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Posts Tagged ‘mental’

The neurochemical reality of placebos

January 17th, 2012

The New Yorker had a great look at the placebo effect last month (unfortunately the full text isn’t available online), focusing on the work of Harvard’s Ted Kaptchuk. He’s the guy who did the study last year that found that placebos can be effective even when patients are aware that they’re receiving a placebo instead of “real medicine.” His hope is that doctors will learn to harness the placebo effect more effectively, and understand that it’s a real physical effect, not just in your head.

To that end, one of the most interesting nuggets in the article was a description of one of the classic placebo studies, from UCSF back in 1978. People recovering from dental surgery were given either morphine or a saline placebo; as expected, some patients responded to the placebo (their pain diminished) while others didn’t (their pain got worse).

What happened next, however, fundamentally reshaped the field. The researchers dismissed the subjects who had received morphine and then divided the remaining participants into those who responded to the placebo and those who didn’t. Then they introduced Naloxone into patients’ I.V. drips. Naloxone was developed to counteract overdoses of heroin and morphine. It works essentially by latching onto, and thus locking up, key opioid receptors in the central nervous system. The endorphins that we secrete attach themselves to the same receptors in the same way, so Naloxone blocks them, too. The researchers theorized that, if endorphins had caused the placebo effect, Naloxone would negate their impact, and it did. The Naloxone caused those who responded positively to the placebos to experience a sharp increase in pain; the drug had no effect on the people who did not respond to the placebo. The study was the first to provide solid evidence that the chemistry behind the placebo effect could be understood — and altered.

In other words, placebo responders were dulling their pain via exactly the same route as morphine recipients. It was a “real” effect. In the realm of sports science, that’s something to bear in mind when we read yet another report showing that some supposedly performance-enhancing substance doesn’t outperform placebos in a controlled trial.

Mental effort increases physical fatigue, reduces HR variability

December 15th, 2011

A pretty neat study just appeared online at European Journal of Applied Physiology, looking at the links between mental effort and physical fatigue. This is a topic I’ve touched on previously, and find really interesting. The new study, from researchers at Michigan Technological University and Virginia Tech, adds some new wrinkles.

The protocol is quite complex, but basically a bunch of volunteers did fatiguing shoulder exercises while doing mental arithmetic (“Here’s a number, multiply it by three… now multiply it by three again…” etc.). The researchers measured how quickly the subjects’ shoulders fatigued, and how quickly they recovered and returned to full strength in the 15 minutes after the exercise bout. As you can probably guess, the subjects doing mental arithmetic lost strength and reached failure more quickly than the controls.

Why does this happen? Well, the researchers discuss some previous work suggesting that mental activity triggers stress which triggers low-level muscular contractions, which can lead to premature fatigue. But I actually find another explanation more convincing:

It has been shown that fatiguing contractions require high attentional demands due to changes in the excitability of motor cortex. As such, it could be argued that additional mental demand in the current study may have reduced available attentional resources needed to increase the drive to motor neurons to maintain the required force levels, resulting in early task failure (i.e., shorter endurance times).

In other words, it takes focus and mental effort to push to your limits, and those are finite quantities that can be squandered thinking about other things. That seems like the simplest explanation to me, and it would fit with the research by Samuele Marcora that I mentioned above.

A neat additional observation: the mental arithmetic resulted in lower “heart rate variability” (HRV). Basically, you measure the time between successive heart beats — if that time is always identical, you have low HRV; if it fluctuates, you have higher HRV. This tells you something about the balance between sympathetic and parasympathetic nervous systems; when you’re under stress, the sympathetic system ramps up and release norepinephrine (aka noradrenaline), which elevates your heart rate but reduces heart rate variability. The result: it takes longer for your heart rate to settle back to normal — which is exactly what the researchers observed in the subjects doing the mental arithmetic.

Which childhood activities predict healthy adulthood?

