Thursday, March 15, 2012

The "Lose Weight, Gain Speed" Myth

WARNING: You might not want to read this post. I have two disclaimers before you go on.

1. This post discusses WEIGHT. I know that the gravitational pull of your body towards the Earth is troubling for some people. It’s discussed here, so if the mere mention of the word incites anxiety for you, stop reading.

2. Possibly even more disturbing, this post involves MATH.

Moving along…

A few years ago, Runner’s World published an article about how losing weight will make you run faster. They even included a cute little table showing you how much time you could drop across various race distances by losing weight.

Lose Weight, Gain Speed
This table, based on changes in maximal aerobic capacity, provides a rough estimate of how much your race times will improve if you lose weight, as long as you have it to lose. If your BMI drops below 18.5, you're at risk of becoming weaker and slower.

WEIGHT LOST
5K
10K
HALF-MARATHON
MARATHON
2 lbs
12.4 secs
25 secs
52 secs
1:45
5 lbs
31 secs
1:02
2:11
4:22
10 lbs
1:02
2:04
4:22
8:44
20 lbs
2:04
4:08
8:44
17:28

The table has a small disclaimer that if your body mass index (BMI) falls below 18.5, you might become slower. But otherwise, obviously the relationship between time improvement and weight lost is pure and linear, right?

The former research scientist in me was skeptical. Luckily, the academic article that was the basis for the piece in Runner’s World was readily available, and I was able to quickly find the improper conclusions that the Runner’s World author had made when reporting on the piece by Vanderburgh and Laubach of the University of Dayton Department of Health and Sport Science. Here are a couple of major errors made in the Runner’s World article:
  • The Vanderburg and Laubach piece only analyzed the impact of weight on 5k times, but Runner's World extrapolated the results to 10ks, half marathons, and marathons. Since absolutely no analysis was done for any other race distance, it is impossible to know if the same relationship between weight and race time applies for all distances. Perhaps the impact is more pronounced for longer races. Perhaps less pronounced. Either way, when only one distance is analyzed, it is not correct to assume constant covariance of weight and speed for all race distances.
  • Specifying that weight loss down to a BMI of 18.5 will lead to faster races, but weight loss beyond that will not, implying that this is a hard cutoff value. Aside from the obvious fallacy here – which is that a variable based on weight and height alone, such as BMI, varies substantially among healthy individuals because of differences in bone density, muscle mass, and glycogen storage capacity – this statement also doesn’t follow from the Vanderburg and Laubach work. They instead used a lower limit weight, not a lower limit BMI, based on the weights of national-class 5000m runners. (This approach is flawed, too. More on that below, but the point here is that the Runner’s World article didn’t even properly report the Vanderburg and Laubach study.)
  • Reporting that the table is “based on changes in maximal aerobic capacity" when it is not. Sorry, Runner’s World. What you’ve got here is a table of time improvement vs. weight loss for race distance. None of those variables – distance, time, or weight – are a measure of aerobic capacity. Try again next time.
  • Making generalizations and absolute statements that aren’t supported by the research.
    • “There’s no denying that healthy runners will race about two seconds per mile faster for every pound they lose.”  To say “will” implies that no other variables make a difference.  How about if the weight loss is from dehydration? That’s not going to work out so well for you on marathon day. What if the weight loss is from reduced muscle mass after a layoff in training, which is very unlikely to make you faster? The research out of the University of Dayton never even implied that the relationship between speed and weight is absolute, or that weight is the main predictor of race time.
    • “Because losing a few pounds makes running easier, you should be able to increase your workout distance and speed.” Losing a few pounds does not always make running easier. Body weight comes from many sources, including muscles, bones, organs, water, and fat. All of these can help you train harder – bone mass can help prevent stress fractures, fat can help you through longer workouts, and muscles are what obviously move your bones. A person doesn’t necessarily drop nonessential and unhelpful mass from their body when they lose weight – muscle, water, and bone mass can all fall away – so losing weight doesn’t necessarily make running easier. You could be losing weight that was helping you run.

