Thursday, June 10

Cycling Clots

Nowadays, a lot of us work in offices at desks. If you’re reading this, you probably ride your bike more than the average person. You ride when it’s cold, or when it’s hot. You may have concluded, as I have, that cycling is fun and safe. Unfortunately, around the edges of things there are risks, and it turns out that Deep Vein Thrombosis (DVT) may be one of those risks. And that risk isn’t as remote as you might imagine. I’ve seen estimates that 15% of unexpected sudden deaths may be linked to DVT and that 3-5% of airline passengers experience blood clotting. This risk isn’t unique to cycling – it will affect people engaging in almost any aerobic activity, but I can think of few that people engage in for such long periods of time at a stretch as cycling. When you put the pieces together, I think you’ll agree that it makes sense. How big a danger is DVT? I have no idea because I have no idea how many unexpected sudden deaths (other than collisions) cyclists experience, nor how their cycling affects their death rate compared to the general public. Even if a cyclist experiences a higher rate, he/she might still be better off due to general condition. Fortunately, most of the preventative steps are very simple.

Exercise as DVT Cause Agent
First, one of the benefits of cycling is that the aerobic activity lowers your blood pressure and resting pulse rate. Your heart doesn’t have to work as hard when you’re lounging around beside the pool. However, this also means that if you are sitting at a desk or in an economy class airline seat, the blood in your leg isn’t getting stirred up as much. A study, summarized here, discovered that 85% of DVT cases amongst airline passengers were experienced by athletic types. I would expect that to be greatest amongst the marathoners and cyclists. After all, swimmers that swim for hours per day are rare. Cyclists that cycle for hours per day are common. If you ride a bike and read this and think "I'm not athletic," think back to when you first started riding frequently and compare it to what you do now. You ARE athletic compared to similar people that do not ride.

Second, as for other long-distance athletic activities, fluid loss and balance can affect your body. Dehydration can cause your blood to thicken. Hmm, now we have blood sitting in the leg in a thickened condition. NOT a good combination.

It gets complicated and not only am I not a doctor, but I’ve never even played one on television. Among other things, temperature extremes can affect you as well. Apparently cold constricts your veins in your legs, and heat causes you to dehydrate quicker. I think I’d worry more about the latter, but then I live in North Texas and summer is upon us.

Finally, if you cycle regularly and over longer distances, you will inevitably experience all sorts of aches and pains along the way. Mostly these will appropriately be shaken off, but sometimes these may signal an early warning for you to go see a doctor. In the link I cited, here, the cyclist got leg pain and swelling, but shook it off. Myself, I got a couple of cramps in the same leg they eventually discovered the DVT on a few occasions. I noticed no swelling or other symptoms. I shall never know if those were leg cramps or early warning signals. DVT is typically mistaken as a simple cramp, even by doctors experiencing it. I think if you get a cramp once, don't worry about it. If you get them repeatedly in the same leg, go see a doctor.

Risk Reduction
Obviously, the simplest and cheapest thing you can do is avoid letting your legs laze around after exercise. If you are stuck on an airplane, do leg flex exercises during the course of the flight.

Next up is to follow the advice that Gail Spann gave us at LCI training – hydrate! I’ve never been a fanatical hydrater. Growing up in Seattle, it was only fairly recently that I learned that hydration was something other than how the grass stayed green. It was only last year that I started regularly carrying a water bottle for trips over 10 or so miles. BUT, water may not be the best solution. Taste your sweat and you’ll notice that it does not taste like bottled water. Sure enough, airline passengers that drink water experienced blood thickening during a flight not all that much differently than did those that didn't do anything. The  reference is here. ON THE OTHER HAND, those that took an isotonic beverage consisting of water, salt, and potassium did NOT experience blood thickening, and it appears they needed less trips to the restroom as well. You could approximate this effect with a sports drink, but those have a lot of sugar which you won't be needing while working in an office or sitting on an airplane. The simple solution is to find a way to ingest salt and potassium along with your water. I have found such supplements, but I'm not prepared to conclude they are strictly necessary, nor to dismiss them entirely. John Forester, in Effective Cycling, is clearly an advocate of "replace the salt you sweat" and has a good discussion on home made electrolitic solutions, though he is oriented towards the "during the ride" solution rather than for "keep your blood from clumping after you get there." Whether you go for a precise mix or not, according to Wikipedia's perspiration article, there is roughly 0.9g/L of sodium and 0.2g/L of potassium in sweat, along with minute quantities of all sorts of things. They also note that the  exact composition depends on all sorts of factors and can vary quite a bit. I wonder how sport drink manufacturers get their composition so precise. Might there be just a touch of marketing exaggeration involved? Anyway, bump up your salt intake along with your water when you ride.

It appears there may well be other simple things you can do to help. For example, herbs such as green tea appear to have a blood thinning aspect to them. Some advocate the use of aspirin, though medical opinions are divided on whether aspirin actually helps, despite being a thinning agent. Conveniently enough, the drug education brochure on the blood thinning drug I've been put on has a list of these things which I am now supposed to stay away from to avoid overthinning my blood. Green tea and aspirin are both on the list, along with things like garlic and ginkgo.

