For the purposes of this post, we are referring to a steady state run (not accelerating) on flat ground…
During a standard running gait evaluation, there are many factors to analyze. Without listing all of them, today I would like to talk about one that is high on the list. That is the step frequency, or cadence. We are referring to the number of times your feet hit the ground in a given time frame – usually measured as steps per minute.
We know that a higher cadence results in:
- Less horizontal braking force
- Less vertical displacement of your center of mass
- Less joint forces at the knee and hip
- Initial foot contact closer to the center of mass (Less overstriding)
- A flatter foot position at initial contact (less heel strike)
- Less peak ground reaction forces (how much force you hit the ground with)
There are implications that have potential to reduce injury for all 5 of those factors, but #3 is the one that I will focus on in this post: Less joint forces at the knee and hip.
A recent study done at the University of Wisconsin took 45 runners and had them run at their preferred pace (average of 9:15/mile). The runners had an average of 172.6 steps per minute (± 8.8 steps per minute). The researchers then had the runners run at the same pace, but under five step rate conditions: preferred, ±5%, and ±10% of preferred. In other words, the same pace, but the number of steps per minute were increased or decreased by 5% and 10%. The runners were able to change their step frequency by listening to a metronome and matching their steps to the beat of the metronome.
The results confirmed all of the 6 factors that I listed above. However, as I said earlier, this article will focus on the mechanical energy at the hip and knee. The table below outlines the changes:
. -10% -5% Preferred +5% +10%
Energy absorbed @ Hip (J/kg) 1.2 0.9 0.7 0.5 0.3
Energy absorbed @ Knee (J/kg) 13.5 11.1 9.2 7.4 6.1
As you can see, the amount of energy absorbed at the hip was 57% less when going from preferred step rate to +10% step rate and a whopping 75% less when going from -10% step rate to +10% step rate. At the knee, it was 33% less for the +10% condition compared to preferred and 55% less in +10% compared to -10%.
This is an amazing finding. Is it enough to reduce injury? We don’t know, but if I had knee pain and could decrease the load on the knee by 1/3 just by increasing my step rate by 10%, I think that would be good.
So, who should adopt a faster cadence? Well, for this post, we are looking at this from an injury perspective. So, if you’re not injured and don’t usually get injured, I would ignore this post. Also, if you are injured, but have a relatively good cadence I wouldn’t change (I usually don’t change people if they are >170 or 175 steps per minute, although other factors weigh into it). However if you are injured, or frequently injured, AND have a low cadence you would probably benefit by changing to a faster cadence.
The easiest way to accomplish increasing you step rate is to listen to a metronome and match your steps with the metronome while on a treadmill. If people do it outside, they tend to run at a faster pace. By doing it on a treadmill, your pace is kept constant.
I have given this type of gait changes to a number of patients, but the one problem I constantly hear is “I’ve looked on the web but I can’t find a metronome sound for my iPod.”. Well, here you go. Simply right click on these mp3’s and then “save link as”:
OK, here are the arguments against increasing step frequency and studies that counter those arguments:
1. “Even if the magnitude of the load is less, I’m taking more steps, so the benefit is offset”
This study suggests that reducing the magnitude of the load outweighs the increased number of steps.
2. “That’s great while I listen to a metronome, but once I stop listening, I will revert back to my old ways”.
This study says that most people can maintain gait changes for at least one month follow up, with no other intervention.
3. “I have longer legs, so my step length is longer and my step rate is slower”
This study showed that people with leg length or height of the runner is not strongly associated with stride length or frequency
4. “If I change my stride frequency, I will be working harder”
This study showed that if you change your cadence by less than 10%, the oxygen consumption doesn’t change much. Once you change by more than 10% of your preferred cadence, oxygen consumption goes up significantly.