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Archive for April, 2010

Sports drinks don’t help for one-hour exercise (unless you’ve been fasting)

April 29th, 2010

If you’re running a marathon or cycling for several hours, you need to ingest some carbohydrates during the session to maintain your performance. If you’re sprinting for 100 metres, on the other hand, you can leave the buffet belt at home. Where things get murky is the middle ground, for sessions lasting about an hour: several decades of research have produced lots of conflicting results. A study in the April issue of the Journal of Sports Sciences, by researchers from Loughborough University in Britain, offers some new insight.

The basics: 10 trained runners did two trials in which they ran as far as they could in one hour (they used a neat treadmill that automatically speeds up if you move towards the front of the belt, and slows down if you lag towards the rear, so it was a freely paced trial). In both cases, they ate a high-carbohydrate meal three hours before the run. They drank either a sports drink containing 6.4% carbohydrates or a placebo before and during the run. The results: no difference whatsoever in performance, blood glucose, lactate, respiration, carbohydrate burning, perceived exertion, or anything else they measured.

What’s interesting is that the same group published a similar paper last year, where the only difference is that the runners were fasted before the trial instead of having a meal three hours prior. In that case, the sports drink group significantly outperformed the placebo group.

So it seems pretty clear: you only need supplemental carbs for a one-hour exercise bout if you haven’t topped up your carb supplies beforehand. There are two ways your body stores glycogen: in your muscles (which is then used exclusively by your muscles), and in your liver (which feeds glucose into your bloodstream to fuel your heart and brain and keep blood sugar levels stable). When you sleep overnight, your muscle glycogen stays relatively stable, but your liver glycogen drops by more than 50 percent (because your brain and heart are still running all night). So the researchers believe that, if you don’t have a pre-exercise meal, the sports drink is needed to make up for your depleted liver glycogen stores.

Practically speaking, this means you don’t need to worry about carbs during short exercise bouts in the afternoon or evening, since you’ll have had a meal or two. In the morning, though, you need to make sure your liver glycogen is restocked, even for a short one-hour run. You can do that by getting up early enough to eat beforehand — or, apparently, by consuming some carbs immediately before and during your session.

One other interesting note from the paper. They discuss the performance boost that comes from “rinsing and spitting” with a sports drink, which some researchers have suggested could explain why sports drinks sometimes help with short exercise sessions even when muscle glycogen stores are full. Interestingly, a couple of recent papers suggest that the same conditions also apply in this case: you get benefit from rinse-and-spit if you’ve fasted beforehand, but no benefit if you had a pre-exercise meal. That suggests that your brain is monitoring levels of carbohydrate throughout your body, and only responds positively to the carb stimulus if your body actually needs it:

Although speculative, the idea of central monitoring of whole-body carbohydrate status, which in turn influences the self-selection of exercise intensity, is worthy of further investigation.

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Off-the-bike running form changes economy in triathletes

April 25th, 2010

Interesting article [LINK FIXED] on what intense biking does to your running form, by researchers at the Australian Institute of Sport and the University of Queensland, coming up in a future issue of the Journal of Science and Medicine in Sport. There has been quite a bit of prior research on what happens when you run off the bike, generally showing that your running economy is worse than it would otherwise be — in other words, tired as you are, you also have to burn more energy to run at a given pace than you normally do. Various reasons for this have been proposed: you’re dehydrated, your breathing muscles are tired, you’re burning a higher proportion of fat because your carbohydrate stores are depleted. But it may also have something to do with running form, thanks to changes in neuromuscular control. That’s what this study set out to investigate, by having a group of 17 moderately trained triathletes do a pair of runs with and without a 45-minute high-intensity bike ride beforehand.

Unfortunately, the results don’t reveal any universal truths about what triathletes do wrong off the bike — but there are some interesting findings. First of all, everybody was different: some people had changes in running form, others didn’t; some had better running economy, others had worse. Crunching the data, the researchers find that the people whose running economy got worse had some things in common. When running after biking, these people tended to extend their knee and dorsiflex their ankle at the moment of ground contact a bit more than when they ran fresh. That makes them more likely to have a jarring heel strike, which wastes a bit of energy. Basically, when they start running after biking, they’re overstriding.

I’m not sure this really says much about fancy concepts like “neuromuscular fatigue,” but it does offer a useful warning about a pitfall that about half the subjects in the study fell into. Yes, you’re tired when you come off the bike, but overstriding isn’t going to get you to the finish line any sooner. (And one thing the researchers note is that their subjects were not elite triathletes, so this advice may be most relevant to less-experienced age-groupers.)

