Preconditioning Techniques
Can we reduce the risk of decompression illness by effectively ‘warming up’ before a dive? Can pushing the boat out be a help – and riding it back fast, too? SIMON PRIDMORE examines the evidence
A little pre-dive exercise in Mozambique.
THIS MONTH’S TECHNIQUE article is adapted from a chapter in my book Scuba Physiological – Think You Know All About Scuba Medicine? Think Again!
The material in the book was derived from a three-year research project called PHYPODE (Physiology of Decompression), and one particularly interesting aspect studied by the researchers was preconditioning.
In other sports, preconditioning strategies such as warming up, passive heat maintenance and prior exercise are used to ensure that athletes perform as well as possible on game day. Why not apply the concept to scuba-diving?
Tiny gas bubbles in the bloodstream are thought to be the main cause of decompression illness (DCI), so the PHYPODE researchers looked at six preconditioning strategies that divers could deploy before a dive to reduce the quantity of tiny bubbles they produced, thus diminishing the risk of DCI and decompression stress in general.
Appeared in DIVER November 2018
1 ENDURANCE EXERCISE
If you are not yet a technical diver and you are contemplating going down this road, don’t be deterred by this. Embrace the feeling of being a novice again and be ready to learn.
Don’t let your ego get in the way. Understand the benefits of being pushed to a point where you feel you may break, or where you find yourself outside your comfort zone and in a situation with which you cannot deal. This just means that you have discovered weaknesses in your skills, mind-set, attitude or teamwork that you need to strengthen if you are to become a safe technical diver.
During the course, a good technical-diving instructor will create stressful situations that mimic real life emergencies. These events are artificial and the conditions are carefully controlled but they feel very real to the students, who are faced with life-threatening problems to solve.
Their failure provides the instructor with opportunities to make teaching points in circumstances in which the students are in the perfect state of mind to receive them.
When divers make mistakes, especially mistakes that they know could endanger their survival in real life, then the memory of the incident and the course of action they should have taken will become seared permanently into their minds. Also, the knowledge that they have encountered the problem in training and dealt with it successfully gives them confidence. This is another crucial weapon in their survival armoury.
2 HYDRATION
Drinking water before a dive is an easy way to reduce the risk of DCI. When you are well hydrated during a dive, you minimise the negative effects associated with post-dive dehydration.
The best way to stay well hydrated is to drink before you get thirsty, a little at a time, say a cup of water every 15-20 minutes. Drinking a large amount of water too fast will increase diuresis, the phenomenon that makes you want to pee, and will not hydrate your tissues.
One study found that loss of body fluids during a dive correlated with bubble count, as measured approximately one hour after surfacing: the greater the fluid loss, the higher the bubble count.
This suggests that it’s also important to rehydrate after a dive, especially if you’re doing more than one dive a day.
3 BREATHING
If you are not yet a technical diver and you are contemplating going down this road, don’t be deterred by this. Embrace the feeling of being a novice again and be ready to learn.
Don’t let your ego get in the way. Understand the benefits of being pushed to a point where you feel you may break, or where you find yourself outside your comfort zone and in a situation with which you cannot deal. This just means that you have discovered weaknesses in your skills, mind-set, attitude or teamwork that you need to strengthen if you are to become a safe technical diver.
During the course, a good technical-diving instructor will create stressful situations that mimic real life emergencies. These events are artificial and the conditions are carefully controlled but they feel very real to the students, who are faced with life-threatening problems to solve.
Their failure provides the instructor with opportunities to make teaching points in circumstances in which the students are in the perfect state of mind to receive them.
When divers make mistakes, especially mistakes that they know could endanger their survival in real life, then the memory of the incident and the course of action they should have taken will become seared permanently into their minds. Also, the knowledge that they have encountered the problem in training and dealt with it successfully gives them confidence. This is another crucial weapon in their survival armoury.
4 HEAT EXPOSURE
Researchers also conducted studies to determine what effect pre-dive heat exposure in a sauna would have on bubble formation after a dive.
Sixteen divers underwent a 30-minute infra-red dry sauna session, followed one hour later by a dry chamber dive to 30m for 25 minutes. Test results showed that the sauna exposure significantly decreased circulating bubbles after the dive, indicating that heat stress might give some degree of protection against bubble-induced injury from decompression.
5 VIBRATION
In the old days, combat divers and commercial divers would drive their boat fast out to the dive-site, but return to shore slowly post-dive in the belief that this strategy would reduce the risk of DCI.
The PHYPODE researchers checked the science and found that 30 minutes of whole-body vibration (such as you would receive in a speedboat driven fast) before
a dive could indeed reduce the quantity of bubbles produced after the dive.
6 BIOCHEMICALS
The vascular endothelium is an organ you probably didn’t know you had. It’s a single layer of cells that completely covers the inner surface of all the blood vessels in your body.
Several studies have shown that diving causes dysfunction of the vascular endothelium, but that taking antioxidants prior to diving can reduce the negative effects.
Preconditioning by taking an antioxidant such as vitamin C might reduce endothelial inflammation at depth and thus limit gas bubble formation.
Other recent studies discovered that eating 30g of dark chocolate two hours before a breath-hold freedive can prevent endothelial dysfunction.
The flavonoids in dark chocolate seem to be the key ingredients. They generate nitric oxide secretion and decrease platelet adhesion two hours after ingestion and this makes it less easy for bubbles to form and achieve stability.
The two-hour time frame is critical.
CONCLUSIONS
Further research is required into all of the effects described here, but a few things are clear:
- Divers should stay in good physical shape and maintain cardiovascular fitness.
- Pre-dive procedures can help reduce decompression stress. Some help maintain endothelial function. Others are better at reducing bubble production.
- Pre-dive oral hydration, exposure to heat, whole body vibration and oxygen breathing may represent relatively easy ways of reducing DCI risk.
- Chocolate is good for you. (But we all knew that!)
See the book for a more detailed summary of the PHYPODE findings on pre-conditioning and other aspects of diving science.
Read more from Simon Pridmore in:
Scuba Confidential – An Insider’s Guide to Becoming a Better Diver
Scuba Professional – Insights into Sport Diver Training & Operations
Scuba Fundamental – Start Diving the Right Way
Scuba Physiological – Think You Know All About Scuba Medicine? Think Again!
All are available on Amazon in a variety of formats.
