Archive

Archive for July, 2010

How exercise affects knees: bone spurs vs. cartilage

July 30th, 2010

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

July 29th, 2010

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

July 28th, 2010

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

July 26th, 2010

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

July 23rd, 2010

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.

Can biomechanical analysis cure Dathan Ritzenhein’s injuries?

July 21st, 2010

Dathan Ritzenhein just announced that he’ll be running the New York City Marathon this November, joining a stacked field that already includes Haile Gebrselassie and Canadian hope Simon Bairu. One thing that jumped out at me from the press conference (as reported by Letsrun) was his coach Alberto Salazar’s assertion that Ritz’s injury problems are a thing of the past thanks to some high-tech analysis:

“Gordon Valiant – the head of biomechanics for Nike – did an evaluation of Dathan and was able to find some things that are unique to Dathan with the way he runs and strikes his foot. With that (study completed), we now have some modified inserts. I wouldn’t call them orthotics – just an insert into the shoe where he has an abnormal amount of force near his third metatarsal. It seems to have alleviated his symptoms completely and we’ve retested him in the lab and shown those forces have been lessened tremendously.”

For those who’ve been following the barefoot running debate, this should raise some flags. For years, critics of the big shoe companies have pointed out that measuring forces in a lab setting doesn’t necessarily equate to a change in injury rates. Australian minimalist advocate Craig Richards said as much in an article I wrote back in 2008:

“Shoe researchers and manufacturers will try and bamboozle you with the results of hundreds of biomechanical studies,” [Richards said]. While these studies tell you how your stride is affected by the shoe, “they cannot currently tell you what this means for either the injury risk or performance of the wearer.”

Fair point — though, as I pointed out last month, minimalists are suddenly more enthusiastic about biomechanical studies now that Dan Lieberman and others have provided them with some studies of their own.

Anyway, we now have a study (with n=1) in which the manipulation of biomechanical forces in the foot is hypothesized to solve a longstanding injury problem. The outcome measure: whether Ritz makes it to New York in one piece, with an uninterrupted build-up. Here’s hoping!

,

How calorie restriction extends lifespan

July 21st, 2010

British researchers are presenting some new research on how calorie restriction works at a conference on aging research this week. In a mouse experiment, they found that it reduces cell senescence (the point at which a cell can no longer replicate) and helps protect telomeres (which exercise does too, researchers have recently found). Interestingly, the effects seems to be significant even if if it’s only started later in life and maintained for a relatively short period of time.

As I blogged about recently, I’m a little ambivalent about this whole calorie restriction thing. I just can’t see a happy ending — if it works, you feel guilty about eating for the rest of your life, and if it doesn’t, you die! Ultimately, I respect that we want to know how the body works, and this line of research is part of that. But I was happy to see some of this ambivalence reflected in the quotes from the press release describing the research:

Professor Thomas von Zglinicki, who oversaw the research, said: “It’s particularly exciting that our experiments found this effect on age-related senescent cells and loss of telomeres, even when food restriction was applied to animals in later life. We don’t yet know if food restriction delays ageing in humans, and maybe we wouldn’t want it. But at least we now know that interventions can work if started later.

And a recognition that extra years aren’t the only thing that counts:

Prof Douglas Kell, BBSRC Chief Executive and keynote speaker at the BSRA Conference, said: “As lifespan continues to extend in the developed world we face the challenge of increasing our ‘healthspan‘, that is the years of our lives when we can expect to be healthy and free from serious or chronic illness.

Do the health benefits of cycling outweigh the risks?

July 18th, 2010

In a Jockology column last summer, I described a few studies about how switching from car to bike for a commute affects your exposure to pollution:

Whether you’re better off inside or outside a vehicle seems to depend on the vehicle and location. A Danish study in 2001 measured pollution exposure while driving or biking along identical routes in Copenhagen. The air inside the cars was bad enough that, even taking into account that cyclists were taking longer and breathing more deeply, the drivers were worse off. On the other hand, an Irish study in 2007 found that the air on buses was worse than the air breathed by cyclists, but that the higher breathing rates led to greater total exposure for cyclists.

