Posts Tagged ‘running’

Running stride: speed vs. injury-proofing

October 1st, 2011

Another great post on Amby Burfoot’s Peak Performance blog explores an important wrinkle in the ongoing debates about optimal running form. We tend to think that “better” running form is better in all relevant respects: we’ll be faster and less likely to be injured. But that’s not necessarily the case. Amby takes a look at a study from a couple of years ago that analyzed the gait of an ultrarunner who ran from Paris to Beijing in 161 days, averaging 53 km per day. As Amby writes:

You would think that 161 days of a marathon-plus per day would turn you into a lean, mean running machine. But that doesn’t happen, at least not when it comes to running economy… His stride became shorter and “smoother,” the word used by the physiologists to describe his decrease in aerial time with each stride… He reduced his landing force and also his loading rate. But his oxygen efficiency, or running economy, decreased by six percent.

This illustrates one of the conundrums faced by those attempting to run with shorter strides. It may in fact reduce your injury rates. It won’t necessarily make you faster.

The adaptations that this runner’s body made over the course of this epic run make perfect sense: after all, his top priority was to survive each day without breaking down. But it’s a good reminder that, when we talk about “improving” running form, we have to think carefully about what, exactly, we’re hoping to improve.

Usain Bolt and Paul Tergat, striding slowly

September 22nd, 2011

A couple of weeks ago, I asked if anyone had footage of fast runners running slowly. The reason: I was curious to see whether the well-known fact that fast runners take rapid strides is (a) because of the way they run, or (b) because of the speed they run at. The Runblogger, Pete Larson, just sent me a couple of great links showing two of fastest runners ever, jogging along comfortably: Usain Bolt and Paul Tergat.

My rough calculations showed Bolt taking 18 steps in 6.7 seconds, for a cadence of 161, and Tergat taking 8 steps in 2.8 seconds, for a cadence of 171. You can also watch Tergat at 1/3 speed here. For the same 8 steps, I get 8.5 seconds, for a cadence of 169 — so let’s say about 170 for Tergat.

The point? Just because they run their Olympic races with a relatively rapid cadence (257 for Bolt!) doesn’t mean they maintain that same cadence when they’re jogging along comfortably. (Okay, I promise I’m done with this topic, at least for a little while!)


Cadence data redux

September 18th, 2011

Last week I posted some data about my running cadence at difference running paces, which sparked plenty of interesting discussion here and at several other sites including Pete Larson’s Runblogger, Amby Burfoot’s Peak Performance and Brian Martin’s Running Technique Tips. All of those folks also sent me some data on their own cadence-vs-pace curves, so I just wanted to share the updated graph:

Without rehashing the whole discussion from last week, the key point I take away from this is that cadence changes as a function of pace (and in a fairly predictable manner, at that). The runners shown here vary dramatically in age, morphology, speed, running shoe preference, running style and probably many other parameters — and as a consequence, at any given pace they have different cadences.

Some might argue that, if all of us took a course to learn the “perfect” form, our cadences would converge toward similar values. That’s an interesting debate — but not the one I’m focused on here. Because even if we did all have the same cadence at 5:00/km, this data suggests very strongly to me that we’d have a faster cadence at 4:30/km, and an even faster cadence at 4:00/km. The moral: any discussion of cadence, whether of an individual or a group, is meaningless without implicitly or explicitly considering pace.

Even Kenyans stride slowly

September 10th, 2011

Just for fun, following up on yesterday’s post on running cadence, I did a little YouTube surfing to find footage of fast Kenyans running slowly. Because the question I’m interested in isn’t: “Do fast runners take quick strides?” I think that’s reasonably well established. The trickier — and I’d argue more relevant — question is: “Do fast runners take quick strides when they’re running slowly?”

The best example I found was this 10-minute clip posted in 2007 by Toby Tanser, which shows all sorts of footage of Kenyan runners at different speeds:

Now, if you spend a little time with a stopwatch, you quickly find that when the runners are shuffling along slowly, then tend to have a slow cadence in the 160s, and when they’re running fast, their cadence tends to be above 180. But that doesn’t really answer the question, because it’s not necessarily the same runner. So I’ve cued to video to 2:49, where you see a clip of Hilda Kibet (1:08 half-marathoner, 2:24 marathoner) jogging slowly, and then another clip of her running quickly around the track. My measurements:

Jogging slowly: 18 strides in 6.7 seconds = 162 steps per minute

Running fast: 16 strides in 5.0 seconds = 190 steps per minute

I realize this is pretty scanty data! And I also realize that there’s a fairly extreme difference between how slowly she’s shuffling in the first clip, and how quickly she’s hauling in the second clip. But that’s the whole point: you can’t talk about cadence without considering speed.

