I just started using a heart rate monitor during exercize. I am a 51 year old female and recently had a complete physical with an excellent bill of health. I run 3 -5 miles three times a week. I also ski, cycle and walk. My resting heart rate is 57. For my age, my recommended min/max is 144 - 169. When I run, it is hard for me to keep my heart rate below 170. On the hills I am close to 180. I do not feel dizzy or light-headed and within 5 minutes of cool-down, I am back down to 110 -120. If I keep it at the recommended 150 range, I am barely breathing or exerting. My question - should I be concerned when my heart rate goes above 170?