Under normal circumstances, the heart rate is 60- 100 beats/min, but it cannot be said that it is abnormal if it is lower than 60 or higher than 100. At best, it is ok to diagnose sinus bradycardia or sinus tachycardia, because the normal value of this interval is only the value of 95% people, so as long as there are no other symptoms such as palpitation, palpitation or dizziness, you don't have to deal with it or bother.
As for the 84-92 you mentioned, it is within the normal range, so don't worry. Besides, the functions of the body will change with the age and physical condition, so you don't need to compare the current heart rate with the heart rate in middle school, because the heart rate of more than 50 times is often diagnosed as sinus bradycardia or athlete's heart rate in clinic, that is, the heart rate of people who exercise regularly is often slow.