Random physical weirdness
Ever have one of those days when it feels like your legs aren't actually connected to your heart and lungs? Two days now I've been feeling the burn in my legs - not bad, not actual pain, just a physical sensation of overwork - but my heartrate stays low and even, and my lungs are barely working at all. Kind of sore after the rides, too.
I pushed my seat up a bit, which probably has something to do with it - I'm working in a new area of my leg, or at least it feels that way. Maybe the glutes aren't getting into the picture as much in the new ride position...