Final answer:
If you can talk but not sing during an activity, it suggests you're engaged in moderate-intensity aerobic exercise, according to the Talk Test and the 2018 Physical Activity Guidelines.
Step-by-step explanation:
If you can talk for long periods of time, but cannot sing, you are most likely partaking in moderate-intensity aerobic activity. The Talk Test is a simple way to measure the intensity of your exercise. According to the 2018 Physical Activity Guidelines, if you're engaged in moderate physical activity, you should be able to talk, but not sing. This is contrasted with vigorous activity, where you cannot say more than a few words without pausing for a breath. Unfortunately, a 2018 report from the American Heart Association revealed that many Americans do not meet the recommended levels of physical activity.