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Archive for March, 2010

How many meals a day should you eat?

March 31st, 2010

In response to a recent reader e-mail:

My question is the following: is it better to eat three meals per day or is it better to eat several small meals throughout the day? I am currently weight training a few times per weeks and I am also trying to lose some weight. Ideally, I want to lose some fat while also gaining some muscle.

This debate has bounced back and forth since at least the 1960s (when some key papers were published in Lancet and the American Journal of Clinical Nutrition). The latest take comes in a study by researchers at the University of Ottawa that will appear in a forthcoming issue of the British Journal of Nutrition. The basic idea is that eating more frequently might keep you feeling more full, possibly by preventing big swings in the gut hormones that influence hunger:

Increased feeding frequency has often been proposed to convey favourable effects on body weight, adiposity and energy intake, but controversy persists. It has been hypothesised that the favourable effect of increased meal frequency (MF) could emanate from a more sustained release of gastrointestinal hormones; however, more studies are needed to confirm this postulation.

In this study, they put 16 obese volunteers on diets with identical caloric deficits for eight weeks. Half of them ate three meals a day, while the other half at three meals plus three snacks. The results: no difference. Or, in science-ese:

The premise underlying the present study was that increasing MF would lead to better short-term appetite regulation and increased dietary compliance; furthermore, it was hypothesised that these predicted beneficial effects of increased MF could have resulted from more favourable gut peptide profiles, potentially leading to greater weight loss. Under the conditions described in the present study, all three hypotheses were rejected.

Now, only a fool would think that, after nearly half a century of conflicting results, the newest study must be the truest. This is just one more data point. But it suggests to me that there isn’t compelling evidence either way — so the choice is up to you. Personally, I snack.

(Thanks to Jim for the question, and to this NYT article for the pointer.)

Why harder is better than longer for post-weight-loss exercise

March 29th, 2010

I posted earlier this month on “why weight loss isn’t just calories in minus calories out,” which led to an interesting discussion on the ways in which the body tries to prevent itself from gaining or losing weight. On that topic, I came across an interesting study published earlier this year in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, from researchers at Columbia University. The gist: it’s the efficiency of our muscles, on a cellular level, that conspires to hold our weight steady.

It’s well-known that, if you lose weight, your metabolism slows down to burn fewer calories. (That’s why, as a recent JAMA paper pointed out, eating one less 60-calorie chocolate-chip cookie per day won’t allow you to keep losing weight forever. Instead, if exercise and other factors are kept constant, you’ll plateau after a few years at a weight six pounds lighter.) Part of that is because, as Phil Koop pointed out, “adipose tissue has a metabolic cost.” Or as the JAMA paper puts it:

A person who consumes an extra cookie every day will initially experience weight gain, but over time an increasing proportion of the cookie’s calories will go into repairing, replacing, and carrying the extra body tissue.

But the Columbia paper makes it clear that the extra tissue, on its own, isn’t enough to explain the changes in how many calories you burn:

Maintenance of a body weight 10% below “usual” for a lean or obese individual is accompanied by a reduction in systemic energy metabolism (~300–400 kcal/day less than that predicted solely on the basis of changes in body weight or composition), neuroendocrine function (decreased circulating concentrations of leptin and of bioactive thyroid hormones), autonomic nervous system physiology (decreased sympathetic nervous system tone and increased parasympathetic nervous system tone), and behavior (decreased satiety) that act coordinately to return body weight to its initial level.

To figure out where these missing calories go, the Columbia group has been doing extremely careful experiments that involve checking volunteers into an inpatient research clinic for several months at a time, and feeding them only a liquid diet (40% corn oil, 45% glucose, 15% casein protein, by calories) so they can precisely monitor energy intake. They control the amount of feeding to make the subjects gain or lose 10% of their body mass, then study the changes to their metabolism. Pretty neat stuff.

Anyway, the major finding of this new study is that “skeletal muscle work efficiency” changes dramatically when you change your body weight. It’s not just because your muscles have less weight to carry around — it seems to have more to do with changes in the ratio of enzymes that determine whether the muscle burns carbohydrate or fat. When you lose weight, your muscles get more efficient — which seems like a good thing, except that it means you burn significantly fewer calories when you move around, which pushes your weight back up. The opposite happens when you gain weight: your muscles get less efficient.

