Given that Str scores are already an abstraction, the encumbrance tables are an abstraction of
that, and the x2-off-the-ground and x5-push-or-drag rule is an abstraction of
that, you're already dealing with an abstraction of an abstraction of an abstraction. Once we're that far removed from reality, the DM in me who just wants to keep the game moving would be inclined to say "it's half what you normally could lift".
I'm sure you could cite all sorts of real-life reasons why this isn't accurate, but again, neither are Str scores, encumbrance tables, or the whole x2/x5 estimate.
(I feel like comparing this to Inception now. You can only lift thing with one hand if you've been sedated. Otherwise, it's too unstable
)