Amazon.com: 25% or more off clearance running shoes - click here to view current selection.
Running Warehouse: HOKA SALE! - Up to 50% select models through 10/31 (view selection).

Heavier Runners Less Likely to Get Injured?: Marathon Study Shows that Higher BMI Is Not Linked to Increased Risk of Lower Extremity Injury

Weight and height are used in computing body m...

Weight and height are used in computing body mass index, an indicator of risk for developing obesity-associated diseases. (Photo credit: Wikipedia)

An oft repeated response to the statement that running injuries continue to occur at very high levels despite “improved” quality of running shoes over the past several decades goes something like this: “Well, shoes have gotten better, but the runners have gotten worse.” In other words, the fact that contemporary runners tend to be heavier and less fit washes out any injury-reducing benefit provided by modern running shoes.

Now, this post actually has nothing to do with running shoes, but rather looks at the question of whether heavier, slower runners are in fact more likely to get injured. Let’s ignore the obvious fact that anyone who hangs around runners would likely observe that injuries hit people of all shapes and sizes – I know plenty of thin, eminently fit people who have gotten hurt. But, although anecdotal observations like this can be helpful, they are far from scientific.

Fortunately, several scientific studies have addressed this question, and one was just published in a 2012 issue of the Journal of Physical Activity and Health. The study, titled “Impact of a High Body Mass Index on Lower Extremity Injury in Marathon/Half-Marathon Participants,” was written by a team from the Mayo Clinic led by Tyler Vadeboncoeur.

The design of this study was fairly simple. The researchers recruited 194 individuals who were participating in a half-marathon/marathon, recorded their BMI just prior to the start of the race, and administered two surveys. The first survey was filled out prior to the race and asked participants if they had suffered a lower extremity injury that had affected their training within the 30 days prior to the race (this survey also collected demographic data and included a personal health questionnaire). The second survey was administered after the race and asked whether participants had suffered an injury during the race.

Male (n = 55) and female (n = 139) subjects were each divided up into three groups based on their BMI (note, the authors openly discuss the limitations of BMI as a measure of body composition, but for practical reasons it was the easiest method to use just prior to the start of a race). You can consider these groups to be Low BMI, Moderate BMI, and High BMI – BMI ranges for each group are provided in the table below:

Tertile Females Males
Low BMI 18.1–21.8 20.3–24.9
Moderate BMI 21.9–25.9 25.0–26.8
High BMI 26.1–42.2 26.9–34.6

They then looked at how a variety of factors (e.g., age, general health indicators, pre-race peak training volume, race finish time, injury outcomes) differed between the groups. Interestingly, they found the following with respect to injuries:

Females – Pre-Race Injuries (no significant differences among groups)
Low BMI – 24%
Mod BMI – 18%
High BMI – 9%

Females – Injuries During Race
Low BMI – 35% (significantly different from other BMI groups)
Mod BMI – 10%
High BMI – 12%

Males – Pre-Race Injuries (no significant differences; only 7 injuries total)
Low BMI – 5%
Mod BMI – 12%
High BMI – 22%

Males – Injuries During Race (no significant differences; only 5 injuries total)
Low BMI – 15%
Mod BMI – 6%
High BMI – 6%

I’m going to focus on the female results here because the male sample was small (this was a race for breast cancer, so gender participation was heavily skewed), and there were so few injuries observed among them that it’s pointless to delve into the data for the guys.

What these results show for females is that there was no increase in injury risk among individuals in the High BMI grouping. In fact, the authors report that “With every 1-unit increase in BMI a female was 13% less likely to suffer a race-related injury.” That’s right, High BMI females were on average less likely to suffer an injury during the actual race than lower BMI females, and there was also a trend for them to be less likely to suffer and injury in training. Why might this be?

One possible explanation is that the authors found that “lower BMI females had
longer peak weekly training miles (P = .007) and ran faster in both the full and half-marathons (P < .001 for both distances)
.” Running higher mileage and running to compete have both been among the only factors consistently linked to increased running injury risk (I discuss this in depth in Chapter 2 of my book), and it’s thus possible that High BMI runners are actually protected by running a slower pace and fewer miles than their Low BMI counterparts. It follows, then, that this study cannot say whether higher BMI runners would be at greater risk if they maintained the same training volume as those in the lower BMI groups, or if they were running the same speed.

The authors conclude the paper with the following paragraph:

“Many people with a high BMI participated in our open-entry marathon. While training for and participating in our marathon/half-marathon was associated with a risk of lower extremity injury, a high BMI was not an independent risk factor. As such, based on our findings, interested high BMI runners should not be discouraged from participating in endurance running based on their BMI alone. In females, a higher BMI may even be protective. These findings should be confirmed in a larger study allowing for more detailed control of confounders.”

