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I'm currently training for a 10k with my girlfriend: the goal is to complete the race without stopping rather than any specific time. However, I'm a foot taller than she is so when we do runs, I shorten my stride quite a bit so we maintain the same tempo.

It seems to me that running 5km @ 6 minutes/km by myself vs. 7 minutes/km with her still feels like the same amount of effort by the end. Shorter strides + longer time vs. Longer strides + shorter time.

Am I imagining things? Should one of these scenarios be more work/effort, or do they equal out in the end?

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You ask a different question in the text than in your title. Could you please change one or the other so that it's clear what you're interested in knowing? –  user3085 Mar 27 '12 at 15:06
    
Sorry..realised I wanted to express the question differently :0 –  Jedidja Mar 27 '12 at 15:10

1 Answer 1

up vote 8 down vote accepted

There is a speed/stride-length/form combination (or maybe a few) that is optimally efficient for a given person, and any variation from that will be less efficient. For example, competitive distance runners have settled in on about 180 strides per minute.

If your efficiency was the same at all speeds, then the amount of work would be dependent only on the distance you run. However, your efficiency does change as you change speeds (and form, and stride length), so these two scenarios that you give will not necessarily result in the same amount of energy used.

As well, your running economy (this is a really good read) changes as you change speed. Runners tend to be most economic at the speeds that they most often run at.

Your two scenarios could just also happen to be equally efficient and economic, resulting in the same amount of effort for you, but it is in no way guaranteed or probable.

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Thanks for the links! –  Jedidja Mar 27 '12 at 15:39
    
Just to point out, the speed/stride-length ratio will be (slightly) different between each person, so its better to find your own, than to optimize for someone else's golden standard –  Ivo Flipse Mar 27 '12 at 16:32
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Sancho has the answer. 180 BPM is ideal. You will probably find it awkward at first, but typically after you get going, you might even find your cadence naturally going a little bit faster. Ivo's comment about slight differences needs to be tempered a little bit when you consider that the 180 BPM is going to be related to your breathing rhythms and your heartbeat, as the body likes to keep everything in sync. People may vary in these areas but for experienced runners who have tuned their body like a well-oiled machine, it's going to be pretty standard. –  alord1689 Mar 28 '12 at 3:32
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@alord1689 then perhaps we need to add your arguments to Sancho's answer. I agree completely with your reasons for why its an ideal point, but obviously length/weight and whatnot will have an influence. Besides I was aiming for a small difference of a couple of steps per minute, not in the order of 10 or more. –  Ivo Flipse Mar 28 '12 at 8:20
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One note - the "ideal" cadence of 180 was taken from a sampling of elite runners while racing. Their cadences in practice runs is much different, and varies depending on their own pace. The vast majority of runners self select the appropriate stride length and cadence for the speed they are running. –  JohnP Aug 6 '13 at 17:06

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