December 8th, 2011

Encouraging kids to be more active is one of those motherhood-and-apple-pie goals that pretty much everyone sees as an excellent idea. Still, it’s worth asking: do the kids who are most active grow up to be the adults who are most active? And perhaps more importantly, which types of childhood activity (school phys ed? sports? unstructured play? walking or biking to school?) are most effective at establishing lifelong habits of physical activity?

Researchers in Australia just published a big study on the British Journal of Sports Medicine that followed up on 2,201 kids who had completed a detailed physical activity questionnaire way back in 1985, when they were between the ages of 9 and 15. The goal was to figure out whether and how “frequency and duration of discretionary sport and exercise (leisure activity), transport activity, school sport and physical education (PE) in the past week and number of sports played in the past year” when they were kids influenced their activity patterns as adults between the ages of 26 and 36.

Depending on how you look at it, the results are either very simple or very complicated. You can delve into all the nitty-gritty details of which childhood factors seem linked to which adulthood factors — and find puzzling and seemingly contradictory trends like this:

Higher levels of school sport among older males were associated with a 40% increase in the likelihood of being in the top third of total weekly activity in adulthood, but with a 40% lower likelihood among younger males.

Does this mean that school sport is bad for 9- to 12-year-olds and good for 13- to 15-year-olds? Probably not. As discussed earlier this week, when you search for links between large numbers of variables in a big collection of data, you’ll always find some relationships that appear statistically significant but in fact have little or no meaning. When you look at this data as a whole, there are a few “significant” associations, but there’s no overall trend, as the researchers acknowledge:

[F]ew associations were evident, most were relatively weak in magnitude and, for some activities, inconsistent in direction.

In other words, if you take a group of 12-year-olds and look at how active they are, you’ll have very little ability to predict which of those kids will have healthy, active lifestyles 20 years later. This is a bit of a bummer, because it makes it harder to decide exactly what types of physical activity are most useful for forming lifelong activity patterns. But don’t make the mistake of thinking that this implies that school phys ed (and other childhood physical activity) isn’t useful! Phys ed for 12-year-olds may not produce healthy 30-year-olds, but it sure as heck produces healthy 12-year-olds — and that’s a worthwhile goal on its own.

And hey, there’s also the fact that (as Gretchen Reynolds wrote about in the New York Times last week), a little bit of physical activity makes you perform better on tests. What kid wouldn’t want a boost of brain-derived neurotrophic factor coursing through his veins and boosting his memory as he heads back to math class?

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Exercise -> serotonin -> antidepressant

November 14th, 2011

It’s well-established that exercise can be a powerful tool against depression (as Gretchen Reynolds wrote about in the New York Times a few months ago). What’s less clear is how and why it might help. A new study in  Medicine & Science in Sports & Exercise, from researchers at the University of Sherbrooke, offers some evidence for the theory that exercise can boost serotonin levels in the brain. This, of course, is pretty much the same as what the most common antidepressants (SSRIs: selective serotonin reuptake inhibitors) do.

The study was pretty straightforward. They had 19 men with an average age of 64 perform a 60-minute bout of exercise at moderate intensity (average HR 129 beats per minute, 68% VO2max). Then they measured several proxies of serotonin production, since it’s very difficult to directly measure neurotransmitters in the brain. The result: levels of tryptophan — the key precursor which is converted into serotonin — roughly doubled.

Is this a surprise? There was previous evidence in studies of rodents and younger humans that exercise boosted tryptophan availability, but it wasn’t clear whether the same effect would occur in older adults. This is particularly important because we become increasingly susceptible to depression as we age, suggesting that some of the mechanisms that help us ward off depression stop working quite as well.

Of course, one of the problems with “prescribing” exercise as a depression treatment (as Reynolds notes) is that once you’re depressed, it can be extremely difficult to summon the motivation needed to maintain a regular exercise program. Still, this study suggests that exercise might help to prevent depression in the first place, particularly as you get older.

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The incredible shrinking hippocampus (and how to stop it)

September 27th, 2011

Over the last few years, a bunch of studies have built the case that aerobic exercise does something to keep your brain in good working order as you age — or perhaps more accurately, it does several good things for your brain. Last week, I blogged about a study showing that exercise stimulates the growth of new mitochondria in the brain. In the comments of that post, Seth Leon pointed out another new study — this one in the September issue of Neuropsychology — that links exercise to greater volume of the hippocampus, which in turn improves memory.

