Psychological Stress and Sky Diving

[moretole 0]

Found this short article that is quite interesting. looks at the psychological influence on your body during skydiving.

http://jcem.endojournals.org/cgi/content/full/83/4/1397

Edited by slotperfect to make the link clicky.

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[bigway 4]

What language is that in?

.Karnage Krew Gear Store
.

[jtlmd 0]

It is in English. Sort of an interesting article but not the first time plasma levels of stress hormones have been assayed in jumpers.

James T. Lee, M.D.
St Paul MN

[Dumpster 0]

Now what does all that mean in blue-collar terms?

Easy Does It

[peregrinerose 0]

That psychological stress (scared shitless) makes you change what brain chemical dosages are released. That psych stress affects brain chemistry in ways that are different from physical stress.

Interesting that it was done with firs time tandem jumpers. You'd think that it would be even more significant for a first jump AFF or Static line jumper.

Jen

Do or do not, there is no try -Yoda

[riggerrob 643]

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Now what does all that mean in blue-collar terms?

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

It's all in your head.
There is very little physical stress incurred during tandem jumps.

[jtlmd 0]

The chemicals are not "brain chemicals" in source as one poster implied. The very high (seven times normal) adrenaline levels claimed in this paper to be in the circulating blood come from the secretions of one part of the adrenal glands almost totally. It is not a conscious response but automatic. Noradrenaline does not come from the adrenal glands but from sources scattered all over the body. Almost all of us have two adrenal glands, one on each side of the body just above the kidney. An adrenal gland is normally about the size of a quarter or less. They have very substantial blood supply so they can "dump" chemicals rapidly into the blood stream when activated.

Lots of different stimuli can "turn on" the adrenal glands which are primitive and essential for life in mammals as far as I know. Sometimes we do total adrenal removal surgically but it is an uncommon operation nowadays and those people have to take artificial replacement hormones forever. The replacement hormones they take are not for adrenaline but for the corticosterioids--that's a more complex story than you want here. The steroids come from a part of the adrenal gland called the cortex.

The paper that was quoted (and I read through it quickly) made the point that psychological "stress", as provoked by the jump, caused a surge in adrenaline that was way more than in noradrenaline. The authors pointed out that there is probably no ethical way to cause that kind of pure surge otherwise.

The reason these academic types were interested in this was that the setting of a skydive provides a "natural" and easy way to study people who are under the influence of this unbalanced surge. The big objection down the road of course will be that skydivers do not represent a random cross section of the population of all humans (and they sure dont).

I have a strong suspicion that very experienced divers like all of you guys probably are much more relaxed in the door than beginners but this has little IMMO (in my medical opinion) to do with "bravery" or "not having the shit scared out of you". Several of our very experienced astronauts have had enormous pulse rates just before liftoff. Adrenaline is reponsible for those high heart rates, sometimes above 150. That's a hell of a lot in a guy whose resting pulse might well be 50. The people who go to space are highly conditioned athletic people who have often had long prior experience in test pilot work, etc. and they are hardly pussies. In addition, the chances of getting killed on a shuttle ride are hugely higher than any skydive data indicate for sport jumps in USA. The Creator was pretty smart and "wired in" reflexes that operate in situations perceived as threatening. I imagine Col. Eileen Collins who is "up" right now is just as "brave" as the most bad-ass swooper at any DZ but both kinds of flyers are still mammals wired the same. Not drowning yourself in adrenaline may be a learned response I would guess. Relaxation, self-confidence, etc. etc. etc. Indeed there have been several astronauts who have GONE TO SLEEP with pulse rates in the 70s while awaiting liftoff. Those are what you folks call "really cool dudes".

Next time you go up on a load look at the pupil diameters (eye measurement, not diameter of students' butts) on AFF students facing their fourth jump as opposed to those diameters on hard nosed 5000 jump pros. People with high blood levels of stress hormones get big pupils. When I have had a chance to make this observation as a student I think I saw pupil dilation in my AFF teacher and he has 6000 jumps. Maybe he was just excited that I had gotten off my butt and back in the game? All other things being equal, might well see a difference between a 5000 jump dude and some eager guy with 8 jumps under his belt. Folks like me probably have pretty huge pupils at the door although on every one of my 8 AFF jumps my pulse has been about 110 just before stepping out and my resting rate is around 55-60. Not bad for a 63 year old guy, eh dude! Having said that, it has been a practice among even experienced jumpers at my DZ that wintergreen mints are passed out on the way up a lot (dry mouth--aka "cotton mouth"--also a side effect of hormonal surge).

