After reading about breathing techniques, I put my new-found knowledge to the test this morning. This is the best run I have ever had. Normally, my heart rate is pegged. This morning, my body just wanted to run and run. I actually got my first negative split today as well. It was awesome. It turns out that I had been taking shallow, chest breaths instead of deeper belly breathing. Here are a couple of things I read about: http://www.military.com/military-fitness/workouts/breathing-during-exercise AND http://www.runningjogging.com/Breathing_Techniques_While_Running.html