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This comes from the latest edition of Undercurrent Online:

Take a liveaboard trip and with all the food and snacks you might easily partake in a 4,000, maybe even a 5,000, calorie day. But, you say, look at all those calories you burn diving. If you're like most sport divers, you think you burn something like 600 to 900 a dive. Wishful thinking. Dr. Jolie Bookspan, the author of Diving Physiology in Plain English
(http://www.undercurrent.org/UCnow/bookpicks.shtml#DivingPhys) told Undercurrent that a diver "burns the same number of calories diving as doing any other light exercise." And she adds, "it's a myth that exposure to cold water burns more. This had been explored some years ago in a study where obese women pedaled stationary bicycles in very cold pools. Beside being unpopular, it didn't work. "Think about an easy dive on a coral reef like a walk in the park. If you weigh 200 lbs., you'll be lucky to burn 200 calories an hour. Dive five times a day, eat up, and go home five pounds heavier -- if you're lucky".  
 
 
 

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[b said:
Quote[/b] (John Gulliver @ May 06 2003,14:12)]. "Think about an easy dive on a coral reef like a walk in the park. "
<font color='#0000FF'>Well, yeah..., might tend to agree with that bit, but when was the last time that was relevant to most of us here? I'm not saying this researcher is necessarily wrong, but my own experience of diving and eating suggests that it is not entirely correct.  

Point to note, most diving researchers tend not to dive, e.g. that woman - whose name temporarily escapes me - who says reverse profiling is ok, it's fine if there's a chamber ready and waiting just in case, but for recreational diving, I don't think so.
Chee-az
steve
 

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Just not enough dive time.
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Steve
I thought reverse profilese WERE acceptable. My understanding is that they are not advisable but if you use the tables/computers conservatively then no harm should come to the diver. I believe that reverse profiles tend to give less bottom time anyway. Also the 'normal' dive deep first rule was something that just happened by accident and is now part of dive folklore rather than based on fact.
What evidence do you have that suggests otherwise, by now I'd hope you know I'm not being argumentive but am curious to know where your knowledge differs from mine.
Matt
 

