Archive

Archive for July, 2011

Inflexibility is genetically determined and makes you fast

July 30th, 2011

Last year I blogged about some cool findings from the University of Cape Town on a gene called COL5A1, a certain variant of which seems to predispose people to be (a) inflexible and (b) efficient distance runners. That initial study looked at participants in the South African Ironman triathlon; the same research group now has a new study in press at the International Journal of Sports Physiology and Performance looking at 72 runners in the 56km Two Oceans ultra-marathon.

The results confirm the previous findings: runners with the “TT” variant of the COL5A1 genotype ran faster (5:41 versus 6:05 on average), and that group was also overrepresented in the “fast and inflexible” quadrant of subjects. The genotype accounted for about 7% of performance variance.

It’s worth emphasizing that the effect of this gene is still quite small overall — there are so many genes that affect performance that any one gene is unlikely to have a large effect. As the paper puts it:

[T]he magnitude of the effect of the COL5A1 gene on endurance running performance was calculated as being “moderate” in this study. Due to the polygenic nature of the endurance phenotype3, it is highly unlikely that a single gene would have any greater magnitude of effect.

There are plenty of other questions that remain to be answered — for instance, does this genotype allow you to directly run faster, or does it (for example) make you more injury resistant so that you can train more? This study apparently represents just one part of a larger cohort being studied, so perhaps there will be further insights before long.

Extreme heat, dehydration and sodium balance

July 28th, 2011

Another interesting hydration study [UPDATED WITH LINK TO STUDY] from Tim Noakes and his collaborators, studying South African Special Forces soldiers marching in hot conditions — following up the one I blogged about last year. The basics: 18 soldiers did a competitive 25 km march (taking about four hours), carrying 26 kg packs and wearing full battle dress, in temperatures averaging 40.2 C and reaching a high of 44.3 C (112 F). They were allowed to drink only water. The main point: they did it, despite

environmental conditions that approached those considered to be unsafe for practice and competition by the American College of Sports Medicine. Furthermore, all soldiers completed the study successfully and none presented with either the signs or symptoms of ‘‘heat illness’’.

But it’s the details that are most interesting. They were allowed to drink as much as they wanted, and the amount they chose to drink led them to lose 3.8% of their body mass on average — too much, according to conventional thinking. But they showed no sign of trouble, and there was no link between the amount of weight each soldier lost and his finishing time. But (as their previous study showed), weight loss didn’t correspond exactly to water loss: for every 1 kg of mass lost, their total body water stores only declined by 200 g (for details of how this is possible, read the earlier blog entry).

More importantly, the sodium concentration in their blood didn’t change significantly (and neither did their overall plasma osmolality), even though weren’t taking in anything but water. They lost some salt to sweat, but they also lost some fluid, so the concentration stayed relatively constant.

At this sweat sodium concentration, average total sweat sodium losses during the march could have been >240 mmol. Yet despite such large losses that were not replaced during exercise, participants maintained their serum sodium concentration. This confirms the now well-established finding that serum sodium concentration can be maintained during exercise without the need for acute sodium replacement during exercise.

I’m sure plenty of people will disagree with that last sentence! Noakes’s argument is that, if you allow people to drink as much as they want and choose their own pace, they’ll automatically self-regulate in order to preserve homeostasis — and the crucial parameter that your body monitors is not weight or water content, it’s serum osmolality. So it’s no coincidence that the soldiers allowed themselves to get dehydrated to precisely the degree that matched the salt they lost in their sweat — that’s just the way the body works.

P.S. Random aside on dehydration: the introduction of this paper cites another study claiming that Haile Gebrselassie lost 10% of his body mass while setting the current marathon world record. Now that’s impressive!

,

Intervals versus continuous training

July 27th, 2011

The age-old debate: which is “better,” interval training or continuous exercise? It’s a stupid debate — but I’ll get to that in a sec. First, a new study in the August issue of the Journal of Strength & Conditioning Research, from researchers in Spain. They put 22 physically active non-runners through one of three different eight-week training programs:

  1. Intervals: Three workouts a week. Mondays were 4-7 x 2:00, Wednesdays were 3-5 x 3:00, Fridays were 2-5 x 4:00, with rest equal to the length of the interval.
  2. Continuous: Three workouts a week, starting with 16:00 at 75% of vVO2max and building up to a high of 40:00 at 75% of vVO2max.
  3. Control: Nuthin’.

