I take comfort in knowing that I am not alone. And especially since, most of time I feel like I have to go to the bathroom (gas, gurgling, bloating, etc) and I can't go,iIt's actually, ummm....refreshing? when I feel like I have "flushed" out everything
I am laughing to myself at all the puns and jokes that are just flying around in my head.
Anyway - I have been eating for my IBS (monitering fiber intake, etc) for many years, so I really don't think it's what I am eating.
My other thought was that I have been fairly nervous, before and during these rides - afraid my lungs would give out, or I wouldn't be able to go the distance. Maybe just the relief of being finished with the ride is relaxing my colon (which is usually very very spastic).
Mosaic's explanation of the blood moving away from that area and then moving back after the ride kinda makes sense too. Like how I get at the beginning of my period.