I’ve been particularly interested in the hippocampus ever since I wrote this article in The Walrus back in 2009, looking at suggestions that increased use of GPS navigation would lead to decreased volume of the hippocampus, where our direction-finding skills reside. And smaller hippocampi are associated with increased risk of age-related cognitive impairment. One of the researchers I spoke to worried that this is part of larger shift:

But Bohbot sees the decline in spatial thinking as part of a broader shift toward stimulus-response, reward-linked behaviour. The demand for instant gratification, for efficiency at all costs and productivity as the only measure of value — these sound like the laments of the nostalgist in the Age of the Caudate Nucleus. But here, they’re based on neuroscience. “Society is geared in many ways toward shrinking the hippocampus,” she says. “In the next twenty years, I think we’re going to see dementia occurring earlier and earlier.”

I can’t count the number of times I’ve taken wrong turns since writing that article because of my stubborn refusal to use GPS unless absolutely necessary! But I digress…

Anyway, this new study, by researchers at the University of Illinois, looked at a group of 158 sedentary adults between 60 and 80 years old, to look for evidence for the following model:

The basic gist is straightforward: they hypothesize that fitness (as measured by a graded exercise test to exhaustion) predicts hippocampus size, which in turn predicts working memory, which in turn predicts how frequently you forget things. What’s new about this study is that they separately consider age, BMI, sex, physical activity, and education to see if any of them are skewing the results. Here’s what they find:

By and large, the data supports their hypothesis. There are a few wrinkles: for example, age, in addition to affecting fitness, also has a direct effect on hippocampus size. That means no matter how fit you are, your hippocampus is still getting smaller. Also, physical activity (that’s the PASE box) didn’t directly contribute to fitness — but that’s not surprising, because the volunteers had to be sedentary in order to be admitted to the study, so they all had roughly the same (lack of) physical activity.

Bottom line: aerobic fitness is good for the brain — and in particular, it’s good for the hippocampus. So maybe if I get enough exercise, I’ll start letting myself use that GPS navigation system.

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All exercise performances are sub-maximal

September 12th, 2011

Another interesting pacing study, with many similarities to the one I blogged about last week, published once again in Medicine & Science in Sports & Exercise. Cyclists are asked to do a series of 2,000-metre time trials in a pseudo-virtual reality set-up. Most of them they perform solo, but in one of the trials they race against a virtual competitor (who, unbeknownst to them, is actually programmed to exactly mimic their own previous trial). The result is obvious: competition improves performance, so they’re able to beat their doppelganger and race significantly faster.

What’s interesting is how they manage to beat their previous performance. Throughout the race, the power generated from aerobic sources is exactly identical in all the different trials. But the power from anaerobic sources is significantly higher in the “racing” scenario during the second half of the race (during the last 90 seconds or so, in other words).

What does this mean?

Consequently, it has been argued that all exercise performances are sub-maximal, since they are terminated before there is a catastrophic metabolic or cardio-respiratory failure, and that a physiological ‘reserve’ capacity will always remain. The ergogenic effects of the [head-to-head] competition might therefore result from the central influence of some motivational or dissociative effect enabling the use of a greater degree of the physiologic ‘reserve’ capacity.

That’s actually quite a powerful statement: “all exercise performances are sub-maximal.” If the stakes are raised sufficiently, you can always squeeze out a little extra. I think most of us grow up knowing this intuitively, but at some point — after we start learning about VO2max and lactate threshold and so on — it’s often forgotten.

