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Fitness and Diving - Exercise

Dr Jules Eden, dive medicine specialist and founder of e-med, answers divers' questions - as published in Sport Diver magazine:
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Q - How "fit" do I have to be to dive? I'm a rather out of shape blubbery 56 year old ex smoker who has rather inconceivably won a beginner's course in diving. I blame my addictive personality and too much time to do crosswords on the daily commute. Anyway, the dive operator has sent me a questionnaire and, although I can swim, I think I would be lying if I said I could perform moderate exercise of the type suggested easily. Any guidance on this would be much appreciated, as diving is something I have always wanted to do.

A - 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.

Q - Two years ago I passed my open water course in Cyprus. My age now is 55, I am 5'10" tall and weigh about 14 stone. Last year I went to Sharm el Sheikh for the superb diving I was told of.

Before undertaking the scuba review, I filled out a medical form telling them of my hiatus hernia plus the medical history of my father who suffered from angina and also had a heart bypass. Taking my age into consideration as well as those facts the dive centre decided to take me for a medical. At the medical my blood pressure and pulse were taken. Then I was asked to squat up and down for a minute whilst supporting myself on the doctor's deck with my hands, after doing this my blood pressure and pulse were taken again. I was not told the results of this test but the doctor informed the dive centre that I was alright to dive but to keep me clear of strenuous dives. I am now worried that I might be taking all my diving equipment out to Sharm again this year only to find that I will not be allowed to dive.

I have a treadmill at home which I am now using on a day to day basis plus I am combining this with a diet. As I have gadgets for taking my blood pressure and pulse at home I thought I could reconstruct the test I took in Sharm. But what I need to know from yourself is what should my blood pressure and pulse read to enable me to sail through the medical that I expect to take again this year.

A - 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.

Q - Hi. I'm a novice diver so I hope this question doesn't sound stupid. I'm a bit of an exercise freak and train with weights most days for at least 2 hours. Some of the lads at the gym are divers and were saying that you shouldn't exercise when you dive as it might trigger the bends. Is this true? I'm booked on a dive trip to Egypt next month and I chose the hotel because it's got a fantastic gym, although it's expensive. Can I still do my weights or should I bin it and do a liveaboard instead?

A - 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.

Q - Having given up smoking over four years ago, I've now caught the fitness bug in an effort to ease into my fortieth year.

I currently work out at the gym on average 6 days a week, completing three different programs formulated to complement diving / swimming. These programs are a balance between cardiovascular and weight training.

My question is, I generally dive on the rest day. Is this a safe option, (dives are up to 36 metres, these deeper dives are on Nitrox), or should I make it a total rest day and substitute a gym day for the diving?

A - 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.

Q - I wrote to you almost about a year ago about diving after a tympanoplasty, everything worked well, and the diving was great.

I have a general query. At home, I do quite a lot of exercise - running and swimming regularly at a reasonably vigorous level. I have found in the past, that when I go on a diving holiday, although I get tired by diving, I lose fitness, as there is no aerobic element. On my last holiday, I ran every morning, before my first dive - which certainly helped when I came back to the UK. However, my Godson, who is a BSAC diver, tells me that I shouldn't run before diving - is this true?

A - 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.

Q - While I've been diving (90%) in the UK for 2-3 years and I have recently qualified as PADI Rescue, I'm also active in a number of other sports, which means that I'm at least reasonably fit. However, I have heard contradicting views regarding running before or after diving. (Not with all the gear on of course)

The minimum distance is usually 4 miles and often cross country. So could you tell me if it's safe to run one or two hours before or after diving or even on the same day? I'm not suggesting running to the point of exhaustion and then diving but a reasonable pace that means you can still walk afterwards. I also understand the added importance of the need to ensure re-hydration after a run if diving is going to follow.

A - 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.

(other dive medical questions)



   


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