system
Given the following post, respond as if you're commenting on Reddit:
human
[Marvel] Apart from "magic", what physiological reasons are there for Asgardians extreme strength?

Also is it science or nature? Are they a race that manipulated their own genes long ago for instance, or are these strength levels inherent?  
  
I propose that possibility as they were described as a race that advanced their science to levels we can only call magic.
gpt
In 616 at least, their muscles are three times as dense as a human's.  Thor, for example, is around 6'6'', but weighs something like 650lbs. 

The "why" of this is probable "genetic manipulation via magic," but that's just speculation. Regardless, any Asgardian born now benefits from an enhanced physiology, so it's part of their DNA now.