I should point out that this is not the only study to show that high BMI is either not correlated with increased injury risk (see Macera et al., 1989), or was actually found to be protective (see Taunton et al., 2003).

The take home message here is that if you’re a Clydesdale or an Athena, you might be a bit slower than some of the other runners lining up at the start of a race, but you may actually be less likely to get hurt than some of your more fleet-footed counterparts. Not a bad tradeoff if you ask me, and certainly calls into question the argument that the reason injury rates have remained high is because because contemporary runners aren’t all built like Frank Shorter or Bill Rogers.

Enhanced by Zemanta
Running Warehouse: Great prices on closeout shoes! View men's and women's selections.
Amazon.com: 25% or more off clearance running shoes - click here to view current selection.
Trivllage: Save 18% on run, swim, and cycle gear. Use Code: RBTri18.

Recent Posts By Category: Running Shoe Reviews | Running Gear Reviews | Running Science

About Peter Larson

This post was authored by Peter Larson. Pete is a recovering academic who currently works as an exercise physiologist, running coach, and writer. He's also a father of three and a fanatical runner with a bit of a shoe obsession. In addition to writing and editing this site, he is co-author of the book Tread Lightly, and writes a personal blog called The Blogologist. Follow Pete on Twitter, Facebook, Google+, and via email.

Comments

  1. Maybe it is easier for lighter runners to mentally push their muscles and tendons to the limits since their cardio system is less stressed? I’m thinking that heavier runners might have a better feel for the fatigue and slow down appropriately much sooner.

  2. Samuel Hartpence says:

    I often wonder why you even post about studies that are so poorly controlled you can’t draw a conclusion about the results.  BMI does not protect runners from injuries.  Low training volumes/intensities (which is also correlated to BMI) is much more likely to contribute injuries.  The other thing that has recently been brought to my attention is the ratio of intensity to volume that is used among age-groupers and elites.  Elite runners pretty much stick to the 80/20 rule with only 20% of their mileage being intervals and threshold work, while age-groupers run closer to 50% of their mileage at those higher intensities.  

    link to running.competitor.com… 

    An additional hypothesis is that age-groupers increase the likelihood of injury by not allowing themselves to recover from hard efforts and most have the perception that they have to make up for volume by substituting intensity (Fuman’s “Run Less, Run Faster” doesn’t help).  Serious age-groupers (who are likely the low BMI people) are not elite, but attempt to train like them by matching their workouts and miss out on the fact that the vast majority of their training is composed of recovery runs.

    • Pete Larson says:

      The profile of runners in this study was hardly one of “age groupers.” Even in the low BMI group the mean marathon time was over 5 hours – it was a race for breast cancer event. Given the mean times, I suspect all groups did a fair amount of walk-running. I don’t think anyone is suggesting that having a high BMI is something to strive for in terms of reducing injury risk, but rather that having a high BMI should not preclude you from doing something like training for and running (or run-walking) a half or full marathon, which could in turn provide health benefits and lower your BMI.
      —-
      Pete Larson’s Web Links:
      My book: Tread Lightly – Form Footwear and the Quest For Injury Free Running<http: 1616083743=”” gp=”” product=”” ref=”as_li_ss_tl?ie=UTF8&amp;tag=thviofli-20&amp;linkCode=as2&amp;camp=1789&amp;creative=390957&amp;creativeASIN=1616083743″ http://www.amazon.com=“”> Work: link to anselm.edu
      Blog: http://www.runblogger.com
      Dailymile Profile: link to dailymile.com
      Twitter: link to twitter.com</http:>

  3. Amby Burfoot says:

    Pete: Great post. If you had to guess, wouldn’t you imagine that the higher BMI runners are running in thick, motion-control shoes?

    • Pete Larson says:

      Thanks Amby! If I had to guess, every runner in this study was probably in big bulky shoes of some sort – it was certainly the case when i filmed my race in 2009. The race in this study was in 2008 I think, and all groups had mean finish times of greater than 5 hours. I can send you the PDF.
      Sent from my iPad

  4. Pete, did they enter weekly mileage and bmi into a regression? This would allow them to test how much of the effect is driven by mileage. It would be hard to imagine they didnt collect those data.