Here’s how the three groups progressed (MAS is their speed at VO2max):

As you can see (and as the paper concludes), the interval training and the continuous training produced virtually identical results. Which proves… well… nothing, really. Comparing a steady diet of 100% intervals to a steady diet of 100% continuous runs is like one of those “If you could only bring one album to a desert island to listen to for the rest of your life, what would it be?” conversations. Every different workout provides a slightly different stimulus to the body, so trying to identify “the best” is a pointless exercise. For optimal performance and health, we need a mix of different workouts.

The authors of the new study make an important point when trying to explain why previous comparisons of interval and continuous training have produced mixed results:

[I]t may be suggested that the exercising intensity and the subjects’ training background influence subsequent endurance training adaptations.

This is key! Take someone who has been “jogging” five days a week for a few years and have them start doing hard interval sessions a couple of times a week, and you’ll see dramatic improvements. But if you have someone who has been doing sprint training but no sustained running for a few years, and then add a tempo run and a long run each week, you might see equally dramatic improvements. In neither case does this “prove” that one type of workout is best — it’s context-dependent.

So what’s the perfect mix of workout types? Science doesn’t have an answer, but elite athletes have settled into some consistent patterns through trial and error. A reader (thanks, Marc!) recently sent me a link to an interesting review published a couple of years ago in Sportscience (full text freely available) that analyzes this question very thoroughly based on studies of elite endurance athletes in many different sports. They conclude that there’s an “80:20″ rule for intensity:

About 80 % of training sessions are performed completely or predominantly at intensities under the first ventilatory turn point, or a blood-lactate concentration. The remaining ~20 % of sessions are distributed between training at or near the traditional lactate threshold (Zone 2), and training at intensities in the 90-100 %VO2max range, generally as interval training (Zone 3). An elite athlete training 10-12 times per week is therefore likely to dedicate 1-3 sessions weekly to training at intensities at or above the maximum lactate steady state.

Other researchers like Carl Foster break it down into three zones rather than two, and say that athletes do about 70% of their training below threshold, about 20% at or near threshold, and 10% above threshold. That’s a pretty small diet of intervals. Of course, elite athletes have different goals (and more time to train) than the recreationally active volunteers in the Spanish study — so the breakdown of three workouts a week might be quite different from 10-12 workouts a week. Still, my advice for anyone at any level is to include at least one interval session and at least one continuous session in your weekly routine — even if you’re just training twice a week!

Pre-drinking to hyperhydrate, and other heat-related research

July 25th, 2011

There’s a great (and timely) article called “Myths About Running in Heat” in the current issue of Running Times (linked to from Amby Burfoot’s latest blog entry), in which Phil Latter takes a look at six common myths relating to topics like thirst and acclimatization. It’s all good stuff, and worth a read.

The one that I hadn’t really thought about before was the idea of “hyperhydration” before running in the heat. In general, if you try to load up on fluid in the days or hours before a run, you’ll just pee it out. But Latter suggests two options. First:

Hyperhydrating, or drinking more fluid than is necessary to maintain fluid balance within the body, is effective right before an event because blood flow is severely reduced to the kidneys during exercise, thus limiting fluid excretion. “The trick then is to be able to absorb quickly and then tolerate the bloating feeling for a couple of minutes into the exercise period,” says [University of Sherbrooke exercise physiologist Eric] Goulet. “As the exercise progresses the intestine will slowly absorb the fluid, which will then be used for physiological regulation.”

Second is the idea of drinking “lightly salted water in the several hours preceding hot weather exercise” — a technique with a long anecdotal history that Goulet is currently testing in the lab:

The biggest trick, Goulet concedes, is making the substance palatable. For his trials, Goulet had the salt water ( just over ¼ teaspoon of table salt per cup) blended with Crystal Light and served at roughly 35 degrees, but adds, “You have to find what works best for you.”

One other interesting point is the idea that drinking fluids helps you deal with heat better — a claim that most people (including exercise physiologists) accept absolutely uncritically. Not everyone agrees, though:

After performing a thorough meta-analysis, Loyola University’s Jonathan Dugas, a well-known blogger on the Science of Sport website, explains why. “I’m not saying there’s no effect of fluid on body temperature, but you have to really qualify it,” he says. “The effect is really small. Maybe a half degree in temperature, maybe less.” [...]

