Final answer:
The method used by second trimester Soldiers to determine the intensity of their cardiovascular workout is by measuring their target heart rate range.
Step-by-step explanation:
The method used by second trimester Soldiers to determine the intensity of their cardiovascular workout is by measuring their target heart rate range. The target heart rate range is the range of heart rates in which both the heart and lungs receive the maximum benefit from an aerobic workout. It is usually calculated based on a person's age and fitness level. By exercising within their target heart rate range, Soldiers can ensure that they are working at an appropriate intensity level.