Jonah Lehrer on marshmallows and executive function

September 8th, 2011

In the comments section of last week’s post on delayed gratification and the Marshmallow Test, Seth Leon pointed out a really interesting article by Jonah Lehrer (first published in the Wall Street Journal but mirrored on his excellent blog, Frontal Cortex) that discusses ways in which you can improve your focus and impulse control — how to boost your performance on the Marshmallow Test, in other words:

The key is strengthening what psychologists call “executive function,” a collection of cognitive skills that allow us to exert control over our thoughts and impulses. When we resist the allure of a sweet treat, or do homework instead of watch television, or concentrate for hours on a difficult problem, we are relying on these lofty mental talents. What we want to do in the moment, and what we want to want, are often very different things. Executive function helps to narrow the gap. [...]

But here’s the good news: Executive function can be significantly improved, especially if interventions begin at an early age. In the current issue of Science, Adele Diamond, a neuroscientist at the University of British Columbia, reviews the activities that can reliably boost these essential mental skills. The list is surprisingly varied, revolving around activities that are both engaging and challenging, such as computer exercises involving short-term memory, tae-kwon-do, yoga and difficult board games.

The whole article (which isn’t very long) is worth a read, as is Lehrer’s previous post, which describes in considerably more detail the history and implications of the marshmallow studies.

The finishing kick is in your head, not your legs

September 7th, 2011

Another cool study showing that your brain always holds back a little energy even during “maximal” effort — and that you can access this reserve during your finishing kick. This one comes from Northumbria University in the UK, published in Medicine & Science in Sports & Exercise, and it’s fairly straightforward. Nine trained cyclists each do three 4,000-metre time trials on a stationary bike hooked up to pseudo-virtual-reality computer system:

  1. a baseline trial where they go as fast as they can;
  2. a “race” where they compete against an avatar representing their baseline performance;
  3. another “race” where they compete against an avatar which they’re told represents their baseline performance, but is actually going 2% faster (the second and third trials were given in random order to avoid learning effects).

The results: as you might expect, when racing against their previous performance, the cyclists were able to eke out a little extra energy, finishing 1.0% faster on average. But crucially, when they were deceived into competing against a faster avatar, they managed an even bigger boost, improving their time by 1.7%! Interestingly, an earlier study that tried something similar but gave feedback that was off by 5% produced the opposite result, because the cyclists were tricked into going out too fast and eventually crashed — so this isn’t an unlimited technique that will allow you to travel at the speed of light.

On the surface, these results aren’t really that surprising. Knowing how the human body (and mind) work, that’s pretty much what we’d expect. But it’s important to realize that this conflicts with the conventional understanding of how physiological constraints limit our performance. Whatever factors determined the baseline finishing times, they clearly weren’t absolute physiological limits, because the cyclists were able to beat them a few days later.

Further analysis of the data shows that in the deception trial, the cyclists had to start supplying more anaerobic power in the final 10 percent of the race in a desperate attempt to keep up with their supercharged rival. Here’s the graph of aerobic and anaerobic power contributions in the three trials (baseline, accurate and deception):

This graph sheds some interesting light on a longstanding debate about the origins of the “finishing kick,” which is a pretty much universal phenomenon in endurance races lasting longer than a few minutes. Why are we able to accelerate at the end, when we should be at our most tired? The conventional answer is that we’ve been relying primarily on aerobic energy throughout the race, but as the finish line approaches, we can mobilize anaerobic sources — the same ones we’d use to sprint 100 metres — and exhaust them just as we cross the line. The “alternate” explanation is that the brain has been limiting exertion in order to preserve homeostasis, but permits us to access some of those reserves as we approach the finish line (with the implicit promise that we’ll then stop and allow the body to recover).

It’s certainly true that the extra power needed for the finishing kick comes from anaerobic energy sources. But it’s also clear that, in the baseline trial and even in the “accurate” competition trial, the cyclists didn’t fully exhaust their anaerobic energy stores. Why not? The answer can lie only in the brain.

So what’s the practical takeaway? Well, I suppose if you can convince your real-life competitors to run 2% faster than normal without telling you, that would help! But realistically, I think this is a situation where knowledge is, literally, power. When you approach the finish of a race, you DO have energy remaining, despite what your mind and body are telling you. Believing that beyond a shadow of a doubt is, I believe, the first step to accessing it.

