“An ordinary sunny day with no plans and the ease that comes with maturity.” That’s how Hudson-based Pilates instructor Nicole Meadors Keegan defines happiness. But she also finds joy and delight through her Pilates practice and teaching classes at her stunning studio which she says has attracted celebrities, artists, doctors, stone masons, parents, carpenters and kids since it opened in 2003.  “Exercise is essential for my own well-being,” says Keegan. “As for my older generation Pilates clients, they have joie de vivre. For them, exercise is a tonic for vitality and longevity—a mood boost.” Keegan teaches Classical Pilates, which was…