Posts Tagged ‘sports technology’

Full-body compression makes your heart work harder

September 13th, 2011

Quick look at a study just posted in the European Journal of Applied Physiology, from researchers at the University of Otago in New Zealand. They investigated the effects of full-body compression garments (Skins) on cyclists, looking in particular at three outcomes:

  1. Did it make the cyclists faster?
  2. What effect did it have on their body temperature?
  3. What effect did it have on their cardiovascular workload?

To separate the effects of compression from the effects of wearing a full-body suit in reasonably warm temperatures (24 C), the subjects each did three trials: a control trial in gym shorts; a trial with “properly fitting” Skins; and a trial with oversize Skins. The results:

  1. No difference in cycling performance
  2. Skin temperature was higher by 0.5-0.9 C during exercise when wearing compression gear, but core temperature was unaffected.
  3. Their hearts had to work about 5% harder with the compression gear on, and they finished with a heart rate 4-7% higher than in the control condition.

The authors make their skepticism clear pretty much from the start: the first sentence of the abstract is “Sporting compression garments are used widely during exercise despite little evidence of benefits.” They make several interesting points in the paper — for instance, the vast majority of “evidence” cited for increased venous flow and reduced venous pooling comes from studies of people (generally with some sort of circulatory condition) at rest. Do the same findings apply during exercise? It may be that the “calf muscle pump” — the squeezing of the calf that shoots blood back toward the heart, which supposedly gets a boost from compression socks — is already acting at maximal capacity during vigorous exercise.

Bottom line from this study: the garments didn’t really make much difference (the mild changes in temperature and cardiovascular function, though negative, weren’t enough to be a big issue). The authors are careful to note that the study has nothing to do with whether compression garments help recovery. But as far as wearing them during exercise, this certainly doesn’t change my opinion that wearing a full-body speed-suit while jogging on a hot summer day (and I see plenty of people doing that here in Sydney!) may look cool, but doesn’t do anything for your performance.

Cryosaunas enter the realm of real sports science

August 18th, 2011

Okay, I admit I enjoyed making fun of the “cryosauna” last fall, after it emerged that Alberto Salazar had arranged to have one shipped to New York so that Dathan Ritzenhein could use it before the New York Marathon. With the manufacturer promising “tighter, healthier skin,” “increased libido,” and “stronger, fuller hair,” the concept was ripe for a few jokes — especially since there was no actual science supporting its use for athletes.

But now I have to get serious, because a legit study has been published, funded by the French Ministry of Sports (and not by the manufacturer — actually, it’s a German company that made the cryosaunas used in the study). The full text is freely available via this link. The study had 11 trained runners do a pair of 48-minute hilly treadmill runs (i.e. including enough downhill to trigger muscle damage and soreness) separated by at least three weeks. After one of the runs, they were given three minutes of whole-body cryotherapy at -110 C immediately after, and then again once a day for the next four days. After each cryotherapy session, blood tests were taken to measure a bunch of inflammation and muscle damage markers. After the other run, they followed the same protocol, except replacing the daily bout of cryotherapy with 30 minutes of passive sitting.

One thing to emphasize: this study appears to have been very carefully executed. Throughout the study, the subjects were told exactly how much they were allowed to run, and they weren’t permitted to use anti-inflammatories or other recovery aids. They also controlled food and drink intakes.

The results? They’re pretty complicated because they tested a lot of things. For most of the markers, there was no difference. But there were three key differences:

  • C-reactive protein, a marker of muscle damage, stayed almost unchanged in the cryotherapy group, whereas it spiked after 24 hours in the control and was still elevated three days later.
  • Interleukin-1beta, a pro-inflammatory cytokine produced after strenuous exercise, was slightly suppressed by cryotherapy (though not by much, if you look at the data below).
  • Interleukin-1ra, an anti-inflammatory cytokine inhibitor that counteracts the pro-inflammatory cytokines, was temporarily but significantly enhanced immediately after the post-exercise cryotherapy session.