    • Pete Larson says:

      Here’s their paragraph on analyses:

      “Data were manually transferred to the electronic SAS/DMS platform for analysis. Continuous variables (age, BMI, peak mileage, and race time) were reported
      as median and range, while categorical variables were reported as frequency and percentage. The Wilcoxon rank-sum test was used to compare the continuous variables between the BMI categories. Fisher’s exact test was used to compare gender, comorbidity prevalence, use of a training program, marathon distance (full vs. half), and injury incidence between BMI categories. Odds ratios for the association between lower extremity injury and its predictors were estimated using logistic regression. Results were considered statistically significant for P < .05.”

  5. KevinK30 says:

    Interesting. This looks like a solid study. I’m open, but in the past couple of years I’ve subscribed to the barefoot runners’ theory that when you run with bare feet, you will naturally land on the balls of your feet rather than heel to toe. Have their been any studies with barefoot runners vs. shoe runners and injuries that you’re aware of?

  6. Matthew Fleisher says:

    It’s not that “heavier runners less likely to get injured” it’s “heavier runners get injured less.”  Back when I was a pizza delivery boy I used to get pulled over by the cops all the time.  Now that I just drive to work once a day and drive back home once a day I never even see cops.  Would it be correct to say “pizza delivery drivers more likely to speed”?  No, I speed just as much, or more, than I ever did back then.  High mileage runners have greater risk/exposure to injury just as higher mileage drivers have greater risk/exposure to police.  Let’s try to be logical, not statistical.

    • Pete Larson says:

      Two potential problems here. First, there was no mileage difference between the groups of male runners, and no increased injury risk for the high BMI group. Second, in females there was higher peak training mileage in the low BMI group, and they were more likely to get in the race, not in training. Now, look at it another way. Take two people at the starting line of the race. One undertrained, the other put int he work. Who do you think is less likely to get injured in a marathon?

      You might claim excessive high miles in one group is the cause of increased injury rates, but it could equally be the case that they were adequately trained and the lower mileage group was underpreprared, in which case the finding would be all the more unexpected.

      What this study does is raise a lot of interesting questions for further investigation, and that is the nature of good science.

      —-
      Pete Larson’s Web Links:
      My book: Tread Lightly – link to ow.ly
      Work: link to anselm.edu
      Blog: http://www.runblogger.com
      Dailymile Profile: link to dailymile.com
      Twitter: link to twitter.com

  7. When I first decided to start dealing with my on “miserable running”, I took a look at the folks who appeared to be the most unlikely of runners, and examined their gaits with a neutral eye.  The two categories of runners who immediately popped up were 1) the very old, and 2) the very heavy.

    I saw several twisted, hunched, scoliatic seniors who were still able to throw down the miles, despite appearing to be way out of balance.  I saw lots of surprisingly large, even enormous folks, all of whom were chugging through their miles with no apparent harm or even significant discomfort (aside from copious sweating).

    I was amazed to see the gaits of both groups almost universally shared two key characteristics: 1) Their steps were short, and 2) their steps were quick.

    Incorporating those to my own gait were literally my first steps toward comfortable and even joyful running.

    Those folks are my heros.  They give a whole new meaning to the phrase “Survival of the Fittest”.  Sometimes, you just need to know where to look.

    • Pete Larson says:

      Bob,

      Thanks for the input, and I agree. When you watch heavy runners their gait often has very little or sometimes even no flight phase, and short strides. I can’t quantify it, but it’s pretty distinct, and I can’t help but wonder if it plays a role.
      How are things going with the Miserable Runners?

      Sent from my iPad

      •  A new job with longer hours and a longer commute has cut into my training time.  But even with that limitation I’ve found that if I focus on being comfortable, I go faster.  If I focus on speed, I start stressing my legs and back.

        The main realization this year is that my most enjoyable, least stressful, and fastest stride feels exactly like running in place, at least where the initial foot contact is involved. 

        I seem to be an inveterate overstrider, possibly due to a lifetime of hard heel-striking, and I’m always having to correct it.  My run warmup includes some running-in-place, during which I close my eyes to “lock in” the sensations, to focus on how my balance feels.

        When I come to wide, smooth parts of my run, I often do some brief checks with my eyes shut.  When I stay in the zone where my foot strike feels identical to that felt while running in place not only do I feel like I’m smoothly floating over my feet, but my Garmin also records a faster pace.

        Another part of limiting my overstriding is keeping my cadence high, and I’m still running with a metronome set to 185 bpm to provide a constant reminder of the stride rate I need to maintain.  Without the metronome, even a small amount of fatigue causes my stride to slow and lengthen, making the fatigue increase faster and my discomfort quickly to get dramatically worse.

        I have trouble believing that despite collapsed discs and a lifetime of bad running, I’m now running faster, further and with far more joy than I have for over 30 years.  I’m still working my way toward my goal of doing my first-ever half-marathon before the end of this year, and to do so at no slower than an 8:30 pace.