Mental fatigue and “armchair marathon training”

September 5th, 2011

As I mentioned earlier, I went to a conference called “The Future of Fatigue in Exercise” a few weeks ago. One of the researchers I was most interested in hearing from was Samuele Marcora, now at the University of Kent, who has produced a bunch of interesting results on the role of mental fatigue in physical performance over the past few years. For this week’s Jockology column in the Globe and Mail, I wrote about Marcora’s theories and his latest research:

“Improve your marathon time while sitting at your computer” is the kind of claim you expect from an infomercial or a spam e-mail, not from the keynote speaker at an academic gathering.

“It sounds crazy,” Samuele Marcora admitted during his talk at a conference on fatigue at Charles Sturt University in Australia last month, “but it’s actually not.”

Dr. Marcora, a professor at the University of Kent’s Centre for Sports Studies in Britain, has spent the past few years unravelling the surprising links between tired brains and physical performance. His initial results suggest that what we perceive as physical limits are actually highly dependent on our levels of motivation and mental fatigue – and that we may be able to use this fact to our advantage. [...]

READ THE WHOLE ARTICLE HERE.

Decision fatigue and workout planning

August 19th, 2011

John Tierney has an interesting article in New York Times Magazine about the concepts of “decision fatigue” and “ego depletion” — the idea that the simple act of making decisions, no matter how seemingly trivial, uses of a finite store of willpower. The idea seems intuitively obvious, but the studies he describes are fascinating and unexpected.

For example, prisoners appearing before Israeli parole boards have a 70 percent chance of getting parole if they appear first thing in the morning, but just a 10 percent chance if they appear late in the day: the judges are tired of making decisions, and react unconsciously by sticking to the default option. Lots of different factors affect decision fatigue, including glucose levels in the brain — so the chance of parole drops to 20 percent by midmorning, then rises to 65 percent after the midmorning break, during which sandwich and fruit is served to the judges. Just before lunch, probability is back down to 10 percent, then back up to 60 percent immediately after lunch, and so on.

It’s a long article, and I don’t want to oversimplify by summing up — but this is the passage, near the end, that I found interesting in the context of exercise:

“Good decision making is not a trait of the person, in the sense that it’s always there,” Baumeister says. “It’s a state that fluctuates.” His studies show that people with the best self-control are the ones who structure their lives so as to conserve willpower. They don’t schedule endless back-to-back meetings. They avoid temptations like all-you-can-eat buffets, and they establish habits that eliminate the mental effort of making choices. Instead of deciding every morning whether or not to force themselves to exercise, they set up regular appointments to work out with a friend. Instead of counting on willpower to remain robust all day, they conserve it so that it’s available for emergencies and important decisions.

I think this is a really important point. Strangely, I’ve found it’s much easier for me to stick to a routine where I run every day than to run six or five or four days a week. In terms of my current fitness goals, six days would be plenty and possibly even preferable to seven — but as soon as you introduce that element of choice, every morning suddenly gets much more complicated. Should I take my day off this morning? How tired am I? Is it going to rain? How do I expect to feel later in the week?

When I was training more seriously, a periodic rest day was much more important in order to get adequate recovery — but even then, I found it much easier to schedule a regular rest day (I took every second Monday off) than to make those decisions on a day-to-day basis. It wasn’t a question of being too obsessive to take an unplanned day off — it was simply too much mental effort to have to decide every morning “Am I running today?” There’s a great passage in Once a Runner about that idea (unfortunately I don’t have my copy here, or I’d quote it), how you have to make the decision about what you’re going to do, then close the book and just do it, rather than revisiting the decision every time it gets hard, or every time you wake up in the morning. (Of course, you still have to allow a certain amount of flexibility: sometimes it really is smarter to take an unplanned day off — but that’s different from having a regular weekly day off that can be taken any day of the week.)

When people ask me for advice about planning an exercise program, that’s one of the things I emphasize. Being flexible and fitting in exercise when it’s convenient may sound good in theory. But for me, at least, my will power isn’t strong enough to do that on a regular basis. Better to make the decision in advance, then just follow my own orders when it’s time to workout.