Hope this helps. I of course envy all of you who would claim to have "no adrenaline surge" but I will bet you lunch that part of the "kick" in the sport comes from the complex effects of cycling powerful chemicals (not just adrenaline) up and then back down in the blood stream. But of course, maybe not. If you really want to stimulate your adrenal glands try being a surgeon and having somebody else's life in your hands during an emergency operation for uncontrolled bleeding. Now THAT'S a stimulating event, it lasts a lot longer than a single skydive (although it's a different kind of fun), and some people love the buzz more than you might know.

Blue Skies,,,,,there will be a written quiz on this next week. Be prepared to diagram the chemical pathways for adrenal hormone metabolism !

JT Lee, MD
Minnesota

[peregrinerose 0]

As adrenaline is a neurotransmitter and the person asked for a 'plain english' version of the text, I chose not to go overboard in explaining the mechanism of action nor biochemistry of adrenaline in the body

Without knowing baseline pupil diameter, you can't possibly know if your instructor's pupils were dilated or they have physiologically large pupils. Many more things than adrenaline affect pupil size

Do or do not, there is no try -Yoda

[ladyskydiver 0]

Wow! Thanks for the write up. The human body and it's responses are pretty cool.

Life is short! Break the rules! Forgive quickly! Kiss slowly! Love truly, Laugh uncontrollably. And never regret anything that made you smile.

[jtlmd 0]

Good points all around. My mention of looking at other folks pupils on jump run does not imply the planning of a scientific experiment or the gathering of pupillary diameter data to some very accurate standard.with equipment in the plane, etc. etc. etc. Lighten up ! The comment about a quiz on adrenal hormone metabolism was a JOKE.

As an optometrist (I think I saw that in your profile)you see people all day long who are walking around, stable, and basically healthy enough to walk into your office suite. I doubt that you examine very many people for glasses fitting or for vision tests who are in shock or in extremis, where there is most definitely a major adrenal response and pupils are often huge. OF COURSE I have not measured my AFF guy's pupils on the ground but they are equal in size and react grossly normally to light, etc. Of course you are correct that "many things affect pupillary diameter". However, the dilation of pupils in people under the surge of adrenal hormones in so-called "fight or flee" circumstances has been described in both adults and children since antiquity--it's one of the main features of the Hippocratic faces and any busy surgeon who takes care of really sick people has seen it more than a few times. I have done so more than those few times myself. If a tandem jump actually gives a 7-fold plasma surge in adrenaline then I think we are talking serious stimulation of all sorts of fight or flee end organs--cardiac, bronchial, pupils, muscle, etc.

To change the subject a bit--do you know anything about retinal detachment ever being described as a result of hard openings or rough landings ? I have looked all around and cannot find anything. Even NLM searches turn up practicaly nothing. Cannot find anything in military sources and people I have known in Airborne said that they had not seen it. My ophthalmologist is very experienced but, alas, she thinks that all skydivers are nuts, sort of tunes out, and also has never heard of it either. I was injured in a golf cart rollover two years ago and had some eye changes with several full workups for retinal detachment, all negative but am actually very very nervous about aggravating things. Appreciate your comments and your expertise here. Seriously.

As for the neurotransmitter issue, the person you were trying to help seemed to my reading of the posts to indicate that he/she had things backwards. The brain via our interpretation of threatening scenarios is what signals the adrenal glands to dump epi. It's not that the adrenals per se sense danger and do something to the brain with circulatijng epi. That's the semantic danger of using the term "neruotransmitter" here. The stimulus in the paper was the psychic event of jumping and the response variable was the plasma hormone level. The paper, to my reading, was about creating a "useful model" for generating pure adrenaline surges in normal humans via a psychic stimulus so that noradrenaline would not be also stimulated simultaneously.

[Erroll 80]

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do you know anything about retinal detachment ever being described as a result of hard openings or rough landings ?

