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Posts Tagged ‘cardio’

Micro-exercise and the shortest possible (useful) workout

August 1st, 2011

This week’s Jockology column in the Globe and Mail takes a look at “micro-exercise”: what is the smallest bout of exercise that actually offers health benefits?

Exercise generally obeys the normal rules of mathematics. You can replace one 40-minute workout with two 20-minute bouts, or even four 10-minute bouts, and get roughly the same health benefits. But beyond that, the rules break down: Exercise in bouts lasting less than 10 minutes simply doesn’t count.

At least, that’s what exercise physiologists and public-health authorities have been telling us for years.

But influential groups such as the American College of Sports Medicine are now reconsidering the value of ultra-short bouts of activity, and a new Canadian study suggests that the gradual accumulation of “incidental physical activity” – sweeping the floor, taking the stairs – in bouts as short as one minute can also contribute to your cardiovascular fitness level… [READ THE WHOLE ARTICLE]

The column focuses on the findings of a recent study by Ashlee McGuire and Bob Ross at Queen’s University. For more details on that study, check out Ashlee’s guest post describing the study’s results over at Obesity Panacea. Also, the print version of the study was accompanies by Trish McAlaster’s graphic, which hasn’t yet been posted online [UPDATE: now it’s posted here]. Unfortunately, it doesn’t really fit in this blog’s format, but nonetheless:

I’m reasonably confident that this is the first mention of the caloric expenditures involved in butchering small animals to make it into the Globe!

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!

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…]

 

Testing your max heart in 30 seconds

July 5th, 2011

It’s widely known that the old “220 minus your age” equation isn’t very good at determining your maximum heart rate. So what’s better? A new study from the University of Hawaii, recently published online at the Journal of Strength and Conditioning Research, tested nine different prediction equations, along with a surprisingly accurate way of determining your true max heart rate in about 30 seconds (sort of).

The study looked at 96 volunteers with an average age of about 22. That’s the first caveat: these results are only relevant for people in that general age group. And the volunteers were phys ed students, which means they’re likely to be more physically active than the general population.

I’ll start with the less interesting part of the study. Here’s the data from the equations they tested for all 96 subjects:

“CHRmax” is basically the “real” max heart rate. So they conclude that Gellish2 (191.5 – 0.007*age^2) and Fairbarn (201 – 0.63*age for women, 208 – 0.80*age for men) are the most accurate for this population. Maybe so — although trying to fit a function of age to data taken from subjects who are all virtually the same age seems a little weak to me. But the bigger problem is something they themselves note in their introduction:

The most commonly used Fox equation [i.e. 220 minus age] has been reported to have an SD [standard deviation] between 10 and 12 b/min. Thus, when estimating HRmax using the Fox equation, approximately 66% of the population should fall within +/-10 beats of the actual HRmax, but for the remaining population, the actual HRmax could differ by as much as 12–20 b/min or more.

I don’t know why they’re saying this is a property of the Fox equation. This is a fundamental property of human physiology: heart rate varies between individuals, so ANY equation based only on age will be more than 10 beats off for at least a third of the population. So for practical exercise prescription purposes, who cares which equation is more accurate?

Much more interesting is the way they calculate HRmax. They did the usual graded treadmill test to exhaustion to determine “true” max for 25 of their volunteers. Then they tested two other protocols. One was the Wingate test, which is basically 30 seconds all-out on an exercise bike. It was a crappy predictor, more than 10 beats below the actual average.

The second test was really simple: they had the subjects sprint as hard as they could for 200 metres on a standard track, with a running start. That’s it. And they measured their heart rate during the sprint. The average from the treadmill test was 190.0; the average determined from the 200m sprint (which takes a little over 30 seconds for most people) was 190.1. Pretty darn good.

Now, there are some caveats. The fact that the averages were close doesn’t mean everyone got identical values on the two tests. In fact, the “mean absolute error” was 5.8 bpm — but since the treadmill test was higher about half the time and the sprint was higher the other half, the averages balanced out.

Also, they didn’t do just one 200 sprint. They actually did two, but separated by at least three days. Each individual sprint, on average, underestimated the HRmax. The first sprint produced an average of 187.9; the second sprint produced an average of 186.3. So this test wasn’t as reliable at getting right up to HRmax. But when they gave people two tries, most people seem to have nailed at least one of the tries. Presumably if you gave them five tries (spread over several weeks), you’d get an even higher average max value. Of course, the same is true of the treadmill test: not everyone will execute it perfectly, so if you do it twice, the average value will probably creep up a bit. But what this study tells us is that, for this group of subjects (and remember, these are young phys ed students who are capable of sprinting 200 metres all out without pulling up lame halfway), give them two cracks at sprinting 200 metres and then take the highest heart rate they produce, and you’ll have a very good estimate of maxHR. It’s a heck of a lot cheaper and quicker than a graded exercise test — and a billion times more useful than any equation based only on your age.

