When I so lightly remarked at the end of the last post that I would write about steps per minute (spm) – aka cadence in the world of runners and gait analysts – and over striding, I little thought how complex and contradictory the topic would turn out to be. I feel like I am now about to embark on an essay from my student pod days (I hope you aren’t reading this Alex Izod!), and this will definitely count towards my CPD for the year!
You can relax and rest assured I am NOT going to write a complicated piece about gait and physics. 😉 Here goes: Speed = cadence x stride length. First – cadence (also sometimes called stride rate). This is basically a measure of how many steps you take per minute. Elite runners’ cadence is about 180 – 200 (+) spm. The best (or most efficient) cadence for each runner depends on many variables – height, weight, leg length, strength… There are a lot of running commentators on the ole Interweb that feel that we should all be aiming for 180 spm. An interesting article by Matt Phillips in 2013 points out that this number started from an observation made of elite distance runners in 1984 by a certain Jack Daniels (famous running coach). He noticed that nearly all had a stride rate of at least 180 spm. In the usual way of the world this has been garbled about and now the Holy Grail of Cadence seems to be 180 spm for everyone. But we are not all elite distance runners going for gold in the Olympics! (Maybe in our dreams – it’s free to dream.)
Let’s look at some real life examples. My average spm on a recent 6 km run was 168, which according to my trusty Garmin is in the ‘green zone’ when I am running at a speed of 5:43/km. A recent interval run had an average spm of 156, and you can see clearly that spm decreases when I’m walking. I had to walk between intervals as I haven’t done any training like that for a while!
If we have a look at Tom’s marathon last Sunday his average spm is lower. The Garmin screenshot shows that it is in the ‘amber zone’ for most of the 26.2 miles. The green dots indicate short periods of faster running (and therefore higher spm) possibly to overtake someone or avoid an obstacle.
Compare this with Jack’s data – of the same race, which they finished in exactly the same time.
Does this matter? What are the implications of a lower stride rate? Well perhaps it doesn’t matter so much. There is a great article by Alex Hutchinson, a man who actually looks at the research, and then applies it to the real world, where he writes that the variability of cadence between runners can only partly be explained by factors such as age, height, experience and speed. In another article Alex writes about leg length – which of course will influence stride length. Shorter runners have a higher cadence than longer runners typically. (Speed = cadence x stride length). That’s one reason why my cadence is higher than Tom’s or Jack’s. If you have time follow the link and scroll down to the link to a YouTube video of the closing moments of the 10,000m race between Gebrselassie and Tergat in the 2000 Olympics. The tall guy and the short guy! Amazing!
Sometimes – and I really must stress sometimes – a lower cadence may indicate that the runner is over-striding – their step length is ‘too long’ and that is why they take fewer steps per minute. Over-striding? What is this? In very simple terms it means landing your foot in front of your centre of mass. This is not efficient biomechanics because landing with the knee in extension and the heel striking the ground creates a braking force, and shock through the leg which can lead to injury. It is explained in this article by Matt Phillips pretty well.
I think the main point I will be taking away from this is that every runner is unique – and therefore every runner’s gait is unique. When I am either standing by the side of the road cheering on the runners or participating, a lot of my attention is caught by the gait styles of fellow runners. Sometimes it is amazing to me that some of them can run at all, let alone for 13 or 26 miles because their gait looks so awkward! But – they do. And long may we all continue to run. My next ‘official’ race is this Sunday – the Thames Towpath Ten. I will be watching out for the ‘over-striders’. 😉