How exercise affects knees: bone spurs vs. cartilage

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As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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Conventional wisdom tells us that running and other forms of vigorous exercise will ruin your knees. A number of studies, on the other hand, have found that long-term runners are actually less likely to develop osteoarthritis in their knees than non-runners, as I’ve written about before. So how we reconcile these conflicting beliefs?

Australian researchers have just performed a large-scale analysis of existing research in an attempt to answer this question, in a paper that was posted online by Medicine & Science in Sports & Exercise earlier this month. They started by scanning 1,362 relevant studies, and eventually winnowed that number down to 28 high-quality studies (which gives you some idea of the number of lower-quality studies out there!). Six of them were MRI studies, with the remaining using X-rays to assess cross-sectional and longitudinal links between exercise and knee joint status.

Here’s what they found:

i) strong evidence (from multiple high quality cohort studies) that there is a positive relationship between osteophytes and physical activity;

ii) strong evidence (from multiple high quality cohort studies) that there is no relationship between joint space narrowing, as a surrogate for cartilage thickness, and physical activity;

iii) limited evidence (from a cohort study and two cross-sectional studies) that there is a positive relationship between cartilage volume and physical activity;

iv) strong evidence (from multiple high quality cohort studies) that there is an inverse relationship between cartilage defects and physical activity.

In other words, exercise results in fewer cartilage defects, and may actually result in increased cartilage volume, but also results in more osteophytes (also known as bone spurs).

So what does this mean? Bone spurs aren’t generally a good thing, but decreased cartilage (as measured by joint space narrowing) is the most common way of monitoring the progression of degenerative conditions like arthritis. The researchers suggest that, in this case, the bone spurs may simply be a reaction to the forces of exercise, and don’t indicate that the joint is degenerating:

Thus, in response to mechanical stimuli, such as physical activity, osteophytes may enhance the functional properties of the joint by increasing joint surface area for the greater distribution of load or reducing motion at a joint and improve joint stability… While it is possible the higher prevalence of osteophytes identified in people exercising may be detrimental to the knee joint, it could also be argued, in the absence of cartilage destruction, that physical activity is beneficial and osteophytes are simply a response to mechanical stimuli.

To be perfectly honest, it sounds like they’re stretching a bit to make things sound good. “What, exercise causes bone spurs? Well, maybe bone spurs are actually good for us!” But for most people, loss of cartilage is a far more serious consideration, so overall these results are (once again) good news for people who exercise regularly and don’t want to have to replace their knees when they turn 60.

Too much sitting will kill you, even if you’re fit

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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A new study that just appeared online in the American Journal of Epidemiology (abstract here, press release here) adds to the evidence that spending most of the day sitting down has bad effects that aren’t cancelled by daily workouts at the gym. The study looked at 123,000 men and women between 1993 and 2006:

Women who reported more than six hours per day of sitting were 37 percent more likely to die during the time period studied than those who sat fewer than 3 hours a day. Men who sat more than 6 hours a day were 18 percent more likely to die than those who sat fewer than 3 hours per day. The association remained virtually unchanged after adjusting for physical activity level.

It’s that last bit that stings. The obvious question is: how much exercise did the subjects do? In their analysis, the category for “most active” was those who got more than 52.5 MET-hours per week of physical activity (including both day-to-day chores and exercise). According to the ACSM’s Compendium of Physical Activities, running burns anywhere from 7 METs (for “jogging”) to 18 METs (at 5:30/mile). Still, it suggests that the most active people in the study were doing the equivalent of almost an hour a day of jogging, which isn’t insignificant. And the lack of change with respect to physical activity (except at the very lowest level) doesn’t give us much reason to hope that just a bit more exercise — say 100 MET-hours per week — would be any different (though clearly this is a question that should be explored by future studies).

A similar study was covered a few weeks ago by Gretchen Reynolds, and another related study made news back in January, so clearly this result isn’t a one-time fluke. (Interestingly, the study reported by Reynolds focused on men, while the new study found a bigger effect in women — so no one’s immune!) As a committed desk jockey, this is somewhat worrying to me. I’m not quite sure what to do about it. Maybe those standing-desk people aren’t so crazy after all…

Running shoes, injuries, and the Great Nike Conspiracy

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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Over the last week, there has been another bubble of excitement about the impending demise of conventional running shoes, spurred by the publication of a couple of studies that found no reduction of injuries when runners are fitted with shoes specific to their running stride — “motion control,” “neutral,” “stability” and so on. Gretchen Reynolds at the Times does a nice job of summing up the studies.

These are important studies. But I found the reaction to be a bit overblown, in some cases. Chris McDougall, the author of Born to Run, wrote a blog post with the title “Breaking news from Nike: We’ve been talking a lot of crap, and selling it,” calling the results “mindboggling and explosive stuff.” I don’t think he can be referring to findings themselves — he wrote a book on this stuff, so there’s no way he doesn’t already know that there’s never been a study linking shoe choice to injury rates. What he finds so  amazing is that one of the co-authors of one of the studies works for Nike. (It’s actually Gordon Valiant, who figured in a blog post just last week.) To him, this is evidence that Nike is peddling stuff that it knows doesn’t work.

Another point of view comes from blogger Pete Larson. In his initial summary of the research, he also marvels at this apparent contradiction:

Makes one wonder if the shoe makers actually have “proprietary data” supporting these designs, or if the whole pronation-control shoe paradigm is nothing more than a giant marketing gimmick.

Larson followed up a day later with another post titled “What is Nike doing? Speculation on a Shoe Market in Motion,” which I think is more on the money. In that post, he notes that “the questionable benefits of pronation control shoes have been present in the scientific literature for some time now (see this 2001 paper by expert biomechanist Benno Nigg).”

