There are many different factors can play into how fast your heart will beat during exercise. For consideration would be your body weight, body size, age, gender and other factors can cause your heart rate to differ from another person.
A benefical aorobic exercise for the cardiovascular system is 220 minus age, and to go above that rate for a an extended period of time may have some unfavorable consequences. You should consult your doctor what is a safe heart rate for you! My suggestion would be at least don't exceed what is considered normally a safe heart rate during exercise.
Thanks for sharing, take care,
I would take my pulse the old fashioned way to make sure your gamin forerunner is correct.
This happens to me too. I am 28 years old now but I've always had a really high heart rate during exercise. And I can keep it up over 200 for a prolonged period of time. I was told I have a high o2/co2 ratio. They never did quite explain to me what the heck that meant.
I am speculating but to the extend your heart rate is greater than recommended with some regularily with aerobic exercise, etc. may increase the left ventricle size with harmful effects.