I am 16 and I just started a daily cardiovascular exercise routine as i recently have decided to be more fit. I have been running up 7 stairs and jogging down the hall 7-8 feet and back, and doing this for 30min-1hr for the last almost a week now. Ive recently been tracking my heart rate by counting how many beats per 10sec and multiplying by 6. My heart rate during my routine stays usually between 27-29 beats per 10 seconds, so 162-174 beats per minute. I dont get too tired at this high rate even after an hour i feel i could keep going on indefinetly. I picked up the pace quite a bit once for a minute and my heart rate went up to 32 per 10sec or 192 beats per minute. To me this sounds pretty high but not during any of this time do I get too tired or do i feel dizzy or anything.