Heart rate shoots up in the mid to late hundreds after doing 100 pushups? i'm 18 male 5'9 160-170 pounds. rest is around 100. i'd say i'm fit so why

high heart rates: A resting heart rate of 100 is abnormally high. This is call tachycardia and requires medical attention. See your doctor for a check up and meanwhile go easy on the push ups etc. You are not fit.

Heart rate: Your exertional heart rate sounds appropriate for that level of exertion. Your resting heart rate is higher than expected, and i would consider getting checked for anemia, hyperthyroid condition, etc. Some people just run high with no explanation (inappropriate sinus tachycardia).