Learn Danish: Hun er muskuløs nok til at løfte byrden. - She is muscular enough to lift the burden.

When expressing a consequence or purpose after nok (enough), Danish requires the preposition til followed by the infinitive marker at. You can think of nok til at as a fixed grammatical chunk meaning "enough to". Using just at here would be incorrect.

Could I put nok before the adjective and say nok muskuløs?

No, that would be grammatically incorrect. When nok means "sufficiently" and modifies an adjective, it must come immediately after that adjective. This perfectly mirrors the English word order: "muscular enough", never "enough muscular".

If the subject were plural, how would muskuløs nok change?

The adjective would take the standard plural -e ending, becoming muskuløse. The word nok acts as an adverb here and does not change. So, "They are muscular enough" would be De er muskuløse nok.

Does byrden refer to a literal physical weight or a metaphorical burden?

It works perfectly for both, exactly like the English word "burden". En byrde can be a literal heavy load you are trying to lift, but it is also frequently used for metaphorical weights, such as financial burdens or heavy responsibilities.