Final answer:
During systole, the systolic pressure is the greatest force on a blood pressure reading, indicated by the first and larger number such as 120 in a "120/80" reading.
Step-by-step explanation:
During systole, the force exerted by the blood against the artery walls is the greatest. On a blood pressure reading, this is represented by the first, largest number, known as the systolic pressure. The pressure during systole when blood is ejected from the heart through the arteries is typically around 120 mm Hg for a normal adult, which is why you might hear a blood pressure reading referred to as "120 over 80" or "120/80". The second number, diastolic pressure, is lower and represents the pressure in the arteries when the heart is at rest, between beats.