How should we train? Is strength training for freediving a good idea? Are bigger muscles better or worse? Should we hit up the gym in the off season?
I have alluded to some of these questions in previous posts and newsletters. In my mind, there is no doubt that a well trained muscle performs better during freediving activities. Unless you are purely interested in statics, strength training will benefit you.
Muscles store both energy and oxygen, and a trained muscle can store more of both. But (there is always a but), it is difficult to load a muscle with oxygen, or rather, the oxygen carrying protein myoglobin. So instead I’ll show you how you can load it with energy, or rather, the phoshate molecule creatine phosphate.
This post was submitted by Luca Malaguti. Luca dove with a 3 mm suit in the cold water of the Pacific for the longest time. In this article he shares some tricks to stay warm.
The Canadian Pacific Northwest is a stunning place for scuba diving, freediving or snorkeling. It offers some of the cleanest waters in the world, fantastic underwater landscapes and unbelievable marine wildlife. The only issue for many people that wish to take part in these activities around Vancouver, the Gulf Islands or Victoria, is that for most of the year the water is quite cold.In the summertime, the Howe Sound can have surface water temperatures that range between 14 to 20 degrees Celsius. However, it’s always cold below the thermocline.
Rome wasn’t built in one day, you won’t be able to do the split tomorrow and you are not going to increase your breath hold by 3 minutes overnight.
You might have some freediving goals for yourself in 2018. Perhaps a CWT dive to 50 m, or a 7-minute breath hold. Chances are that you have already trained for over 20 hours to get there. But what if that training intensity doesn’t last throughout the year?
In this article you can read how to create a daily ritual to get you to your goals. You will achieve more by 15 minutes of training per day over the course of a year, than by training several hours per day for a few weeks. No matter what the goal. You also get a blueprint to design your own 15-minute daily ritual.
So you want to increase lung volume? There are several ways to do this, but you should probably start with becoming a better breather. That means, you should be able to fill up the entire volume of your lungs with a deep inhale before you actively start to do exercises that will increase lung volume.
Let me show you what I mean.
Active breathing vs. passive breathing
Most people go through life without taking active control of their breathing. The autonomous nervous system takes over the act of breathing if you don’t think about it, which means that you don’t have to think about it…
And that means that most of us never think about breathing.
The body responds to simple stimuli that will increase or decrease the breathing rate. For example, the breathing rate will increase if CO2 in the body increases or if the temperature decreases.
The body does not optimize each breath. If you are relatively untrained your inhales could be short and you may be using less than 75% of your vital capacity for each breath.
Optimizing the respiratory system is something we have to do by consciously using it. In other words, you need to become aware of your breathing, and consciously change the way you breathe.
Get your shoulders out of the way first
But first, let’s become somewhat aware of what our posture does to our breathing. The shoulders are only attached to the rest of the skeleton by the collar bone. Because of that, a substantial weight pushes down on the widest part of the rib cage: the weight of your shoulders and arms combined.
Don’t believe me? Then try this:
Stand up or sit up straight with your arms hanging down the side of your body. Breathe in as deep as you can.
Stand up or sit up straight with your hands on your hips and your elbows out. Breathe in as deep as you can.
If you noticed it was easier to breathe in that second time, you felt what I am talking about.If you did not you are either a blessed freak of nature or you are hardly using your upper intercostal muscles.
Funny side note. Opera singers have their arms wide and in front of them when they sing a strong note for a reason: it opens the chest.
In order to loosen up the shoulders:
Stretch arms out overhead, and in a wide arc let the left arm come underneath the right. Clasp your hands together (as best you can). Hold for one minute and then switch sides. This is part of the yoga ‘eagle pose‘.
Put your hands on your glutes, fingers pointing down look forward and up so that your spine is slightly arced back. Try to gently move the elbows closer to each other behind your back. You should feel a stretch in your front shoulders.
This simple preparation goes a long way. It won’t help you actively increase lung volume yet but it will allow you to get the most out of your breathing later. There are many more ways to open the chest with stretches but let’s move on to the actual breathing.
Three simple breathing exercises
One of the best ways to actively increase your lung volume is by limiting the flow of air through your throat and training yourself to keep that flow constant. Try it:
Keep one hand on your belly, and one on your chest.
