Hello, I have been running for almost 20 years - long distance the last 8 or so, and marathon distance for the last 4 years. My first marathon was 4:09, most recent 3:40, and I want to run 3:00. I have been running about 800-1000 miles a year for the last 4-5 years. I toe strike, with rapid cadence, and I think my form is fine when I am going moderate to fast speeds, I have had little if any issues with pain or injury thus far running. I have never trained with HR before. About 5 weeks into…See More