Lucille has been told she needs to improve her heart health, and she is ready to get started. There are many activities she is considering for her new routine, but she knows she must first calculate her target heart rate zone. To do this calculation, when is the best time for her to begin gathering data?
A. When she is resting
B. When she is working out
C. When she is at the gym
D. When she is finished working out