Here’s what the data for those three factors looked like (WBC is whole-body cryotherapy; PAS is passive recovery):

So does this settle any debate? Well, there’s always a big gap between seeing a minor change in some blood test and translating that to a functional benefit for an athlete. Does cryotherapy permit a better next-day or day-after-tomorrow workout? We don’t really know. On a more general level, do the benefits of (hypothetically) more rapid recovery outweigh the (hypothetical) disadvantages of suppressing the inflammatory signals that tell your body to adapt and get stronger? Again, we don’t really know — that’s still in the realm of coaching art, not science. Is a massively expensive cryosauna any better than a bathtub with a few blocks of ice thrown in? Still don’t know.

But having said all that, this study does suggest that we can move the cryosauna from the category of “wacky techno-schemes that sound like you mail-order them from the back of a comic book” to “serious recovery modalities that are as likely as anything else we currently rely on to work.” (Though I’m still reserving my judgement on the “better hair” claims.)


Platelet-rich plasma for tennis elbow

August 10th, 2011

Platelet-rich plasma therapy was a super-hot topic a couple of years ago (see earlier blog posts about it), in part because of reports that top athletes like Tiger Woods were using it to speed their recovery from injuries. These days, the fuss has died down a bit. The novelty is gone, subsequent studies haven’t produced the “miracle” results promised by initial case reports, and maybe no one wants to emulate Tiger Woods anymore.

Anyway, studies of PRP continue to trickle in, but the picture isn’t necessarily getting much clearer. Two new studies have just been posted online at the American Journal of Sports Medicine, one of which is a randomized trial of PRP for tennis elbow by researchers in Greece. The design seems pretty good in theory: 28 patients were split into two groups; one group received an injection of PRP (their own blood, spun to produce plasma with elevated levels of healing-enhancing platelets), while the other group received an identical injection of their own unenriched blood. This should eliminate the problem of placebo effects (which are very big in invasive procedures that involve lots of needles), and test only whether the platelets themselves make any difference.

But there’s a problem:

This is a single-blind study. Patients were aware of the treatment because it was practically difficult to mask the process.

I don’t understand this. Maybe there’s something I’m missing — if you know why it would be “practically difficult” to mask the process, please let me know. It seems to me that all you have to do is put the blood-spinning machine in the room next door, and you’re in business with a double-blind study. But that’s not what they did — and to me, that’s an enormous problem, given how much publicity PRP has received over the past few years.

Anyway, the results: they measured subjective pain and perceived elbow function at various points over the next six months. There was only one case where the two groups showed statistically significant differences: pain was lower in the PRP group after six weeks, though the difference was no longer significant at the next measurement (3 months). On the other hand, if you ignore “statistical significance,” the trend was that the PRP patients did better in every measurement.

So how do you interpret these results? It’s pretty clear that the authors of the paper are big boosters of the technique:

[T]here is enough proof to support the superiority of PRP treatment over autologous blood, regarding pain, in the short term…

More studies on this topic could further enlighten aspects of this promising treatment…

In conclusion, we showed that PRP led to pain relief earlier than autologous whole blood, and we believe its application will be increasingly widened in the near future…

Really, I don’t think they showed any such thing. They found results that were statistically insignificant in five of their six outcomes, using two measurements that are largely subjective, in an experimental design that does nothing to eliminate placebo effect for one of the most heavily hyped sports medicine treatments of the past decade. To justify the cost and extra effort required for PRP therapy, they’re going to need more definitive results than that.


How tight should your compression tights be?

August 7th, 2011

As the various brands of compression gear compete to distinguish themselves, one of the claims you hear a lot (I’m looking at you, CEP) is that you need “medical grade” compression to achieve true performance benefits. Seems reasonable. So let’s test it…

Australian researchers just published a new study in the International Journal of Sports Physiology and Performance, looking at the effect of wearing Skins tights on endurance running performance. The twist: their subjects (11 well-trained distance runners) did three sets of testing, once in loose shorts, once in the “right” size of Skins leggings, and once in a set a Skins leggings one size too small (to get extra compression). The correct size produced an average of 19.2 mmHg pressure gradient across the calf, while the smaller size produced 21.7 mmHg. For comparison, CEP’s socks promise a max of 22-24 mmHg at the ankle, with 18-20 mmHg on the calf.

