Never Walk.
180 isn't a magic number - Stride Rate and what it means
This is one of the best articles I read recently on the magic “cadence 180” mantra.
For a little while I ran with a Garmin footpod which allows me to measure my cadence - it’s extremely hard for me to get myself up to a 180 cadence (though I don’t overstride). My normal cadence is around 170 - my hypothesis is that due to the fact that I am very tall (6’4”) and have long legs, I would need to shorten my stride significantly to get to a 180 cadence (and thus beyond a point where it makes sense).
Link: http://www.scienceofrunning.com/2011/02/180-isnt-magic-number-stride-rate-and.html
