Does anything slow down or reset running speed?

As I run, I notice things slowly speed up - which is to be expected. Naturally at some point this makes things very challenging. I've logged some 1 mil+ runs, and I'm wondering: Are there ways to slow down? I'm interested, as I think slowing down could increase my maximum run distance. Bearing in mind that I am more interested in how fast pixels are moving, as opposed to how fast in meters the game claims I am going. Things that seem to slow me down:

• Tripping
• Dying and respawning
• Using a speed power-up
• Using a head start

Do these things really have an effect on my speed, or is that just in my head?