His research suggests hydration levels have almost no effect on one’s likelihood of suffering from even the most extreme of all heat-related issues, heat stroke. [...]

“On a very hot day,” Dugas says, “no amount of drinking is going to change the fact that you’re going to go slower. You can drink up to 100 percent of your body mass, and it won’t keep you from running slower.

For practical purposes, of course, this doesn’t mean that water isn’t a special concern on hot days. The heat will make you sweat more, so you’ll need to drink more that match thirst. But it challenges the widespread assumption that when someone at a race collapses from heat stroke, one of the causes was that they didn’t drink enough water:

Current research suggests that some combination of genetic predisposition, infection, muscle damage, sleep deprivation and high levels of exertion may lead to heat stroke… water intake (or the lack thereof) isn’t mentioned.

 

,

Tendon length, joint flexibility and running economy

July 22nd, 2011

We already know that pre-exercise stretching makes you less efficient at running and cycling. But is it the stretching that’s bad (e.g. by temporarily interfering with the signals from your brain to your muscles), or is flexibility itself a potential problem? For running (though not cycling), your legs function like springs, storing energy with each stride then releasing it in the next stride. If you’re too flexible, the thinking goes, those floppy springs will be less efficient at storing energy.

A new study from the University of Alabama at Birmingham in next month’s issue of Medicine & Science in Sports & Exercise takes a look at this question. They took 21 male recreational runners and measured a bunch of physical traits, then measured their running economy to look for correlations. The key traits they measured were tendon length (Achilles, patellar and quadriceps) and joint flexibility (knee and ankle). They expected that longer tendons would be a good thing: they can store more elastic energy simply because they’re longer. On the other hand, they expected greater joint flexibility to be a bad thing (as far as running economy goes). And that’s exactly what they found:

In conclusion, lower limb tendon length, especially Achilles tendon length, is associated with improved running economy in male recreational distance runners. In addition, plantar flexion and knee extension flexibility are negatively related to running economy.

I don’t think the finding about longer tendons being more efficient means that we should aim to do lots of stretching (after workouts, perhaps) to lengthen tendons. Instead, I think that’s likely just something that’s genetic: some people (including a lot of Kenyans, it seems) have long, thin tendons, and they’re more likely to be efficient runners. But I’m not sure if that’s the correct conclusion. We don’t know whether a couple of years of dedicated stretching to lengthen tendons would have increased or decreased economy, and this study has nothing to say about the question. One problem is that stretching to lengthen tendons will also increased plantar flexion and knee extension, which hurt running economy — so it may be a case of one step forward, two steps back.

I’d also like to point out the contrast between these results and the cycling study I blogged about last month. The two studies seem to point to completely different mechanisms by which stretching could impact endurance performance. This study suggests that stiff musculo-tendon complexes are good for storing energy; the cycling study (which doesn’t involve this stored-energy effect) suggests that stretching does something to the muscle fibres or neuromuscular signalling. So it’s not a simple picture.

Finally, we should bear in mind that running (or cycling) economy isn’t the whole picture. Many athletes — particularly recreational ones — would happily accept a 0.5% decline in economy if it reduced their chances of injury by 50%. I personally don’t think that the evidence for stretching and injury prevention is convincing, but it’s important to remember that we’re balancing different desired outcomes in making training decisions.

Pacing and cognitive development

July 20th, 2011

Here’s a bit of a loaded question: does your pacing strategy — even? positive splits? negative splits? — reveal something about your cognitive development? I blogged a few weeks ago about the perennial question of 1,500-metre tactics and whether going out a fast pace is smart or stupid, so I was interested (and amused) to see a new study from Dominic Micklewright at the University of Essex, just posted online in Medicine & Science in Sports & Exercise, called “Pacing Strategy in Schoolchildren Differs With Age and Cognitive Development.”

