MEDICAL FAQs

QUESTION

ANSWER

He's right.

It's all a question of nitrogen absorption. Basically any exercise, either before, during or immediately after is going to affect the rate your tissues absorb and release the nitrogen gained from your blood. If you've been for a run just before a dive then your heart will still be pounding pushing the blood round your body at an accelerated rate, and increasing the amount of N2 in your tissues. Tables won't really count after that as you will have a shed load more N2 on board than predicted by these. This all basically ends up with DCS or the increased risk of it if you can't get rid of the N2 in your ascent or deco stops.

I must say that I admire your dedication to aerobic fitness even when on holiday as most divers seem to use their time away as an excuse to let their hair down and go for a broke despite that nasty beer in the Camel Bar. I include myself here if anybody thinks I'm being too sanctimonious. But if its aerobic exercise you need when you are away then sadly diving will never offer that. The best thing I suggest is a workout to perhaps a cable channel in the late evening in your hotel room. Make sure you draw the curtains though as there's no point embarrassing the rest of us still in the bar.

QUESTION

ANSWER

There's been some evidence to show that exercising before diving can increase bubble formation and thus decompression sickness. There has to be a degree of moderation like in most things and also if you are fit, what you call a little jog may seem like a marathon to others.

I suggest that you refrain from anything you would call exercise on the morning of a dive. There is also evidence that shows that exercise after a dive can increase chances of developing a skin bend and that you should leave anything that increases your heart rate and makes you sweat for at least 3 hours after a dive.

QUESTION

ANSWER

I hate you. Everything I should be. A non-smoker and fit as a butcher's dog. I could be really mean here and say you must get back on the tabs and lard out, to make me feel better, but, no. Well done.

The issues of exercise around diving can be summed up easily. Anything, that increases on gassing, or decreases off gassing from various tissues after a dive, can contribute to a bend.

Imagine going for a dive straight after a work out, muscles still screaming for oxygen and heart pounding. Or your tissues quietly off gassing back in the hacienda, and you diverting all your blood to your quads, abs and traps as you pound away on the Nautilus. Get my drift. There is other evidence about exercise and cells releasing odd radicals done by NASA, but i'ts fairly theoretical at the moment.

I suggest that if you want to dive, give the gym a miss for the day. You won't lose fitness as you seem to inhabit the place every other day of the week.

QUESTION

ANSWER

Good question. These days kids are ballooning in weight, gyms are big business and everyone is being admonished from all sides for not doing enough exercise. Diving can be a physically demanding sport: those tanks don't carry themselves, and unexpected currents can put a sudden strain on the fittest of finners. As you say though, there are concerns that exercise can increase the chance of DCI. How to balance the two?

Like a good gag, it's all in the timing. Vigorous exercise is thought to produce micronuclei, ie. the beginnings of very tiny bubbles, due to blood being agitated and warmed, and shearing of tissues with movement. These micronuclei can turn into bigger bubbles or act as "seeds" around which bubbles can form. And more bubbles means a higher risk of DCI. Luckily, about 98% of micronuclei vanish within 6 hours, so the advice is to leave a minimum of 6 hours after exercising before diving. Another (admittedly preliminary) study has shown that exercise 24 hours prior to diving might actually reduce the chance of DCI – the cause of this phenomenon is being investigated. So a workout 24 hours beforehand might be protective, but you should reduce the duration and intensity of any exercise closer to a dive, and avoid any from 6 hours before a dive. The other aspect is dehydration – remember to tank up on fluids too.

During a dive, the idea is to minimise your inert gas absorption – flapping around like an untrained seal will increase your nitrogen uptake and make bends more likely. On the ascent, however, there is now good evidence that light exercise will accelerate off-gassing, and can therefore reduce DCI risk. By light I mean leisurely finning, rather than hanging motionless on the shot line. Heavy exercise is more likely to produce more bubbles though, as explained above, so don't start any 200m races with your buddy at the safety stop.

What about after a dive? The same suggestions apply: strenuous gym sessions could cause more micronuclei to form, and gas might be liberated from muscles as the blood flow to them increases. Any post-dive workout should be gentle and at least 6 hours after the dive to allow sufficient time for micronuclei to disappear.

QUESTION

ANSWER

I’m still trying to visualise what squatting up and down on the doctor’s deck must have involved… probably best left to the imagination. This is a good illustration of the wide variability of “exercise testing” carried out in dive resorts. Anything from squat thrusts to step tests to odd gyrations on rickety chairs seems to suffice. In these enlightened days there is a lot of discussion about what sort of exercise test is best, or in fact whether a test is necessary at all. For PADI recreational divers, the standard 200m swim test and 10 minute water tread (yawn) are probably sufficient. For those in the commercial sector (including PADI instructors), more stringent rules apply. In the UK, the governing body, the HSE, state that “there is no ideal single exercise test to measure aerobic and physical demands and the capacity required for all the possible combinations of work such as diving activities, equipment configuration, gas mixtures and emergencies.” So why do we do them?

The standard answer is to pick up those people with underlying heart disease, but in fact, exercise tests are notoriously bad at detecting this risk group. The real reason is simply to emphasise the fact that physical fitness is important for safe diving, particularly in those who have responsibility for other divers, often novices. It also enables some sort of comparison of fitness from year to year, acting as a motivating tool for health promotion. But there are ethical dilemmas here: there is a small but finite risk of a potentially life-threatening cardiovascular event in these tests, so is it right to expose someone to this if the test may not produce a useful result?

I digress from your question however. In your case, you would be best off seeing a diving doctor in the UK before you jet off to Sharm, who can assess your blood pressure and cardiovascular health in a properly controlled environment. Nebulous suggestions such as “keeping you clear of strenuous dives” are sometimes difficult to apply practically.

Incidentally, if you look at diving fatality statistics, very few could have been predicted from known medical conditions; most are accidental and involve inappropriate diving beyond the diver’s experience and training levels. So is there any point in having medicals at all? Lots of countries don’t require them, but lack of evidence means that this is actually a difficult one to answer or quantify. Food for thought though.

QUESTION

ANSWER

Much like the newspaper cryptic, what sounds like an easy question to answer, is anything but. Much depends on the type of diving, the weather and water conditions you are anticipating, past and present medical history, and many other factors. However, I can give you some pointers. Divers need to be aerobically fit, and strong enough to meet the normal rigours of diving, with sufficient reserve to deal with rare but exceptionally demanding situations, such as unexpected currents or equipment failures. Unfortunately, the relative ease with which exercise capacity can be improved in one's 20's does not carry over into the mid-50's, and age- related medical issues may make sudden crash gym workouts dangerous. As an ex-smoker, I'd recommend you get a pre-exercise assessment by your GP first.

Any form of cardiovascular exercise will help, so think about swimming, cycling or running. When training, the oft-used formula of calculating maximum heart rate, 220 - age, turns out to be somewhat inaccurate; you're better off getting a calculator and punching in 206.9 – (0.67 x age) for a closer estimate. Then try to keep your heart rate at 60-80% of this. At 56, your max heart rate works out at 169, so you want to be somewhere in the range 102 – 136 for maximum cardio bang for your buck. And do read on for some other pre-season tips.