No one variable such as gender or skin surface area makes anyone more
to chilling or hypothermia than anyone else.
Losing body heat, by itself, does not mean that you are chilling.
FACTORS IN SUSCEPTIBILITY
SURFACE AREA TO MASS RATIO. Much is made of the "surface
to mass ratio." What is it? Your heat production roughly proportional
your body mass. On the other hand, radiation of heat from your body to
the environment is in proportion to the area of your skin that covers
The proportion of how much external surface area you have compared to
much internal mass is your ratio.
Car and home heat-redistributors are built to have long thin
Their high surface area-to-mass ratio gives off, or radiates, lots of
Imaginatively, they are called radiators. Long, thin spaghetti cools
Short, round, bulky, baked potatoes stay hot longer. Like spaghetti,
fingers and ears are long and thin with much exposed surface. Fingers
ears chill faster than your torso. Fingers have less total surface than
your torso, but a higher ratio. Your torso, very much like a potato,
more internal mass compared to its outer surface of skin, giving it a
ratio of surface area-to-mass.
Bodies, and body parts, that have a large surface area compared to
mass, can radiate more heat than those with smaller surface
ratios. Although a higher ratio does allow more relative heat loss, it
is not the main determinant of chilling. Someone with a larger ratio
lose more heat through that particular pathway yet still not be at
risk of chilling, because of all their other heat-conserving and
mechanisms. Moreover, a larger person has more total surface area and
more total heat than a smaller person. For example, a large male has
total surface area, and so loses more total heat than a smaller man or
woman, but is not more susceptible to chilling for that one reason.
AGE. Young children are less able to thermoregulate in the
than adults for a variety of reasons including size, active heat
vasomotor control, and other factors. Risk of chilling also generally
with aging, although changes in physical fitness and body composition
accompany aging, is often confused for aging itself.
BEHAVIOR. Is the person who gets out of the water first,
the cold one? A thermal stress workshop held at the Institute for Naval
Medicine in England by the Diving Medical Advisory Committee discussed
what they called the non-responder to cold. They stated, "It is still
known what the differences are between the man who responds to and
of the cold, and another man who cools and is unaware that he is
Presumably this latter type of diver is a potential hypothermic
MEDICATIONS. Medications called beta blockers are commonly
for migraine headache. They are also sometimes taken for high blood
although other medications have gained greater acceptance as
People taking beta blockers sometimes report reduced cold tolerance. A
possible reason is that beta blockers, particularly a class called
beta blockers, were found in some studies to block non-shivering
which is one small means of heat production.
EXERCISE. Contrary to popular belief, you won't always get
by exercising in cold water. Both heat loss and heat production
when exercising in cold water. Whether you get cold or warm depends
you have more of. Often the exercise can generate enough heat to
you, as USNavy divers found out during Desert Storm operations in the
FITNESS. Your thermal tolerance can improve with physical
although cold tolerance better increases with exercise in cold
than from exercise alone. In other words, to get used to the cold, you
need to be out in it. Often.
PROTECTIVE CLOTHING. Clothing studies yield interesting
Subjects' core temperatures are sometimes lower with protective
than without. Lack of input from cold receptors in their hands,
the body's ability to make the needed blood flow changes necessary for
cold protection. Sensory information from cold receptors in the
seems of high importance in thermoregulation. Still, protective
is important, and makes a life-and-death difference in extreme cold air
and water. Protective clothing protects you from losing more heat than
you can replace.
GENDER. Women are not more susceptible to hypothermia than
as commonly thought. To the contrary, several studies show women are
less susceptible. On average, women have better ability to limit heat
They may generate less (and sometimes more) total heat than men
on work load, fitness, body size, and other variables. Men, on average,
usually lose more total heat from higher skin temperatures due to their
lesser vasoconstrictor response (evidenced by often warmer hands), and
from their larger total skin surface area, and for that reason, must
with increased heat production from typically greater mass and
It takes more calories and metabolic work to keep up such heat
making a very extreme survival situation more problematic for males -
may be more likely to starve and freeze. Evidence is strong that women
protect their core temperature in the cold as well or more than men.
What about the warmer hands issue? That doesn't mean that men fare
in the cold. It indicates that women are losing less heat through their
periphery. Men's warm hands pour heat out into the environment. Your
temperature is not 98.6F (37C). That familiar number is the average
of your core. Skin temperature is far cooler than core temperature. One
of the ways your body resists heat loss through your periphery is by
warm blood flowing to your skin surface. In the cold, your skin
quickly drops to that of (or close to) the surrounding air or water. If
skin surface temperature is close to surrounding temperature, the
is small, so heat loss is small. (Heat travels down gradients from high
to low, just as with nitrogen load.) People with cooler skin in the
have a smaller skin-to-environment gradient to lose heat. An analogy is
if you stand outside your house in cold weather, touch the exterior
and find it warm, you would notice the expensive loss of heat and know
your home needed better insulation. You may even wonder who designed
an inefficient structure.
BODY SIZE AND SHAPE. A large person can produce and
more heat than a smaller person. Adaptations in body shape and size,
to aid survival as a species in cold climates, is summarized in
rule. Bergman's rule is a generalization that peoples originally native
to cold climates are larger than those from warmer climates.