It’s actually a really neat and thought-provoking study. Here’s the gist: the researchers studied four groups of children (aged 5-6, 8-9, 11-12, and 14). Each group was asked to run a time trial over a distance that took them about four minutes to finish — so similar to the demands of a 1,500-metre race in adults, actually. Here’s what the pacing for each group looked like:

The basic conclusion from this data:

Younger schoolchildren with less advanced cognitive development exhibited a negative pacing strategy indicating an inability to anticipate exercise demand. Older schoolchildren at a more advanced stage of cognitive development exhibited a more conservative U-shaped pacing strategy characterised by faster running speeds during the first 15% and last 20% of the run.

In other words, young kids go out very fast and fade from the front, while older kids understand the pain that awaits them and hold some energy back until they’re sure they’ll make it to the finish. But there’s more to it than that. The researchers also administered tests to determine where the kids fit into Piaget’s four stages of cognitive development — and they saw roughly the same pattern: kids with a lower stage of cognitive development went out hard and got progressively slower, while the kids with more advanced cognitive development had the U-shaped curve — which, I should point, is exactly the pacing strategy adopted by world-record-setters at distances from 1,500 to 10,000 metres ever since the IAAF started keeping records.

I should clarify (before Rob Watson kicks my ass) that the link between pacing between cognitive development and pacing is mostly related to age. Once you’re a grown-up (and in particular, once you’re racing against other people rather than just against the clock), there are many different reasons to adopt different pacing strategies. Let me repeat: I’m not saying that going hard means you’re dumb!

What this research is really about is “anticipatory regulation of effort” — which is basically just a rebranding of what’s sometimes called the central governor theory. (Debate about the central governor has become so personal that many scientists seem unable to actually read new studies about it, instead criticizing the ideas that were proposed 10 years ago.) Here’s how the authors of the new study put the idea into evolutionary context:

The survival of certain animals is contingent upon the successful deployment of energy conservation strategies such as the regulation of feeding, physical exertion and rest. Such energy conservation strategies are imperative to successfully completing predetermined survival activities within biological and environmental constraints. Humans use similar energy regulation strategies to successfully conduct their daily living activities albeit with less emphasis than other animals on survival. This is particularly apparent in the way humans pace themselves during athletic activity to avoid premature fatigue.

What’s fascinating is that this anticipatory pacing strategy appears to be hardwired into us. By the time we reach the third Piaget stage, we’re already pacing ourselves in exactly the same (much-debated) way that the runners who set distance-running world records do: a fast start, a slower middle, then a fast finish.

Jockology: how much exercise is too much?

July 18th, 2011

This week’s Jockology column in the Globe and Mail takes a look at the debate about whether too much exercise is actually bad rather than good for you, drawing on recent studies about cardiac fibrosis in elite endurance athletes, epidemiological data from the National Runners’ Health Study, and — to be topical — Tour de France riders:

Given the number of cyclists in this year’s Tour de France who have skidded off mountain passes, been sideswiped by passing cars or catapulted into barbed-wire fences, it’s obvious that riding in the Tour can be hazardous to your health.

But what about the riders who make it to the finish line in Paris, having covered 3,430.5 heart-pounding, leg-draining kilometres in three weeks? Does their gruelling training regimen make them healthier, or does too much of a good thing leave them worse off? Medical opinion has flip-flopped over the years as our understanding of the heart’s response to exercise has increased, but a new study on the most important outcome of all – staying alive – suggests that Tour riders do better than average. [READ THE ARTICLE...]

 

Ice baths for recovery: 15 minutes at 10 C

July 17th, 2011

Post-workout ice baths are one of those things that everyone believes in, no matter what the science says. There have been a bunch of ice bath studies, but they’ve used lots of different water temperatures, immersion times, and outcome measures, and the results have been very mixed. This month’s European Journal of Applied Physiology has a study from France’s National Institute of Sport that looks like the strongest evidence yet in favour of ice baths — and offering some concrete advice on water temperature and immersion time.

One key difference from previous studies: they used elite athletes — 41 football, rugby and volleyball players — whose recovery might be expected to be faster than untrained volunteers. They tested four different protocols:

  • TWI: body-temperature water (36 C) for 15 minutes;
  • CWI: cold water (10 C) for 15 minutes;
  • CWT: contrast water (10 C and 42 C), alternating 90-second bouts for 15 minutes;
  • PAS: no water — just sitting there for 15 minutes.

