Final answer:
The percentage increase in heart rate is calculated by comparing the resting to the active rate and using a specific formula. The rate increases due to the body's need to maintain blood pressure and flow to the brain when moving from squatting to standing, countering the effects of gravity.
Step-by-step explanation:
To calculate the percentage increase in heart rate, you would compare the resting heart rate to the increased heart rate when moving from a squatting to standing position and use the formula: percentage increase = ((new rate - original rate) / original rate) x 100%. The heart rate increases to ensure adequate blood flow to the brain, overcoming gravity's effects on blood circulation, which becomes more significant as one changes from lying down to sitting and then to standing positions. The increase in heart rate and force of contraction helps to maintain blood pressure and blood supply to essential organs, especially the brain.
The heart needs to beat faster in response to changing body positions because as someone stands up from a squatting position, gravity causes blood to pool in the lower extremities. To prevent a drop in blood pressure and to ensure the brain continues receiving sufficient blood flow, the body's cardiovascular centers stimulate the heart to beat more quickly and forcefully. This response is part of the body's baroreceptor reflex, which helps to regulate blood pressure.