As if the misreporting by Runner’s World wasn’t enough, it turns out that the Vanderburgh and Laubach research itself was deeply flawed, which was disappointing given that it was done at a university department of exercise science.
  • The hypothesis that weight loss leads to faster times is based on research which shows that VO2 Max, which is a good predictor of performance in a 5000m run, increases with reduced body fat and higher physical activity levels. While lower body fat and more physical activity will usually lead to weight loss, my suspicion is that those two factors are far more important than absolute weight when it comes to turning in a good 5000m time. Vanderburgh and Laubach would have had a much better study on their hands had they used body fat and/or training hours as the independent variables predicting 5000m run times.
  • The study used body weight as the independent variable for predicting race times, and did not consider height at all. The authors did mention this, and noted that they neglected height because weight and height covariate – that is, taller people are, as a group, heavier than shorter people. While multicollinearity (inclusion of two variables that report overlapping information) is a problem in linear regression, a technique commonly used to evaluate the relationship between two variables, this can easily be solved by replacing the two variables that are closely tied (such as weight and height) with one variable that accounts for both (such as BMI). This would have been a simple substitution that would have made the conclusions of the study more valid, but the authors failed to do so.
  • The study identified the ideal weight as that of the top 5000m runners in the U.S. In other words, selecting on the dependent variable, OR assuming that the weight of whoever is currently best is the best weight to be, as if no other variables carry any other explanation. A more appropriate approach would be to evaluate weight, or even better, BMI or body fat, against the times of runners of varying abilities to see what range of weights produced the best times.
  • The study is based on an adjustment factor used powerlifting competition rather than any real data or actual running times or athlete weights. This sounds ridiculous, but it is true. Go look at page 4 of the article. In summary, their conclusions are based on a formula for equalizing how much weight people of differing body weights can lift. It has nothing to do with running. All they do is take this factor and use it to make a linear equation with one data point – the weight and time of the best 5000m runner in the country.

This isn’t research. This is letting a well-trained monkey loose with some numbers, an equation or two, and contact information for exercise science journal editors.

In other words, if you’ve decided that you’ll drop 10 minutes from your half marathon time by dropping 12 pounds and changing nothing else – it might be time to rethink that. Instead, train hard and eat to support that, both in terms of quality (fruits and vegetables are good, so are lean proteins) and in terms of timing (eat some high quality carbohydrates before you train, get in some more along with a bit of protein after you train so that you replenish your glycogen stores and rebuild muscle). Your body will adapt to support the harder training, and in turn, the faster racing. That adaptation might involve weight loss, it might not. Either way, you’ll run faster because you trained to run faster.

57 comments:

  1. Emphatically agree. I'm not near the 18.5 BMI, but I still find that I run best with a bit more weight, rather than a bit less (only talking 2 pounds or so).

    ReplyDelete
  2. So you're saying that if I lose 10 pounds I might get even MORE than 20 seconds faster? Only half a celery stick for me today!

    ReplyDelete
  3. This is perhaps one of the most sensible things I have read in a long time. Thank you for unpacking the research.

    ReplyDelete
  4. This is a GREAT post and I wholeheartedly agree. I remember seeing that article in RW and being disappointed (and confused) by the flippancy of the way they wrote the article (lots of "assurance" words that my risk-weary consultant side hate like "will" and "ensure"). 12+ seconds on a 5k is a LOT of time...that gave me a definite red flag. Thanks for debunking!

    ReplyDelete
  5. Wow. Really disappointing in how misleading the article is. I usually just scan their stuff anyway- but now will be sure to double check before I believe any of it. Thanks for this.

    ReplyDelete
  6. this is so true, when I joined a cycle club they all commneted n how good i would be climbing, yes I can climb but if you don't have the physical strength its no good. it annoys me that they automcatically think thhat if your lighter you will be faster. I'm actually trying to gain weight and my times are improving, as I am not at a normal weight.

    ReplyDelete
  7. OMG I can't even believe you mentioned weight. Now I have to eat nothing but rice cakes and spinach for a week and cry.

    I dropped 46 minutes off my time from my first to third marathon and yet somehow my whooty remains.

    I love this post for so many reasons.

    ReplyDelete
  8. Reason number 1000 why I love you. Anyways-I think people get the mistake that they lose weight and they will go faster. When in reality, people who are losing weight are probably eating a lot better and thus losing weight. I def don't think people get the whole concept. This is such a great post FYI.

    ReplyDelete
  9. Very interesting post. I had read that article awhile back and have ascribed to it without skepticism. It seemed natural to me that lighter people go faster. As I have lost weight, I have gotten faster but moreover my body doesn't seem to work as hard as it used to to go the same speed. I suppose it doesn't have to work on 'feeding' the me that isn't there anymore. Also, it's obvious on group rides when the light people climb faster (when cycling), although doesn't necessarily help them on flats. Anyway, I appreciate your input and you bring up some excellent challenges. That said, for most people, assuming training is kept the same and the only change is 'normal' weight loss, I do believe those people get faster while running.

    ReplyDelete
    Replies
    1. I think it is true to an extent, but when you are dealing with tiny quantities of weight (5-10 lbs), it is really more important to get in proper nutrition and solid training, which will make your body adapt to its optimal weight for the sport. This is better than just working to drop weight.

