The other day, I tried running with a metronome beat in my ears while running to try to increase my cadence to 90 steps per minute (from the same foot). The biggest difference I noticed while running at 90 BPM compared to my very consistent 84 BPM is that it is REALLY hard!
Before my little experiment, I thought there wasn't that big a difference between 84 and 90 BPM, I was incredibly wrong. The faster cadence felt way too fast for my sluggish legs. I made very tiny steps. I felt like I looked really silly. My heart rate felt like it was in the 190s. I also found it really difficult to relax, I was running with a lot of tension in my shoulders and muscles in my upper legs.
Some positive things I noticed were that my arms dropped to a 90 degree angle all by themselves (usually I have to think about it). I also ended up going much farther than usual. I've been running 4 minutes and walking 30 seconds times 5 intervals along the same out-and-back route for a while now and end up in about the same place every time, this time I ended up turning around much farther than my usual spot. And I only ran the higher cadence for 3 of the intervals.
Some things I'll try for next time will be to try and relax my shoulders and quads as much as possible. I'll also bring a heart rate monitor with me so I know what the difference is between my comfortable cadence and the faster one. I also think the HR monitor will help me track my progress as I practice the new cadence.
I think running at 90 BPM will help my running in the long-term so, although it's difficult for me now, I know it will get easier with more practice. And who knows, I might even end up getting faster. :)