Divers should be physically fit.
Not only are fit divers better prepared
to handle the rigors of
scuba, but also they are less likely
to develop detectable gas bubbles.
Yet, while regular exercise and
proper conditioning are in the
diver's best interest, certain types of
exercise before, during, and after a
dive cause changes that may predispose
a diver to DCS. While
there are unknowns, there are
enough theories, anecdotes, and
research to provide guidelines for
healthy divers observing recreational
profiles.
Why the worry over
exercise?
The goal of slow ascents and
safety stops is to safely eliminate
excess nitrogen from blood and
extravascular tissue in the dissolved
state as it was absorbed. Improper
exercise may impede this by contributing
to bubble formation, the
root cause of DCS. While it is as yet
uncertain whether the primary
mechanism of development is biochemical
or biophysical, it appears
prudent to steer clear of all suspected
causes of bubble generation,
and certain types of exercise
are certainly among them.
Light aerobic activities, like
walking and swimming, mildly
increase heart rate and redirect
blood from organs to muscle and
associated tissues. Before a dive,
such exercise will not affect nitrogen
uptake. After a dive, it would
be expected to promote safe offgassing
and inhibit bubble formation
and expansion. In fact, some
studies suggest light exercise
decreases the incidence of DCS.
However, vigorous aerobic exercise, like hard running or
strenuous hiking, produces pronounced
changes. Markedly
increased temperature, blood flow,
and oxygen use within tissues
immediately before a dive could
result in an undesirably rapid
uptake of nitrogen upon descent.
After a dive, such exercise or an exhausting surface swim to the
boat could contribute to a dangerously
accelerated elimination rate.
A diver, especially one who fought heavy current,
should keep from getting chilled and maintain
slow, steady motion during the safety stop. |
Some scuba venues, like
Hawaii, invite arduous post-dive
hiking to altitudes that can seriously
compound the worries. Don't
hike too soon after diving, and if
trekking remotely near altitudes of
8,000 feet, follow DAN flying-afterdiving
recommendations of waiting
12 or more hours after making
a single no-decompression dive
and 17 or more hours after making
repetitive dives.
Stay Warm
Temperature and circulation
alterations during a dive also have
implications. Dr. Jolie Bookspan
notes in Diving Physiology in Plain
English that "Being uniformly cold
throughout your dive seems to
decrease decompression risk. . . . A
diver starting a dive warm absorbs
more nitrogen at depth than a
cooler diver. If the warm diver
then chills, common toward the
end of a dive, eliminating the additional
nitrogen gas burden slows, increasing risk."
Another effect of exercise
relates to the rapid moving apart,
and rubbing together, of joint, tendon,
and other musculoskeletal surfaces;
they are bathed in fluid that
becomes turbulent when forcibly
disturbed. Wrestling with cylinders and reentering the boat in full gear
can generate seed bubbles that may
serve as receptacles for nitrogen
passing from the dissolved stage to
the free gas phase upon ascent.
While scientists are uncertain about
their effect on DCS, it would be
prudent to avoid or minimize activity
stressful to joints.
Another worrisome effect of
strenuous exercise is bubble creation
in synovial fluid caused by
the rapid moving apart, and rubbing
together, of joint, tendon and
other musculoskeletal surfaces. In
fact, Dr. Michael R. Powell, a NASA
research scientist, opines that there
is no single causative factor greater
than strenuous exercise shortly
after a dive for increasing the risk
of DCS.
While it is impossible to confidently
attribute DCS to strenuous
activity in other than a laboratory
setting, there are anecdotal
reports. For example, Fiona
Watson, a medical professional in
the U.K., told Undercurrent that in
many years of scuba, including
deep decompression dives, she had been bent only once, during
the recovery of a heavy copper
soup tureen that had to be wrestled
with before being lifted to the
surface. Upon reaching the boat,
she pulled in a heavy shotline and
unloaded gear and weights. Thirty
minutes later, while handling her
cylinders, an itch and skin mottling
intensified in her arm and elbow,
and she developed marked muscle/
joint discomfort. Being a long
way from a recompression facility,
she drank water and breathed 100
percent O2 for 3 hours. The skin
manifestations soon disappeared,
but the muscle/joint pain took
seven days to resolve. Later discussions
with chamber personnel confirmed
that this almost certainly
was a DCS hit.
She also relates the situation of
a male buddy, also a serious diver
with no history of DCS. He made
an air dive of 34 minutes to 90 feet,
then meandered back to 45 feet
for most of the dive, and completed
a three-minute safety stop.
Upon exiting the water, he helped
raise a heavy shotline. About 25
minutes later, he experienced continuous
dizziness, vomiting, nausea,
and incoordination. He was
transferred to a chamber and
required hyperbaric treatments for
several days. He permanently gave
up scuba diving.
How Long to Wait
DAN's Medical Center website
suggests a two-hour delay after
exercise as a minimum guideline
for diving and considers four
hours safer. Since vigorous postdive
exercise almost surely is more
pernicious than pre-dive activity,
additional conservatism seems warranted.
Some studies suggest that
while the biggest increase in risk
may occur within an hour or two
of arduous exercise just before and
just after a dive, risk likely remains
somewhat elevated up to six hours.
Of course, the number and frequency of dives on any trip will
bear on the degree of conservatism
that would be prudent. For
example, after 3-4 days of diving
deep walls, you'll want to be more
cautious than when doing only a
single shallow dive and then
returning home.
These estimates are consistent
with Dr. Ern Campbell's (aka
Scubadoc) suggestion: "If one
were to put four restful hours
between exercise and diving and
six between diving and exercise, a
diver should be in good shape in
terms of absent bubbles."
However, regarding the postdive
interval, don't take "restful"
too literally. Sleeping immediately
after a dive could slow nitrogen
elimination to an unhealthy degree. Sensible amounts of light
activity such as easy walking or
warm water swimming, will promote
nitrogen elimination.
Are there other exercise-
DCS associations?
Dehydration and exerciseinduced
pain are exercise-related
factors that can prove problematic.
Risk statistics consistently show a
sizeable association between dehydration
and susceptibility to DCS.
Perspiration due to vigorous exercise,
especially in hot weather, can
further the fluid loss already inherent
in scuba.
Given that joint pain is among
the most common symptoms of
DCS, injuries to joints and muscles provide fertile ground for confusion
between DCS-related pain
and exercise-induced discomfort.
Avoid them, and the unnecessary
chamber visits they may occasion.
The best advice is moderation.
Stay well hydrated and warm.
Avoid strenuous exercise of any
type for 4 and 6 hours before and
after diving, respectively, but
remain mildly active between dives
and for a while after the last dive.
Reduce anxiety and confusion
about symptoms of DCS by knowing
the location and characteristics
of your pre-dive aches and pains,
and be alert to changes in their
nature or intensity.
-- DocVikingo