Why does ALS make it harder to breathe?

Let’s start with the basics of breathing. Here’s what typically happens when someone takes a breath:

1. The diaphragm and muscles in the chest contract to take in a breath of air. 
2. Air is sucked in through the nose or mouth.  
3. Air goes past the tongue, down the back of the throat, and through the vocal cords on its way into the lungs. 

ALS makes the muscles in your chest weaker, which makes it harder for you to take in a breath of air, even though there is nothing wrong with your lungs. This respiratory muscle weakness progresses (gets worse) over time. As your muscles get weaker, it will become harder for you to breathe.