So what’s the take-home (other than “Try not to gain weight, because it’s really hard to lose once you do.”)? Because the ratio of carbohydrate-to-fat utilization depends on the intensity of physical activity, there’s reason to believe that the efficiency changes are only relevant at very low intensities — corresponding to the activities of day-to-day life as opposed to “exercise.”

From a therapeutic standpoint, exercise post-weight reduction might be more effective at higher workloads, i.e., that the weight-reduced individual might “escape” this increased efficiency by altering the intensity of exercise even without necessarily increasing the work performed.

In other words, exercise harder rather than longer might be the most effective strategy for keeping weight off.

Live Q&A: Thursday, March 25, 3 p.m. EST

March 24th, 2010

Just a heads-up that I’ll be doing a live web-chat Q&A on the Globe and Mail website tomorrow (Thursday, March 25, 3 p.m. EST), taking questions about running, training and preparing for races. Feel free to pop by with any questions you’ve got — the session will last an hour, and will be located at this link.

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The secret of Kenyan success: it’s not the hemoglobin

March 23rd, 2010

April’s issue of Medicine & Science in Sports & Exercise brings another in the long line of studies trying to figure out why Kenyan runners are so much better than the rest of the world (other than some of their East African neighbours). As researchers from the universities of Bayreuth and Tubingen in Germany write:

Possible reasons for this performance superiority range from the physiological to the biomechanical, social, and economic, but none of them appears to be exclusively responsible.

Earlier studies have found that elite Kenyan runners have better running economy than elite Caucasian runners — in other words, they require less oxygen to run at a given level of effort. One theory is that Kenyan muscles somehow use oxygen more efficiently, but studies of muscle morphology and function haven’t been able to pick up any significant differences. Another possibility is that, thanks to adaptations from having ancestors living at altitude for 100,000 years, Kenyans are able to transport more oxygen in their blood to fuel the muscles.

To investigate this possibility, the new study measures total hemoglobin mass (tHb-mass) and blood volume (BV), the two factors that predominantly determine oxygen transport. They compared 10 Kenyans with an average 10K time of 28:29 who were staying in Germany for six weeks with a group of 11 German runners with average 10K time of 30:39. Cutting straight to the chase: when the Kenyans arrived in Germany from altitude, their total hemoglobin mass and blood volume per kilogram of body weight were essentially identical to the Germans. As the six weeks in Germany progressed, the Kenyans got fatter (added 3 kg of bodyweight, including 1 kg of fat), and their hemoglobin and blood measures got worse. The conclusion:

The oxygen transport of the blood, that is, tHb-mass and BV, cannot explain the superior endurance performance of Kenyan runners. All of these parameters are in the same range when compared with those of elite German runners, and tHb-mass even deteriorated after adaptation to near sea level.

Jockology: some (but not all) pre-run stretching slows you down

March 18th, 2010

I posted last month about a new study on how static stretching before your run makes you slower and less efficient. To find out more about the study, I got in touch with the lead author, FSU’s Jacob Wilson. The result is this week’s Jockology column:

For years, researchers have been finding that the more flexible you are, the less efficiently you run – a message that tradition-bound runners have been reluctant to hear. Now, research to be published later this year in The Journal of Strength and Conditioning Research makes it clear that some (but not all) prerun stretching makes you slower. [read the whole article]

The most significant new piece of news in the article is that Wilson and his colleagues have just finished a follow-up study, in which they used the exact same protocol to study dynamic stretching. They’re still completing the analysis, but the results appear to show no significant decrease in performance for pre-run dynamic stretching. This means that you can still get your flexibility fix before a run without compromising performance — you just need to use dynamic stretches instead of static ones. (Some examples, with illustrations, are provided in the Jockology article.)

Drilling deeper into the dynamic stretching data, Wilson said it appeared that the most experienced runners weren’t affected by the pre-run stretches. Less experienced and less fit runners, on the other hand, still saw a bit of performance decline, probably because the unfamiliar stretches fatigued them a bit. So make sure you practice these stretches before trying them in a race situation. (This last stuff is very preliminary, so it may not be statistically significant — we’ll have to wait until the study is published to see.)

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How salty is your sweat? A home test kit

March 17th, 2010

I just noticed, a little belatedly, that an article I wrote for the March issue of Canadian Running magazine is now available online. It describes my experiences with a home sweat analysis kit from Medion Corporation, and compares the results to a laboratory sweat test I did with Lawrence Spriet of the University of Guelph and the Gatorade Sports Science Institute.

