Monday, June 25, 2018

How much slower did you run at the 2018 Boston Marathon because of the weather?



After this year’s incredibly windy and rainy Boston Marathon, I was curious to find out how much slower the race was. I’ve published analyses of courses and conditions in the past, such as with the infamously hot Grandma’s Marathon in 2016, and when I (correctly!) predicted that the new course for the Twin Cities Mile would be too slow to see a sub-four mile in 2015. However, in both of these cases, the environmental factors affecting race times were amenable to precise scientific study: the physiological effects of heat on running performance are well-known and can be examined in a controlled environment; ditto for the effects of elevation.  I’ve even got standardized formulas that I use when analyzing a road race course for my coaching clients that can accurately predict how fast or how slow each mile of a marathon will be, based on its elevation gain and drop.

With this year’s Boston Marathon, the situation was different. The reason for the slow performances was a combination of stiff, gusting wind, cold temperatures, and rain.  Even the elites kept warm running gear on for most or all of the race.  None of these things can be easily studied in a rigorous way, and even if they could, it’d be impossible to actually measure how “exposed” the athletes in the race were to these environmental factors as a function of time.

Instead, I chose to use a statistical approach.  The Boston Marathon is run on the same course every year, so previous years can be used as a control.  I chose to use the results from three years of fairly good weather at the Boston Marathon: 2016, 2014, and 2013.  The temperature at the finish line when the men’s winner crossed the line was between 64 and 61 degrees F for all three of these years, and the weather was amenable to good performance. In contrast, 2017 was too hot for optimal marathon performance, and 2015 was rainy and windy as well.  I sampled the finish time for the 10th, 20th, 50th, 100th, 150th, 200th, 250th, 500th, and 1000th place finishers in each of these years, for both men and women, and compared these to the finish times for the same places for men and women in 2018.

It looked like an exponential decay curve best-describes the trends: the slower you ran, the less-affected your time was by the weather.  The actual data points are in black in the figure above; the exponential decay function that I fitted to the data is shown in color.  These plots allow you to quickly figure out how much slower you ran at Boston this year, compared to an equivalent performance on the same course in ideal conditions.

What about the race winners? Or, Why does the model cut off below 2:30 and 3:00?

Put simply, the statistical model collapses for times below these thresholds.  There just aren’t enough people who run this fast to get a consistent sample of the expected finish for a 2:20 marathon at Boston for men, or a 2:50 for women.  Truly elite performances start to get affected by things like the depth of the field and the tactics of how the race played out, so I didn’t want to extrapolate the model beyond its capabilities.

Why were slower runners not affected as severely by the weather?

From a purely physics-based perspective, this makes sense: air resistance is proportional to the square of your velocity, so a faster runner is going to be affected to a much greater extent by a stiff headwind. Slower runners may have had the benefit of more “shielding” from runners around them, leading to less of an effective headwind. The temperature in Boston also climbed steadily throughout the day, so slower runners had the benefit of warmer temperatures later in the race.

Why were women more severely affected by the weather?

I think this has to do with the temperature.  Women, as a whole, tend to be much smaller than men of an equivalent marathon time.  Picture a few male three hour marathoners that you know, and compare them to a few female three hour marathoners.  The women tend to be vastly smaller in terms of body mass and height.  One consequence is that they have much more surface area (i.e. skin area) relative to their body mass.  This is great if it's hot out, because you can radiate away heat much more effectively.  But when it's cold, the same effect works against you: your body temperature drops far faster in cold conditions because you lose so much heat.  This same effect may also explain why faster runners were more severely affected: they tend to be smaller than slower runners.

Better late than never right? Hopefully you found this little statistical exercise useful, and best of luck at your next marathon!

Saturday, April 7, 2018

What causes metatarsal stress fracture in runners, and how can you prevent it? Research-backed solutions


 Do you have a sharp, aching pain on the top of your foot when you run? If so, it might be a metatarsal stress fracture. The metatarsals are perhaps the most elegant bones in your lower body.