I am not in any way medically qualified, but I have done some superficial research for personal reasons. I too have never read of retinal detachment as a direct result of skydiving. The main reason, as far as I have been able to establish, is the attitude of the body relative to the canopy during the decelaration/deployment process. The instant decelaration starts the body is pulled upright as opposed to, for example, a bunjy jump where body is in a head-down attitude. Retinal detachments from bungy jumping have been documented.

A more serious risk of the deceleration in skydiving is tearing of the aorta during a rapid opening sequence, but that is a different subject.

[Lindsey 0]

Quote

Quote

Now what does all that mean in blue-collar terms?

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

It's all in your head.
There is very little physical stress incurred during tandem jumps.

Skydiving is like drugs....lol

Peace~
linz

--
A conservative is just a liberal who's been mugged. A liberal is just a conservative who's been to jail

[apley 0]

thanks for dumbing that down for me. i was sorta gettin it through the article, but it was so dry, i gave it a miss...

[peregrinerose 0]

I don't know of any RD specifically from jumping/hard openings, but see no reason why it could not happen. Any kind of whiplash injury (car accident) can cause a RD, particularly in high myopes or those with pre-existing peripheral thinning (lattice, etc.). My first patient ever as an intern walked in my office and said 'doc, I think I have a retinal detachment'. What a way to start a career. He was right, too.

Do you know specifically what eye changes you had? PVD? Angle recession? Commotio retinae? PVD will slightly increase your chances of RD, but if that happens, it is typically within the fist 6 months after the PVD occurs. Angle recession is associated with glaucoma which can occur right away or years down the road, so something to keep an eye on at least yearly IOP readings. Commotio typically heals itself up.

Yep, I'm an OD, but most of my patients are far from healthy My specialty is neuro/low vision rehab. Of course, they'd probably question my mental health if they knew I jumped out of 'perfectly good' airplanes, eh?

Jen

Do or do not, there is no try -Yoda

[jtlmd 0]

Nice comments. The aorta issue has crossed my mind more than once. Ironically, just THINKING about it (or any other potential injury) constitutes one kind of "stress" that can accompany the jump (and thus trigger the various hormonal issues heretofore mentioned by all). Does being 20 years old and having only slight curiosity about the human body, its anatomy, and its various vulnerabilities actually make you less "stressed out" when stepping to the door ? Possibly. Besides obvious issues of muscular strength, etc. it is no accident that soldiers are mostly young folks. Being able to intentionally throw yourself into a dangerous situation without a lot of thought for your own safety is an admirable human skill and, by the way, a tip of the hat to all of our troops out there right now.

We all get issued just one aorta at the beginning of life, we all live in the gravitational field of earth, and some of us intentionally accelerate and decelerate our bodies in that field. There's no doubt that huge deceleration force along the correct axis will surely--in some people --lead to dangerous lesions up in the aortic arch where it "turns the corner" and heads south. I think the usual textbook scenario for what people call a "torn aorta" is a falling elevator where the car by defintion is going straight down with its occupants standing vertically. The force at impact is almost purely in the direction of the Y axis and the humans inside take the force along their "Y axes" (line from toes to brain). Or a car crash or plane crash or motorcycle wipeout at very high speed sometimes will do it. Falling elevators are not very common these days but we cannot say ditto for car crashes. Less ditto for planes thank goodness. Don't know about the two wheel instruments.