If I were not already on a blood thinning medication, let's assume a scenario where I'm a cyclist that rides enough that my resting heart rate is significantly lower than the general public that otherwise fit my age, weight, and gender profile. What do I do that might help myself if I'm going to work in an office for the day, or if I'm leaving on a long airplane flight?

Office for the Day
In this case, the main task is to replace the salt and fluid lost to sweat during the bike commute. John Forester recommends using unsweetened lemonade with added salt. In reality, it's probably simpler to toss a couple of grams of salt down and bump up the banana consumption a bit. A bit trickier is to figure out how much sweat you have produced. You can approximate that by a careful weighing plan (as a first approximation, most of the weight change is due to  water consumption or sweating as long as you haven't gone to the bathroom and it's fairly warm out). You can improve that approximation if you also estimate your water loss due to breathing, but we're quickly getting complicated here. Anyway, regardless, periodically get up from your desk and do simple leg exercises to keep the blood from solidifying. Basically, I've got six months to get this one dialed in. Luckily, as your commute gets shorter and colder, this gets simpler. In my own case, I need to determine the right amount of water and electrolytes to consume when it is 60F out or 105F out. Fortunately, the results really only need to be in the right general ballpark. If I  can find a way to summarize all this in a way it might be coherent, I'll post it, but such a post will not occur in the near future - I've got six months to figure this out and only one shot to get it right. If anyone has a good source for this, I'd be eternally grateful, as I could move up to an early "trust but verify" stage. I suspect, however, that the most we might hope for is a good "here's how you determine your profile now."

Airplane Flight
In this case, in addition to the exercises, there are several added steps I'd take. First off, it probably makes sense to get a sugar-free isotonic powder to bring along. That will not be available on board. Then order water and consume the powder along with bottled water as the flight progresses. I hear one cup per hour is a good consumption rate. Taken prior to the flight, an aspirin will thin my blood a bit. Opinions are divided on how much, if any, good this does, but aspirin is readily available and will help keep the blood thinner. I'd put it into the "might help and won't hurt"category. In addition, I'd probably order a green tea at the local coffee concession, rather than the coffee I might have had otherwise.


cafiend said...

My biggest hazard when I had an office job was falling asleep at my desk. I guess I'm fortunate now that I spend most work days on my feet. I may get varicose veins, but I won't clot.

Khal said...

I fidget constantly, esp. my legs. Wonder if that helps against DVT.

Glad you are OK.

cycler said...

Good post, I'm going to forward it to a couple of friends.
Fortunately potassium and sodium are water soluble so it's really hard to overdose on them.
Although my ride is so short (5-6 miles depending on which route I take) that I don't think dehydration from the ride is a major issue, (and I hardly qualify as an endurance athlete these days..) I have been trying to make a habit of always having a big glass of water right after I get into work. I elevate my feet at my desk, but I probably should move my legs more.

John Romeo Alpha said...

Even on a relatively short commute avg. of 7 miles each way, I am careful to hydrate in Phoenix, because as hot and dry as it is here you lose a lot of water fast, and more than you think. Since this is somewhat of a medically oriented discussion, I don't mind sharing that urination or lack thereof is the indicator I use. When hiking or biking if there's not enough water in you to make you go a normal amount, with normal characteristics, you're probably dehydrated and need to drink more.

Steve A said...

cafiend - falling asleep at the desk is best if the feet are elevated. The desk would be a good height.

Khal - I shall keep my eyes open for any research into fidgeting but I fear you may want to do a bit of leg flexing just to be safe.

Cycler - if your friends are interested, there is also a fair bit of info on the cycling forums, but it isn't as concentrated as in the links in my post.

JRA - remember it's more than just water. You are very right that you can lose a lot of water fast when it gets hot. Even more than you notice if the humidity is low.

Velouria said...

I cycle a lot and fly a lot, so this holds an immediate relevance for me and thank you for such a detailed and thorough article. It will take me some time to think this over and weight the seriousness of it.

But here are some things I can say about salt and potassium intake, from the pov of a frequent flyer:
. Most airlines serve sparkling mineral water. Drink that instead of regular water.
. Most airlines serve tomato juice. Drink that too.
. Do not drink alcohol in flight, ever.
. Bring a banana or two. Eat little pieces of it during the flight.
. Unless there is a reason you should not, take Ibuprofen before take-off.

That should keep the levels pretty stable.

Big Oak said...

Steve - first off, I'm glad you are OK. Second, thanks for sharing the information about DVT. I thought that all of the cycling miles I cover provide so many cardiovascular benefits that I am immune to most anything vein-related. But alas, I work mostly in an office, and I cycle many miles for long periods of time. And occasionally I fly. I'm going to pay more attention to my activity level in the office, and I'm going to keep hydrated better.

Steve A said...

I thought as Big Oak. I guess it is the flip side of doing stuff that provides otherwise overwhelming health benefits.

Jon said...

Glad you are okay, too. I've suffered from some pretty bad episodes of leg-cramping, through the years. Maybe I'll mention it to the doc, next time I'm there...

Hugh Greenough said...

Hey Steve,
I`m Glad to hear you are OK and back on your bike. I have come to the conclusion that life is a fatal condition. So I`m gonna try not to worry about it. I recently had to change professions due to health issues. So now I work on bikes every day. I wish I had done this years ago. I`ve never enjoyed working this much!

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