The five long, slender bones extend from your midfoot to your toe joints, and despite their small size, must handle a tremendous amount of stress when you run. As a result, the metatarsal bones are a common location for stress fracture in runners.

If you have pain on the top of your foot or pain in your forefoot, you’ll want to read on. We’ll dig into the scientific research on who gets metatarsal stress fractures, why they happen, how to prevent them, and how you can return to running as quickly as possible.

The basics: Metatarsal anatomy and symptoms of stress fracture



You have five metatarsal bones in your foot. Each one corresponds to a toe, and they are numbered, by convention, starting from the inside. So your first metatarsal corresponds to your big toe, and your fifth metatarsal corresponds to your pinky toe.

When you run, the metatarsals act like a lever, helping you to catapult your body forward by using your forefoot as a base of support. They’re a critical part of allowing your body to use your calf muscles and Achilles tendon to store and generate power when you run. This is why the metatarsals are longer and thicker than their upper-body analogy, the metacarpals on the hand.

Sunday, March 25, 2018

A long overdue update on Running Writings!


Hello to all readers! You’ve no doubt noticed an embarrassing lack of content on Running Writings in the last year or so, so I’m here to provide a brief update.  I’ve been surprised and pleased by the fact that despite this, RunningWritings continues to be quite popular in search results, and I’m still contacted rather frequently by runners around the world with questions and insights on training and injury. Sometime in the last year or so, RunningWritings hit two million views! To top it off, Modern Training and Physiology—which is coming up on its fifth anniversary of publication!—is perennially popular on Amazon.com.

You will be happy to know that RunningWritings is not retired, and I do still have projects in the works.  Last spring, I accepted an offer to pursue a PhD in biomechanics through Indiana University. As a result, I’ve been pretty busy over the last year! The good news is that I now have access to an incredible array of technology through the Indiana University Biomechanics Lab to study running mechanics and running injuries.  Since my program is a part of Indiana University’s School of Public Health, I’m also able to apply the tools of epidemiology to ask bigger questions about what affects your risk for running injuries and even how we might be able to prevent them.

Me, markered up in the IU Biomechanics Lab!
 I’ve also submitted a number of findings to scientific conferences, and soon, to scientific publications.  As these are accepted and published, I’ll be providing summaries on my blog about what these findings mean for regular runners. I’m doing my best to make enough time to share what I’ve learned here on my website. Finally, I’m currently working on another major injury article (this one will be on metatarsal stress fractures; my tibial stress fracture article is still one of the most popular I’ve ever written!).  I’m shooting to get this next article up by mid-April, so keep your eyes open!

After publishing another big injury article, the next major project is to revamp the design of Running Writings.  This website is over seven years old now, and the Blogger platform is showing its age: the layout does not look very good on mobile platforms, and the ads are not very relevant.  Further, many of you have no doubt noticed the spam comments on many of my articles, which I don’t have the time to remove. Sometime in the next few months, I’m aiming to re-launch RunningWritings with a website design that’s better than ever.  You might even see some new features alongside as I move to a platform with greater flexibility. I’m going to be moving away from the ad content you see now and towards a revenue model that’s more fitting with what the fans of this website (including myself) want to see.  But don’t worry—all the content will always be free. After the website overhaul, any articles you’ve bookmarked should still remain at the same URL as before.  Preserving article comments may be more difficult—I’ll do my best, but no promises.

Following the big website overall, I should have more time to dedicate to reviving regular content, like training analysis and the Brief Thoughts series.  Who knows, I might even bring back the YouTube channel!

Thanks in no small part to the readers of this blog, my running journey has taken me to some pretty incredible places—and right now, that’s the ability to study the causes of running injuries for my doctoral degree.  While Running Writings can’t be my top priority while I’m working on my PhD, I’m just as excited as you to put out some new content.