The interesting thing about your comment is that I cannot find any credible series in trauma literature that really lays out the issues for high G force events of different types because aortic injury in isolation is basically rare when different ways of "slowing down too fast" are taken altogether. It is my understanding as a very inexperienced skydiving student (but pilot for 34 years and surgeon for 25 years) that we take a big G load hit during normal opening but that it is spread over several seconds as the bag comes out, lines stretch, bag opens, and the slider does its thing. No problemo. After having a few beers and sketching things out on a napkin, it looks like to me that the attachment point of the risers to the harness creates a "hinge point" so that as the body decelerates during opening of the canopy some portion (a lot?) of the force gets distributed into the "whip" motion that the suspended body makes as the legs swing down from horizontal to vertical and back up. This swinging of the body around the "hinge" goes PAST vertical judging from videos of my own deployments where my legs (initially "behind me" in free fall) end up out in front of me parallel to the horizon about the time the slider has come all the way down. If you deploy going straight down in a "standing position" (feet to earth head to sky) seems to me that there is no way to soak up force in such an "angular rotation mode". The force of deceleration would be taken on the leg straps and 100% "vertically". In a line dump (?) or other uncontrolled opening it sounds like we may get a big G load that is NOT spread over several seconds but that we have to take almost "all at once". Aside from issues of being in a position that allows the container to come away from you cleanly, it is important to be in a stable belly to earth position so that the force can distribute in the least harmful way. That's what a master rigger tells me. When I have asked folks who have both large skydiving experience AND medical sophistication (a very rare duo) the only answer I have ever gotten is to "be in a good, stable position at opening". With the enormous number of sport jumps being pulled off (no pun intended) every year and with some unknown number of those perhaps involving deployment of the main without being in a "good stable position" one would think that we would hear a lot more about aortic trauma if it were worth worrying about that much. Modern parachutes thank goodness seem to inflate correctly with a very, very high frequency so the odds that a line dump etc would happen in a jumper who just happened to be in a bad position must be very slim. I am sure the "pros" will not jump all over the next comment: We minimize the risks that we can influence and that is ALL we can influence. If I am off base in my understanding of the physics here I would APPRECIATE a lucid correction. Lucid correction does not mean pissing all over me because I do not have 3000 jumps. That kind of response in this forum seems to be rather common and it's not only adolescent, it's pretty unimaginative and frankly tiresome. It is not productive usually because it does not provide knowledge. Having a lot of jump experience is not the same as having understanding of the physics involved and that is easy to prove; I have talked to jumpers with big numbers about opening shock issues and their eyes just glaze over or they issue a nearly incoherent mumbling. HELP ! For God's sake, begining jumpers need rational explanations of these forces and their operation so that they can move forward undistracted by needless worry and focus on the numerous learning issues to surmount in the progression of AFF training and preparation for licensure.

I have obviously excluded in this discussion of aortic damage the "aortic tear" secondary to "going in" at high speed under a malfunction. That nearly instantaneous deceleration with arrival at Mother Earth is of course very damaging to all sorts of things like bones and soft tissue including blunt force injury to the viscera, brain, etc.

Sometimes what is definitely known about low frequency bad events can definitely drive you nuts if you indulge in too much self-centered rumination. Indeed, one of the problems that every doctor has to surmount in his or her early training is to get the worrying about personal mortality, one type of worrying about the self, out of consciousness at the same time that hundreds of different illnesses are being studied in detail and talked about constantly. Otherwise there can develop a nearly paralyzing hypochondria that can be almost comical and that will definitely prevent progress in the profession. Some very subtle intra-psychic stuff has to go on to get some kind of peaceful equilibrium here and the harder you try to NOT think about your personal mortality the harder it is to escape the worry. The easy way to illustrate this is the old trick of telling somebody "Do not think about watermelons". The only damn thing that person will think about is WATERMELONS. Getting one's knickers in a twist over what might happen to the aorta during parachute opening shock uses up energy that could be applied instead to more pressing public health issues at every DZ in the country. For example, cigarette smoking by some of the dudes and dudettes sitting around waiting for their loads to be called. Now THERE is something that really will kill you dead as a doornail, just not instantly. Ditto for certain other popular recreational "chemicals" that are out there.


JTL

[jtlmd 0]

My ophthalmologist says I don't have lattice. I am not a high myope. Very slight correction for reading or in my operating room loupes. Normal pressures in glaucoma checks q 2 year for past 20 years. Apparently, I had a rather substantial vitreous separation immediately upon hitting the ground. It was a tremendous impact, too. A sideways impact with body hitting ground on left side and 250 lb golf partner (another surgeon) landing on my right side along with the golf cart itself. Could have been dead.

I am nearly 63 and am told that vitreous separation is going on at my age anyway. There were some new floaters and, for a while, some worrisome flashes from traction (I guess) on the retina. Those have gone and it has been > 2 years since the accident. Two completely normal retinal exams within first 6 months. It would be a shame to leave skydiving, sit around awaiting the Grim Reaper, and get a retinal detachment some night when a large jar of Metamucil falls out of the kitchen cupboard onto my head. I am thinking really strongly about going forward as if there is no added risk due to my past history.