Extreme exercise: Tour de France cyclists live longer

June 21st, 2011

A little bit of exercise is good for you, but too much is bad for you. That seems to be a fairly widespread societal view — certainly anyone who trains seriously as a runner or cyclist or other endurance athlete is familiar with all the comments about how training so much can’t be good for you. And to be fair, there has been some recent research that raises questions about whether running multiple marathons over an extended period of time can damage your heart.

So I was very interested to see a study, forwarded by Brian Taylor (thanks!), that just appeared in the International Journal of Sports Medicine. Spanish researchers decided to study the records of cyclists who rode the Tour de France between 1930 and 1964 — an example of “extreme” exercise if ever there was one — and see how long they lived compared to the general population. They focused on riders from France, Italy and Belgium (who comprised 834 of the 1229 riders for whom birth records were available), and they compared the longevity of those riders to the general population from their home country in the year of their birth. Here are the aggregate results in graphical form:

The trend is pretty clear. The age by which 50% of the population died was 73.5 for the general cohort, and 81.5 for the Tour de France riders — who, according to the paper, ride about 30,000 to 35,000 km per year (though I’d be surprised in the riders competing in the 1930s were training as hard as modern riders).

So what does this tell us? Well, as in any case-control study, there are plenty of limitations on the conclusions we can draw. First of all, this doesn’t prove that “extreme” exercise is better than “moderate” exercise. It may be that riding 30,000 km/year is significantly better than doing no exercise at all (or than doing the relative pittance that the average modern person does), but is still worse for you than riding, say, 10,000 km/year. But it’s pretty clear that extreme levels of aerobic training don’t shorten your life. As the authors put it:

In our opinion, physicians, health professionals and general population should not hold the impression that strenuous exercise and/or high-level aerobic competitive sports have deleterious effects, are bad for one’s health, and shorten life.

It’s also worth mentioning some potential confounding factors. The paper notes that former athletes tend to smoke less, drink less alcohol and have a healthier diet than the general population. Fair enough: these factors almost certainly contribute to the increased longevity of the riders. Again, the conclusion we can draw isn’t that extreme riding makes you healthier; it’s that it doesn’t make you less healthy.

What about genetics and selection bias? Maybe the Tour de France riders tend to be the type of lucky person with a great metabolism who’s destined to be healthy for his entire life no matter what he does, and it’s those great genetics that predisposed him to become a competitive cyclist. Again, not an unreasonable point. In response, the authors point out a 2010 British Journal of Sports Medicine paper in which researchers in Sweden compared the genetic profiles of 100 world-class male endurance athletes (“Olympic finalists or Europe/World Champions and Tour de France finishers”) with 100 matched controls. They looked at 33 “risk-related mutations and polymorphisms” associated with cardiovascular disease, hypertension, insulin resistance, cancer, and other major causes of mortality — and found no difference:

[T]he overall picture suggests that there is no evidence that elite male world-class endurance athletes are genetically predisposed to have a lower disease risk than non-athletic controls. Thus, the previously documented association between strenuous aerobic exercise undertaken by elite athletes and increased life expectancy is likely not biased by genetic selection.

Bottom line: if the question is “How much exercise is too much?”, I still think the answer is “Way, way more than you think.”

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Feeling healthy v. objective fitness

June 10th, 2011
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Which is more important: feeling healthy, or being fit? That’s the question addressed by a new British Journal of Sports Medicine study from Steven Blair’s group at the University of South Carolina. Blair is best known for pioneering the research that suggests that fitness is more important than fatness as a predictor of health outcomes. In this case, he and his colleagues take a look at “self-rated health” (SRH), which has been touted lately as a valuable health-assessment tool.

SRH is assessed by simply asking:

How would you rate your overall health?

The answers are poor, fair, good or excellent. The researchers compared the predictive values of SRH to aerobic fitness, assessed using a maximal treadmill test (with the modified Balke protocol, which is apparently highly correlated to VO2max). The study followed 18,488 men who were tested between 1987 and 2003, 262 of whom died during the 17-year follow-up period. They controlled for age, BMI, physical activity, smoking, alcohol, heart disease, diabetes, cancer, and several other confounders.

