Final answer:
The next step after lying down and checking heart rate is to record it. This provides a baseline resting heart rate. Changes in body position affect heart rate and blood pressure due to the circulatory system's adaptation to gravity.
Step-by-step explanation:
After a 16-year-old lies down to check their heart rate (HR) for a physical education assignment, the next step would be C. Record the heart rate. This measurement is important as it provides a baseline for understanding the student's resting heart rate before further physical activity.
When the body changes position from lying down to sitting or standing, the heart typically has to beat faster to ensure adequate blood flow and maintain blood pressure, combating gravity's effect on the circulatory system.
The pulse you feel is the expansion of your arteries each time the heart pumps blood through them. If a student measured their pulse for 10 seconds and then for 1 minute, there should indeed be a factor of 6 difference, assuming the heart rate remains steady during this time.
Understanding this physiological response is crucial for interpreting changes in heart rate and blood pressure, which are both key indicators of cardiovascular health.