Archive for November, 2010

Drinking during exercise: maybe you don’t need as much as you thought

November 30th, 2010

My column in today’s Globe takes on a pretty controversial topic: how much water can you afford to lose as sweat before your performance suffers? I gave a little preview of one of the studies in a blog entry a few weeks ago, but this article is a much more detailed look at some recent research suggesting that the amount of weight you lose during exercise doesn’t necessarily correspond to the amount of water you lose:

Here’s a riddle posed recently by South African scientists: A group of soldiers undertook a gruelling 14.6-kilometre march during which they lost an average of 1.3 kilograms. But sophisticated measurements with isotope tracers showed the total amount in water in their bodies actually increased by 0.53 kilograms. Where did this “extra” water appear from?

Groups such as the American College of Sports Medicine have long advocated weighing yourself before and after exercise to determine how much fluid you lost. A litre of water weighs exactly one kilogram – so by this calculation, if you’re a kilogram lighter, that means you sweated out one litre more fluid than you replaced by drinking. Lose more than about 2 per cent of your starting weight, the ACSM warns, and your performance will suffer due to dehydration.

But the South African study, published in the British Journal of Sports Medicine by researchers at the University of Pretoria, adds fuel to a simmering debate about whether weight loss during exercise corresponds to water loss. They argue that some of the weight loss is from the energy stores you burn, and that your body has “hidden” stores of water that are released during exercise – which may mean we need to rethink how we approach hydration. [READ THE REST OF THE ARTICLE…]

The print version of the article is accompanied by a fantastic graphic by Trish McAlaster that breaks down the various ways your body gains and loses water during a marathon. So far it’s not available online (I’m hoping it will be posted later), but it you have a copy of the paper around, check it out.

Treadmills make you walk slower but work harder and feel worse

November 28th, 2010

A bit of an unusual study from Brazil just published online in Medicine & Science in Sports & Exercise. Basically they asked 34 young adults to go for a 20-minute walk either on a treadmill or outdoors on a 400-metre track, at whatever pace they would “feel happy to do regularly.” The results: they chose to walk significantly faster on the track than on the treadmill — but their percent of VO2max and their perceived exertion was higher on the treadmill, despite the slower speed. In addition, their “affective valence was more positive” (i.e. they were happier) on the track.

The goal of the study was to figure how to convince more people to exercise (and in that sense, it was somewhat unsuccessful because the volunteers chose paces that were too slow to elicit significant fitness gains), and to figure out whether recommendations formulated in the lab can be applied to normal outdoor conditions.

Leaving aside the psychology (which is certainly interesting — I know I’m happier outside than on a treadmill!), the fact that people walked more slowly but worked harder on the treadmill is odd. This wasn’t a biomechanics study, but it seems like more ammunition for those who say that movement on a treadmill is fundamentally different from overground — a debate that’s been dragging on for a long time now. I still don’t really understand why it should be different (other than wind resistance, which wouldn’t explain the current results), but apparently this is one of those deep mysteries…

Beta-alanine: a boost for anaerobic power… and finishing sprint?

November 26th, 2010

In general, I’m not a big fan of performance-boosting supplements, in part because of some vague notions of “the spirit of sport” and in part because the vast majority of them are expensive placebos. But one of the sessions at the sports nutrition conference in Canberra earlier this week made a strong case that beta-alanine now has enough evidence to join the very, very short list of supplements with solid performance-enhancing science behind them (e.g. caffeine, creatine). The first important study of beta-alanine was only in 2006, but there have been 27 more studies since them, according to Trent Stellingwerff, a researcher at the Nestle Research Centre in Switzerland who also works with Canadian Olympic teams.

(Sorry for the delay in reporting on the sports nutrition conference — really busy week! There’s lots more to come, which I’ll post over the next few weeks.)

Basically, beta-alanine works just like baking soda to buffer pH, but does it from inside the muscle rather than outside (and, happily, doesn’t cause diarrhea). The actual buffering agent is something called carnosine, which is present in meat. When you eat meat, the carnosine is split into its two constituent amino acids (beta-alanine and histidine), which are absorbed into your muscles and recombine to form carnosine again. The rate-limiting step is the absorption of beta-alanine into your muscles, so if you take some extra beta-alanine you end up with more carnosine.

So when does this work? The sweet spot is thought to be exercise lasting between 60 seconds and 10 minutes. Studies dating way back to the 80s showed that sprinters have twice as much carnosine in their muscles as marathoners do. More recently, a Belgian study measured baseline carnosine levels in a group of rowers (i.e. without supplementation) and found that higher carnosine levels correlated to higher performance. Supplementing with beta-alanine then led to a 4.3-second improvement over ~6 minutes for the rowers.

