This is because the shape of the paper cup (conical) is very stable and can exert a great deal of power, even though the contents are empty.
I like to refer to this empty structure as “The Space.” When “The Space” is adjusted properly, an object will be stable.
The same idea applies to muscles.
空っぽの250ccの紙コップ６個の上に、乗ることは可能。なぜなら、この紙コップの形が重要であり、紙コップの中の空の空間が支えているから。これは筋肉も同じ。