Inhale slowly and constrict your throat slightly so that your inhale is audible (another way to inhale audibly is to make a whistling sound with the lips).
Focus on the belly first. Your lower hand should be moving outward.
Keep the sound of your breath constant.
Once it becomes difficult to keep that lower hand moving out, your chest should start to inflate. Try to keep the lower hand outwards as much as you can and continue with inflating the chest. Exhale slowly and repeat.
Alternate nostril breathing
Alternate nostril breathing is a similar exercise but additionally clears your nasal cavities. The exercise is fairly straightforward.
Sit with a straight back and close your right nostril with your right thumb. Inhale fully and slowly through the left nostril.
At the top of your inhale, pause and release your right thumb. Close the left nostril with the ring finger of the same hand.
Exhale fully and slowly through the right nostril, and then inhale fully and slowly. Pause and close the right nostril.
End range of motion exercise
When I was recovering from a rotator cuff injury I was given an exercise to work on the power and strength at the end of my range of motion. It was an easy exercise and I realized it could be done with intercostal muscles as well. I believe that out of the three exercises here this one will give you the fastest results.
Sit with a straight back
Put your hand on your hips (so the shoulders don’t weigh down the ribcage)
Inhale slowly and fully
Once you are at the max inhale, use your diaphragm and intercostals to keep it at the max.
Do not lock the throat or mouth. The air should be able to move freely from your mouth into your lungs, and you need to use your respiratory muscles to keep it in the lungs
Exhale after 10 seconds
repeat 5 times
How long should you exercise? Just remember that five minutes per day beats one hour once per month.
Forget about packing for now
Packing, or over-inflation of the lungs, is a simple tool that can increase lung volume directly and dramatically. However, because it is a passive tool it works against the resistance of the rib cage. The over-pressure in the lungs has caused embolisms resulting in partial paralysis, and a range of other serious injuries in freedivers on land and in the pool. It should be avoided for anything but dives that are well below residual volume. From AIDA’s Facebook announcements:
“Recently several packing related incidents with lung damage and/or transient neurological symptoms have been reported. Keep in mind that lung packing and pack stretching are very advanced techniques that may lead to serious medical conditions and even death. Packing should be performed with care and is something that we do not recommend in the AIDA education program”
Packing alone is not worth your time. Breathing exercises are always good, both to increase lung volume and better breathing overall. Once you are going to push the numbers during very deep dives packing is something you may want to consider. If you are interested in more info, Walter Johnson has a great article on packing on his website Freediving Solutions.
When and how many exercises should I do?
Great question. When considering how much time to put in any exercise remember that consistency and moderation are the long term winners. Five minutes per day will increase lung volume, but one hour on one day per month is not going to do much for you. The best time to do these exercises is right in the morning, so you can reap the benefits all day.
This post goes with a webinar that I gave on data collected with the Moxy Muscle oxygen monitor. In the webinar I test some specific exercises and try to speculate on myoglobin desaturation and training to increase myoglobin stores.
I want to use this post to give some extra thought to some keypoints, and to make the webinar a bit more understandable. But first, keep these things in mind:
The Moxy measures oxygen in the muscles. I put it on my left Vastus Lateralis (quadriceps).
The Moxy gives you one number for total SmO2 (muscle oxygen). This number is a weighted average of myoglobin and hemoglobin.
Everything I tested only relates to me and my (left) quad. The numbers will be different for you. The squats that work for me may not work for you. The apnea walks that don’t work for me may work for you.
On all the graphs in the presentation, the x axis = time in seconds. The left y axis is for heart rate, muscle oxygen and SaO2. The right y axis pertains to Thb and is a measure of blood flow to the muscles.
Ok now you can watch:
I used the Moxy to test a series of exercises. What do these exercises actually do?
For example, the apnea walks that I described here actually did not train my muscles to perform under hypoxia at all. The body has a fantastic set of feedback mechanisms in place to make sure that oxygen is delivered where it is needed, and without the vasoconstriction and blood shift during a dive that oxygen will go right into your muscles. Apnea walks debunked. Sorry everyone.
It didn’t matter whether I did them on an exhale or inhale. I think that apnea walks on an inhale probably don’t work for anyone. On an exhale, they may work for some people, but I doubt it.
