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.