Monday, January 23, 2012

Stride Rate and what it means

180 isn't a magic number- Stride Rate and what it means

Speed= Stride Rate X Stride length

How do we increase speed:
There seems to be an ingrained belief that stride rate is constant and that to increase speed we simply lengthen the stride. This is a staple teaching in Chi Running for example, but others such as Amby Burfoot in his recent post brough up the same concept.

The general idea that we use stride length to increase speed (via an increased force application, not by reaching out) to a greater degree than stride rate is true. But there becomes a problem when we think in absolutes and limit ourselves to we ONLY see changes in speed with stride length.

We’ve got two different ways to pick up the pace, why limit ourselves to one particular way?

If we look at a previous post of mine that showed how elite 10k runners ran at just below 10k pace and then picked it up during the race, you see clearly, that runners use several different methods to increase speed. Bekele for instance went from running 10k pace to running just faster than mile pace solely by increasing his frequency from 190 to ~216. He did this without a change in stride length. On the other hand, some of the other runners increased speed by lengthening their stride or doing a combo of both. The point is, that the data shows us that to increase speed from 2:45 per kilometer to a sub 60 last lap, athletes employed several different methods. And the method they used was that which they hadn’t relied upon all race (i.e. Bekele had relied on a long stride and “slower” frequency so he increased the frequency).

If we look at some other data from a group of top notch NCAA athletes from UTEP 2-3 years ago, you can see their stride rates and relative stride lengths (a ratio of their height) at a mix of paces (note this is the average for the group so we can’t see how individuals pick up the pace):
Pace ---Stride Rate---Relative stride length
7:40--- 175--- .68
6:43--- 181--- .76
5:58--- 185--- .82
5:22--- 191--- .83
4:58--- 196--- .93
(Data from De Heer, 2008)

For these athletes you go from a very easy pace to about marathon pace or a tad faster, so still not that quick in the big scheme of things. As a whole, their stride rate changed by an average of 21spm to accomplish an increase in stride length.

Lastly, I think it’s important to realize what happens during fatigue. When we tire our ability to produce force quickly starts to fade. Since we aren’t imparting as much force into the ground we do one of a couple options. We either slow down as our stride length diminishes or we compensate. We compensate by increasing stride frequency to take up the slack and maintain or increase speed (remember speed=rate X length, so if length drops, we got to increase rate to maintain the same speed), or we do something to allow us to maintain force production such as increase the range of motion of our arms. (Open up the arms like a sprinter- allows for increased force transmission.)

What’s the point of all this? To show that, yes we do rely on stride length more so proportionally to increase speed, but don’t neglect the role of stride rate. They both change, and to try and hold one constant is not a good idea. We don’t simply increase stride length to change speeds like is often taught.

What the heck is a high stride rate?
The other part of this debate is the notion that everyone should have a high stride rate. That’s the argument coming from several in the running industry. I don’t disagree on the surface that a quicker stride is better compared to what most people do, but how high is a high stride rate?

In several running form publications they tout 180 as the magic number. There is nothing special about 180. It comes from work back in the day when Jack Daniels counted stride rates during competition of elites and found that they all had a stride rate of over 180. People forget the “over” part and they also forget the question of what speed were they running at? As we can see from the data above, speed matters. If we measured the Kenyan Runners warming up at the same pace, they would have been at 175, with some being at 165 and some being at 188 (based on guessed from Standard Deviation data). If we only looked at when they were running a tempo run, then the average is 196, and its almost guaranteed that they are all over 180.
If we go further to faster paces, stride rates get even higher. Elite sprinters like Tyson Gay reach around 300spm when sprinting the 100m. In the Bekele data, he reaches 215 or so for the last 400m. I’ve got data from travelling around watching world class athletes that have guys running 200spm and 220spm roughly at the same 3k pace.

To back this idea up further I took some data from myself as I picked it up from a slow jog 7:30 pace to down to about 5min pace, which is about threshold pace for me at the moment. At 7:30 pace I was around 166, in the mid to high 160’s. At the tempo pace I was 192-198 consistantly.