The problem with 180 strides per minute: some personal data

September 8th, 2011

My wife is out of town at the moment, which means I’m doing lots of running on my own. Plenty of time to ponder the meaning of life — and, when I get tired of that, to count my footsteps. Sparked by interesting discussions with the likes of Pete Larson from Runblogger and Dave Munger from Science-Based Running, I’ve been wondering what my own cadence is like — particularly in light of widespread belief in the magic of 180 strides per minute. Over the past few weeks, I counted strides for 60-second intervals at a variety of paces. Here’s what I found:

Most surprising to me was (a) how consistent my cadence was when I repeated measurements at the same pace, and (b) how much it changed between paces: from 164 to 188, with every indication that it would decrease further at slower paces and increase further at faster paces. This certainly confirms what Max Donelan, the inventor of a “cruise control” device for runners that adjusts speed by changing your cadence, told me earlier this year: contrary to the myth that cadence stays relatively constant at different speeds, most runners control their speed through a combination of cadence and stride length.

So the next question is: am I a freak, running with a “bad” slow cadence at slower paces, but a “good” quick cadence at faster paces? To find out, I plotted my data on top of the data from one of the classic papers on this topic, by Peter Weyand:

The graph is a little busy, but if you look closely, you’ll find that my data is slightly offset from the Weyand data, but has essentially identical slope. So compared to a representative example of Weyand’s subjects, I have a slightly quicker cadence and shorter stride at any given speed, but my stride changes in exactly the same way as I accelerate. So I’m not a freak: the fact that my cadence increased from 164 to 188 as I accerelated from 5:00/km to 3:00/km is exactly consistent with what Weyand observed.

One key point: I’ve highlighted two key “speed zones.” One is the pace at which typical Olympic distance races from the 1,500 metres to the marathon are run at. This is where Jack Daniels made his famous observations that elite runners all seemed to run at 180 steps per minute (which corresponds to 1.5 strides per second on the left axis). The other zone is what I’ve called, tongue-in-cheek, the “jogging zone,” ranging from about 4:30 to 7:00 per kilometre. This latter zone is where most of us spend most of our time. So does it really make sense to take a bunch of measurements in the Olympic zone, and from that deduce the “optimal stride rate” for the jogging zone?

This isn’t just a question of “Don’t try to do what the elites do.” If Daniels or anyone else had measured my cadence during a race, it would have been well above 180. But at jogging paces, it’s in the 160s. I strongly suspect the same is true for most elite runners: just because we can videotape them running at 180 steps per minute during the Boston Marathon doesn’t mean that they have the same cadence during their warm-up jog. In fact, that’s a pretty good challenge: can anyone find some decent video footage of Kenyan runners during one of their famously slow pre-race warm-up shuffles? I’d love to get some cadence data from that!

Of course, this doesn’t mean I don’t think stride rate is important. I definitely agree with those who suggest that overstriding is probably the most widespread and easily addressed problem among recreational runners. But rather than aspiring to a magical 180 threshold, I agree with Wisconsin researcher Bryan Heiderscheit, whose studies suggest that increasing your cadence by 5-10% (if you suspect you may be overstriding) is the way to go.

[UPDATE: Make sure to check out the interesting discussion in the comments section! Also, Amby Burfoot did his own cadence test and posted the data. I’ve added it to the graph below to show how it compares to my own and Weyand’s data. Feel free to try it out on your next run, and I’ll add your data to the graph too!]

Read more…

Running on grass bursts more red blood cells than asphalt

September 1st, 2011

Interesting new study in the September issue of Journal of Sports Sciences that Amby Burfoot recently tweeted about, which appears to show that running on grass causes more hemolysis — the rupture of red blood cells — than running on asphalt.

It’s been known for a long time that prolonged running causes hemolysis. In fact, most forms of prolonged exercise can cause some hemolysis, simply because blood is being pumped around so vigorously and exposed to high oxygen fluxes. But running is particularly susceptible because of the footstrike: the cells get squashed as they pass through the capillaries of the foot at the moment of impact. Is this a problem? Well, excessive hemolysis can play a role in iron insufficiency — but this is generally only a problem if there are other exacerbating factors like overtraining. In this case, hemolysis is mainly interesting not because it’s a serious problem, but because it can tell us something about how different surfaces affect footstrike impacts.

