Curious question about our lungs?!

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Your lungs do not require rest as they do not function like muscles. Regular muscles such as those found in the arms and legs were not designed to withstand force and resistance indefinitely. For example, try holding a can of peas with your arm straight out in front of you for as long as you can. You will eventually have to lower your arm because of fatigue.

Your lungs on the other hand are being controlled by your diaphragm and other muscles in the body. The lungs simply take in oxygen because of the action of the diaphragm and expel carbon-dioxide, again because of the action of the diaphragm. The lungs are designed to do this for a life-time 24 hours a day and whether you are asleep or awake. Think of blowing into a very soft and flexible balloon and letting the air out. You could probably do that activity for a very long time before the balloon eventually wore out. While they do not wear down like other parts of the body [joints, muscles, skin] your lungs can become less efficient and fail if diseased.

Regarding the heart: One answer is that the “cardiac” muscle that comprises the heart is of a different kind than the “skeletal” muscle comprising the hand for example. Skeletal muscles are attached to bone structures and cannot stay long in a flexed position without depleting their energy reserves. Those energy reserves come from mitochondria: structures inside the cells that use the energy taken in from food. Thus the more mitochondria it has, the greater the available energy for the muscle.

Because it has not been necessary for humans to be able to flex our skeletal muscles for prolonged periods of time, the total volume of skeletal muscle contains an average of only 1 to 2% mitochondria. This is an entirely sufficient energy source for such intermittent muscular tasks as walking or running. The total volume of the heart, by contrast, is between 30 and 35% mitochondria.

That massive amount of energy-generators means cardiac muscle, in a healthy state, need never rest: there is always some energy being transferred to the muscle at the same time that more energy is being derived from caloric intake. And always just in time for that next beat.

http://indianapublicmedia.org/amomentofs…

http://www.nhlbi.nih.gov/health/dci/Dise…