after efforts in vain; all efforts having been in vain
Used adverbially to indicate that despite one's efforts, the result was futile or unsuccessful. Often appears at the beginning of a sentence or clause.
After all his efforts in vain, he failed the exam.
Despite their efforts, the project was canceled.
Similar meaning but more explicitly states that the effort yielded no reward. 努力も虚しく emphasizes the emptiness or futility of the effort itself.
Standard kanji spelling using 虚しく.
Alternate kanji spelling using 空しく; both are used.
A set phrase composed of 努力 (effort) + も (even) + 虚しく (adverbial form of 虚しい, meaning 'empty' or 'futile'). The expression is a fixed adverbial phrase.