The dosing details: unlike baking soda, it’s not a one-shot deal. Trent suggests that taking 3-6 g/day for four to eight weeks will increase muscle carnosine content by 40-50%. It then stays high for quite a while, so you can expect to continue seeing a performance boost up to a month after stopping supplementation.

For endurance athletes, there are a couple of potentially interesting wrinkles. A 2009 study in the Journal of Applied Physiology (Van Thienen et al.) found that cyclists on beta-alanine performed better in a 30-second all-out sprint at the end of a 110-minute time trial. So the buffering might help with the anaerobic demands of a finishing sprint even during a very long race, though this is just one study so far.

The other thing to consider is whether beta-alanine could help endurance athletes sustain higher levels of intense training — after all, interval sessions often include intense running within that 60s-10min sweet spot. Stellingwerff, who coaches a bunch of athletes including his wife, a 4:05 1,500m runner, gave one piece of practical advice. He said for a workout like 10x400m, athletes on beta-alanine tend to feel really good in intervals 1, 2, 3 and 4 — in fact, they sometimes feel too good and wreck the rest of the workout, so that intervals 7, 8, 9 and 10 get really ugly.

Anyway, food for thought. But as Trent pointed out, there’s no point even thinking about these kinds of supplements if you haven’t already taken care of the far more important basics of good diet and recovery and so on.

Swelling helps healing, so are ice and NSAIDs bad?

November 23rd, 2010

Lots more to come from the sports nutrition conference in Canberra, but first I just wanted to quickly put up a link to my article in today’s Globe about new research suggesting that swelling may help injuries heal faster:

Every weekend athlete knows the RICE rule for dealing with minor sprains and strains: rest, ice, compression and elevation, with the latter three tactics aimed at minimizing inflammation.

But a study published last month by researchers at the Cleveland Clinic adds to growing evidence that swelling actually plays a key role in healing soft-tissue injuries. The result is a classic tradeoff between short-term and long-term benefits: reducing swelling with ice or anti-inflammatory drugs may ease your pain now, but slow down your ultimate return to full strength.

“This whole discovery has really thrown into question all of our traditional approaches to treating injuries,” says Greg Wells, a University of Toronto exercise physiologist who works with national-team athletes at the Canadian Sport Centre. [READ THE WHOLE ARTICLE…]

Maximizing carbohydrate absorption during exercise

November 22nd, 2010

Great first day at the International Sport Nutrition Conference in Canberra. Several interesting sessions that I’ll post about in days to come. For now, since I have just a few minutes before dinner, a few notes about Asker Jeukendrup‘s session, which he called “Carbohydrate: boring old or exciting new?”

In the “boring old” category, he took aim at the ACSM’s position stand, which states:

For longer events, consuming 0.7 g carbohydrates/kg body weight/h (approximately 30-60 g/h) has been shown unequivocally to extend endurance performance.

Now, it’s well known that if you take a drink with glucose in it, the fastest you can possibly make use of it is at a rate of about 0.8-1.0 g/min, no matter how much carb you have. The rate-limiting step is absorption from the intestine, which doesn’t depend at all on how big or small you are, so the guidelines shouldn’t be expressed “per kg body weight” — it should just be 30-60 g/hr (with the high end corresponding to the 1.0 g/min which is the fastest we can make use of glucose).

However, there are ways around this rate-limiting step. Over the last five or six years, Jeukendrup’s group has done a long series of studies on combining glucose and fructose. On its own, fructose is absorbed slower that glucose. But it’s transported across the intestinal wall by a different mechanism, so you can have both glucose and fructose being absorbed at the same time. Add them together, and you can get about 1.7 g/min that the body actually makes use of.  (And this is, indeed, the formulation used in Power Bar’s “C2 Max carb mix” bars and gels.) So Jeukendrup suggests that ultra-endurance athletes should aim for closer to 90 g/hr of carbs, and he showed some data from Ironman triathlete Chrissie Wellington, who does precisely that (and who just set a new Ironman world record in Arizona).

Does this apply to everybody? Well, it’s not such a big deal for shorter events. He offered these loose guidelines (which I copied down quickly — if I made any mistakes, I’ll correct them when I get the official proceedings):

  • less than 45 min: no carbs needed (but he later noted that some new studies are now showing that “mouth rinsing” with carbs can have an effect with exercise bouts as short as 30 min)
  • 45-75 min: mouth rinsing, with any type of carb
  • 1-2 hr: up to 30 g/hr, any type of carb
  • 2-3 hr: up to 60g/hr, carbs that are oxidized rapidly like glucose or maltodextrin
  • more than 2.5 hrs: up to 90g/hr, MUST be a combination of carbs that are absorbed via different mechanisms (e.g. glucose or maltodextrine combined with fructose in a 2:1 ratio)

Anyway, that’s a quick overview of some of the take-home messages he offered. There was lots of discussion afterwards, so if you have any questions about any this stuff, feel free to post ’em in the comments section and I’ll answer if I can.