The researchers tested pretty much every parameter they could think of, and then some. The performance parameters were simple: a progressive VO2max test, and a time-to-exhaustion test at 90% of VO2max. The physiology measures included heart rate, blood lactate, expired gases, and near-infrared spectroscopy of the leg muscles to measure how much oxygen-carrying hemoglobin and non-oxygen-carrying hemoglobin was passing by in the blood.

The results: in a nutshell, actual running performance was unchanged in any way. Compression tights didn’t make the runners run faster, and there was no difference between the two levels of compression. Repeat:

No improvement in endurance running performance was observed in either compression condition.

But… they measured all these lovely physiological parameters. And sure enough, after sifting through all of them, it turns out that they weren’t all identical. At low speeds, compression garments seemed to increase muscle blood flow; at high speeds they increased non-oxygen-carrying hemoglobin in the vastus medialis; etc. etc. The picture is pretty messy, but the message is still clear:

However, the magnitude of this improved venous flow through peripheral muscles appears trivial for athletes and coaches, as it did not improve [time-to-exhaustion] performance. This would suggest that any improvement in the clearance of waste products is insufficient to negate the development of fatigue.

But all is not lost for compression fans:

However, the data presented may have helped to identify and support the responsible mechanisms that relate to the postexercise recovery improvements associated with wearing [lower-body compression garments].

Note that this study didn’t actually find anything involving improved recovery. It just found that if you squeeze a limb, blood flow through that limb changes. That might result in improved recovery (and indeed some other studies do suggest that’s the case), or it might not. But the idea that compression will help you run faster is seeming less and less plausible.

Platelet-rich plasma doesn’t work for rotator cuff (shoulder) tendons

February 22nd, 2011

Yet another salvo in the ongoing debate about whether platelet-rich plasma (PRP) therapy — sometimes known as “blood spinning” — is a miracle tendon healer or an expensive placebo. At an American Orthopaedic Society for Sports Medicine conference in San Diego, researchers presented the results of a new study of PRP for rotator cuff tendon repair — and the results weren’t encouraging.

The study involved 79 patients who all received standard surgical rotator cuff repair and post-operation rehab; half of them were randomized to receive a form of PRP treatment. There were “no real differences” between the groups:

“In fact, this preliminary analysis suggests that the PRFM [the form of PRP used in the study], as used in this study, may have a negative effect on healing. However, this data should be viewed as preliminary, and further study is required” said study author Scott Rodeo, MD, of New York City’s Hospital for Special Surgery.

Right now it’s just a conference presentation; the study will presumably be published eventually, at which point we’ll get some more details on the design and specific results of the study. But the scientists still seem optimistic:

Researchers think there may be several reasons for a lack of response in healing, including variability in the way platelets are recovered, platelet activation and the mechanisms for the way the PRFM reacts with the tendon cells. The study was also unable to document the number of platelets actually delivered to patients who received the PRFM…

“Additional research needs to be performed to figure out the mechanisms for why PRP is successful in healing certain areas of the body and not others…” said Rodeo.

I’m not really sure which areas of the body he’s talking about. I only know of one properly controlled clinical trial that came to a positive conclusion, on tennis elbow — but even that study was subject to criticism. So far PRP is one of those ideas that makes perfect sense in theory, but hasn’t yet proven itself in practice.


More about stride length, rate, and “cruise control” for runners

February 20th, 2011

I posted last week about a newly invented “cruise control” device for runners, which controls pace by cueing stride frequency with a metronome. That ignited an interesting discussion about how we change pace while running: do we take quicker strides, longer strides, or a combination of both?