Not surprisingly, being fit and having a high SRH reduced your chance of death dramatically. The real question is what happens when you separate the two factors. Aerobic fitness was strongly protective against mortality even when all other factors were controlled. SRH and mortality were were still inversely correlated, but the association was “only marginally significant (p=0.09)” once aerobic fitness was controlled for.

Given the previous research topics of this group, I suspect they set out to show that all the apparent predictive power of SRH is just a byproduct of aerobic fitness. It seems safe to conclude that fitness is indeed the more important of the two, but it’s interesting that SRH retained some predictive power. Their thoughts on why this might be:

One plausible explanation is the afferent information that conveys messages from the organism to the brain. These messages are usually not brought to consciousness because they function at lower levels of the central nervous system. However, this afferent information is perceived by the individual as sensations, feelings and emotion and is the sense that reflects the physiological condition of the entire body. Another theory explaining a person’s perceptions of their health involves a family of proteins called cytokines. Cytokines are involved in inflammation processes and play a major role in infectious conditions and also the pathogenesis of many chronic diseases. Research is beginning to show that the inflammatory process and certain cytokines are associated with tiredness, impaired sleep, depressive mood and poor appetite.

On one level, this seems a bit needlessly complicated. After all, most of us can probably make a reasonable assessment of how healthy we are without relying on unconscious afferent feedback and cytokines! Still, the idea that our “sensations, feelings and emotion” can reflect our underlying health status is also interesting — and inarguable. After a few late nights, skipped workouts and junk-food binges, we tend to feel like crap. This isn’t just guilt and fatigue: it’s the body sending a distress signal.

Active vs. passive warm-up

April 6th, 2011
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What exactly is the purpose of a warm-up before exercise? According to a new study in the Journal of Strength and Conditioning Research, it’s:

to enhance physical performance, to reduce muscle soreness, and to prevent sports-related injuries by increasing the body temperature.

But if the main mechanism of the warm-up is literally to warm the body, could we accomplish the same thing by, say, sitting in warm water? That’s what this study tested: three different cycling tests (six minutes at 80% VO2max) after (1) no warm-up, (2) an “active” warm-up of 20 minutes easy cycling, or (3) a “passive” warm-up of soaking the legs in 39-C water for 20 minutes. The result: the active warm-up allowed subjects to use more oxygen (measured VO2) with less effort (lower HR), and possibly lower lactate accumulation (though the latter wasn’t statistically significant).

So what does this mean? It suggests that the benefits of a proper warm-up aren’t just the result of raising your temperature. Higher temperature does confer some benefits: for example, your muscles and tendons become more elastic, reducing the risk of injury. Nerve signals from brain to muscle are transmitted more quickly. The rate of metabolic reactions inside your cells speeds up by 13% for each degree C that the temperature increase.

But there are other benefits beyond temperature. Crucially, the active warm-up causes your blood vessels to dilate to speed the flow of oxygen to working muscles. When you start the main workout or race, the sudden increase in demand puts you into temporary oxygen debt, because your heart, lungs and muscle metabolism can’t respond instantly to the higher demand. If you’re properly warmed up, your systems are already partly ready for the increased demand (blood vessels dilated from the warm-up, heart rate already elevated, etc.), so they can deliver more oxygen than if they were starting cold. That means the short period of initial oxygen debt doesn’t last as long — and since aerobic metabolism is more efficient that anaerobic metabolism, it means that you’re more efficient overall.

The practical take-away: well, we all know that warm-ups (as opposed to sitting in a luke-warm bath) are important, so this doesn’t change anything. But there’s still lots of debate about exactly what a warm-up is supposed to do, and what the best way to do it is — hence all the posts about dynamic versus static stretching, for example. In the long run, figuring which parts of a warm-up really do boost performance will help us design better warm-up routines.

Heart damage markers disappear 72 hours after marathon

April 3rd, 2011
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The debate about whether “extreme” exertions like running a marathon can damage your heart continues to simmer. The latest addition is a paper published online last week in Medicine & Science in Sports & Exercise by a group from TU Munich. One of the co-authors is Stefan Moehlenkamp, whose recent studies of fibrosis in the hearts of veteran marathon runners have stirred up controversy.

In this study, they took blood tests (and various other measurements) from 102 participants in the Munich Marathon, before, immediately after, 24 hours, and 72 hours after the race. They were looking at the rise and fall of various “cardiac biomarkers” that signal possible heart damage, in particular and newly developed test for cardiac troponins that is much more sensitive than previous tests.