The exercise they used to induce fatigue and muscle damage was alternating bouts of hard rowing and counter-movement jumps. They took blood samples and tested muscle strength (MVC), jump height, and power produced during 30 seconds of rowing — and they did those tests before and immediately after the exercise, then again one hour and 24 hours later.

As you can imagine, with all those different test groups and protocols, the results are a bit of a jumble. The key result, as far as I’m concerned, is right here:

This is the data for creatine kinase, which is a commonly measured marker related to muscle damage. Its exact significance is often debated, but the authors of this study suggest it’s a sign of “reduced passive leakage from disrupted skeletal muscle, which may result in the increase in force production during ensuing bouts of exercise.” The key: the ice bath outperforms all the other interventions, including the contrast bath.

Of course, nothing is quite that simple. If we look at the performance measures, the picture gets muddier:

What we’re interested in here is the cases where performance returns to “normal” quickly. The asterisks indicate where performance is reduced from the first bout by a statistically significant amount. The broad conclusion we can draw is that both the ice bath and the contrast bath seem to offer some advantages compared to room temperature water or not bath. The main reason I included this data is to show that it’s not a simple, magical effect. It’s complicated. But for practical purposes, this data gives me more confidence than any previous study to support the very strong anecdotal evidence that a sustained cold-water bath — in this case, 15 minutes at 10 C — helps to speed up recovery after hard workouts.

Vitamin D and muscle injuries

July 15th, 2011

I’m on the record as a bit of a vitamin D skeptic. Not a total skeptic, mind you — it’s actually the only supplement of any kind that I take on a regular basis these days. But the claims that vitamin D enhances athletic performance have seemed pretty weak to me so far. However, I’ll dutifully pass along this press release from the American Orthopaedic Society for Sports Medicine, which describes some new research linking vitamin D levels with muscle injuries in NFL football players.

The study: 89 players from one NFL team were tested for vitamin D levels in spring 2010, during pre-season. Not surprisingly, the levels were generally low compared to what’s considered desirable (which seems to be true for pretty much every population group in the developed world):

Twenty-seven players had deficient levels (< 20 ng/ML) and an additional 45 had levels consistent with insufficiency (20-31.9 ng/mL). Seventeen players had values within normal limits (>32 ng/mL).

The team then provided data on time missed due to injuries during the season. Sure enough, players who suffered muscle injuries has “significantly lower levels” of vitamin D. How much lower? It’s not clear: this is conference data, so not yet published in a journal, and unfortunately the press release release doesn’t do a very good job of presenting the data. The average level for players with a muscle injury was 19.9, but it doesn’t tell us what the average for uninjured players was.

First thing to wonder: is it this cause or correlation? Do the players with crappy diets also neglect their strength, flexbility and warm-up routine? Second thing: if it is causal, what’s the mechanism? Why does this work?

Leaving that aside, I’ll just reiterate my hair-splitting distinction between a “performance-enhancing” substance and one that hurts performance if you’re deficient in it. Water helps your performance if you’re dehydrated, but we don’t consider it an ergogenic aid. As far as I can tell, vitamin D falls into the same category: something that you shouldn’t be deficient in, whether you’re an athlete or not. But I’m still not convinced that more is better if you’re in a healthy range.

To clinch victory, shoot for the left side of the net

July 14th, 2011

Interesting press release about an upcoming study in Psychological Science. In an analysis of every World Cup penalty shoot-out from 1982 to 2010, researchers from the University of Amsterdam found that goalies tend to dive to the right when their team is down and the game is on the line. (In other situations, they were equally likely to go right or left.)

Many studies have found that people and animals that want something tend to go to the right. When dogs see their owners, they wag their tails more to the right; toads strike to the right when they’re going for prey; and humans are more likely to turn their heads to the right to smooch their sweeties…

In an experiment, the team found that people who are told to divide a line in half tend to aim a bit to the right when they are both thinking about a positive goal and under time pressure—just like the goalies.

So how will this affect strategy in the next World Cup? Now the goalies know about this innate tendency; but the shooters know that the goalies know; but the goalies know that the shooters know that the goalies know…

[Minor gripe: the press release doesn't actually reveal what the split in the data was -- i.e. 51:49? 70:30? And the paper itself isn't yet available online. A rather crucial detail, I'd have thought.]