It’s one of those issues that might make you think twice about cycling through a busy downtown core to get to work — that, and the risk that you’ll be flattened by an impatient driver. There’s an interesting study that just appeared online in the journal Environmental Health Perspectives weighing the balance between cycling and driving in cities (the full text is freely available here). They make an interesting distinction between what’s good for society and what’s good for you:

Though society may benefit from a shift from private car use to bicycle use (e.g. because of reduced air pollution emission), for the shifting individual disadvantages may occur. While the individual may benefit from increased physical activity, at the same time he/she inhales more pollutants due to an increased breathing rate. The risks of getting involved in traffic accidents may increase as well as the severity of an accident.

To tackle this question, the researchers (from the University of Utrecht) crunch an enormous data set to determine what would happen if 500,000 people switch from car to bike for short trips in the Netherlands (though they argue that the conclusions are widely applicable in other countries). They use demographic information along with studies on air pollution, traffic safety and physical fitness to reach the following encouraging conclusions:

For the individuals who shift from car to bicycle, we estimated that beneficial effects of increased physical activity are substantially larger (3 – 14 months gained) than the potential mortality effect of increased inhaled air pollution doses (0.8 – 40 days lost) and the increase in traffic accidents (5 – 9 days lost). Societal benefits are even larger due to a modest reduction in air pollution and greenhouse gas emissions and traffic accidents.

One of the interesting points that emerges in their discussion of the pollution studies is how big a difference your route choice can make (which I also discussed in the Jockology article linked above). In fact, they cite one study that found “walking close to the kerb in London greatly increased personal exposure”!

(via USA Today and — once again! — Amby Burfoot)

Bike-run time is fastest when you go all-out on the bike

July 18th, 2010

For the triathletes out there, an interesting study has been posted online for publication in a future issue of the European Journal of Applied Physiology: “Combine cycle and run performance is maximized when the cycle is completed at the highest sustainable intensity.”

A pair of Australian researchers asked a group of triathletes to perform a series of four 20K bike/5K run time trials, with the intensity of the bike ride varying from 80% to 100% of max intensity (compared to an isolated bike trial they’d done previously). As expected, going harder on the bike led to slower times for the run — but the effect was most pronounced for just the first kilometre of the run, after which it didn’t really matter how hard the subjects had gone on the bike. As a result, the fastest overall bike-run times came when the effort on the bike was highest. In other words, holding back in any way on the bike loses you time that you can’t make up on the run.

Now, there are a number of caveats. The study was small (5 men, 3 women), but the effect was very clear-cut (average times of 62:40, 59:53, 58:29 and 56:37 for the four trials, going from easiest to hardest for the bike leg), so that’s not likely to be an issue. The fact that the distances were 20K-5K instead of 40K-10K is unfortunate. The authors do a song and dance about how the sprint distance is “growing in popularity” so that’s why they decided to study it, which seems absurd. I assume the real reason is that it would have been much harder to get volunteers to do that many 40K-10K efforts in succession. Also, it was a lab study done on stationary bikes with no wind resistance, and the triathletes were recreational — their average 5K time (not preceded by a bike ride) was 19:51.

Still, bearing all these things in mind, it’s a data point:

It is unclear if this relationship would hold for longer-style triathlon race formats, full triathlon races which also include a prior swim leg, races that involve a draft-legal cycle leg or with highly trained or elite triathletes. However, our results suggest that time lost on the cycle leg is unlikely to be made up on the run leg.

Sailing on Lake Superior

July 15th, 2010

Not really related to sports science, but a story I wrote for Canadian Geographic about a sailing trip on Lake Superior that I took last year (from Thunder Bay to Red Rock) is now available online. It’s an absolutely beautiful area, and I hope to visit again before long.