Thinking good (or bad) thoughts increases endurance

April 22nd, 2010

A new study from Harvard University suggests that it’s good to be a good guy, but better to be a bad guy:

Study participants who did good deeds — or even just imagined themselves helping others — were better able to perform a subsequent task of physical endurance. The research, published in the journal Social Psychological and Personality Science, shows a similar or even greater boost in physical strength following dastardly deeds.

The researcher,  a psychology grad student named Kurt Gray, calls the effect “moral transformation.” It suggests that we may have cause and effect backwards, he says: It’s not that people who do great things have incredible strength and willpower; instead, people who attempt great things gain strength and willpower by making the attempt.

So what does this mean for exercisers? Well, I haven’t been able to dig up a copy of the original paper, so I’m relying on a press release whose details are somewhat sketchy:

Gray’s findings are based on two studies. In the first, participants were given a dollar and told either to keep it or to donate it to charity; they were then asked to hold up a 5 lb. weight for as long as they could. Those who donated to charity could hold the weight up for almost 10 seconds longer, on average.

In a second study, participants held a weight while writing fictional stories of themselves either helping another, harming another, or doing something that had no impact on others. As before, those who thought about doing good were significantly stronger than those whose actions didn’t benefit other people.

But surprisingly, the would-be malefactors were even stronger than those who envisioned doing good deeds.

So it doesn’t sound like this will be a magic ticket to unlimited strength and endurance. Still, it might be worth keeping the power of mental imagery in mind next time you’re working out — you might combine the power of evil thoughts with the ergogenic effects of swearing for maximum effect.

Pickle juice stops muscle cramps

April 21st, 2010

No, really, this is a serious blog entry. There’s an article in the May issue of Medicine & Science in Sports & Exercise by researchers at Brigham Young University called “Reflex Inhibition of Electrically Induced Muscle Cramps in Hypohydrated Humans,” and that’s what it says:

The most significant and novel observation of this study was that ingesting small volumes (73.9 +/- 2.7 mL) of pickle juice alleviated electrically induced muscle cramps in mildly hypohydrated (3%) humans. Pickle juice required approximately 85 s to alleviate muscle cramps (cramp duration after ingestion ranged from 12 to 219 s). Although this was much longer than the purported claims of pickle juice’s efficacy, it still relieved a cramp 45% (85 vs 153 s) faster than when no fluid was consumed. In contrast, ingesting similar volumes of deionized water had no therapeutic effect on cramp duration (cramp duration after ingestion ranged from 71 to 246 s).

What’s interesting about this is not so much the promise of a “cure” for muscle cramps. (There are some reasons to think that downing a bunch of vinegar and salt probably isn’t a great habit, for one thing.) Instead, it’s how it stops cramps that is intriguing and suggests that conventional thinking on cramps may be mistaken.

The pickle juice cure has been around for at least a decade (it was described in a 2000 article in the Journal of Athletic Training), and most people assumed that it had something to do with all the electrolytes. But the authors of this new study aren’t convinced. First of all, the amount of electrolyte in 73 mL of pickle juice has a negligible effect on concentrations in the body. Second, the 85 seconds it took (on average) to relieve the cramps is far too short for the pickle juice to exit the stomach, be absorbed by the small intestines, and reach the relevant part of the body. Earlier studies have found that it takes at least 30 minutes for small volumes of pickle juice to leave the stomach.

Instead, the researchers suggest that the pickle juice acts on neural reflexes — a plausible suggestion, given that earlier experiments have found that vinegar can provoke reflexes and affect neurotransmitter levels. This fits with an alternate theory that cramps have nothing to do with dehydration or electrolyte loss, first proposed in the 1990s by Martin Schwellnus of the University of Cape Town:

Schwellnus et al. proposed that [cramps] were due to neuromuscular fatigue. Neuromuscular fatigue is thought to create an imbalance between muscle spindle and Golgi tendon organ activity, resulting in increased alpha motor neuron excitability. Thus, if [cramps] are caused by an imbalance between excitatory and inhibitory stimuli at the alpha motor neuron pool, pickle juice ingestion may cause an increase in inhibition from supraspinal sources, thereby resulting in cramp alleviation.

If you’re interested in the details of Schwellnus’s theory and the controversies surrounding muscle cramps, the Science of Sport blog did a good series on it back in 2007 (Part 1, Part 2, Part 3 and Part 4). It’s interesting stuff — and now, courtesy of pickle juice, there’s some new evidence.

