Sunday, July 8, 2012

Do All Elites Run at a 180 Cadence: None of the 5K Finalists at the US Olympic Trials Did

One of the most common myths I encounter in discussions about running form is that 180 steps per minute is some kind of magic number (Google “180 cadence” to see what I mean). It’s not, and I’ll be happy when this one gets put to rest. Much of the mythology about this number stems from a misinterpretation of what Jack Daniels reported in his book “Daniels’ Running Formula” regarding the cadence of elite runners at the 1984 Olympics. He did not observe that they all ran at a 180 cadence, he observed that they ran at a cadence of 180 steps/min or more. My emphasis on the “or more.”

We cover the topic of optimal running cadence for efficiency and reduction of joint loading extensively in Chapter 8 of Tread Lightly, but here I wanted to share some data that I compiled from a set of slow motion videos taken by physical therapist Jeff Moreno at the 2012 US Olympic Trials. Jeff obtained footage filmed at 210 frames per second from both the Men’s and Women’s 5000 meter finals (as well as the 1500, which I hope to examine in a separate post).

Here are the two videos:

Women's 5000 Meter Final

Men's 5000 Meter Final

Because I know the frame rates at which these videos were captured (210 fps), I can simply count the number of frames between various stride events (e.g., initial contact, toe off, etc) by importing the videos into Quicktime. A few simple calculations in Excel allows me to produce a bunch of data on stride kinematics, which are presented below. Runner order is the order in which they pass the camera at this point of the race, not the final finishing order – If I’ve made any ID errors please let me know! Contact time is for the first footstrike observed, swing time is the time from toe off of the first contacting foot to the next contact of the same foot. Cadence is determined by determining stride time and using that to extrapolate the number of strides that would be taken in 60 seconds, then multiplying that value times two to yield steps/minute (a stride is from the contact of one foot to the next contact of the same foot). All times are in fractions of a second.

Here are the data (Update 7/10/2012 – I initially made a dumb Excel error in my calculation of flight time – doesn’t affect any of the other numbers though – data are now correct):

Order Name Cadence Contact Time 1 Swing Time Flight Time
1 Bernard Lagat 195 0.143 0.471 0.167
2 Galen Rupp 187 0.138 0.505 0.176
3 Lopez Lomong 192 0.157 0.467 0.157
4 Andrew Bumbalough 202 0.148 0.448 0.143
5 Mo Trafeh 191 0.171 0.457 0.143
6 Benjamin True 192 0.162 0.462 0.148
7 Elliott Heath 205 0.162 0.424 0.138
8 Hassan Mead 191 0.171 0.457 0.143
9 Scott Bauhs 188 0.157 na 0.162
10 Ryan Hill 191 0.162 0.467 0.152
11 Trevor Dunbar 197 0.176 0.433 0.129
           
           
           
Order Name Cadence Contact Time 1 Swing Time Flight Time
1 Julia Lucas 202 0.152 0.443 0.152
2 Molly Huddle  197 0.167 0.443 0.138
3 Julie Culley  195 0.171 0.443 0.133
4 Abbey D'Agostino 189 0.167 0.467 0.143
5 Emily Infeld 192 0.162 0.462 0.157
6 Elizabeth Maloy 188 0.176 na 0.143
7 Kim Conley  197 0.171 0.438 0.124
8 Lisa Uhl 210 0.157 0.414 0.124

What you’ll note is that at least at this point of the race, none of these elites were running with a cadence of 180. In fact, the vast majority of them were running with a cadence above 190, with some pushing higher than 200! My hope is that data like this will put the 180 cadence myth to rest for good. I’ll say it again: 180 is not an “optimal number”!

[Note: A few people have commented to me that cadence may be on the high end for these runners because they are nearing the end of the race. Even if this is true, which we can’t tell from limited video footage, it further makes my point – cadence varies with speed (I will say that I have video from the Boston Marathon of elites with equally high cadence numbers). It’s quite possible that Lisa Uhl has a high turnover here because she’s making a move to pass. I’ve done a bit of experimentation with how my own cadence changes with speed here: http://www.runblogger.com/2011/09/running-speed-human-variability-and.html]

One interesting thing to note about these data is the overall similarity of the numbers between runners. Contact and swing times, for example, seem to fall in a fairly narrow range for most of the competitors, though there are a few notable individuals. Galen Rupp, who won both the 5K and 10K at the trials has the shortest contact time and longest swing time of any of the competitors. Unfortunately, it’s hard to know if these gait characteristics contributed to his success. Among the women, Julia Lucas had the shortest contact time at that point in the race – she was in the lead, but ran out of steam in the final lap. Lisa Uhl had the highest cadence of any runner, male or female. All interesting observations, but what they mean from a practical standpoint is hard for me to know given my lack of a coaching background or any attempt to research factors that contribute to elite performance (my interest is in trying to understand how shoes work and why recreational runners get hurt).

I’ll finish by saying that the value of the 180 number is that it’s higher than the cadence of most recreational runners, and a cadence significantly lower than 180 can indicate a problem with overstriding. But, holding fast to a single number for an optimal cadence makes no sense to me, and I prefer to think in terms of a range (say 170-190), or even just aiming to increase you cadence by 5-10% from baseline if you believe you are an overstrider.

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