What about holding your breath until contractions and then starting exercise? Same thing. The muscles actually never get hypoxic. In fact, even doing this with a more strenuous exercise like a wall sit the muscles never dipped below ~35 %.
Doing a wall sit or even one-leg stand with breath did not help either. You can do a wall sit until failure, but there will be plenty of oxygen in your quads. It’s not a lack of oxygen that causes your muscles to fail, it’s the accumulation of waste.
The only exercise that I found effective was a set of isometric squats with short recovery intervals, done after a forceful exhale. Using these squats and tinkering with the variables (length of recovery, initial static, and squat) I was able to consistently let SmO2 dip below 10%.
Now before you all start doing a 150 kg squat on breath hold, remember that if you do this with too much resistance you might simply be training for fast twitch muscle. If I focus on slow twitch muscle I try to stick to no higher than 30% of my personal max resistance.
How do you know this works? Are you increasing myoglobin in the muscles?
I don’t know if this works. But here is my rationale. In order to get the body to generate hemoglobin (red blood cells) you need to desaturate the blood of oxygen. This is why being at altitude increases your red blood cell count. The body will automatically create more red blood cells once it realizes it does not have enough of them to efficiently bring oxygen to where it is needed.
Along the same lines of logic, we need to desaturate myoglobin of oxygen in order to tell the body to create more of it. This happens naturally on some deeper or longer dives thanks to vasoconstriction and blood shift, but is hard to achieve when cross training.
I can’t promise you that by lowering SmO2 you will cause more myoglobin to be generated. I do think it is a sound hypothesis. Keep SaO2 high, and decrease SmO2. This is what naturally happens in our bodies during a dive, and one of the things to aim for during cross training.
The in-water method of training for myoglobin is called the Foundational Training and described in Eric Fattah’s book Holistic Freediving.
Is freediving an equal opportunity sport? Is participation different for men and women? What about the way freediving women are perceived on social media, or how they are represented?
We wondered about these questions, but cannot answer them from our own experience. Hence, we decided to ask five women in freediving: Jeanine Grasmeijer, Valentine Thomas, Sara Campbell, Tanya Streeter, and Radziah Radzi.
This read will take you about 10 – 15 minutes.
First things first: introductions
Is freediving an equal opportunity sport?
Jeanine: It is definitely an equal opportunity sport in the Netherlands. If anything women are encouraged to take part in freediving. Why we don’t have half as many female athletes as male, I don’t know. It’s not like soccer, which is still considered a very masculine sport. This can be a pretty big barrier for girls to start and/or continue, society basically discourages them from it. But freediving is both: Very masculine because of it’s extreme nature and very feminine in it’s gracefulness and spirituality. So it fits both parties.
But since you ask, I’ll whine a bit. As in most sports men will always be better, when you look at the numbers. They always go deeper, further and longer. So their performances will always be seen as the ultimate performance, the maximum of human capability. It’s only when a woman exceeds a man’s performance that she rises to his level. As was the case with Natalia Molchanova (all hail the Queen!)
I’ve heard say that women should physically be able to reach the same depths as men and that it’s a matter of training. I don’t believe this. It’s a mental sport yes, but 20% is still physical. As far as I know there are no physical sports where women’s world records consistently equal or exceed men’s. Men and women are built different. So I believe women should sooner be seen as exceptional in their own right. This is for all sports, not just freediving.
Valentine: I am more into spearfishing than into ‘pure’ freediving, but I think it is. The women in my freediving classes sometimes have a bigger mental barrier, but once they go past that they are amazing!
Sara Campbell: Absolutely! Mainly because it’s not a professional sport yet so it’s open to everyone to get involved and do their best. As and when (and if) it becomes more professional, with government subsidies and more serious and broader sponsorship offers, then we might see things change. But for now, each athlete creates his or her own opportunities and can embrace equally all the the sport and the ocean has to offer.
However, I do recognize that for people living in Europe, or away from opportunities for regular, quality depth training, it can be challenging and frustrating. To have depth training limited to a few short weeks a year, and still be relaxed with a goal of improving a PB or competing at a big event, such as the worlds, is almost asking the impossible. But this applies to all freedivers, not just women.
