Having something accessible like a heartrate meter. Use your pointer and middle finger and feel on the underside of the side of your chin. Find a beat and that is your pulse, while walking you can count how many times that beats in 30 seconds multiply by 2 and that is your heart rate.
It helps burn of calories that contains bodie fat
The respiratory system, and the cardio vascular systems.
Your organs are really not a big part for jumping jacks but cells,mussels,blood,and nerves help with jumping jacks. The brain triggers the nerves and gets the mussels moving while the cells are going through the body and the heart is pumps blood and keeps you going.