  8. Ric Moxley says:

    Fascinating study! But, like Mr Hartpence points out, the variables in the study aren’t sufficiently controlled to make the results worth much.  The biggest buggaboo for me: overweight runners are so much less likely to be competing at the same level as someone who is trying to place that OF COURSE they are less likely to be injured from running. 

    For example, I’m not very muscular, right? and i have no injuries from weight lifting.  None.  Does that mean that muscle-beach manly men are more injury prone because they statistically have more weight-lifting-related injuries?  LOL. 

    • Pete Larson says:

      As I pointed out in response to the other comment, all three groups had mean finish times of over 5 hours, so although the higher BMI group was on average slower, none were what you would typically classify as “age groupers” or highly competitive runners. And even if the results show that running to be competitive is a risk factor for injury, that’s something interesting to know :) Point is that there is some reason why the high BMI group got injured less often, and figuring out why would be an interesting topic for further study. All we can do is speculate.

      —-
      Pete Larson’s Web Links:
      My book: Tread Lightly – Form Footwear and the Quest For Injury Free Running<http: 1616083743=”” gp=”” product=”” ref=”as_li_ss_tl?ie=UTF8&amp;tag=thviofli-20&amp;linkCode=as2&amp;camp=1789&amp;creative=390957&amp;creativeASIN=1616083743″ http://www.amazon.com=“”> Work: link to anselm.edu
      Blog: http://www.runblogger.com
      Dailymile Profile: link to dailymile.com
      Twitter: link to twitter.com</http:>

  9. Adolfo Neto (UTFPR) says:

    Sorry, the message below lost the formatting. Here it is corrected:

    It’s been my experience (from watching many runners of all shapes and sizes) that the heaviest-weight runners do run lightly… it’s a necessity in their case, even with shoes, not to crash their feet into the earth with several times their body weight!

    There may be some heavy-weight hard-stomppers out there occasionally, but they don’t/cannot continue running very long before they cannot run anymore (at least not that way).

    Among the loudest foot/shoe-stomppers I hear are often light-weight (under 100 pounds) children who recently hit their growth spurt, and are running exclusively in shoes (so they don’t get the feedback necessary to relearn how to run with their “new” body shape/size).

    • Pete Larson says:

      Thanks for sharing this. Blaise Dubois often talks about how he thinks heavier runners should avoid “big, bulky shoes” because he feels that they need to develop their intrinsic impact moderating behavior. He feels this can be better accomplished with proper form than a heavily cushioned shoe. This would seem to sync with what Ken Bob is saying. But, initial risk in transition may be higher since additional weight will increase loads.

      —-
      Pete Larson’s Web Links:
      My book: Tread Lightly – Form Footwear and the Quest For Injury Free Running<http: 1616083743=”” gp=”” product=”” ref=”as_li_ss_tl?ie=UTF8&amp;tag=thviofli-20&amp;linkCode=as2&amp;camp=1789&amp;creative=390957&amp;creativeASIN=1616083743″ http://www.amazon.com=“”> Work: link to anselm.edu
      Blog: http://www.runblogger.com
      Dailymile Profile: link to dailymile.com
      Twitter: link to twitter.com</http:>

  10. Larry Wasserman says:

    Following up on David Steinberg’s comment:
    it need not even be a collider. This is clearly association
    not causation because there are many unmeasured
    confounders. Be careful about drawing conclusions from
    observational studies.

    Larry Wasserman

    • Pete Larson says:

      I absolutely agree – I highly doubt that a high BMI in and of itself is a protective factor, and I suspect the study authors would agree.

      But, the fact that 3-4 studies now have found this type of pattern suggests that there is something about high BMI runners that allows them to avoid what would intuitively seem like an increased injury risk due to their body composition (i.e., the confounders). I’m betting it’s a combo of lower mileage and reduced speed, though I also would not discount some aspects of running form. I have a lot of video of runners in the 5:00 plus marathon finish time range and one of the things I notice is that many of them don’t even have an aerial phase, even though they aren’t walking. Could be that they are seeing less vertical oscillation of the center of mass or something along those lines. I need to look into the literature on how weight affects running form in more detail.

      What I like about this study is it leads us to ask why we see a pattern like this, and digging into the confounders can be really informative, and could uncover patterns applicable to all runners.

