How do you switch gears on the run?

[Plainsman]

On the bike I keep a cadence of around 90 rpm at whatever gear I'm in. Keep a steady cadence, switch gears to go faster. Simple enough. How does this apply to the run? I just had the most erratic run workout. I keep a cadence of 90 when I run (180 footfalls/minute). I did a series of 3 minute drills. At the same run cadence I had average speeds of 7:00/mile, 8:00, 8:30, and even a 9. I can't figure out what the variable is. They did not necessarily come in that order. More kick? Shorter strides? Lifting the knees higher? A somewhat frustrating mystery to me, any ideas?

[jpeek29208]

i would guess stride. I find there are basically two big factors, cadence and stride.

[fsr402]

It is your stride that's changing. A 2-3 inch shorter or longer stride will make a HUGE differnce over a mile.