      For example, light people don't always climb faster - they still need to be able to produce the power to get up the hill. With insufficient muscle, it just won't happen, so they need to eat and train properly to get that muscle strength rather than just lose weight.

      My guess is that your personal experience with time improvement (congratulations!) is due to better training and nutrition, which has coincidentally led to weight loss. Again, this is why I believe that the most important factor is good nutrition and training.

      Delete
  10. Hi Victoria: Thanks for the great article. I've only skimmed it, but I would agree with many of your individual points. That said, I think you might have missed "the big picture" in several ways.

    1. RW is obviously not a scientific journal, and it's not our job to write thousands of words about the pros/cons of various study results and designs. We just try to find ones that seem important to runners, and to summarize the main points.
    2. The Chart I created is obviously a gross oversimplification. However, I'll still argue that weight-loss is more likely to produce performance (and health) benefits for more typical runners than any other change in their behavior.
    3. You site training and carbs, but most runners already eat too many carbs, in all likelihood, and training is not a simple subject,
    especially not for those who are time-pressed and can't train much.
    4. There's certainly an inverse relationship, though not perfect, between weight and vo2 max.
    5. I would agree that losing muscle with body weight is a potential problem. Fortunately, running itself provides a good deal of protection against this, and we nearly always advise that readers do some resistance training as well.
    6. Don't get me started on "dehydration," which includes much more mythology (though slowly changing at last) than weight loss and performance.
    7. I can't tell from your post if you have a main point (other than deconstruction) or not. Do you think weight loss makes runners slower? I doubt that. If you're just saying, Life, science and physiology are complex, I would agree with you. But I don't think that's very informative.

    Best. Amby Burfoot

    ReplyDelete
    Replies
    1. Amby – thanks for reading, and for the very thoughtful questions. I do think I understood the main point of the article – that all else (training, talent level, etc) being equal, an athlete will run better with a more optimal body composition. However, the way the article is written, most people interpreted it as “losing weight will make me faster” when in reality, training effectively and getting proper nutrition overall is more important than weight loss itself. My issue is tying specific time improvements to weight lost, especially since the study supporting those numbers was not designed to support the conclusions.

      Regarding your specific points/questions:

      1. It is true that RW isn’t a scientific journal, however, I believe that RW should be a responsible publication, which means only reporting on studies of high fidelity that are conducted properly, and accurately reporting on those studies with the key relevant information included in the summary. For example, in this article, I think that it should have been noted that only the 5k distance was evaluated and that extrapolations to other distances may not be as accurate.
      2. I will assume that here, you meant non-training factors that could produce performance benefits (otherwise, I could have skipped the progressive tempo run I did this morning in a raging downpour that turned into a thunderstorm when I was several miles from home). While I agree that weight loss CAN be helpful, I am not sure I agree that it is more likely to produce performance benefits above any other behavior change. Improved nutrition overall, which may or may not lead to weight loss, might be even more helpful. So could improved sleep quality, quitting smoking, abstaining from alcohol, or numerous other lifestyle changes. It’s hard to say which is most beneficial – though my bias would be to guess quitting smoking (and we ALL know runners who smoke).
      3. My citation of carbohydrate consumption was in the context of nutrient timing, not overall intake. In other words, eat an apple an hour before a key workout, and maybe eat half a turkey sandwich within an hour of completing the workout to replenish glycogen and support muscle repair, but not necessarily a pound of pasta at 9 pm on a light training day. I didn’t in any way suggest that athletes should down massive quantities of carbohydrates – and only mentioned them in the context of pre- and post-workout nutrition.

      Delete
    2. (continued...)
      4. You are correct that the relationship between VO2 Max and weight is inverse, however, the relationship between VO2 Max and body fat percentage is a much tighter correlation. Discussing this relationship would have been more accurate.
      5. I do appreciate that RW does this – and further appreciate that a lot of the exercises described are helpful for preventing injuries that runners are susceptible too. However, on a severely calorie restricted diet that an athlete might put themselves on to try to get to a potentially unhealthy weight in hopes that it will help them drop time, they are almost guaranteed to lose muscle as the body cannibalizes it to make up for the insufficient nutrition. Strength training will do little to prevent this process.
      6. I would be interested in learning more about the dehydration mythology you are referencing.
      7. My main point is that the numbers presented in the article have no defensible basis. This concerns me, because I know many runners who have become nearly obsessed with reaching “racing weight” and focus on that rather than getting in proper nutrition and training – in fact, RW even had an article that touched on this last month (http://www.runnersworld.com/article/0,7120,s6-241-285--14203-0,00.html). Putting specific numbers to the “weigh less, run faster” concept is quite dangerous, since weight can vary appreciably among healthy, well-trained athletes for many, many reasons. Regarding whether or not weight loss makes runners slower – in some cases, I think it can. Personally, I actually run faster when heavier – my best 5k and half marathon times came when I was at my heaviest as a runner. On the other hand, my worst 5k time came when I was within 5 pounds of the lowest weight I’ve been in my adult life. Granted, there is only a 15 pound range in there, but that makes me question how much weight matters in achieving faster race times.