In the name of science, I dabbed some shaving cream on the back of my leg and scraped clear a fist-sized area of bare skin. I was about to undertake a new home sweat test to find out exactly how much salt my sweat contains, and I needed to make sure the absorbent patches would stay glued to my skin once the fluid started to flow…

It was an interesting experience, and the home test kit was pretty neat (though a little pricey at $250). It measured a lower sodium concentration than I got in the lab test, something that I think may be due to the fact that I was dehydrated before the lab test (I cycled for 40 minutes in hot sun just to get to the lab).

Overall, I’m not sure what to make of this information. I’ve just been reading The Runner’s Body, the book by the Science of Sport bloggers, and they argue that the theory linking electrolyte loss to muscle cramps is mistaken (a topic I’m looking forward to digging into a little more deeply). Personally, I’ve generally focused on (relatively) shorter distances, so my training runs don’t tend to be multi-hour affairs — which means I’ve never really worried about electrolytes. But for marathoners and triathletes out there, is knowing how salty your sweat is a piece of information that would help you plan your hydration strategy?

Kevin Sullivan’s training: seven years of detailed analysis

March 16th, 2010

I don’t know how I missed this, but there was a paper in the December issue of the Journal of Strength and Conditioning Research that is pure track-geek heaven. It’s called “Performance Modeling in an Olympic 1500-m Finalist: A Practical Approach,” and in it, researchers from Eastern Michigan University take seven years of Canadian miler Kevin Sullivan’s logs (from 2000 to 2006) and subject them to detailed analysis.

The goal of the research is to see if they can use basic “impulse-response” training theory to predict upward and downward trends in Sullivan’s race performances. To put it simply, they assume that:

Performance = Fitness – Fatigue

Makes sense so far. Every time time you train, you create some fatigue… and then a little while later, your body compensates by increasing your fitness a bit. So at any given moment, your performance ability can be estimated by adding up the contributions of every training session you’ve done toward your fitness and fatigue. Yesterday’s training session will have a big impact on your fatigue, but none on your performance. A session from three weeks ago, on the other hand, will have a performance impact but not much of a fatigue impact.

So how do you model the impact? Without getting too far into the nitty-gritty, the researchers add up every bit of running Sullivan does and calculate its pace as a fraction of the pace he could maintain all-out for an hour (akin to what runners would think of as threshold pace). A day in which he ran all-out for an hour would get a score of 100. As it turns out, over the course of a full year, he tends to average between 50 and 55 of these “points” per day. During base training, he averages over 60, with individual days sometimes exceeding 100.

So they plug this training data into the “impulse-response” formulas to see if there’s any correlation with performance. Previous studies in other sports have found good predictions averaged over whole teams, but it’s trickier with an individual athlete. They’re not trying to predict exactly how fast he’ll run in a given race — rather, it’s a question of looking for trends, to see whether his “performance score” is getting higher or lower. That way, coaches can react by taking extra rest, training harder, or whatever.

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As an example, I’ve included one of the figures here. It shows (A) his 2000 season, when he came fifth at the Olympics, and (B) his 2004 season. The dotted line shows his “training score” — basically how hard he’s training — and the solid line shows his predicted performance. The triangles show his race performances, converted to Mercier points. The circled ones are at the Olympics. In their discussion section, they suggest that maybe he peaked a little too early in 2000 — but it seems to be they’re using their 20-20 hindsight vision to make that call, because that’s not what their model predicts. On the contrary, the solid line is highest right after the Olympics, so maybe he peaked a little late… or maybe he peaked just right. There are many debates that track geeks could have about this data — which is why it’s so much fun!

The original reference: J Strength Cond Res. 2009 Dec; 23(9): 2515-23.

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Stretching is still bad even if you follow it with more warm-up

March 9th, 2010

I’m a little more than a year late in reporting on this paper, but I just stumbled across it while researching another story, and thought it was interesting. As I discussed in a recent post, there’s a
lot of evidence emerging these days that stretching has some acute negative effects. When I wrote about this topic in the Globe back in 2008, one of the researchers I spoke to basically said (and I paraphrase): “The studies all show that pre-game stretching makes you weaker and slower, but athletes don’t really care. So the best thing you can do is encourage them to stretch early in their warm-up, and then do some more dynamic activity afterwards to help ‘shake out’ the negative effects of stretching before game time.”

