The persistance of treadmill memory

My apologies for writing such a bad Dali pun as a headline but I have discovered something interesting about treadmill data. The cold weather and snow that we have experienced this past week has forced me to spend a lot of time running indoors. The treadmill is clearly a subject for discussion as most people view it either as an enabler or a necessary evil but you can't argue with its convenience. After using it as my third choice after street and track for months I realized that my basic assumption of its measurement accuracy is flawed. I've always assumed that maintaining a constant speed on the treadmill will accomplish the same for the runner. In other words, assuming the reading is accurate, when the treadmill says 7 MPH you're running 7 MPH.

The treadmill forces you to run (as long as the tread is moving you'd better be running) but there can be a measurable variance in treadmill speed and runner speed. I noticed this on Saturday when I had a strong start and after a mile my Sportband showed my distance about .05 miles ahead of the treadmill's. Throughout the run I saw that gap begin to close and at 2.7 miles the treadmill distance began to exceed the Sportband distance. This intrigued me and also annoyed me because I knew I'd need to run a little extra at the end to achieve my planned distance. After thinking about it I realized it makes sense. You don't have to run the same pace of the treadmill as you run on it as long as your feet are moving. There is a minimum speed you'll need to maintain lest you get swept off the tread but there's some latitude there. My experience showed me where I peak in terms of pace and where I begin to lose speed over time. Knowing this will help me better tune my performance by pushing my crossover time further and further into my run.

I was hoping to run on the track today but, like yesterday, we've received another few inches of snow. I ran about 3.5 miles yesterday on top of Saturday's 3.6. I may shoot for longer distance today or go the other way and cross train with the elliptical and the shovel.