Your heart rate also naturally lowers while you sleep and may even dip into the 40 bpm-range briefly. However, Dr. Dalawari says that sometimes a low RHR, such as one that falls below 50 bpm ...

Target heart rate refers to a range of heart beats per minute to aim for during intense ... the target heart rate is approximately 50% to 70% of the maximum heart rate, while with more vigorous ...