The new study, by researchers in India, is very simple. Ten runners ran for an hour at 60-70% max heart rate on grass, while another 10 did the same on asphalt. Blood samples were taken before and after. The researchers expected to find more hemolysis from the harder asphalt surface, but they instead found the opposite. So what’s going on? Although the grass was superficially smooth and even, they speculate that its underlying unevenness affected the runners’ strides:

Running on uneven and inconsistent surfaces like the beach or grass can cause more injuries because each step creates varying pressures and forces in the feet, ankles, knees and hips as runners most constantly adjust to the surface. These natural surfaces also tend to slope and create a dangerous off-centre force on the ankles and feet while running. Even though the grass surface appeared to deform relatively more than asphalt, it was assumed that the uneven nature could have led to inappropriate pressure distribution and impact forces on the foot, which could have resulted in an increased haemolysis in these runners.

As Burfoot points out, this is reminiscent of Benno Nigg’s ideas: whether a surface is hard or soft, your leg automatically adjusts to cushion the impact. But on surfaces where you’re unable to correctly predict exactly how your foot will land — i.e. grass — that automatic adjustment can’t take place, and that’s when strong uncompensated forces shoot up your legs.

So it all fits together, right? Well, I have one caveat. Here’s the data from the new study for the two key measures of hemolysis (unconjugated bilirubin and lactate dehydrogenase, for those keeping score at home):

As you can see, the pre-run differences between the two groups (which were assigned randomly) are greater than the change from pre- to post-run! So statistical analysis may suggest that the two groups responded differently, but for now I’d treat this finding very cautiously. This study really should have been conducted as a randomized crossover trial, so that each runner was measured under both conditions. Bottom line: great idea for an interesting study, but until the results are replicated somewhere else I’d take the conclusions with a grain of salt.

The benefits of coaching for recreational runners

August 21st, 2011

Instead of a Jockology column this week, my editors at the Globe and Mail asked me to write about the phenomenon of recreational runners hiring elite distance runners to coach them. I spoke to a bunch of runners ranging from beginners to veterans road warriors, working with coaches like Marilyn Arsenault, Jerry Ziak and Brandon Laan, to find out why they decided to get coaching and what they’re learning from it:

As she recovered from a hysterectomy last year, Dee Ogden was eager to resume running but nervous about the post-surgical impact on her running form. So she did something that surprisingly few runners do: She hired a coach.

“When you learn tennis, you learn about your stroke and form,” says Ms. Ogden, 44, a registered nurse in Victoria. “Why wouldn’t you do that with running?” [READ ON…]


Breathing patterns and stride rates

June 28th, 2011

Do you ever find that your breathing locks into sync with your stride when you’re out running? Or with your pedal cadence when you’re cycling? (No points if it happens when you’re swimming.) It happens to most people, but it comes and goes, so there’s been decades of debate about whether it’s a “good” thing, and whether we should try to synchronize breathing with stride. I go into this topic (plug alert) in my new book (pp. 83-85, for the record), but I just noticed a new study in the European Journal of Applied Physiology which adds some interesting insight. It’s a little bit involved, but it’s pretty interesting — so bear with me!

First things first: this was a study (by researchers at UMass-Amherst) of walking, not running — but it’s likely that the same basic processes are at work. Essentially, there are two cyclic systems at work: the “locomotory” system (your legs) and the respiratory system (your lungs). Both are fulfilling separate goals (to keep you moving as efficiently as possible, and to keep your muscles supplied with oxygen), but they also interact with each other — e.g. changing stride can drive greater demand for oxygen. So you’ve got what physicists call a “coupled oscillators” system. The question is: when the two systems are in sync, do they function more efficiently? Do you burn less oxygen at a given pace if your breathing matches your pace?

Here’s what the study did: it had volunteers walk at a natural pace at whatever stride frequency felt natural. Then, keeping the same pace, it had them increase or decrease stride frequency by 10% and 20%, while doing sophisticated monitoring of how closely the breathing rate matched the stride rate, and also monitoring oxygen consumption (a measure of efficiency).

First finding: forcing stride frequency away from its preferred “natural” value made the walkers less efficient. They consumed more oxygen when they either increased or decreased their stride. This is exactly as expected, and has been observed in many previous experiments.

Second finding: changing stride frequency had no effect on how often breathing rates locked in with stride rates — it stayed pretty much the same. Since efficiency changed and synchronization didn’t, this suggests that synchronization doesn’t help (or hurt) your efficiency. Previous studies have found conflicting results for this question, so this is an interesting observation.

But here’s the key finding. The number of different synchronization patterns was greatest at the naturally chosen stride rate. At the lower and higher frequencies, subjects were more likely to lock into their favourite pattern, which was two strides per breath. At the preferred stride frequency — where they were most efficient — they spent a greater proportion of time jumping to different patterns, like 3:1, 4:1, 2.5:1, 4.5:1 and even 7:1. Here’s the data:

So what does this mean?

