In BBC's excellent series 'The Truth About ... Getting Fit' , an episode shown in January 2018, the excellent and always evidence-led Dr Michael Mosley (the 5:2 diet, Fast 800 etc) meets Prof John Brewer (Google him) who shows him a surprising and counter-intuitive result when comparing the forces exerted on the body when walking compared to when running.
Namely, over a given distance, walking exerts more force on your knees than running does. It's due to an increased contact time with the ground.
For the mathematicians.... it's the AREA UNDER THE CURVE!
I was interested to note his over-striding while walking - only had a chance for a quick peek at the video, mind! I wonder if that's normal? I am too busy watching runners to notice what walkers are doing 😊😊😊
Bear in mind that *if* the data shown *was* from Dr Mosley's walk and run, then (1) that over-stride when walking could be a factor and (2) he's only n=1 - you would hope/expect that the conclusions are the result of carefully-controlled experiments on a suitably large group of subjects, with various factors controlled for, e.g. walking and running gaits.
It's also perfectly possible that the data shown wasn't (*gasp*) from his demo.
All i am saying is if that is 'his' data which shows that for a given distance his loads are greater walking rather than running , it would be even more significant if he didn't actually heelstrike when running
I'd have thought the amount of "jerk" (the derivative of acceleration) is more damaging. With correct foot placement (ie. not heel striking) this is minimised.
From Newton, F = ma, therefore the integral of force is proportional to momentum (mv).
I think I have seen this as Dr Mosley is the only advice I feel is tried, tested and unassuming. Thank you for posting and it is a relief to know that some knee problems are not caused by running, and can even be alleviated. I can honestly say one of my knees was stiff prior to running but since doing C25k, it is normal! My doctor also told me that running would most likely improve my lower back osteo- arthritis which I was quite cautious about, and it has eased it greatly.So I have no doubt about these findings and welcome the spreading of this positive news.
I'm a huge fan of Dr Mosley. He's my favourite science communicator: clear, concise and always evidence-led. His wife is a GP and is an interesting follow on Instagram@ 'drclarebailey' .
John, I almost hesitate to ask you to help me understand this video, in case somebody objects, but let’s just keep it quiet. I am doing so because I simply cannot see what of importance is being proved by this experiment. It is probably due to my lack of statistical and scientific education and I sincerely hope you can educate me.
I get that the statistics can prove that per metre, the forces can be shown to be greater, when walking because of the longer duration. This, I presume, is by taking a mean (or perhaps median) average of the total loads across the duration of contact time. Please correct me if this assumption is incorrect.
Mosley queries why this counterintuitive result is meaningful, when the peak loads of running are obviously more impactful compared to walking. Brewer doesn’t explain anything, but just says that the body is perfectly capable of absorbing the peak loads of running, saying that the body is “designed” (which raised alarm bells for me) to take these loads.
Have I gone wrong yet?
The body, in my view, is evolved to be perfectly capable of absorbing both the mean or median loads of walking and indeed running, but……...and this is where I get stumped…….it is not the mean nor median loads of either running or walking that cause issues. It is the peak loads of running that, for those whose bodies have not been conditioned to handle those loads, causes damage and symptoms such as shin splints.
Can you please explain this to me, because I am feeling really thick in that I cannot get beyond what seems like a statistical trick to prove that running causes less stress than walking.
Of course Brewer’s theory that repeated compression and release of the joints can be beneficial may well be true, but does not seem directly to bear on this experiment, since it is of very short duration. I would love to see the evidence.
I have watched this video through several times and just don’t get it. So please, John can you educate me.
I told you this was bugging me and I have just realised where I slipped up in the statistics.
The block graph is not derived simply from an average of the loads, but represents force per metre therefore an extra calculation is involved based on the number of strides required to cover a set distance in both walking and running modes, which has to be combined with the average to gain the block graph..........I believe.
However I would still value your opinion on how the knowledge that per unit of ground covered walking, statistically, that stresses are greater than when running, can be usefully employed by the average runner.
Still haven't forgotten Tim and still mulling how best to frame my reply. I'm thinking diagrams and video - so not trivial! But what we're talking about is O'Level/GSCE Maths - there is *NO* statistical trickery going on and there are no mathematical tricks being pulled. In fact, there are NO statistics involved (by the normal definition of statistics) but in fact, simple calculus. But that is to look at the trees and not the wood.
There are no averages or means or medians being calculated to generate the 'block' graphs.
As a first step (and this is to side-track from the bigger picture, the 'wood') have a look at this :
My latest post was a plea to anybody who could, to explain to me how and why John Brewer's conclusions are of any importance and of any relevance that it has to a runner. Nobody has yet done so.
If the maths clear it all up, then please put it in reply to my post, where a greater number of people can benefit from the knowledge.
The maths will absolutely NOT clear up the debate but you seemed to have been vexxed by it previously. I repeat: this is not a statistical matter, nor one of averaging, median or means, but of calculus , in order to calculate the area under the respective curves.
The calculus stuff that supports the conclusion in the TV show. You said you understood it. I don't. It makes no sense to me as someone who studied physics to degree level.
In some ways it's actually rocket science.
You don't send stuff into space by firing it from a cannon. You could, but the acceleration forces would cause massive damage to your cargo. Astronauts aren't much use if they've been turned into pancakes.
So what you do instead is use a smaller force, sustained over a longer amount of time to do the same amount of work against gravity. This causes much less damage to your cargo.
The "area under the curve" (transfer of chemical energy into gravitational potential energy) is the same, but the effects are totally different.
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