I feel like flight attendants must experience extreme physical exhaustion

Even when I'm just traveling for fun, if I sit in economy class for just 8 hours, my whole body feels completely exhausted and heavy by the time I get home.
But flight attendants have to actually work on that same plane. They have to stay mentally focused and keep moving physically.
Doing that every single day, I feel like their health would deteriorate so quickly. Especially while wearing uncomfortable uniforms.
If they do it for a long time, it feels like it would cause chronic physical ailments.