[jtlmd 0]

Oops--third paragraph, "the bag to come away cleanly"' not "the container". If your container comes away cleanly or uncleanly, a discussion of opening shock would be moot.

Sorry, and do spare me a sarcastic correction for this typo.

[nicknitro71 0]

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The Deceleration Project

As far back as 1945, service personnel realized the need for a comprehensive and controlled series of studies leading to fundamental concepts that could be applied to better safeguard occupants of crashing airplanes. The initial phase of the program, as set up by the Aero Medical Laboratory of the Wright Air Development Center, was to develop equipment and instrumentation whereby airplane crashes might be simulated, and to study the strength factors of seats and harnesses, and human tolerance to the G forces encountered in simulated airplane crashes.

The crash survival research program was originally slated to be conducted near the Aero Medical Laboratory, but Muroc (now Edwards Air Force Base) was chosen because of the existence there of a 2,000-foot track, built originally for V-1 rocket research. That particular program had been completed and was taken over for the deceleration research program to save building a new track.

Designed to Aero Medical Laboratory specifications and fabricated by Northrop Aircraft Inc., of Hawthorne, Calif., equipment was maintained and operated on service contract by the Northrop Company.

The "human decelerator" consisted basically of a 1,500-pound carriage mounted on a 2,000-foot standard gauge railroad track supported on a heavy concrete bed, and a 45-foot mechanical braking system believed to be one of the most powerful ever constructed. Four slippers secured the carriage to the rails while permitting it to slide freely. At the rear of the carriage, 1,000-pound-thrust rockets provided the propelling force. Braking was accomplished by 45 sets of brakes, each consisting of two clasping pairs of brake surfaces installed on the road bed between the rails. These brake pairs clasped the 11-foot-long braking plates beneath the carriage chassis to apply the desired slowdown or deceleration. By varying the number and pattern of brake sets used and the number of carriage-propelling rockets, it was possible to effect the controlled decelerations to almost any G force.

The first run on the decelerator took place on April 30, 1947, with ballast. The sled ran off the tracks. The first human run took place the following December. Instrumentation on all of the early runs was in the developmental stage, and it was not until August 1948 that it was adequate enough to begin recording. By August 1948, 16 human runs had been made, all in the backward facing position. Forward facing runs were started in August 1949. Most of the earlier tests were run to compare the standard Air Force harnesses with a series of modified harnesses, to determine which type gave the best protection to the pilot.

By June 8, 1951, a total of 74 human runs had been made on the decelerator, 19 with the subjects in the backward position, and 55 in the forward position. Dr. Stapp, one of the most frequent volunteers on the runs, sustained a fracture of his right wrist during the runs on two separate occasions.

Dr. Stapp's findings on the decelerator have been applied to practical use. For instance, the backward facing seat concept, which was known previously, was given great impetus by the officer's crash research program, which proved beyond a doubt that this position was the safest for airplane passengers and required little harness support, and that a human can withstand much greater G forces than in the forward position. As a result, all of the Air Force Military Air Transport Ships (MATS) were equipped with this type seat. Commercial airlines were made aware of these findings. The British also installed it on many of their military transports.

As a result of Dr. Stapp's findings, the strength requirement for fighter seats was increased considerably (up to 32 Gs) since his work showed that a pilot could walk away from crashes when properly protected by harnesses, and if his seat does not break loose.

The "side saddle" or sideways facing harness was developed also by Dr. Stapp. The new triangular shaped harness gave vastly increased protection to fully-equipped paratroopers sitting side-by-side in Air Force airplanes. It was made of nylon mesh webbing, fit snugly over the shoulder facing the forward part of the airplane, and protected the wearer from the force of crash impacts, takeoffs and landing bumps. It withstood a crash force of approximately 8,000 pounds at 32 G's and was developed to replace the old-fashioned lap belts which gave inadequate protection to their wearers.

