The only time I participated in a writing sprint was during NANOWRIMO — National Novel Writing Month a few years ago during a meeting of a writing group. I won! But I did not enjoy it. Like you, I’m an academic but I’ve never sprinted or counted words. I just write, then I will delete or add and count words to meet the publisher/manuscript word count requirements. I just let the words/ideas flow. I think it comes with years of writing, and teaching college writing. And I’m constantly writing and jotting down ideas and inspirations as they come to me 24/7, even in my sleep.