Radziah: I think it is equal opportunity for men and women. Actually, if we look into competitive freediving, our late freediving queen Natalia has held world records that were higher than the contemporaneous men’s records! Perhaps, because it is such a mental sport, maybe women have the upper hand haha! Just kidding ;)… In Malaysia, some of the women’s national records are higher than the men’s.
Unfortunately, because it is a sport without much sponsorship, it is not equal opportunity for people in different countries. Naturally, if you live in a richer country with access to deep and warm water you will have much more opportunity than if you live in a landlocked developing country. Unless you can pay for international airfare, competition fees, and the cost of training you won’t be able to compete on the same level.
Tanya: I do believe freediving is an equal opportunity sport! The playing field is pretty level!
Are there (or have there been) any barriers for your participation in the sport?
Jeanine Grasmeijer: Not when it comes to gender inequality. The barriers I’ve faced were either financial or personal.
Tanya Streeter: There have been no barriers for me, but I did retire from competition before having children, by choice.
Sara Campbell: Living in Dahab I never experienced any barriers for participation. The limitations of the sport as it is right now in terms of sponsorship, creates barriers for athletes to open up opportunities for more time training depth. I think however, that this year has seen a break-through of that paradigm – the invention of the Dive-Eye underwater camera at the worlds will hopefully break the vicious circle that athletes have found themselves in; it is not possibly to convince big serious sponsors to get involved either at the event or personal level, until there is serious, mainstream coverage for them to realize return on their investment. The Dive-Eye will hopefully be the break in that cycle that athletes and event organizers have been waiting for.
Valentine Thomas: My brain haha. Freediving is such a mental sport and sometimes my mind plays tricks on me, it tells me to go back up and that I’m out of air when I’m not. I used to suffer from a lot of anxiety when I was younger, so this sport helped me overcome that. When you manage to let go, it is the best feeling in the world. The second barrier has been my ego. There is a competitive side of this sport and sometimes it makes you forget about what is truly important. We tend to forget that it is essentially a team sport!
Radziah Radzi: No, there have not been any barrier so far for me to participate in the sport either competitively or just for leisure.
But there are some challenges for me as a female Muslim freediver.
I consciously choose to sacrifice performance to adhere to my religion. It is not just about the headcover, but also about wearing a loose outfit rather than a snugly fitting wetsuit. I still wear a wetsuit but I do cover it with a rashguard, tennis skirt and long pants. Of course this is a personal choice, and everyone should decide for themselves. To other Muslim freediving women I just want to share these:
If you choose to wear draggy clothes outside your wetsuit, realize and embrace the fact that you are losing performance (only slightly).
Come to terms with the sacrifice you choose to make to adhere to our faith. If you don’t glide as far per stroke as someone not wearing a loose-fitting rashguard, it’s okay, and you can try to compensate another way to swim the same distance.
What do you think of the way women who freedive are represented (or the way you represent yourself) on social media?
Jeanine Grasmeijer: People choose how they present themselves in photos and on social media, it’s in their own hands. Someone once told me: ‘If you want followers as a girl, you need to show some skin’. This is a fact and you can use it to your advantage. There is no doubt in my mind that the most popular freediving women on social media are very fit and feminine and not afraid to show it. But it’s certainly not specific for freediving and it’s not the only way. You can also be funny, inspirational, motivational, educational, etc. Either way, I think anyone who has the courage to put himself out into the superficial world of social media and inspire people, is amazing.
Valentine Thomas: A lot of women in freediving are naturally sexy and fit. I think it is admirable to be comfortable with your body and who you are. That doesn’t mean posting pictures of you bending over, it just means that you acknowledge you can be a sexy woman. I believe confidence is sexy. Some men like to complain that women get more popularity just because they show bikini pictures. The reality is that it is still a men’s world, and women are at a disadvantage for a lot of things in society, so I don’t think using our looks to empower ourselves is a bad thing. And in the end, we should all get together and have each other’s back.
As a woman, a lot of people accused me of posing with fish that weren’t mine. I did this once when I started out, on my second time spearfishing. Initially I just didn’t think it mattered, but I quickly realized that if you are a woman, you have to achieve double if you want credibility. But I don’t want to sound pessimistic. In the end it was all the bad talk that pushed me to do a freediving course and made me push my limits as a diver.