Wednesday, April 12, 2017

Low ferritin and iron deficiency anemia in distance runners: A scientific guide for athletes and coaches

Low iron can slow your performance on the track and on the roads

When I see a runner getting fatigued early on in workouts or struggling mightily in races for no good reason, there's one potential cause I always consider first: low iron.

Iron deficiency is a significantly underdiagnosed problem in distance runners. Low levels of hemoglobin in the blood, or low levels of the iron storage protein ferritin, can have a profoundly negative impact on your ability to have successful workouts and races.

Hemoglobin is the main building block for red blood cells, which carry oxygen from your lungs to your muscles. If you don't have enough hemoglobin, you can't make enough red blood cells, and as a result, your distance running performance will suffer. Furthermore, research and practical coaching experience suggests that low ferritin levels can cause poor performance, even when hemoglobin levels are normal.

We'll take a close look at the science behind low iron and distance running performance, then analyze the best ways to treat and prevent iron deficiency in runners.

The biology of iron and red blood cells

One red blood cell contains millions of hemoglobin proteins
One red blood cell contains millions of hemoglobin proteins
Hemoglobin is an essential part of your body's oxygen delivery system. It's a protein with four iron atoms at its core, and these iron atoms are what grant red blood cells their ability to transport oxygen (as well as give them their red color).

Because red blood cells must be replaced fairly frequently, your body keeps extra iron on-hand in a storage protein called ferritin. Your body's iron reserves are mostly locked up in ferritin, which can be called upon when needed to synthesize hemoglobin for new red blood cells, or other proteins and enzymes in your body that also require iron.  Low ferritin by itself is termed iron deficiency.

As you might guess, when ferritin levels in the body are inadequate, hemoglobin synthesis slows down and your body can't produce as many red blood cells. Abnormally low hemoglobin levels is a condition termed anemia, and when the cause is low iron, this is iron deficiency anemia.

The prevalence of iron deficiency and anemia in distance runners

According to research from the Centers for Disease Control and Prevention, between 9 and 11% of teenage and adult women are iron deficient, while only 1% of teenage and adult men are iron deficient.1 In this context, "iron deficient" means serum ferritin levels below the standard lab reference ranges for the general population (typically 12 ng/mL). As we'll soon see, these ranges need to be increased for endurance athletes.

Tuesday, October 11, 2016

Connect Run Club podcast on the science of running

I'm the featured guest on a new podcast episode from the Connect Run Club! We talk about the science of distance running, including VO2 max, more effective training strategies, and injury prevention.  Check it out! Thanks to the folks at Connect Run Club for having me on—check out their website here.

Hope you all enjoy it! I'd like to start doing more audio and video content in the near future.  Perhaps once the fall running season wraps up I'll have a bit more time to devote to those projects!


Here are direct links to the podcast:



Monday, July 25, 2016

What does it mean to be a talented runner? Considering types of talent


Perhaps because of the popularity of David Epstein's talent-centric book The Sports Gene, much of the modern conversation about high-level distance running has turned to talent: where it comes from, how to spot it, and how to develop it. One piece often missing from the conversation is what it actually means to be talented. We speak about "talented runners" as if there is one specific set of criteria that we evaluate talent against, but in truth, there are several different types of talent which don't have any inter-dependability. By this I mean that just because one runner is talented in a certain way does not necessarily imply he or she will also be talented in another.

Broadly, I believe there are (at least) four different ways one can be naturally talented as a runner. Some are more easily assessed than others.

Natural running ability

This is what most people are thinking of when they say someone is a "talented" runner. They mean he or she has a high natural set-point of aerobic endurance, someone who can run fast times or impressive workouts without much or anything in the way of formal training. Some people like to explain this mostly in terms of genetics, while others point to an active childhood as the determining factor. Both, of course, are important, but for a coach, neither matters—you work with what arrives at your doorstop on day one. And if that newly-minted runner can already run at a high level without any history of training, that is always a good thing. This does not guarantee success, as I'll explain below, but people who start at a very high level of fitness naturally have a distinct advantage.

