In addition to helping in training the HRM will also tell you when you need to slow down or are getting in trouble. I know that when I go over 92% MHR, I only have a few minutes before trouble starts. I can keep 85%-90% for an hour. If I find that I am riding on a long ride at a lower pace say 17mph and I am >85% MHR I know that I am starting to get into trouble with hydration. I really only pay attention to two things during my ride %MHR and cadence. If I keep these things in my sweet spot then I will have a good ride.
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The problem with the gene pool is that there is no lifeguard and the shallow end is much too large
2013 Noah RS