Here, for the record, is a list of the footwear companies that have employed Nigg’s consulting services, including Nike, Adidas and Mizuno. All the major shoe companies are perfectly aware of the strengths and weaknesses of current shoe research, and they all fund studies trying to learn more. It certainly looks like what Larson calls the “pronation control paradigm” is due for revision, as more than one shoe researcher has acknowledged. (Asics consultant Simon Bartold, for instance, told me earlier this year that Asics has completely abandoned the concept.)

The question is, what do we replace the pronation paradigm with? Nigg’s advice is to run in a shoe that feels comfortable to you — his group has produced some interesting studies suggesting that your body “knows” what will help it minimize the energy needed to stabilize your muscles.

To Larson (and McDougall, needless to say) the answer is even more obvious: “Your body evolved to run long distances, and it evolved to do so barefoot.” On the surface, it’s hard to disagree with this statement. But if you’re asking “What shoes are best for recreational runners in modern Western societies?” rather than “How did our ancestors run 100,000 years ago?” then I’m not sure we can assume the answer in the absence of studies. The barefoot/minimalist argument is extremely logical and makes a lot of sense — exactly like the “use shoes to cushion feet and reduce biomechanical forces” argument was in the 1980s and 1990s. Let’s not fall for the same mistake again by skipping the part where we check that the idea actually works in the real world.

[AUG. 5 follow-up: orthotics study suggests there’s life in the pronation paradigm after all.]

Checking in on vitamin D intake recommendations

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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Jane Brody has a piece in today’s New York Times on vitamin D needs — nothing particularly new, but summing up the trend of the last few years to believe that insufficient vitamin D in modern sun-phobic societies is behind a whole range of chronic diseases, and noting that current recommended intakes are far below the levels some experts believe are necessary:

The current recommended intake of vitamin D, established by the Institute of Medicine, is 200 I.U. a day from birth to age 50 (including pregnant women); 400 for adults aged 50 to 70; and 600 for those older than 70. While a revision upward of these amounts is in the works, most experts expect it will err on the low side. Dr. Holick, among others, recommends a daily supplement of 1,000 to 2,000 units for all sun-deprived individuals, pregnant and lactating women, and adults older than 50.

With that in mind, it’s worth pointing out the press release from Osteoporosis Canada that I noticed last week, announcing a revision of their recommended vitamin D intake:

The new guidelines recommend daily supplements of 400 to 1000 IU for adults under age 50 without osteoporosis or conditions affecting vitamin D absorption. For adults over 50, supplements of between 800 and 2000 IU are recommended. For people who need added supplementation to reach optimal vitamin D levels, doses up to the current “tolerable upper intake level” (2000 IU) are safely taken without medical supervision.

I’m still a little gun-shy about the very broad claims made by vitamin D advocates, but the evidence is strong enough that D is the only supplement I’ve taken (albeit sporadically) over the past few years. The bottle I have right now is 400 IU per pill — maybe I need to ramp that up, or at least take it every day during the winter.

How to work out during a heat wave

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

***

This week’s Jockology column in the Globe and Mail deals with exercising in the heat, covering topics like acclimatization, pre-cooling and (when needed) post-cooling. Actually, the version available online is only about half the article — not sure whether the rest will be posted later. In case it isn’t, here’s a sidebar that ran with the article (I hope!):

Beating the heat

1) Acclimatize: Research shows you significantly improve your heat tolerance after 10 to 14 days of exposure. But it’s not enough to just sit on the porch fanning yourself – you have to actually sweat. In a study published last year, researchers from San Diego State University had eight volunteers exercise for 10 days, 90 minutes a day after having Botox injected into one arm to block sweating. At the end of the study, the sweat glands in the sweaty arm were producing 18 percent more sweat – a sign of good acclimation – while the glands from the arm that remained dry became less productive.

2) Slushies: Olympic athletes have long been using fancy ice vests and cold baths prior to competing in the heat. In 2008, the Australian team unveiled a new, more convenient “pre-cooling” technique: slushies. They brought seven slushie machines to Beijing, using them for soccer, track, cycling, triathlon and a host of other sports. The secret formula: they diluted a standard sports drink by half with water, cooled it to -1° C, and drank 14 millilitres per kilogram of bodyweight shortly before competing.

3) Breathable clothing: A forthcoming study in the journal Applied Ergonomics put the claims of athletic apparel makers to the test, with volunteers exercising for an hour wearing either a cotton T-shirt or a polyester/elastane blend. As expected, the polyester shirt permitted greater sweating efficiency, and the sweat-soaked cotton shirt weighed 50 per cent more. Interestingly, though, the cotton shirt didn’t actually make the subjects any hotter – so if you’re committed to your retro gear, you can stick with it.

4) Dunk yourself: If you do find yourself overheating, the quickest way to cool down is to plunge into the pool – and you don’t necessarily need to subject yourself to an ice bath to cool down quickly. Some researchers now argue that pleasant water temperatures of 24-26° C are just as effective as colder temperatures, and can bring heat stroke victims back to safe temperatures in less than three minutes. The key: the warmer water doesn’t constrict the blood vessels under your skin, allowing more efficient heat transfer.

Plus an explanation of “wet bulb globe temperature”:

Wet bulb globe temperature (WBGT)
Developed for the U.S. Marines in the 1950s, the WBGT scale accounts for temperature, humidity, solar radiation and wind. The commonly reported humidex, in contrast, only accounts for temperature and humidity. Proper measurement of WBGT requires three separate thermometers, including one inside a black globe and another covered with a wet cotton wick. As a rough estimate, WBGT is higher than air temperature when the relative humidity is above 50 per cent, and lower when it’s below 50 per cent. The key difference from the humidex: direct sunlight raises WBGT compared to a cloudy day, even if the temperature is the same.