Well, okay... sort of wierd question

Cardiovascular System: When you are being physically active your heart starts to beat faster and it sometimes gets hard to breathe.. This becasue 1. your blood is rushing to yuor heart to make it pump faster and 2. your lungs are getting filled with oxygen so thast what makes it so hard to breathe... you start huffing and puffing...

Muscular System: We need muscles to be able to move around and do physical activity.. Muscles make us stand up.. So its kind of really important to have them if you want to be active.. When we start growing up our muscles begin to start growing more and more .. but it depends on how much work you are putting into getting bigger muscles...

Skeletal System: Well, your bones protect your organs so to have a skull its pretty darn important... you dont want to be walking around with no skull.. That would be wierd and im pretty sure most people dont do that...

What is nessacary to keep these healthy??

Cardiovascualr: Excersise and get yuor heart pumping... Get those lungs filled up ... huffinga nd puffing is definatly a good sign... So is sweat!!!

Muscular: Dont be the stand by who dosent do anything during gym.. when we do those warmups be apart of them.. actually do the excersises, we dont do them to get fat.. we do them to get in shape.. so if you want to see the results do the work..

Skeletal: Eat Healthy... take yuor vitamins.. they are not just for kids... even though Flinstones ROCK!!!! lol... so yeah just dont be sitting around and eating junk all day...