      Thanks again for sharing your thoughts.

      Delete
    3. Amby - the amount of detail in your points makes me think you should read the article rather than skimming it. Particularly when one of Victoria' points is that Runner's World may have may too many quick assumptions in the article.

      Delete
    4. To say that losing weight and running faster is a myth is a bit sensational and a simplification as well. Also it looks like apologetics at work here to respond to Amby--notice the length of the answers and amount of hypothetical language, outlier evidence, and confirmation bias/anecdotal evidence. Apply Occam's Razor here and generally the simpler the better the answer. So here is the simplest answer:

      There is a strong correlation between lower body weight and speed.

      Eat well, train well, and have a low body fat and you will have a greater correlation of running better. The gains for biking might even be more dramatic. Swimming might be the exception, but the water neutralizes the effects of weight.

      However in Victoria's defense to say that weight loss will cause x amount of time increases is also missing the bigger picture. This is a correlation rather than a cause-effect relationship.

      I say that both Amby and Victoria are missing the larger statistical picture. A correlation exists between weight and speed, but not causality.

      Delete
  11. What, I was hoping to lose more weight so I can finally fun fast. Bummer :(

    ReplyDelete
  12. I dislike BMI because it's such a general measure and doesn't take into account muscle vs. fat. I know with swimming my weight always went up during the season as I got muscle mass back and that led to faster times. Sure, if you're carrying around a ton of extra weight it's going to slow you down, but simply lowering that number isn't some magical solution.

    ReplyDelete
  13. Well... the less you have to carry with you, the faster you get (not linearily).
    Same as in cars... but this theory stops if you take out the motor or gas tank because they weigh a lot. And it's the same with human bodies. It matters a lot what you take away (or make bigger). An information you will not get from your scale (not even the fancy pancy ones), as the human body is more complicated than a machine.

    Thank you for this post!

    ReplyDelete
  14. Hey Victoria,
    Very well written and thought out. Thanks!

    I was curious of your thoughts that Joe Friel wrote on his blog about a "similar" concept. First glance, these reads like practical advice. Take a look. I would love to know your thoughts.

    http://home.trainingpeaks.com/articles/nutrition/weight-management.aspx

    Thanks
    Tyler

    ReplyDelete
    Replies
    1. Well, his concluding advice seems to be to maintain your protein intake when cutting weight to minimize muscle mass loss, and to avoid cutting weight during intense training because this makes it difficult to fuel workouts appropriately. I agree, seems practical.

      Delete
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  45. The optimal weight in pounds for running the marathon distance for men is (height in inches)x2 and for women is (height in inches)x2x.85. We can train our VO2max, our lactate threshold and perform core strength exercises until we puke, but we will always finish behind the Kenyans if we continue to deny the fact that we are overweight as a nation.

    ReplyDelete
    Replies
    1. First, good job finding a blog post that is over 3 years old. Second, can you provide a reference for that formula?

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  46. When I talk weight loss I am talking specifically fat loss only, heavier runners may well be better performing than light runners, I do not really care about that.

    Someone with an extra 5KG of fat compared to the next person of the exact same make up will be slower on average.

    If I add 5kg of fat to my body then everything I do from running, swimming, jumping & cycling will be negatively effected. When people read this title they assume you are just talking about fat & if that is what you are saying then I would say you would be wrong because how can a dead weight improve a well nourished, appropriately hydrated person who has enough energy reserves to complete whatever event they are intending?

    There is no benefit to this dead weight & I also realise this is old.

    ReplyDelete
    Replies
    1. It is true there is no benefit to dead weight. However, it is hard to tell what is and is not dead weight, and hard to truly isolate the effects of carrying extra fat.

      In order to drop fat, does one have to go into a calorie deficit that causes hormonal fluctuations that reduces one's performance? If so, carrying the extra fat does provide some benefit.

      Some people may not be able to remain well nourished and appropriately hydrated while dropping fat, while others may be able to do so.

      Delete