We already know that troponin levels rise after a marathon — but we don’t whether that’s a signal that heart muscle cells are dying, or whether it just signals some temporary damage, in the same way that your leg muscles are temporarily “damaged” by a marathon but quickly recover. When heart muscle cells actually die, as in a heart attack, levels of troponin stay elevated for four to seven days, as troponin continues to leak from the dead cells. In contrast, temporary damage causes a sharp peak in troponin that returns to normal after a few days. Here are the results:

troponin levels return to normal 72hrs after marathon

Combining this sharp peak and quick decline with the other measurements in the study, the researchers conclude that “cardiac necrosis [i.e. cell death] during marathon running seems very unlikely.” Instead, the evidence points to temporary damage to cell membranes, possibly caused by decreased availability of oxygen or ATP during the race.

Referring to the earlier study that found fibrosis in veteran marathon runners, the researchers write:

Findings of myocardial injury, as seen in older marathon runners (5) are probably independent of marathon running but rather related to cardiovascular disease or risk factors, particularly smoking.

Does this mean the controversy is over? Far from it. For one thing, this study was written before more recent results showed possible heart damage in elite athletes who weren’t former smokers. More research, as always, is needed. But the results are encouraging — I remain pretty firmly convinced that the cardiac benefits of training for and competing in marathons dramatically outweigh the putative risks.

High-intensity interval training improves insulin sensitivity

April 2nd, 2011

“High-intensity interval training” (HIT) has been a big buzzword for the past few years, with plenty of studies showing that short, intense bursts of exercise can produce many of the same results as long, steady cardio sessions. Martin Gibala’s group at McMaster just published a new study in Medicine & Science in Sports & Exercise with a couple of points worth noting:

  • You don’t have go “all out”: Many of the early studies used 30-second Wingate tests at 100% exertion, which is pretty challenging for inexperienced or unfit exercisers. The more moderate protocol Gibala has been studying is cycling 10 x 60s hard with 60s recovery. The hard sections were done at 60% peak power (80-95% of heart rate reserve) — so hard, but not fall-off-the-bike hard.
  • Anyone can do it: Instead of using relatively fit subjects, this study used older (average age 45) subjects who were sedentary (no regular exercise program for at least a year).

The most interesting result for me: subjects improved their insulin sensitivity by 35% on average after just two weeks, three sessions a week. Lots of other parameters also improved, but insulin sensitivity is something that we know is crucially important in avoiding and managing metabolic syndrome. And the whole workout, including the three-minute warm-up and five-minute warm-down, takes less than half an hour.

By no means am I suggesting that interval training is the One True Answer to fitness (and neither are Gibala et al.). There are good arguments for varying what type of workout you do. But in terms of bang for buck, it’s hard to compete with HIT.

Who’s the mystery man with the 90.6 VO2max?

March 30th, 2011

Interesting riddle posed by a case report in the European Journal of Applied Physiology (third post from that journal this week — I need to check it more often!): who is the mystery cross-country skier who appear to have one of the highest VO2max readings ever recorded, at 90.6 ml/min/kg?

Here are the clues:

  • The test was performed at the University of Innsbruck in Austria.
  • The subject was “a young elite cross country skier,” male, 22 years old.
  • The test took place 4 years before the skier won an Olympic gold medal.

Austria didn’t have any gold medalists in XC skiing in 2010 (and none of the winners are the right age anyway). Same with 2006. They had a gold medalist in 2002 (Christian Hoffmann), but he’s two years too old. They did win the 2006 men’s team event in Nordic combined, and one of the team members — Michael Gruber — would have been 22 years old in 2002, four years earlier. But come on… are you telling me that the man with one of the highest VO2max readings in history was a part-time ski-jumper?! If so, that’s a pretty good reminder that VO2max isn’t everything…

So what is the ultimate highest value? The paper notes an “anecdotal report” in a 2003 textbook by Astrand of someone testing 94 ml/min/kg (anyone know who that was?). They also discuss some measurements on cyclists in the 1990s by Randy Wilber (who is a co-author of this paper) at the US Olympic Training Center. The 1997 paper they cite is a comparison of 10 mountain bikers with 10 members of the US Cycling Federation National Road Team, but they also cite some unpublished data on “American elite male road cyclists who had won individual stages (and the General Classification) of the Tour de France.” There aren’t many of the latter around, are there? Anyway, a few of these cyclists tested at over 80 ml/kg/min at 1860 metres, which they argue equates to 85-86 at sea level, and roughly comparable to about 90-91 if they were doing arm-and-leg exercise (like skiing) rather than just leg exercise (cycling).

But that’s a lot of approximations. I’ve never seen a peer-reviewed report over 90 until this one. Anyone else?