Sara Campbell: I think it’s great to see more and more women approaching and breaking through the 100m ‘glass ceiling’. Many of them are doing really well with self-promotion, but it varies according to their own expertise, contacts and drive and desire. Ideally, with sponsorship, each athlete could employ a social media/brand manager to handle their online presence to really promote themselves and maximize opportunities for both promotion and earning, through public speaking and media appearances. Currently, it’s ad hoc, according to the individual athlete’s own abilities, budget and feelings.
As for my personal marketing, I’ve moved away from promoting myself as an athlete and am now working to promote my teachings, my school, Discover Your Depths, and my online training program ‘Yoga for Freediving‘. As I’m now working in the sport, I have a dedicated social media manager, as well as graphic designer, website manager etc. But this is beyond the reach of most athletes, and some coaches. It’s tough, I struggled, and still do. And of course the more popular the sport comes, the busier the market and the harder each of us has to work to be seen and heard. Big diving results, such as national and world records are invaluable for both men and women when it comes to promotion because the world and the media loves to benchmark us, but of course they are not the be all and end all when it comes to the greater experience of the sport – that is something between the athlete/diver and the ocean itself.
Tanya Streeter: I think the freediving world is currently full of women representing themselves and the sport responsibly. And I think they bring a softer approach to a fiercely competitive sport, which is great.
Radziah Radzi: I think that the women in freediving are represented well, fairly and with respect of their capabilities as athletes. If we compare how men and women are represented in social media, we can’t deny the fact that women’s physical beauty, attractiveness, and sex appeal do play a role in their “popularity”. However, for the athletes, I don’t think this overshadows their freediving ability, after all they are all well performing freedivers and deserve the recognition.
I do remember a recent post about a female freediver breaking a National Record for Static (I don’t remember her nationality though). Her post appeared in the AIDA International FB page. So, naturally people congratulated her. However, one guy thought it was funny to comment something along these lines: “You know she is good gf/wife material as she can keep her mouth shut for that long”. Of course a lot of people expressed their distaste (guys included). It was very distasteful, and comments like these belittle her fantastic performance for no reason.
There are certain recurring themes in social media. Some female freedivers identify themselves as mermaids, spearfishing women, underwater models, freediving instructors or experts, freediver yogis, vegan/vegetarian/clean eating freedivers, while other freedivers just share their activities; training or excursions on social media. I do not have any issue with this. What I do have an issue with is posts of over exposing butt and cleavage shots. I think some of the social media accounts that have these posts are run by men, but even so the women are legit female freedivers, and maybe they do spearfish too. Unfortunately, most of the photos just show them wearing sexy bikinis, and holding a big fish in a seductive pose! Sometimes they do have underwater shots while wearing a very sexy bikini and holding a spearfishing gun but many times these are shots from (the) “behind”. It could just be my culture, or maybe I am too old-school, but I don’t find those are tasteful photos. Though maybe they do dress that way while spearfishing and maybe they are really proud of the big fish they caught, but I can’t help but cringe while thinking of how those photos are viewed by men. And I think it only portrays female spearfishers as seductive and sexy, not as great spearfishers. Not everybody does this of course. I think these shots are mostly on spearfishing social media accounts for or by men, which I unfollow instantly.
Is there anything else you’d like to share?
Jeanine Grasmeijer: Yes! I do. There is something that I noticed during the AIDA Depth World Championships in Roatan: The men and women’s performances were separated and what a difference it made. Because they were separate the women’s competition was much more exciting. A 90-m dive for a man may not mean a medal while that could be gold for a woman This is what I was talking about before. Competing at the same time as men doesn’t do justice to the performances of women.I think separating the men’s and women’s dives should be standard procedure, after all, they don’t dive for the same medals.
Radziah Radzi: I just would like to share something about the experiences I had as a Muslim freediver. I need to plan a little different from other divers. For example, changing attire is something that needs to be planned for someone who can’t show any skin. I have gone, fully prepared in my wetsuit, from hotel room to dive spot and vice versa to avoid showing any skin.