International Sport Nutrition Conference in Canberra

November 21st, 2010

I’m at the Australian Institute of Sport in Canberra for the next few days, for the International Sport Nutrition Conference. Looks like some great sessions on tap from leading researchers around the world:

  • “Sports nutrition for the brain” (Romain Meeusen)
  • “Beta alanine & carnosine: science and application” (Trent Stellingwerff)
  • “Protein, timing and muscle gain” (Stuart Phillips)
  • “Train low, compete high” (Louise Burke and John Hawley)

Plus lots of other talks and workshops. The first session starts in half an hour — I’ll try to post some updates over the next few days with highlights. It’s the first conference I’ve been to that started with a 7 a.m. run (during which, needless to say, I and few others got hopelessly lost, and almost got run over by a pair of kangaroos that bombed across the path about two feet in front of us).

Dehydration and change in body mass: not linked after all?

November 17th, 2010

I (and everyone I know) have always taken this for granted: if you weigh yourself before and after a workout, the difference tells you how much fluid you lost to sweat (after correcting for any water that you drank during the workout). If you lose more than about 2% of your bodyweight, dehydration will impair your performance. That’s what the ACSM guidelines on hydration say:

If proper controls are made, BW [bodyweight] changes can provide a sensitive estimate of acute TBW [total body water] changes to access hydration changes during exercise.

But it turns out there’s actually a hot debate currently raging in the literature about this. The latest salvo just appeared online in the British Journal of Sports Medicine, from researchers in South Africa (Pretoria, not Cape Town, though Tim Noakes is indeed listed as a co-author). They studied 18 soldiers doing a 14.6-kilometre march while drinking “ad libitum” (however much they wanted), and took careful measurements of a whole series of physiological parameters. One of those parameters is “total body water” — the sum total of all water stored in the body, typically totalling about 60% of body mass — which they  measured using radioactive tracers. When we talk about hydration and dehydration, that’s what we’re really talking about: is there sufficient TBW to ensure that all the tissues and cellular processes in the body are working optimally.

The surprise: the subjects lost 1.98% of their body mass on average, but their total body water stayed roughly the same (actually, it increased by 0.53% on average). They drank 0.85 litres per hour, but sweated out 1.289 litres per hour. In other words, they were losing fluid — so how did their total body water stay the same or increase?

Some of the possible explanations are explored in this 2007 paper by Ron Maughan. One is “metabolic water”: when your body converts fat or carbohydrate into ATP, it release some water as part of the sequence of chemical reactions (one estimate is that it releases 0.13 g per calorie burned). A more significant possibility, especially for endurance athletes, is that every gram of glycogen you store ties up an estimated 3-4 g of water. A marathoner who carbo-loads and packs in 450 grams of glycogen, for example, could in theory have 1.35 kg of “hidden” water that will gradually be released into the body as carbohydrate stores are released during exercise.

So what this study claims is that these soldiers were sent out on a march and told to drink however much they wanted; they lost 2% of their body mass, but weren’t dehydrated. Their  interpretation: the body’s thirst mechanism is built to maintain the osmolality (the concentration of “stuff,” essentially) in the blood and tissues, which was indeed preserved in this experiment.

Is the debate over? Far, far from it. For one thing, a laboratory experiment at Penn State published last year found exactly the opposite — that the amount of weight you lose during exercises correlates perfectly with the loss in total body water. How to reconcile these diverging views? I’m not sure, but I’m digging into the literature and doing some interviews for an upcoming article.

Another blood spinning study finds no improvement in Achilles tendons

November 15th, 2010

Actually, the title isn’t quite true — this is a just new wrinkle on the same Dutch study reported earlier this year that found no difference between platelet-rich plasma injections and placebo (saline) injections for 54 patients with chronic Achilles tendinopathy. The new paper, just published online at the British Journal of Sports Medicine, presents further data from this experiment: in addition to the previously reported pain scores (which, admittedly, are a bit wishy-washy and subjective), they used “ultrasonographic tissue characterization, a novel technique which quantifies tendon structure.”

