Maximum Effort (for now)

Today it was one more trek to Airport Rd. and back.  Even though it was a personal best time (33:08), it felt kind of empty.  I really pushed myself to maximum (safe) effort, including leg and foot biomechanics, pace (just about 132/minute throughout), and stride.  I lost concentration for part of the way back with the usual mental chit-chat, but I kept calling myself back to the effort -- a kind of walking Yoga workout.  So I'm not sure why it didn't feel better...