By riding the decelerator sled himself, Dr. Stapp demonstrated that a human can withstand at least 45 G's in the forward position, with adequate harness. This is the highest known G force voluntarily encountered by a human. Dr. Stapp believed that the tolerance of humans to G force had not yet been reached in tests, and is, in fact, much greater than ordinarily thought possible. He incurred two wrist fractures (the second of which he reset himself while walking back to the Aeromedical Field Laboratory), rib fractures and retinal hemorrhages, but no permanent disability or sustained loss of consciousness.

Also developed by Dr. Stapp as an added safety measure was an improved version of the currently used shoulder strap and lap belt. The new high-strength harness withstood 45.4 G's, compared to the 17 G's, which was the limit that could be tolerated with the old combination. Basically, the new pilot harness added an inverted "V" strap crossing the pilot's thighs added to the standard lap belt and shoulder straps. The leg and shoulder straps and the lap belt all fastened together at one point, and pressure was distributed evenly over the stronger body surfaces, hips, thighs and shoulders, rather than on the solar plexus, as was the case with the old harness.

Dr. Stapp also participated in wind-blast experiments, in which he flew in jet aircraft at high speeds to determine whether or not it was safe for a pilot to remain with his airplane if the canopy should accidentally blow off. Dr. Stapp stayed with his aircraft at a speed of 570 miles per hour, with the canopy removed, and suffered no injurious effects from the wind blasts. He also supervised research programs in the fields of human factors in escape from aircraft and human tolerance to abrupt acceleration and deceleration.

In the years before his death, Dr. Stapp was president of the New Mexico Research Institute, headquartered in Alamogordo, N.M., as well as chairman of the annual "Dr. Stapp International Car Crash Conference." This event, which is underwritten by several automotive manufacturers, meets to study car crashes and determine ways to make cars safer. In addition, Dr. Stapp was honorary chairman of the Stapp Foundation, which is underwritten by General Motors and provides scholarships for automotive engineering students.

Dr. Stapp died peacefully at his home in Alamagordo, N.M., Nov. 13, 1999. He was 89.

Memento Audere Semper

903

[jtlmd 0]

Beautifully told. Thanks.

JTL

[peregrinerose 0]

Quote

My ophthalmologist says I don't have lattice. I am not a high myope. Very slight correction for reading or in my operating room loupes. Normal pressures in glaucoma checks q 2 year for past 20 years. Apparently, I had a rather substantial vitreous separation immediately upon hitting the ground. It was a tremendous impact, too. A sideways impact with body hitting ground on left side and 250 lb golf partner (another surgeon) landing on my right side along with the golf cart itself. Could have been dead.

So what you are telling me here is that golf is more risky than skydiving, right?

Based on what you have said, I can't imagine that your odds of RD are much higher than someone who didn't have the golf related injury. Anything can happen at any time, as you know from your Metamucil induced RD hypothesis
When you learn to pack, learn to pack for soft openings, when you buy your own gear, get recommendations for canopies that tend to give softer openings. And have fun!

Once you get your B license, consider getting involved with RAM, they have been planning on trips that you skydive in to remote areas to provide medical care. Once the student loans are whittled a bit, I will definitely be doing that.

Jen

Do or do not, there is no try -Yoda

[jtlmd 0]

But in none of the sled runs was Col. Stapp positioned prone or supine as I understand this nice article which I assume you have copied from some source (?). He was always essentially sitting upright, whether sitting facing forward or facing backward, and so the force of acceleration and the later force of deceleration were imposed at 90 degrees to his longitudinal axis. As I understand things, the aorta would be least susceptible to a tear in those postures as opposed to a prone position, for example, with the forces applied in line with the long axis of the body. Some of this has to do with the way the aorta is positioned and "suspended" in the chest just where it turns from an upward course out of the heart to a course that runs straight down south toward your pelvis. I will bet that they did not put him in the sled prone or supine for just that reason (?). That having been said, it doesn't detract from the incredible bravery of the man or the great knowledge base they accumulated in New Mexico using the sled--high performance aircraft operators were greatly aided by the changes in equipment thereafter. One other issue bears repeating. The extremely high G loads can be tolerated but what is germane is the time course over which the force is imposed. I doubt very seriously that the effects of 15 Gs on a human are the same for this force applied over 0.1 second vs. over 2 seconds.