This would indicate that the greatest variation in the dominant coupling strategy used allowed the participant to explore coupling strategies with the goal of minimizing oxygen consumption.

In other words, we’re efficient at our “natural” stride frequency not because we can breathe in sync with our strides, but (in part) because we don’t let ourselves get locked into one breathing pattern. Instead, we’re unconsciously trying different breathing patterns constantly, finding the one that’s most efficient at that moment and then re-optimizing a  moment later. The moral: don’t try to consciously lock your breathing into a prescribed pattern.

(This doesn’t mean you should never pay any attention to your breathing. It may be, for example, that in stressful race situations you have a habit of breathing shallowly because of nerves. Trying to look out for this and correct it is different from, say, trying to exhale on every second left footstrike.)

Muscular endurance linked to running economy

June 26th, 2011

I blogged a few weeks ago about a study on strength training and cycling efficiency, and a commenter asked why so many of these studies are done on cyclists rather than runners. In response… here’s a interesting running study, just posted online at the Journal of Strength and Conditioning Research, that looks at muscular endurance and running economy.

The question they set out to ask was: does having better muscular endurance allow you to maintain better running economy (i.e. burn less energy while running at a given pace) as you get tired? To test it, they asked 10 well-trained runners to do two 30-minute runs at a moderate pace. In the middle of one of the runs, the runners had to speed up to VO2max pace for four minutes, then slow back down — enough to tire them out a bit without exhausting them. As expected, their running economy got worse after the four-minute surge by 3.0%. This is typical: as runners get tired, their running economy gets worse.

What remains hotly debated is why, exactly, running economy gets worse with fatigue. I’m not going to delve into the details of all the various mechanisms that have been proposed to explain this — it’s almost certainly caused by a mix of many different factors. One possibility relates to your knee flexors (a.k.a. hamstrings and surrounding muscles on the back of your leg above the knee) [UPDATED 6/27: had mistakenly written knee extensors], which contract eccentrically to act as a “brake” during each stride. There’s some evidence that eccentric contractions decline more quickly than concentric contractions during exercise — so as that braking action gets less effective as you fatigue, your stride gets less efficient.

Okay, now we finally get to the point. The researchers also tested the eccentric muscle endurance of the knee and hip flexors and extensors of all their subjects, then looked for correlations with the running economy results. Sure enough, they found that eccentric knee flexor endurance was “strongly related” to how much running economy worsened after the fast section of the run. Bingo!

So what does it mean? Well, there’s a big chasm between saying “hamstring quad endurance and running economy changes are linked” and concluding “therefore, you should do X, Y and Z in training.” However, it’s not crazy to see this as a good argument for some lower-body strength training and plyometrics. Here’s what the authors conclude:

Our results suggest that coaches and athletes could effectively implement conditioning strategies that challenge eccentric muscle actions. These strategies include plyometrics, resistance training with an emphasis on eccentric portion of repetitions, down-hill running and over-speed training.


Is less really more in warm-ups?

May 31st, 2011

A few people have e-mailed me about this University of Calgary study, (“Less is More: Standard Warm-up Causes Fatigue and Less Warm-up Permits Greater Cycling Power Output”) which has received a bunch of press. It seems to run counter to the message from this blog post a few weeks ago, which argued that a hard effort during your warm-up could enhance performance.

The new study had cyclists perform either a “standard” long warm-up (designed in consultation with elite track cyclists and coaches), or an experimental short warm-up. Then they tested performance, and the short warm-up group had a 6.2% advantage in peak power. Okay, cool. This is valuable information. But let me add two caveats:

  1. What was the “standard” warm-up? It was “about 50 minutes with a graduated intensity that ranged from 60 to 95 per cent of maximal heart rate before ending with several all-out sprints.” That’s one heck of a warm-up. In comparison, the experimental warm-up was “about 15 minutes, and was performed at a lower intensity, ending with just a single sprint.”
  2. What was the performance test? It was a 30-second Wingate test.

Now, bear in mind what athletes are hoping to achieve with a warm-up. According to the paper, it’s:

[I]ncreased muscle temperature, accelerated oxygen uptake kinetics, increased anaerobic metabolism and postactivation potentiation (PAP) of the muscles.

In the blog post a few weeks ago about the “priming” effect of a hard warm-up effort, the focus was on accelerated oxygen uptake kinetics. But in a 30-second sprint, oxygen kinetics have nothing to do with it. We’re talking about two different animals here.

Bottom line: if you’re a track sprinter who spends nearly an hour warming up at up to 95% of max heart rate, then this study tells you something very important. But if your event is longer than 30 seconds (so that oxygen kinetics matter), and your warm-up tends to be shorter and less intense, don’t assume that this study is telling you to shorten it even more!