How does the this concept check out?:

A genetically-altered (i.e. raised from birth) human with muscle proteins that have been developed, "folded", or otherwise modified to be more effective while retaining the same density. Therefore, they're proportionately stronger than a baseline human while not having any increase in muscle mass.

How does this concept check out?.

A genetically-altered (i.e. raised from birth) human with muscle proteins that have been developed, "folded" (i.e. the way muscle fibers interact with one another), structured or otherwise modified to be more effective while retaining the same density. Therefore, they're proportionately stronger than a baseline human while not having any increase in muscle mass.