I have been taught that the danger of a parachute "opening all at once" is specifically tied to this issue--there needs to be a little passage of time (2 seconds ?) as the force of the deceleration distributes into the harness and thus into the jumper's body. Since the body is not a solid block of wood, but a hollow structure with all sorts of delicate internal parts "hanging" from various suspension points, the distribution of force into all of those parts during acceleration or deceleration becomes a fascinating issue. To cite an actual case--a former special forces operator, a parachutist, was sitting in his pickup in front of my hospital one night and was rear-ended by some moron. I ended up operating on him (the special forces guy, not the moron) for an interesting lesion--the force of the acceleration and then deceleration in the accident had avulsed (i.e. torn off) some of the arteries and veins in the mesentery of his small intestine. This happened because the truck was accelerated, his body was accelerated with it, and then his body decelerated by hitting the steering wheel when his foot hit the brake pedal. Inside his belly, the small intestine went through the same cycle but the direction of the deceleration force was in just the right orientation to put a load on the small blood vessels all at once when the body stopped but the intestine "kept going" for a fraction of a second. A freak accident I am sure. I was not a parachutist at the time but I remember thinking Holy Shit--he had a career in the military doing all sorts of things he cannot talk about, and this gets him. He did fine. He actually ran off with, and later married, one of the operating room nurses at the hospital.

After the canopy is open, every part of the body is moving at the same vertical speed. The catch here is that all of those parts have to somehow get from terminal velocity to that same vertical speed under canopy without much difference in the relative speeds of the many parts during the fast-to-slow transition. "Everything is attached to everything else" in the human body. Newton's laws of motion come into play here as every dude sitting around a DZ can tell you. I am sure many of the dudes will be writing in to explain this for me if they are having wind or cloud problems this afternoon. Each of us has to decide which body parts would be most treasured if something had to take most the hit in a huge opening shock. At my age, I could not care less if my external genitalia were harmed, but I am real concerned about my eyes, my cardiac equipment and my spinal cord. Unfortunately we don't get to designate an organ to be the sponge for soaking up the excess force.

We are all darn lucky that, having been designed to walk upright and not fly, we two-legged mammals can tolerate nicely the deceleration forces in modern parachute operations.

JTL

[jtlmd 0]

Thanks for your comments.

I am telling you that probably the most common fallacy that is encountered in talking about "the risk of skydiving" has to be that many people use the wrong reference basis when they are doing the mental "what if" experiments. The issue is a RELATIVE RISK of activities and the basis is never zero risk. Riding in a golf cart at a mountain golf course is not zero risk. Even staying home and doing nothing is not zero risk.

[nicknitro71 0]

Quote

as I understand this nice article which I assume you have copied from some source (?).

Have you noticed the quote?

The whole point of the experiment was to prove that the human body can take very high G loads (`45) if for a short period of time. You're right stating that 15Gs do not have the same effect if experienced for different times. Hence the amount of damage to the human body is proportional to the rate of onset of the acceleration. If that rate exceeds 300G/sec chances are there will be some damage.

For instance when jet pilots eject they experience G loads between 12-20. Usually spinal cord and lumbar or thoracic vertebrae burst fracture don't occur if the load is less than 25G but sometimes things go wrong and pilots end up 3" shorter

They can also experience injuries due to the wind blast (retinal and conjunctival hemorrhages for the most part) and due to the rapid deceleration from the canopy inflation (usually cervical fracture).

Ejecting from a jet, although it seems like a lot of fun, could have serious consequences. Maverick going back up few days later of Goose death is just BS.

It's my understanding that if you experience two ejections you are grounded for life, maybe some airforce or navy guys can add something.

Memento Audere Semper

903

[MisConFit8 0]

I have one question ... isn't the body's response to extended periods of Cortisol release - weight gain? Does that mean that while you are still "stressin'" on the way up for your first 200 jumps, you are releasing repetitive amounts of Cortisol; therefore leading in weight gain?

I have some historical endocrine issues that assist in arising this curiosity when reading what jtlmd had to say.
Thanks

"Dream as if you'll live forever, and live as if you'll die tomorrow." James Dean

[jtlmd 0]

I am not an endocrinologist so I would not venture an answer. I would guess that short periods of cortisol "surge" don't hurt anybody.