Quote Originally Posted by PeteS View Post
Lag for HR on watches is usually due to sampling rate and subsequent smoothing of that data typically a moving average. My old suunto used to exhibit the same behaviour for ascent where that would continue to rise even after going over a peak and starting the descent.
But is it your watch or is it your heart rate peaking before recovery? I have read that HR monitors are not the best for gauging short hard efforts because your HR does take time to catch up with your actual exertion. If you think about it when you do an interval sprint your HR doesn't instantly rise and will continue to rise a little then stay high until you recover.
It won't matter if you are primarily interested in speed and distance but my personal experience with optical HRMs has been poor. That's not to say it's perfect with a belt - I still get spikes and strange readings but I think this is common to most if not all systems. Reasons given include picking up cadence, poor contact (I wet my belt before starting an exercise, it often works fine for 5-10 minutes then body heat dries it out. Then I get silly, high readings for a while until I get sweaty, presumably the contact then improves and I usually get good readings for the rest of the run).
Its interesting to note on the Uphill Athlete site that they don't rate optical HR monitoring and stress the need to use a chest belt for accurate results.