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Discussion Starter · #4 ·
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If you are diving against a strong current ot otherwise exerting yourself, the dive is of course more than "a walk in the park" but I think you'll find that your energy expenditure on most of the dives you do is in fact at that sort of level rather than being equivalent to, say, a 5 km run.
As regards reverse profiles, the following is a summary from Undercurrent of a symposium on the subject organised by the Undersea and Hyperbaric Medical Society:
Always Do Your Deep Dive First?
Though that's what we've always been told, it may not be necessary.
For many years, recreational
scuba divers have embraced a
maxim that it is unacceptable to
perform reverse profile dives,
i.e., to make a repetitive dive to
a depth deeper than a previous
dive or to make the deeper part
of a single multilevel dive after a
shallower part. While it is widely
recognized among recreational
divers that reverse dive profiles
are forbidden, these profiles are
often done anyway.
It’s not clear where the rule
against reverse dive profiles
came from or how significant it
really is. Except in rare instances,
neither the military nor
commercial diving communities
prohibit reverse dive profiles or
even recognize them as unique.
Most sport diving computer
programs do not prohibit
reverse dive profiles and even
allow the calculation of such
profiles without apology. The
primary consequence is that
there may be less no-stop bottom
time available on a repetitive
dive. So the long-standing
prohibition against reverse dive
profiles is being questioned by
the sport diving community.
To get more bottom time,
most sport divers have observed
the prohibition of reverse order
and perform dives only in
“forward” order. However, for
scientific divers the “rule” can
impose a significant operational
limitation. To reexamine the
rationale for this rule, a high-level
international workshop was
organized by Michael Lang,
head of the Smithsonian
Institution’s Scientific Diving
Program, and by Charles
Lehner, Diving Physiology
Laboratory, University of Wisconsin,
Madison. Divers Alert
Network (DAN), the Diving
Equipment & Marketing Association
(DEMA), and Dive Training
magazine were also sponsors.
The October workshop’s objective
was to examine whether
reverse dive profiles cause
increased risk and whether there
is a justifiable reason to prohibit
such profiles.
Workshop Sessions
In the first session, a discussion
of the literature revealed
that the prohibition against
reverse profiles probably related
less to safety issues than to
“optimizing” bottom time over a
series of dives. This comes from
gas-loading considerations that
allow more usable bottom time
by making the deep dive first.
The next two sessions
concentrated on physics, physiology,
and modeling. Among the
modeling approaches, bubble
formation and growth models
were prevalent. Although there
was diversity among the bubble
models, they tended to arrive at
similar conclusions. For example,
most call for lower
allowable supersaturation
gradients on the initial stops
(deep stops) and shorter no-decompression
limits than
conventional dissolved gas
models. The bubble models
included David Yount’s varying
permeability model (VPM), also
known as the “tiny bubble”
model; Bruce Wienke’s reduced-gradient
bubble model (RGBM);
the Duke University bubble-volume
model; the DCIEM
bubble evolution model based
on Doppler scores; a gas-dynamics
model by Valenie Flook based on
Van Liew’s concepts; and
Michael Gernhardt’s tissue
bubble-dynamics model.
Hugh Van Liew argued that
they need experimental validation
to confirm the existence
and role of micronuclei for
bubble formation, including
whether such gas nuclei can be
“crushed” to the point of elimination
or inactivation. Another
presentation showed that,
although the reverse dive profile
may have a higher predicted
incidence of decompression
sickness (DCS), the differences
were trivial for pairs of no-stop
dives, and decompression using
the U.S. Navy tables would be
adequate. However, for dives
involving decompression stops
or for more than two dives in a
row, these tables might not
provide a reliable decompression.
All of this pointed toward
an urgent requirement for more
information and, to this end, Alf
Brubakk suggested an animal
model that might at least show
which profiles result in the most
bubbles.
Another session included a
discussion by several dive-computer
manufacturers. Many
older computers on the market
use conventional dissolved-gas
(Haldanian) algorithms that
take into account only gas
loading and supersaturation
limits (M-values) and do not
specifically consider the order in
which dives are conducted. In
these cases, the user manuals
accompanying the computers
may recommend against reverse
dive profiles. Some of the latest
dive computers incorporate
algorithms based to varying
degrees on bubble models.
These computers have specific
warning features or penalties for
dive patterns associated with
increased risk (bounce, yo-yo,
repetitive dives with excessive
pressure differentials, etc.).
Many horror stories have
been associated with reverse
profiles, the classic one being
the instructor making a short,
deep dive to release the anchor
chain after a day of diving and
getting severe DCS. Such situations
are hard to interpret
because the number of subjects
is very small and buddy divers
doing the same profile may be
unaffected. Other data show that
studies of 100 dives may be
insufficient for statistical analysis,
but one comment put this
issue into perspective: “We are
better off having that 100 dives
than no observations at all.” Many
participants reviewed data from
the U.S. Navy, commercial diving
records, decompression chambers,
DAN records, and various
recreational dive sources.
An argument can be made
that the present lack of data
proving whether reverse profiles
are dangerous could be due, in
part, to the arbitrary prohibition
against such profiles for many
years — in other words, not
many of these dives have been
done.
Although there were some
problems with reverse dive
profiles in isolated examples, the
conclusion drawn from the
analysis of actual diving data was
that reverse profiles have not
shown a higher risk for DCS
than forward profiles. However,
this holds most confidently when
the differential pressure for the
reverse profile is not too great —
one cannot get big differentials
without having significant depth.
It appears that decompression
tables, algorithms, and dive
computers adequately handle
the issue of reverse dive profiles.
Another observation is that
this subject may be a matter of
repetitive diving and, in general,
this is handled differently across
the many decompression algorithms.
The discussion turned to the
participants to arrive at findings
and conclusions, and the discussion
got heated. Several people
who work with bubble models
had serious reservations about a
“complete retraction” of warnings
against reverse dive profiles
since the bubble models suggest
that you might get into trouble
on an improperly planned or
executed reverse dive profile.
Many were concerned that
divers, especially inexperienced
sport divers, would get the
wrong message about reverse
profiles and think that it was
okay to do them without any
special consideration.
The bubble modelers
obtained a couple of key concessions.
Practical diving experience
showed few problems with
reverse profiles, but bubble
models showed there could be.
Thus, they adjusted some
wording to make it clear that it
was only in the diving experience
that there had been few
problems, not that there’s a lack
of evidence that reverse profiles
are or could have a higher DCS
risk. The sentiment prevailed
also that there should be a
pressure differential limit,
noting that most of the safely
executed reverse profiles were in
40 fsw or less between the
repetitive dives. Another point
of agreement was that the sport
diving limit of 130 fsw should
apply to any relaxation of
current prohibitions on reverse
profile diving,
Findings and Conclusion
Neither the U.S. Navy nor
the commercial sector has
prohibited reverse dive profiles,
and they are performed in
recreational, scientific, commercial,
and military diving. Since
the prohibition of reverse dive
profiles cannot be traced to any
definite diving experience that
shows an increased risk of DCS
and no convincing evidence was
presented that reverse dive
profiles within the no-decompression
limits lead to a measurable
increase in the risk of DCS,
the workshop participants found
no reason to prohibit reverse
dive profiles for no-decompression
dives less than 130 fsw and
depth differentials less than 40
fsw.
This is a summary of an article
that appeared in Pressure, the
newsletter of the Undersea &
Hyperbaric Medical Society, Inc.
(Volume 29, Number 2 2000
March/April). It was written by R.
W. Hamilton and Erik Baker.
To order the full workshop
proceedings, contact Underwater
Hyperbaric Medical Society, 10531
Metropolitan Avenue, Kensington,
MD 20895, call 301-942-2980, fax
301-942-7804, or visit their website
at www.UHMS.org.
 