When I went to Adam Stern’s DeepWeek training in Bali we sometimes had a classroom session in the dive centre before the dive, so I would wear my wetsuit in the classroom session. “Are you not hot?”, is a normal question. I wear just a 1.5 mm wetsuit and I don’t have any problems with heat but I do need to plan ahead of time to avoid changing trouble.
There can also be a bit of social awkwardness because different cultures mix. For example, I try to adhere to the rule of not touching men that are not of blood relation to me. I struggle between choosing not to be rude versus strictly adhering to that rule.
Some people from western countries are not aware about this and they will offer a hug or shake hands. I sometimes accept the hand shake but I will try not to hug. Every now and then someone won’t give me a choice though, and I am too slow to say “urm.. sorry I can’t hug you” haha.
On another note, some Muslim female freedivers from abroad have also asked me for advice, on how do I freedive while protecting my aurat (female muslims’ parts that have to be guarded from non-family males’ eyes). They ask questions like what kind of head cover I use, how do I keep it on while freediving and doing water activities and what are good swimming attires for Muslimah (female Muslim). This makes me feel that I have a purpose that even while I’m not a big performer, athlete or instructor, I can still contribute.
Join in on the conversation with the comments below!
We at Freedive Wire are excited to announce Airpockets. Airpockets is a map that allows you to share and find places you love to dive, as well courses, workshops and more.
Airpockets: share places you love to dive,
find places you’ll love diving
Instead of having to look through Scuba Dive listings, you’ll be able to plan using the recommendations of freedivers like yourself. Where are the waters warm, safe and full of life? Where are the dive centers, courses, and competitions? You’ll be able to find it on Airpockets.
It is also a place where you can let others know of the state of reefs, pollution and marine debris.
Now is your chance to get in touch! Let us know in the comments or by e-mail to firstname.lastname@example.org what you would like to see on Airpockets. What can Airpockets do for you and how would you like to use it?
The MOXY is a muscle oxygen sensor that can measure the saturation of hemoglobin and myoglobin of for example your quads.
Do you think your apnea walks are effective?
They might be. You can practice apnea walking with an oximeter, but it is hard to know exactly what is going on in the muscles. For some training you don’t need the oxygen in the muscles to drop, and for other training it needs to drop as much as possible.
Now, the guesswork is over.
Using a MOXY muscle oxygen sensor it is possible to measure the oxygen content in the muscles. You can strap the MOXY to your quad, biceps, or any other muscle to gauge the level of oxygen during exercise.
I have tested a set of exercises, including apnea walking, apnea squats, and bicycle interval training using the MOXY and will be sharing my results during a free webinar. The webinar will start at 12 noon CST, Tuesday December 12th, and run until about 12.45. There will be ample time for questions.
A study that has recently gone to press (Bilaut et al., in press) suggests that elite freediving may cause mild, but persistent short term memory loss. The study subjected elite freedivers (>6 min static breath hold), novice freedivers (>4 min static breath hold) and a control group to specific psychological tests.
The time to complete the tests was positively correlated with freediving static performance. In simple words this suggests that a better breath-hold means a slower brain.
Memory loss: reserved for the elite?
More specifically it was the elite breath hold divers that showed poorer performance on the tests. They took longer to complete the tests and made more mistakes. Novice freedivers and the control group showed normal performance.
The divers had not done any apnea prior to the test, nor had they had blackouts or LMCs in the week prior to the tests. Interestingly, there was no correlation between the total amount of blackouts and LMCs and the freedivers’ performance on the tests.
The authors speculate that the improved static time is not the cause of the poorer performance. Instead the static time is an indicator of the amount of hypoxia that the athletes face during training. More hypoxic intervals over the course of a diving career may lead to “mild, but persistent” memory loss.
The results are in contrast to a previous study by Ridgway and McFarland (2006). This study did not indicate long-term cognitive impairments in freedivers.
Billaut, F., Gueit, P., Faure, S., Costalat, G., Lemaître, F., Do elite breath-hold divers suffer from mild short-term memory impairments? (In press) Applied physiology, nutrition and metabolism
Ridgway and McFarland (2006). Apnea diving: long-term neurocognitive sequelae of repeated hypoxemia. The clinical neuropsychologist, 20:160-176
Staying warm while freediving is an art, especially in colder waters. During a normal 2-hour dive session you can easily lose more than 700 kcal just on heat loss, and if you lose heat too fast, your dive session will be cut short. Here I’ll share some surprising information about the performance of your wetsuit, and what you can do to stay warm in the water.