For starters, Pete Larson send me a paper with some nice clear data that shows how the two factors interact (at least in one physically active group of 24 men and nine women between 18 and 34 years old):

The x-axis runs from 0 to 12 m/s, so the data runs from 2.5 to just over 9 m/s, which is 6:40/km to under 2:00/km — i.e. sprinting). Sure enough, stride length is a much bigger factor than stride frequency at typical jogging/running speeds, but the frequency curve is never perfectly flat.

I also exchanged a few e-mails with Max Donelan, one of the co-inventors of the cruise control, who explained a little more about how the device works and what sort of interactions between stride rate, length and running speed they saw in their testing. His answers were very interesting and well-explained, so with his permission I’m going to post them here rather than trying to summarize them. One of the most interesting points, I think, is that when his metronome cues runners to increase their stride rate, they also automatically increase stride length to arrive at the pace they’d naturally associate with the new cadence. Makes sense, but that hadn’t occurred to me.

Q: I’m also curious (as you saw in my blog entry) about how effective cadence is at controlling pace.

A: We have tested a number of subjects running at a range of speeds. It is absolutely true that some runners increase speed predominantly by increasing stride length. In fact, I would say that most runners that we have tested increase stride length more than frequency. However, all the runners we have tested also increase their frequency when they increase speed. We have yet to find a runner that only increases stride length or only increases stride frequency. For our purposes, it doesn’t matter whether people increase speed predominantly with increasing stride length as long as the relationship between speed and frequency is not perfectly flat (and we have yet to find a subject like that).

Of equal importance is a second phenomenon which is less intuitive. When someone is running at a particular cadence and you ask them to match a faster cadence, they not only increase their stride frequency but also their stride length.They alter both frequency and length to converge on the speed that they normally prefer at the new cadence. For example, a 10% increase in frequency might yield a 40% increase in length to get a 54% increase in speed. This allows us to use frequency to have control authority over speed.

Q: What sort of testing did you do?

A: We initially determined how frequency and length change with increases in speed by having subjects run at different steady state speeds on a treadmill. We carefully calibrated the treadmill speed and we measured step frequency with pressure sensitive foot switches. Stride length is simply speed divided by stride frequency.

To study how runners change both speed and step length when you give them an increase in cadence to match, we had them run overground with a metronome beeping in their ear. After a few minutes, the metronome frequency would rapidly increase to a new frequency. Subjects were instructed to match the beat. They were free to choose whatever speed they liked and, in principle, they could have stayed at the same speed. We measured step frequency with the same pressure sensitive foot switches. We measure and record overground running speed using a high-end GPS designed for quantifying acceleration in race cars.

We test our cruise control algorithm also during running overground. When we implement cruise control, we get runners within 0.5% of their desired average speed. This compares well with recreational athletes who average an 8% error, and collegiate runners who average a 4% error:

Green et al. Pacing accuracy in collegiate and recreational runners. Eur J Appl Physiol (2010) vol. 108 (3) pp. 567-572

For the recreational runners, an 8% error means that they will only be within 4 minutes of their target time for a 50 min 10 K. Running 4 minutes too fast may mean a surprisingly fast personal best, but it may also mean crashing and burning.

Very interesting stuff — both from a practical point of view (i.e. the cruise control), and for understanding more about how we run. Thanks to both Max and Pete for their contributions.


Stride rate, running speed, and “cruise control” for runners

February 16th, 2011

A press release from Simon Fraser University in Vancouver reported a few days ago that a pair of biomedical physiologists have invented a “cruise control” device for runners. As far as I can tell, it’s basically a metronome that provides a beat for you to synchronize your strides with; it measures your speed (presumably via GPS) and increases the cadence if you’re going slower than your desired speed, and slows it down if you’re going too fast. Right now, it’s basically a clunky backpack prototype, but future versions might be, say, an iPhone app that provides music with a “sliding tempo” to keep you on pace.

Okay, so not a device I’d feel much need for, but I can see a potential market. One hesitation, though. The entire device is predicated on the following assumption:

“We know that for higher running speeds humans prefer higher step frequencies,” says Snaterse. “This relationship can be inverted – for higher step frequencies, humans prefer higher speeds. The cruise control for runners uses this principle.”