Now imagine a long, tall, slender person. With large body size,
and leg length often increase. More heat is lost through these areas of
high surface-to-mass ratio, and comparatively little fat insulation.
generalization, called Allen's rule, takes limb length into account.
short arms and legs of large people from cooler regions, for example
helps reduce heat loss.
Body size and shape contribute to susceptibility to cold, but,
any other individual factor, do not determine it.
FACTORS IN SUSCEPTIBILITY TO COLD
Water and air temperature
Very young and very old age
Physical work load
State of acclimatization
WHAT IS ACCLIMATIZATION?
Cold acclimatization is a well-documented process of gradually
your resistance to cold injury through regular cold exposure. Following
the recommendation of the International Union of Physiological
the term acclimatization is distinguished from acclimation.
means change from seasonal or geographical exposure; acclimation is
produced in a laboratory.
WHO ACCLIMATIZES TO COLD?
Major examples of geographic acclimatization to cold are the indigenous
people of the African Kalahari, the Australian desert, and Tierra del
in Southern Chile. Many sleep outdoors nearly naked in freezing
Seasonal acclimatization occurs in people working outdoors year round
fishermen who dunk their hands in cold water all winter to tend their
Divers continuing to work late into the winter season, or year round in
cold waters, gradually increase their cold tolerance. Extent varies
individuals and with exposure.
WHAT CHANGES OCCUR IN TRUE ACCLIMATIZATION?
True cold acclimatization involves at least three adaptations.
people begin shivering at lower body temperatures, because they
more heat without shivering. A big hallmark of cold-acclimatized people
is improved ability to sleep in the cold. Cold acclimatization may
either increased or decreased skin temperatures, depending on
In some cases, skin blood flow increases to keep extremities warm and
resist cold injury. In other cases it decreases to reduce heat loss.
example, skin temperatures of Australian Aborigines were lower while
than those of the unacclimatized European investigators.
ACCLIMATIZATION TO COLD
+ Shivering occurs at a lower body temperature
+ Ability to sleep in the cold
+ Changes in peripheral blood flow distribution
LOSING YOUR EDGE
When chronic exposure to cold environments ends, you gradually lose
your cold adaptation. When acclimatized Korean divers switched from
suits to wet suits, their thermal advantage decreased. Loss of
was also documented in the Ama divers of Japan when they began wearing
cotton suit insulation and wet suits.
ACCLIMATIZATION IS NOT ALL THERE IS TO DIVING WARM IN THE COLD
To truly acclimate to cold weather, you need to expose yourself to
cold conditions on a regular basis, and to exercise in the cold. You
reduce or eliminate your acclimatization potential if you keep yourself
in a tropical micro-climate of warm clothing and indoor heating.
How practical is it to live a cold life in order to acclimatize to
Up to a point, it helps greatly. Below critical environmental
obviously, acclimatization is not all there is to diving warm in the
Cold affects many of your body systems as they make adjustments to
heat production and decrease heat loss. Extreme cold exposures
your protective systems, with chilly effects.
One important way to conserve heat and tolerate cold water
is to wear good thermal protection. Various animals dive in Arctic
using both wet suit and dry suit technology. The fur of seals and polar
bears, for example, is an effective wet suit. It adds exterior
to their thick fat layer by trapping a two to ten millimeter water
near their skin. The feather pelt of penguins, on the other hand, works
like a dry suit, maintaining an insulating layer of air. Humans who
no feathers or fur should wear exposure suits that include head
when they dive in cold water.
Some divers ask if pouring warm water in your wet suit, or warming
between dives in a heated car or boat cabin, will cause you to sweat
vasodilate your peripheral blood vessels, increasing heat loss, thereby
making you colder than before. It's unlikely that you will overheat to
such an extent. The additional heat you gain back is important for
You will be warmer than before and will build back a heat reserve.
is an important part of cold water diving.
YOU CAN DO SEVERAL THINGS TO CONSERVE HEAT WHILE DIVING IN COOL
good exposure garments, suitable for conditions
the weather report and make site condition checks
wider diving safety margins with colder conditions
well nourished, rested, and hydrated
your face and hands
diving, dry off, get changed, and get out of the cold
well between dives
in good muscular and aerobic shape to improve your
and heat-producing systems
you are cold, do something about it
DON'T JUST SIT THERE
Diving safely in the cold is a matter of not losing more heat than
you produce. Divers rarely get clinical hypothermia from diving, but
get cold and uncomfortable, which can affect fun and safety.
If you are cold, do something about it. Safety in the cold
action and thought by the diver before, during, and after diving. You
dive safely in cold water when you properly prepare.
For more information on cold and other diving physiology topics,
the fun book, DIVING PHYSIOLOGY IN PLAIN ENGLISH. This book
decompression theory, tables, computers, effects of immersion, DCS, O2
toxicity, lung injuries, heat and cold, swimmer's ear, marine stings,
and nutrition, headaches, why you have to 'pee' when you get in the
and many other topics. Fifth revised printing 2003.
Scuba-doc bookstore link here.