So I was looking at the breakdown of my run this morning. It was a tempo run per a plan I'm trying out under one of the watch manufacturers. Plan was .5 mile at 75%, 1 mile at race pace, .5 mile at 75%. I noticed that when I slowed down after the 1 mile race pace portion my heart rate immediately increased by about 20bpm. I have never noticed this before, but I'm trying to understand it. I've played soccer for over 40 years and used to run regularly. Just started seriously running seriously about 3 months ago. Any ideas?