Is that really true? There’s a lot of dogma floating around the running world that running speed is essentially independent of stride rate — if you go for a jog and gradually pick up speed until you’re nearly sprinting, your stride length will get longer and longer but your stride rate will stay essentially unchanged. For example, check out this recent post from Amby Burfoot’s blog about the potential benefits of shortening your stride:

Most of us, when we increase pace, increase stride length much more than stride rate. So our stride rate stays roughly the same at different paces, slow and fast.

Now, that doesn’t necessarily mean the reverse is true. It’s possible that when you increase speed, your stride rate stays the same, but when you increase stride rate, you speed up. And there’s some evidence that other effects might crop up when people exercise while listening to music — for example, I wrote about a study where British researchers secretly sped up and slowed down workout music by 10% and people on exercise bikes sped up and slowed down without realizing what was happening. If we’re dealing with a cruise control that, by design, is intended to make only small corrections to your pace, maybe a small effect like that is sufficient.

What does the actual research say? It’s harder to dig up than I expected, partly because it’s such an “old” question that some of the relevant studies aren’t online. Here a description of an older (1974) study from a 2009 paper:

Saito et al. [27] showed that trained runners increased their speed to 7 m/s [2:22/km, 3:50/mile] by lengthening their stride, whereas untrained runners increased stride length only up to 5.5 m/s [3:02/km, 4:53/mile]; any further increase in running speed was achieved primarily by increasing stride rate.

In other words, you have to be sprinting pretty darn fast before you start increasing stride rate instead of stride length. Still there must be some better and more recent data out that show the typical relationship between speed and stride rate — if anyone knows where I should be looking, please let me know!


More muscle tension: there is research

February 13th, 2011

A few thoughts following up on the post about Steve Magness’s muscle tension article in Running Times. Steve was kind enough to send me a copy of Marius Bakken‘s medical school thesis, which consisted of two documents: a detailed literature review on efforts to characterize and measure muscle tension, and a clinical trial investigating whether regular cross-friction massage can reduce muscle tension. It’s still a very young field of study, but it turns out there is some literature devoted to the ideas discussed in Steve’s article.

What Steve is talking about here is what you might call “passive” muscle tension — the tension that remains in your muscles even when they’re completely relaxed (i.e. receiving no neural instructions to contract). Bakken adopts the definition of “resting muscle tone” from a 1998 journal paper, which is:

the elastic and/or the viscoelastic stiffness in the absence of contractile activity.

So how do you measure this tension? Most simply, you relax your muscle and press into it to see how stiff it is. This is, obviously, a pretty crude measurement. Bakken is now using a tool developed by an Estonian company called Myoton (shown above), which measures the frequency and damping of muscle oscillations to determine muscle tone, elasticity and stiffness. That’s the tool he used for his massage study, in which five athletes received 20 minutes of massage once a week for four weeks. The Myoton showed that their resting muscle tone decreased by an average of 3.3%, and EMG measurements of nerve signals showed that the decrease was unrelated to changes in active muscle contraction.

If you poke through the references in Bakken’s literature search, you find various interesting hints — e.g. links between overtraining and muscle tension in cross-country skiers in a 2002 study. There are still some pretty big pieces missing from the puzzle, for example showing a link between resting muscle tone and performance. And the mechanisms responsible for this resting tone are still being debated (is it extracellular water pressure? cross-bridges between contractile proteins?). But the documents made for an interesting read, and show that there is some serious science behind these ideas. I’ll be following further developments in this field with interest.

How much compression do socks need?

February 9th, 2011

Over the past few years, there’s been a ton of research into the effects of various types of compression gear, with conflicting results. Some studies show improved performance, others don’t; some studies show changes in physiological markers, others don’t. One of the big problems is fit: no one really know exactly how tight the garments should be.