So the paper I just found, from the January 2009 issue of the European Journal of Applied Physiology, tackles this very question:

Recently, it has been suggested that the published research, testing after an acute bout of stretching, does not reflect current practice where individuals follow up a bout of stretching with further activity. Therefore, the aim of this study was to investigate the use of stretching followed by a secondary bout of movement.

Basically, the subjects did a five-minute warm-up on the treadmill; then did a vertical jump test; then either did nothing, static stretching, or dynamic exercises; then did another jump test; then they all did another set of warm-up exercises (i.e. high knees, skip-steps, side-stepping, cross-overs and zig-zag running); then did another series of jump tests after 10, 20 and 30 minutes.

The results: after the first stage, the static stretching group jumped lower, while the dynamic exercise group jumped higher. After the second part of the warm-up, the static stretchers still jumped significantly lower than both the dynamic group and the controls. So you can’t just “shake out” the negative effects of stretching (at least with this particular protocol): once you’ve done it, you’re stuck with the effects for an hour or two.

UPDATE (a few minutes later): Okay, as I dig more, I find more studies on this topic. For example, this November 2009 study, titled “Negative effect of static stretching restored when combined with a sport specific warm-up component,” which reaches the opposite conclusion. Clearly, this debate is far from settled.

More back-pain breakthroughs: the role of the La-Z-Boy

March 8th, 2010

In the wake of last week’s article on strength training and back pain, I got an e-mail letting me know about another important aspect of back pain recovery that I’d neglected to mention:

While there’s plenty of advice out there about how to exercise correctly, there’s not much out there about how to relax – which should be part of any exercise regimen – particularly for people experiencing back pain.

Fortunately, my correspondent had the answer:

To that end, did you know – and this is something both physicians and chiropractors apparently agree on (see below) – there’s now a recent, and valid, medical argument that time spent in your La-Z-Boy, might actually be good for your lower back?

Gadzooks, what wonderful news!

Okay, okay, you’ve now figured out that my new friend is a PR guy for La-Z-Boy. But I thought the e-mail was pretty funny — and, unlike many of the unintentionally hilarious PR pitches I receive, he thought so too:

I hope you’ll receive this email in the spirit its intended, 50% in all seriousness, 50% tongue planted firmly in cheek.

I have to admit, he had my hopes up. I was looking forward to reading about clinical trials where people watched TV from La-Z-Boys versus flimsy folding chairs or something. In the end, the “medical evidence” was a survey of doctors and an endorsement from the American Chiropractic Association. Their doctor-spokesperson recommends “relaxing in reclining furniture that offers total body and lumbar support as well as varying degrees of reclining, since every person has unique support needs.”

So take it for what it’s worth (i.e. it’s common sense, but it’s not evidence). And lobby your local La-Z-Boy dealer to sponsor an actual clinical trial, so I can really write about this!

Can strength training combat chronic back pain?

March 4th, 2010

This week’s Jockology column takes a look at some rather surprising research from the University of Alberta on back pain and lifting weights:

The question

My lower back is killing me. What can I do about it at the gym?

The answer

It’s the classic moving-day injury: You’re hoisting a dresser or grabbing one end of a sofa, then – bam! – you throw out your back.

So it may come as a surprise to hear that a promising solution for chronic lower-back pain, according to a series of recent studies from the University of Alberta, is lifting weights. A whole-body strengthening program dramatically outperforms aerobic exercise for those whose nagging back pain lingers for many months, the researchers say. And the more you lift, the better. [read on...]

There’s always a risk in reporting on research like this that it will get taken out of context. I should emphasize here this research applies to chronic (i.e. not immediately after you throw your back out) and non-specific (i.e. not related to a specific disc or muscle problem) back pain. And it’s not advocated strengthening the lower back itself — it’s strengthening other areas of the body, like the arms and legs, to take some load off the back.

For that matter, even that diagnosis remains controversial:

This one-size-fits-all approach has limitations, though, according to Stuart McGill, a professor of spine biomechanics at the University of Waterloo .

“There’s actually no such thing as non-specific back pain,” he says. “It just means you haven’t had an adequate assessment.”

Still, the results of the studies are interesting — and very much worth thinking about, in my opinion. They’re just not for everybody with back pain.

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