Basically, they used ultrasonic imaging combined with computer image recognition to get an automatic (i.e. objective) measure of tendon health. The results: scores improved for both PRP and placebo (note that the subjects were also doing a rehab regime involving eccentric exercises during the study), but there was no significant difference between the groups.

Given the results presented earlier, this isn’t a big surprise — and of course, certainly isn’t proof that PRP doesn’t work in any context. But it’s another reason for skepticism. As the authors conclude, “these data argue against clinical use of this form of PRP in present clinical practice.”

Dynamic warm-up restores power lost in cold temperatures

November 11th, 2010
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I ran a trail race last weekend that involved a waist-high creek crossing through pretty cold water. Climbing the long uphill after the creek, my legs were suddenly dead — I felt like I could barely get my feet a few inches off the ground. So I sympathize with the volunteers in this study, published online ahead of print in the Journal of Strength and Conditioning Research by researchers at the University of Connecticut.

The researchers used vertical jump to measure leg power in a group of NCAA D1 athletes, with three main purposes: (1) to see how much power would increase after a dynamic warm-up, (2) to see how much power would decrease if the subjects were pre-cooled by standing waist-high in 12 C water, and (3) to see if the dynamic warm-up could off-set the negative effects of cooling — something that would be of interest to athletes who compete in cold temperatures.

Everything was pretty much as expected. The dynamic warm-up increased jump power by 5%, and the cold water decreased jump power by 21%. When the subjects did a dynamic warm-up after cold-water immersion, they regained 70% of the lost power — not perfect, but still good to know.

Leaving aside all this cold-water stuff, the main reason I’m posting this is highlight the ever-stronger consensus that dynamic warm-up is the way to go. As the researchers note in their introduction:

Traditionally, static stretching exercises have been used by many coaches to prepare athletes for sporting activity. However, studies have shown that static and proprioceptive neuromuscular facilitation (PNF) stretching may negatively impact jump performance and power output. Dynamic warm-up exercises now appear to be preferred after many studies have compared the 2 modes and demonstrated dynamic exercises to be much more effective.

So what does that mean in practical terms? Well, here’s the dynamic routine the researchers used:

Continuous warm-up 1 (20 yds)
1. Arm circles forward X 1: walking forward on the toes while circling the arms forward with the arms parallel to the ground
2. Backward heel walk w/arm circles backward X 1: walking backward on the heels while circling the arms backward with arms parallel to the ground
3. High knee walk: walking forward and pulling the knee up to the chest with both arms, alternates as you walk
4. High knee skip: skipping forward and bringing the knee up so that the quadricep is parallel to the ground
5. High knee run: running while focusing on bringing the knees up so that the quadricep is parallel to the ground
6. Butt kicks: running while bringing the heel to the glutes
7. Tin soldiers: walking forward and kicking a single leg up in front while keeping the knee locked in extension (alternates)
8. One leg SLDL walk forward X 1: walking forward with straight legs, lean forward on 1 leg and reach for the foot with the opposite hand
9. 1 Leg SLDL Walk Backward X 1: walking backward with straight legs, lean forward on 1 leg and reach for the foot with the opposite hand
10. Backward skip: moving backward and skipping at the same time
11. Backward run: running backward and extending the rear foot behind you
12. Back peddle: moving backward while shuffling the feet and keeping them low to the ground
13. Overhead lunge walk: hands on the head while doing walking lunges forward
14. Inchworm: starting in the push-up position, walk the feet into the hands; then walk the hands out to the push-up position

Elite triathletes change muscle recruitment off the bike

November 8th, 2010

Following up on last week’s post about the increasing use of 3-D motion analysis, there’s a new Australian study examining the running stride of triathletes coming off the bike in this month’s Journal of Sports Sciences. They took  “moderately trained” (i.e. club level) triathletes and measured their stride during a 30-minute, either with or without a bike ride beforehand, using EMG to measure muscle activation and motion capture to measure the stride.

The basic finding: 14 out 15 triathletes showed no difference in muscle recruitment between the two runs, but five of them did show kinematic differences (their joints were at different angles and moving differently). What’s surprising is that this is basically the opposite of what they found in a similar study of elite triathletes, who kept their stride pretty much constant but had different muscle recruitment patterns off the bike.

What this suggests is that it’s difficult to run “normally” coming off the bike, but elite triathletes have trained long enough to learn how to send different signals from their brain to their muscles in order to reproduce their normal stride.

Therefore [the authors conclude], training interventions focused on quickly restoring optimal running movement patterns after cycling may be advantageous for moderately trained triathletes’ performance.

The only problem: I’m not really sure what those interventions would be, other than doing your training in a 3-D motion capture system!

[Thanks to Steve Magness for the tip-off.]