Theory hangs by a thread

Bungee jumping

In the process of showcasing our beautiful corner of the island to an inquisitive American, I happened upon a ponderous question which was posed to me in my mind. The two women of our party decided to take a leap of faith in plunging headlong into an abyss that is known as New Zealand tourism, also called the bungy jump. What ill might befall them? Is it really that safe?
Being a concerned physiotherapist mindful of the effect of physics on a loved one's body, and as a land-loving, quivering killjoy, it is firstly common sense to suggest that the bungy effect might have something to do with affecting the structures of the bungeteer's body. I always held an uninformed view that the rapid acceleration suddenly arrested, and then your body flung back from whence it came might influence spine health, or height. Out of sheer curiosity as to what my wife might manifest (although it seems one week on she is coping admirably) I set to the task of an informal literature review for my curiosity, and possibly yours.
Let's look at biochemistry and the brain. Surely with the fear, and the screaming, and the pseudo Olympic falling there must be some chemical markers of change? S-100B protein fits the bill here. It is a marker or evidence of traumatic brain injury and at a generous level of 0.22 micrograms in the normal cerebrum, it would seem a slam dunk to measure this after the "moderate sheer forces" of a bungy are applied to the plummeter's brain. Thankfully for Mrs Bell, the American and the bungy industry, the level is unchanged after the jump, so tick one in the positive box for the bungy fraternity.
Heart rate, blood pressure and cortisol (the stress hormone) all rise, but they all fall back to normal as expected after the jump. You then get a short burst of endorphin which induces the sense of euphoria. That's a good thing.
In their interesting article, How to Most Creatively Injure Yourself Bungee Jumping, Dartnell and Clifford go into the physics of the bungy jump and offer some solid advice which would minimise the chances of injury through rapid whiplash-type forces. As I watched my beloved plunge into the Waikato River, I noticed that because of her obvious reticence to get into a headlong position, her swan dive reaped rapid whipping of the upper body on the pivoting rope attached to her ankles. You've seen it before: a graceful falling human, horizontal, and tranquil. Then suddenly the cord goes taut and the body essentially oscillates rather violently. Perhaps this is discouraged at the departure platform, but who in their right mind on their first and maybe only jump, has the courage to dive like Louganis? Curiously watching first timers from the safety of land sweet land, they seem to exhibit a trait of crouching as if bringing their head closer to the earth by perhaps a life-saving metre. This then screws up the dive and over-rotates them, but several of these individuals happily shell out cash to go once or even twice more.
Our American friend, who you may recall from my last article, was to merely touch the water, however in an unfortunate error of calculation, received a dunking up to her knees. Remember by the time she is meeting water she is inverted, so that's about 75 per cent submerged. Dartnell and Clifford offer a warning in meeting a watery nadir: if you enter the water with your head bent back, you can force air powerfully into the sinuses and then into the eye socket. Also if miscalculations are made and the face hits the water at speed, it no longer feels like water, more something harder. As they creatively put it, tarmac.
One fascinating fact which I cannot understand is not marketed vigorously is the ability to fall at a greater acceleration than gravity, and that of a skydiver, because of the larger mass of the bungy falling with the diver. It is more noticeable with larger jumpers and higher jumps, as more mass is in the longer rope. It then transfers momentum to the jumper. Perhaps not noticeable to the jumper, but knowing you are defying nature would be pretty satisfying.
Fehrens, Stallkamp and Nicol from Munster, Germany evaluated the effect of bungy jumps on the lumbar spine. Their measurements indicated higher loads subjected to the vertebrae in question, but they suspect that muscle action of the core muscles would offer protection, although this was not measured in their study. Interestingly, the larger jumper experienced slower deceleration and so less violent recoil, so the lightweights may have a greater risk to forces applied to their spines. Jordan, who suffers from low back pain, reported no miracle cure after her jump, and I can confirm from her latest blog, she is still a low back pain statistic.
Some advocate tractional forces as therapy for the spinal column. I certainly have used them to good effect in relieving neck pain with referral down an arm. In the case of bungy as therapy, I have to say that it is too transient to offer a salve to a sore back, and also, at $170 a pop, it's cheaper to come to me!
Out of the dearth of internet-based evidence on a young "sport", I would say that the collected works show risk as in any thrill-seeking activity, but then this is part of the attraction, cheating death, getting a rush of endorphins. After observing the two subjects of the recent bungy jump, I would say no harm came to either, and instead, confidence had grown, and self-satisfaction was etched on the walls of their mental brag books. No study or treatise stated that bungy jumping should be halted immediately, and I think that at this point, as long as the risks are outlined and clearly spelled out, then it is ultimately up to the jumper to decide yes or no. I admire my wife immensely because she broke through a barrier that I am not comfortable in knocking over. The American gets kudos for throwing herself off of a huge precipice, in a strange, strange land.
We men stood back and admired.
¦Greg Bell is a physiotherapist practising at Bell Physiotherapy. www.bellphysio.co.nz