A study from researchers at Massey University in New Zealand, which appeared online in the Journal of Strength and Conditioning Research last week, attempted to answer this question. They had 12 well-trained runners complete four 10K time trials on the track wearing four different socks: a non-compressing control, one low compression (12-15 mm Hg), one medium compression (18-21 mm Hg) and one high compression (23-32 mm Hg). All the socks had graduated compression, with maximum compression at the ankle tapering to no compression at the knee.

The results: no significant difference in 10K time, pre- or post-run lactate, heart rate, or several other measures. Now, I have my doubts about the statistical power and repeatability of a 12-person study with four 10Ks over the course of eight weeks, but take it for what it’s worth.

There was an interesting twist, though, represented in the following graph:

We’re looking at the change in “countermovement jump height” from before the race to after the race. The low compression sock shows a significant improvement compared to the control, and the medium sock has an even bigger improvement, while the tightest sock is roughly the same as the control. This test is basically a measurement of leg power, so the researchers speculate that it’s possible that the subjects might be able to produce a faster finishing sprint in the low and medium socks, though it’s not something they measured. I’m fairly skeptical — I never really had the sense that explosive leg power was the limiting factor in the final stretch of a 10K race. But who knows?

In the end, the study is a perfect microcosm of the greater body of research in this area: it shows that something happens when you put properly fitting socks on, but we still don’t know exactly what and we certainly don’t have evidence that it actually makes you faster. But in other ways, the study is a big step forward, in that it makes a serious attempt to determine what a “proper” fit is — at this point, 18-21 mm Hg is looking pretty good. More studies like this will be needed. And one addition that I would really like to see is a placebo compression sock — perhaps something with non-graduated compression that subjects can’t necessarily distinguish from the “real” socks.

Known knowns, unknown unknowns and the limits of science

January 22nd, 2011
Comments Off on Known knowns, unknown unknowns and the limits of science

Every once in a while, I’m contacted by product reps who offer to send me the latest high-tech sports gear to try out and review on the site. While I sincerely appreciate their offers, I decided when I started the site that I wouldn’t do first-person reviews. That’s partly so that readers can assume that when I do criticize or compliment a product, it’s an unbiased opinion. But it’s also because I really don’t place much value on n=1 experiments. (If I try a pair of compression tights, I can obviously judge whether they’re comfortable and come in pretty colours, but it’s impossible for me to tell in any meaningful way whether they made me faster or less sore. Or more precisely, if I run faster and feel less sore, it’s impossible for me know what really caused it.)

This question of what constitutes meaningful evidence is a constant undercurrent on this blog, and it occasionally pops to the surface. For example, I’ve been arguing about the fundamental mechanisms of weight loss for most of this week — and I think I generally agree with the guy I’m arguing with, we just differ on the extent to which the science is settled. Or, for a different take on the nature of evidence, here’s a few lines from a comment that popped up yesterday on an old post about “cryotherapy”:

[Y]ou see people getting in and out of them constantly… like a revolving door! Why would people put themselves in such cold temperatures if it doesnt help them with something?? I only went in once so I dont know if I reaped any long term benifits but I loved the way I felt after I got out! I couldnt stop giggling and I didnt know why! […] I hope you stubborn North Americans learn to see past your ignorance to the rest of the world and try something before you knock it

All of this is on my mind these days because of a few very interesting recent articles on the systematic problems inherent in the medical literature. (And let’s not kid ourselves, the sports science literature has a long way to go before it reaches even that level of unreliability!) So on that note, some suggested weekend reading:

If I could summarize the articles in a few lines, I would. But they’re not simple — particularly Lehrer’s article, which covers some pretty broad territory beyond the obvious problems of publication bias, study design, bad statistics, and so on. If it’s a topic that interests you at all, they’re both worth a read.

Finally, for a slightly more practical (and optimistic) take on how these somewhat abstract concerns intersect with real life, read Steve Magness’s post on “Science Vs. Practice: Should our training be evidence based?

(Thanks to Amby B., Ian R. and Amy M. for pointing these articles out to me.)