Natural running ability is also the easiest type of talent to identify: all it takes is a race or time trial. At the school I coach at right now, our best runner was spotted as a freshman thanks to a fitness test all sprinters on the track team undergo called the Cooper test. It was devised by Dr. Kenneth Cooper, sometimes known as the "father of aerobics" (rightfully so, given that he coined the word), for quickly and accurately evaluating the VO2 max of a large number of test subjects in the field, e.g. military recruits. The test is simple: cover as much ground as you can in 12 minutes, ideally running but taking walk breaks if needed. The distance you cover, in meters, is plugged in to a formula which predicts your VO2 max. Cooper's test is reasonably accurate when comparing test results to lab-determined VO2 max.

In our case, this freshman "sprinter" ended up finishing over 500 meters ahead of everyone else at the twelve-minute whistle. Within a few weeks he was running distance workouts with our top athletes.

For distance runners, any time trial of 1600 to 2400 meters should suffice for evaluating natural running ability. Longer tests can mask true running ability, because it's very hard to run a good 5k or 10k off natural running ability alone—these events just rely too much on training, not to mention proper pacing, which is an acquired skill.  Sprint and true mid-distance athletes should be evaluated with shorter time trials that more accurately measures the shared aerobic and anaerobic components of the specific event—a 300m time trial for the 400 meters, for example, or a 500m time trial for prospective 800m runners.

Tuesday, June 21, 2016

Grandma's Marathon 2016: How much did the heat slow your time? A statistical analysis


Photo: Drew Geraets
The 40th annual Grandma's Marathon was held this past weekend in Duluth, Minnesota.  Grandma's is a staple of the Midwest marathon scene and is perennially praised as one of the best races in America.  The point-to-point course is a beautiful route that starts in the north woods of Two Harbors and follows the shore of Lake Superior into downtown Duluth.  With a slight net elevation loss and very few hills, the course is also usually a fast one.

This year, however, many participants were disappointed with their times.  Warmer than average temperatures and clear, sunny skies caused many runners to finish well back from their goals.  Since several runners that I coach or advise ran the race, I was curious to see how much of an effect the temperature had on their finish times.  So, as I often do, I started crunching some data.

Fortunately, I was able to stand on the shoulders of some Big Running Data giants—a 2012 scientific paper by Nour El Helou and other researchers in France already laid the groundwork for disentangling the effects of climate on marathon race times.  In their paper, El Helou et al. analyzed ten years' worth of results from six World Marathon Majors (London, Berlin, Paris, Boston, Chicago, and New York), resulting in a data set of 60 marathons.  These totaled almost 1.8 million marathon finishers.  El Helou et al. ran statistical analysis on each year's results, trying to find the correlation between ambient temperature during the race and the distribution of the finish times.

El Helou et al.'s methods

Because El Helou et al. (correctly) hypothesized that temperature would have varying effects on runners of different abilities, they analyzed several levels of performance for the top one, 25th, 50th, and 75th percentiles of male and female finishers.  So, for example, if the 2010 Chicago Marathon had 21,000 male finishers, the authors looked at the finish time for 210th place—that's the "one percentile" time.  This marker is more useful than looking at the winning time or 10th place, because those can be affected by things like the quality of the elite field, the tactics employed by the lead pack, and so on.  After extracting the various levels of performance for the 60 marathons in the data set, El Helou et al. then consulted meteorological records to find the ambient temperature midway through each of the 60 races. 

Doing regression analysis allowed El Helou et al. to correlate the ambient temperature with the distribution of finish times.  The broad trend in the results was not surprising: marathon times are slower when temperatures are too hot, and they are also slower when temperatures are too cold.  What was surprising, at least to me, was the optimal temperature for marathoning.  El Helou et al.'s data robustly shows that the ideal temperature for running a marathon is pretty chilly—39 degrees Fahrenheit (3.8° C) for a 2:40 marathon! Race times follow a parabolic curve, slowing significantly on either end of an optimal temperature. 

Click to enlarge