      —-
      Pete Larson’s Web Links:
      My book: Tread Lightly – Form Footwear and the Quest For Injury Free Running<http: 1616083743=”” gp=”” product=”” ref=”as_li_ss_tl?ie=UTF8&amp;tag=thviofli-20&amp;linkCode=as2&amp;camp=1789&amp;creative=390957&amp;creativeASIN=1616083743″ http://www.amazon.com=“”>
      Work: link to anselm.edu
      Blog: http://www.runblogger.com
      Dailymile Profile: link to dailymile.com
      Twitter: link to twitter.com</http:>

  11. Nicole Introvert says:

    Wondering if this study took into account any eating disorder history in the lower BMI range.  That alone would account for folks at a lower BMI to be more injury prone. 

    • Pete Larson says:

      Good, point, and was not specifically discussed. They do talk a bit about low BMI possibly being linked in females to low estrogen levels and lower collagen elasticity, so that is another factor to consider. One study did show that people at extremes of BMI on either end had increased risk, so there is something to consider there.

      —-
      Pete Larson’s Web Links:
      My book: Tread Lightly – Form Footwear and the Quest For Injury Free Running<http: 1616083743=”” gp=”” product=”” ref=”as_li_ss_tl?ie=UTF8&amp;tag=thviofli-20&amp;linkCode=as2&amp;camp=1789&amp;creative=390957&amp;creativeASIN=1616083743″ http://www.amazon.com=“”> Work: link to anselm.edu
      Blog: http://www.runblogger.com
      Dailymile Profile: link to dailymile.com
      Twitter: link to twitter.com</http:>

  12. Colleen Rynski says:

    Interesting.  Since all of the heavy runners I know are running to lose weight and fall into those lower bmi categories I doubt many in the high category would put in the mileage and training without actually over time falling into the lower bmi groups.

    I am a high bmi runner who is working on couch 2 5k myself, and thanks to this blog I am doing the program in a pair of new balance W730s I love dearly.

  13. David Steinberg says:

    This may be a spurious correlation based on a collider – e.g., the toughness/athleticism bar is much higher for heavier runners who even make it into the observable data set of long distance runners.  see this fascinating post – which is really eye opening 
    link to theatlantic.com

    • Pete Larson says:

      Interesting article, thanks for sharing. So you’re suggesting that the heavy runners who make it to the race may be a biased sample in that they may be less injury prone, whereas many may not have even made it to the starting line? It’s a possibility, but I would say also that lower mileage and slower speed could in and of themselves explain why injuries were less common among the heavier runners. High mileage and “running to compete” are two factors that are strongly linked to increased injury risk, so there is a plausible explanation for the observation.

      I’ll have to go back to some of the other studies that have shown similar patterns and see if they tracked runners in such a way that this could be teased apart. You’d have to start tracking them during pre-race training I suppose to account for those who do not make it to race day.

      —-
      Pete Larson’s Web Links:
      My book: Tread Lightly – Form Footwear and the Quest For Injury Free Running<http: 1616083743=”” gp=”” product=”” ref=”as_li_ss_tl?ie=UTF8&amp;tag=thviofli-20&amp;linkCode=as2&amp;camp=1789&amp;creative=390957&amp;creativeASIN=1616083743″ http://www.amazon.com=“”> Work: link to anselm.edu
      Blog: http://www.runblogger.com
      Dailymile Profile: link to dailymile.com
      Twitter: link to twitter.com</http:>

      • David Steinberg says:

        It’s not even that they don’t make it to race day after training, it’s that they may never even take up running in the first place.  In other words, for a heavy runner to select running as a hobby there have to be a lot more things working in his favor.  It may be that the more exceptional (relatively speaking) heavy runners are the ones that are choosing long distance running.  Another way to say it is if you just picked 1000 random people off the street and had them train for and run a marathon, i doubt you’d see the same correlation.

        • Pete Larson says:

          I don’t disagree, but that’s an entirely different question that would require a much different, and likely impossible study. You’d have a heck of a time convincing an ethics board to allow you to randomly choose a bunch of obese non-runners and train them to run a marathon.

          What this study tells me is that if you’re a big runner, you probably aren’t going to suffer any undue risk from running a marathon. It’s not meant to address whether someone who never leaves the couch should take up running. They state as much in their conclusion “based on our findings, interested high BMI runners should not be discouraged from participating in endurance running based on their BMI alone.”

          —-
          Pete Larson’s Web Links:
          My book: Tread Lightly – link to ow.ly
          Work: link to anselm.edu
          Blog: http://www.runblogger.com
          Dailymile Profile: link to dailymile.com
          Twitter: link to twitter.com

    • Pete Larson says:

      This guy seems to make a point that would support what you are saying: link to reddit.com

  14. yang xiaohan says:

    beautiful

Speak Your Mind

*