Lately I've read lots of posts from runners having a panic attack about their inability to run slowly enough to stay in their target heart rate training zone.
Guys, chill, there are lots of reasons that you could be exceeding your target zone.
Reason 1. Your heart rate monitor is wrong.
I've had heart rate monitors tell me my heart rate was in the high 50's during an interval workout. I had one that wouldn't pick up my heart rate if it were below 40 degrees Farenheit. Before you stress, find out how accurate your monitor is.
Reason 2. Your ESTIMATED heart rate zones are wrong. Did you notice the emphasis I put on the word ESTIMATED? In case you didn't let me emphasize it some more. ESTIMATED. How did you decide what your target heart rate is? 220 - age times a percentage? Did you MAF it and go with 180 - age? Did you know that 220- age could be off as much as 30 beats per minute? For perspective, I turn 38 next month. According to the MAF method my maximum heart rate for aerobic work is 142. 30 bpm error factored in it could be 112. What if I tried to run my long run at 142 when I need to run it at 112? That error could also put me at 172 for my maximum aerobic capacity, at 142 I'd be barely working.
Unless you've had your maximum heart rate tested you really don't know what it is.
Reason 3. You are running too darn fast. Slow down.
So what is a fan of Phil Maffetone to do?
Chill guys, I got this. If you are running down the road and you say out loud, "Oh geez, my heart rate is ten beats higher than 180 minus my age. What am I going to do. I just can't seem to run slowly enough to stay in my heart rate range. This is really embarrassing I don't want anyone to see me running that slowly. Oh well, I guess I either have to embrace the shame or ruin my workout."
If you can say all that out loud, you haven't exceeded your aerobic zone, you're OK to keep going at that pace.
It's called the talk test. If you can say about a paragraph's worth out loud you are aerobic, if you can't you've crossed the threshold.
Links to other articles on this are below.