High heat loss despite a wetsuit
Conductive heat loss is something we can calculate. I am not going to try to bore you too much with the details, so here is the condensed story.
How much heat you lose through conductive heat transfer depends on four things. 1) The temperature difference of your skin and the water around you, 2) the thermal conductivity of your wetsuit, 3) the thickness of your wetsuit, and 4) the surface area of your body.
Wetsuits contain up to 94% nitrogen bubbles. The nitrogen is what prevents heat loss. The neoprene itself is actually quite conductive. Nitrogen compresses just like air, so at depth the suit becomes thinner and the overall heat conductivity increases.
Conductive heat transfer does not include water sloshing through your wetsuit. It is simply the amount of heat you lose if you were to be still, in still water.
Here are some interesting results based on conductive heat transfer alone:
A diver in a 3 mm suit and 25ºC (77ºF) water loses more heat than a diver in an 8 mm suit in 8ºC (46ºF) water
Heat loss at 20m is 4 – 5 times as high as at the surface
Heat loss at 40m is 7 – 8 times as high as at the surface
You will commonly lose at least 500 kcal of energy during a 2 hour dive session
At 40m depth, you can lose as much heat as a medium sized space heater generates (3000W), depending on the thickness of your wetsuit
Planning your dives so you stay warm
When I initially calculated the difference in heat loss between cold and warm water divers, I thought I made a mistake. How on earth can a diver in 25ºC water with a 3 mm lose as much heat as a diver in 8ºC water with an 8 mm suit? I know from experience that I can spend all day in warm water, and only a couple of hours in cold water.
The answer is that conductive heat transfer is not the full story. If the sun is directly above you (midday on the equator), it will supply the earth surface with >1000 W/m2 of heat. Those 25ºC waters we talked about earlier get much more direct sunlight. In a 3mm suit you only lose ~300 W at the surface, so the sun is instrumental in keeping you warm.
The sunlight hits regions farther from the equator such as Canada and New Zealand at an angle (see also: solar irradiance). Because of that, the sun supplies much less heat to the freedivers that call these waters home. In these regions, if you want to stay warm you need to plan your dives when the sun is high. That is not difficult in the summer, but in spring and fall you should try to dive in the afternoon, preferably on days without cloud cover. In the winter… may Poseidon be with you.
Wind and evaporation
Part of your body is above the surface during your breathe up. If the apparent air temperature (apparent air temperature takes into account wind chill) is lower than the water temperature, this will cause you to lose heat faster. The increase in heat loss can be as much as 10%, if you dive during a 0ºC day.
More important is the effect of evaporation. When you are above the surface, the water on your suit will evaporate. During evaporation, liquid water extracts heat from its surroundings. Unfortunately its surroundings are you, or rather, your suit. Evaporating water costs a lot of energy, and how cold you become during a dive might be directly proportional to the rate of evaporation. Wind will increase the rate of evaporation, and so does heat. If you have a smooth skin suit, there will be less water to evaporate than if you have a lined suit.
Diving style and getting in and out of your wetsuit
Diving style is another big part of staying warm. Our muscles are very inefficient, and about 80% of the energy we use is lost as heat. A more active diving style will keep you warm for longer. You will of course sacrifice some performance.
Lastly, what you do before you get in the water will also affect how warm you will be. Make sure to store your wetsuit in a warm(ish) place before a dive session, and try to stay warm while you change. I know one diver that changes in a bathing robe, and transports his wetsuit in a cooler with jugs of hot water. The jugs of hot water do excellent service as a post-dive shower.
Try to dive when the sun is high if you are far from the equator
Try to dive in low winds
Check the weather forecast and wear a (thicker) suit if there is cloud cover
Adjust your diving style to suit the water temperature. Long line diving sessions, deep targets and hangs are for the summertime
Stay horizontal at the surface, to allow your entire body to be heated by the sun (if there is some)
Try to stay as warm as you can before you get into the water
Diving with a smooth skin suit is warmer than diving with a lined suit of the same thickness