How many calories does sitting on an exercise ball burn?

April 19th, 2010

In the comments section of an earlier post that mentioned the potential caloric benefits of standing as opposed to sitting, Peter asked how sitting on an exercise ball stacks up. The news is good. A 2008 study in the European Journal of Applied Physiology by researchers at the University of Buffalo compared energy use during clerical tasks while sitting in an office chair, sitting on an exercise ball, or standing up. Subjects burned 4.1 calories more per hour (a 6% boost) when they were either standing or sitting on the exercise ball compared to sitting in the regular office chair. There was no difference between standing up and sitting on the exercise ball. The numbers are consistent with a 2006 study that found a 3.9 calorie per hour (5.6%) boost for exercise balls, with effects that persisted for at least a week.

Presumably, this enhanced calorie gain has the same benefits as standing — that it doesn’t trigger your appetite hormones to make you compensate. On the other hand, some back experts are still cautious about the effects of sitting on exercise balls all day. Stuart McGill of the University of Waterloo, for instance, did a study in 2006 with the following conclusions:

The results of this study suggest that prolonged sitting on a dynamic, unstable seat surface does not significantly affect the magnitudes of muscle activation, spine posture, spine loads or overall spine stability. Sitting on a ball appears to spread out the contact area possibly resulting in uncomfortable soft tissue compression perhaps explaining the reported discomfort.

So, as long as your back doesn’t start bothering you, the exercise ball seems like a reasonable choice. And you don’t have to worry about your productivity, at least according to the University of Buffalo study: in 20 minutes, the men in the study typed 551.8 words on the exercise ball, 535.6 words while standing up, and 519.2 words while sitting in the office chair. (The women were much consistent, at 700.3, 697.8 and 702.5 respectively.)

Burning calories without stimulating appetite

April 19th, 2010

I’ve posted a few times recently on the challenges of losing weight — in particular, the homeostatic mechanisms that your body uses to fight against any attempt to burn more calories than you consume. For instance, exercising stimulates appetite hormones that prompt you to eat more. So I found the following tidbit in the New York Times interesting:

In a completed but unpublished study conducted in his energy-metabolism lab, [Barry] Braun [of UMass-Amherst] and his colleagues had a group of volunteers spend an entire day sitting. If they needed to visit the bathroom or any other location, they spun over in a wheelchair. Meanwhile, in a second session, the same volunteers stood all day, “not doing anything in particular,” Braun says, “just standing.” The difference in energy expenditure was remarkable, representing “hundreds of calories,” Braun says, but with no increase among the upright in their blood levels of ghrelin or other appetite hormones. Standing, for both men and women, burned multiple calories but did not ignite hunger. One thing is going to become clear in the coming years, Braun says: if you want to lose weight, you don’t necessarily have to go for a long run. “Just get rid of your chair.”

This suggest that all those people trying to work at “stand-up” desks may be onto something. On the other hand, I’m still not completely sold on the general message about exercise and weight loss that is more or less accepted as fact in this article:

“In general, exercise by itself is pretty useless for weight loss,” says Eric Ravussin, a professor at the Pennington Biomedical Research Center in Baton Rouge, La., and an expert on weight loss.

The article then describes one of Ravussin’s studies (which I blogged about back in December) in which one group of subjects lost nearly 10% of their bodyweight, or a pound a week, through exercise alone — which seems to contradict the assertion that exercise is useless for weight loss.

But in the exercising group, the dose of exercise required was nearly an hour a day of moderate-intensity activity, what the federal government currently recommends for weight loss but “a lot more than what many people would be able or willing to do,” Ravussin says.

Oh, now I get it. It’s not that exercise is useless for weight loss — it’s doing a little bit of exercise at a low intensity that is useless. Those are two very different statements. I understand that an hour a day of moderate-intensity exercise is a tall order for people in today’s busy, convenience-driven, nutritionally bankrupt society etc. etc. But that doesn’t mean exercise is useless, it just means that it takes a lot of exercise — more, perhaps, than most people are willing to do — to see appreciable changes.

Convincing people to climb stairs

April 15th, 2010

In light of the Jockology column on stair climbing that I just posted, I found this post on the Obesity Panacea blog really interesting:

In this new study, Megan Grimstvedt and colleagues placed signs near the elevators of 4 university buildings in San Antonio. The sign said simply “Walking up stairs burns almost 5 times as many calories as riding an elevator” and included an arrow directing people to the nearest staircase, as well as a cartoon of the school mascot walking up a flight of stairs…

At baseline, only 13% of people used hidden staircases, while 43% of people used visible staircases. Even more interesting is that overall stair use increased 34% as a result of the intervention, an increase which persisted 4 weeks after the signs had been removed.