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Hmmmm, obviously I'm aware of the UHMS proceedings, but I'm still very far from convinced that reverse profile is sensible. No, no-ones prohibitedit, but most adviseagainst it. With multi tissue saturation times (assuming you accept the concept) the tissue desaturation from slow tissues starts gassing into fast tissues upon redescent. This has to get more complicated if you then increase the resaturation pressures. ?Possibly to damage level?
 

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Well, I wasn't advocating reverse profile dives, just passing on what some of the so-called experts think (or thought a couple of years ago). Like most divers, I do my best to avoid reverse profiles, pending further clarification of the picture, but, again I suspect like most divers, there have been days when my second dive was a few metres deeper than my first and I haven't suffered any ill effects as far as I'm aware.
 

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Just not enough dive time.
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John
thanks for that article, it was broadly my understanding, the max depth and differential would be of little consequence to me personally as I dive within those limits anyway.
Steve, I wasnt out to prove a point just didnt want you to be worried unduly if you ever have to do a reverse, obviously a forward profile is better and there is little evidence that really proves reverse is OK, just that there isnt any that proves it isnt. On balance I'd prefer a forward profile, especially in UK waters.

Matt
 

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<font color='#0000FF'>Cheers for the arictle John: Valerie Flook, that was the woman whose name  I couldn't remember. Sorry but it looks like your thread has been a little hi-jacked.

Matt, I've done quite a few reverse profile dives, some by accident (such as the fiirst day of the deco proc course the othr week) and some because the situation demanded it. It's not something I advocate but also it's not something that keeps me awake at night if I do it. Having said that if I did ever get a bend than it might worry me more.

When I was in Florida diving under NOAA regs a couple of years ago, they had just accepted the findings of the symposium John posted above, the deal was no more than 12 metres difference between the first and second dives. Due to the fact that this was scientific diving, and therefore  required HSE certification first, it was looked upon as "work" so if we needed to dive to 20m to get sampes then drop them back in at 30m then that's what we did.

Of course, there was a chamber only 4 miles away, we're on a boat with a speed of about 35knots, plenty of O2 on board for all the divers on board, etc etc. We also did a day or so of saw-tooth profiling - again not recommended for recreational diving.

It's interesting to have "broken the rules" (under the right situation) and seen no ill effects from it, but it was all done with a great deal more preparation and attention to safety than diving with your recreational buddies

Chee-az
Steve
 

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Thanks John , helped me get to sleep did your post above . But in all seriousness if i want to burn calories what's best sex or diving and how deep ??, how long ??
 

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[b said:
Quote[/b] (Scubamuppet @ May 07 2003,11:28)]But in all seriousness if i want to burn calories what's best sex or diving and how deep ??, how long ??
"In all seriousness", people have investigated energy output during sex. I'm sure you'll find the studies if you do a Google search. I'm afraid it's another case of "a walk in the park" for most of us though. So, unless your prowess in that area is exceptional, choose what gives you most pleasure
 

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<font color='#0000FF'>Do both, go diving then have sex... This topic is a bit like asking how long is a piece of string. Some of the dives I do I would feel like a marathon at the park rather than a walk. Anyway we don't really do it for the exercise.  Most dives I reckon that are in in the Uk and similar waters we are sure to spend a good few calories.  As in the tropics it may be easier but it still is good exercise, better than standing by the box with the remote at least
 

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[b said:
Quote[/b] (Chris Guimaraens @ May 07 2003,15:35)]It still is good exercise, better than standing by the box with the remote at least
I second that, but why stand by the box? Haven't you got an armchair, Chris?
 

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<font color='#0000FF'>Good one John, the case where my fingers type faster than my brain cells (that is slow brain cells not fast fingers!)
 
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