Which brings us to the current topic of increasing stride rate that everyone seems to be talking about. If we know elites go from anywhere from the 170 range for easy distance pace (~7min/mi) up to 215+ for 3k race pace, what does that mean for the rest of us? Do we copy the elites in having relatively “high” rates even though some recreational runners might be jogging 4+min slower/mi on the distance pace side of things?
Does it make sense for a recreational runner running 10-11min miles to be trying to hit 180spm? Probably not, unless that is a quicker pace for him. Just to do the math, if we had a runner doing 180spm at 11min mile pace, he’d have a stride length of just 32inches!

Then why is everyone in a rage over increasing stride rate? Because as I’ve pointed out before, most recreational runners simply overstride, which artificially creates a very low stride rate. Why? Because the foot lands so far out in front of the Center of Mass that it takes a while for your body to be over it and ready to push off. So, when some running form coach says to increase stride rate to X, what ends up happening is the runner is trying so hard to increase stride rate, he chops his stride a bunch by putting his foot down earlier and landing closer to his center of mass, thus decreasing the overstriding. Nothing particularly wrong with that.

Where we go wrong is in the logic that the stride rate increase is the key. No, it’s not. It’s the elimination of the overstriding. Using the cue to increase stride rate is a way for coaches/runners to reduce the heel striking overstride.

This doesn’t seem like a big deal, until people start taking it to the extremes. That’s when you get the claims of a magic stride rate and the idea that you can NEVER have a low stride rate. Or another bad direction is when you have people who stick to a certain stride rate without variance.

Stride Rate, footstrike, and Ground Reaction Forces
All of this somehow brings us to the excellent post by Jay Discharry on stride rate and GRF/loading rates. To really cover this topic, another post is required, but briefly I’d like to make some points.
I agree with Jay that footstrike isn’t everything. I’ve seen it numerous times where you can have an athlete forefoot or even midfoot strike while still reaching out with their lower leg. We used to call it toe reaching and there was a pretty good elite runner about a decade ago who routinely would fall into that pattern when fatigued. I also agree that it’s quite possible to heel strike with a low impact loading rate if you land close to your center of mass without reaching out. You see this with athletes who have always been taught to dorsiflex like crazy (i.e. Toe up- coaches love yelling that for some reason), instead of just letting the ankle be neutral and do its thing.

The thing to keep in mind though is that it doesn’t mean that footstrike isn’t important. We’re looking at one variable, GRF loading rates, which are important presumably but we still don’t know their exact role. If GRF was all that mattered, great, we could just say land close to your COM and that’s it. Except for the fact that transmission of forces, not just how they load, must play a role. As does putting the foot in position for push off, maximizing elastic energy, etc.

I certainly don’t have all the answers, and the questions regarding foot strike, loading rate, or what have you are very complex. But we’ve got to be careful when focusing on single variables. It’s fun and easy to do and gives us seemingly concrete answers. The problem is when we get into business of tailoring towards single variables, we lose the big picture. You see this in running training when people started to focus on improving single variables like VO2max or Lactate Threshold. Ya, you might improve that, but your making a leap that that one thing is the key to performance and forget the complexity of performance.

The same goes with biomechanics and performance or injury prevention. A single footstrike isn’t the answer. Neither is simply changing stride rate nor simply getting that strike closer to your center of mass. All are pieces two the puzzle. Don’t become obsessive over one and forget the others.

If you really want to minimize loading rates, run really slow with a tiny stride length where your foot barely comes off the ground. It’s simple and it would do the job…but that’s the point, there are more things than just loading rate

For instance, high GRF aren’t all bad. Sprinting is partially dependent on producing high GRF.

What does this all Mean:
In a roundabout kind of way, we get back to the original point of this blog post. Stride Rate is a variable. If you combine it with stride length you get a calculation of speed. It’s very easy to measure, anyone can do it. Because it’s easy to measure, we’ll put more emphasis on it (you don’t see a magic stride length # do you??) I don’t mean that it isn’t a good variable, just don’t give it more meaning than it deserves.

It’s simply one of two ways in which we pick up speed. It’s simple really, turn over faster or lengthen the stride, or some combination of both. Don’t limit yourself to only one of those options artificially.

What I’ve found in my years working on running mechanics and in being taught by some of the best minds on the subject, is that I nor them have ever focused on stride rate or length. Those are outcomes of what you do. They are feedback. They are not things you directly change. If you take care of the mechanics, whether it’s arm swing, body position, force application, footstrike or whatever, the rate and length will optimize. Is it useful to measure length and rate? Sure, but remember that they are data. If one of them seems “off” you’ve got to figure out how to fix it.