There’s more data and analysis in the original post. Time to make some signs!

Jockology: taking the stairs actually makes a difference

April 15th, 2010

This weekend, about 7,000 people will tackle the 1,776 steps of the CN Tower in support of the World Wildlife Fund. Meanwhile, in Calgary, people will be climbing the Calgary Tower in support of the Alberta Wilderness Association. Also this weekend in Germany, there’s the Mt. Everest Stair Marathon, in which competitors go up and down a 397-step staircase 100 times, climbing the equivalent of sea level to the top of Everest and covering the distance of two marathons along the way.

Seriously.

So, all in all, it seemed like a good time to take a look at research into the health benefits of stair climbing for this week’s Jockology column. If you choose the stairs instead of the escalator or elevator a few times a day, does it really make any difference to your health?

Researchers in Ireland have been studying the benefits of dashing up the stairs periodically over the course of a workday, and they’ve observed surprising fitness gains.

“I think the key thing here,” says Colin Boreham, a professor at the University College Dublin Institute for Sport and Health, “is that stair-climbing is one of the few everyday activities at a moderate to high intensity that one can do surreptitiously without having to change, use special equipment or look foolish.” [read the rest of the column...]

As an aside, that’s the Colin Boreham who once held the British high-jump record and represented Britain in the 1984 Olympics as a decathlete alongside Daley Thompson.

Perceived exertion, not muscle failure, determines “exhaustion”

April 14th, 2010

There’s an interesting preprint available online from the European Journal of Applied Physiology, by Samuele Marcora and a colleague from Bangor University in Wales. Its title is “The limit to exercise tolerance in humans: mind over muscle?,” so you might think it’s another paper supporting Tim Noakes’s “central governor” theory. It is, and it isn’t — but either way, it’s interesting.

Marcora took 10 elite rugby players and (after various preliminary testing and so on) had them do a five-second “maximum voluntary cycling power” (MVCP) test. Then they did a very intense cycling trial to exhaustion which took about 10 minutes (they offered cash prizes to the top performers and circulated the results publicly to stimulate competition and make sure the subjects went all-out), followed immediately (within one second) by another MVCP test.

Now, if you subscribe to traditional exercise physiology, you’d say that the subjects stopped the test-to-exhaustion when they were no longer physically able to generate enough power to continue. Possible reasons for their failure would include “limited oxygen delivery, metabolic and ionic changes within the active muscles, supraspinal reflex inhibition from muscle afferents sensitive to these changes, and altered cerebral blood flow and metabolism.” But that’s not what Marcora saw. The subjects had to maintain an output of (on average) 242 watts in the test to exhaustion. But as soon as they stopped, one second later, they were able to output (on average) 731 watts in a five-second burst — nearly triple the required power! Clearly the subjects didn’t stop the test because their couldn’t physically produce the needed power:

These results challenge the long-standing assumption that muscle fatigue causes exhaustion during high-intensity aerobic exercise, and suggest that exercise tolerance in highly motivated subjects is ultimately limited by perception of effort.

The interpretation of these results gets a little tangled. Marcora is an advocate of something he calls the “psychobiological model of exercise tolerance,” which seems to basically mean that we stop exercising when it gets hard. He says this is different from — and much simpler than — Noakes’s central governor theory. I’m not sure I really a see a difference that extends beyond semantics, but perhaps that’s because I haven’t given it enough thought. I downloaded a couple of Marcora’s other papers where he explains the theory in more detail, so I’ll be interested to see what he has to say. Either way, these results are certainly interesting in that they once again support the notion that, when we collapse from exhaustion, we’re generally running up against barriers imposed by our brain rather than absolute physical limits imposed by our body.

Staying healthy after 153,300 miles

April 12th, 2010

Runner’s World has an interesting interview by Amby Burfoot with marathoning legend Ron Hill, now most famous for the daily running streak he’s kept alive since 1964. A passage I liked:

I saw a woman who said, “Running’s not good for your knees.” I said: “Okay, but I’ve got 150,000 miles on these knees and they’re working quite well.” She said: “That’s only because you’re so slim.” I said: “Well, how do you think I got this slim, and stay this slim?”

He has a good point (as I discussed in a Jockology column a few years ago). On the other hand, I have to admit that the picture accompanying the interview does look like a guy who hasn’t taken a day off in the last 45 years.

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