Core Strength For Dummies, LaReine Chabut. Quote:"It's used in all yoga sun salutations and other poses. It is also a Pilates-based exercise used in many of Joseph Pilates exercises..."
Pocket Guide to Fitness, Louiza Patsis, p. 176. Quote:"The "plank exercise" is used in Pilates classes."
Kettlebells for Dummies, Sarah Lurie, p.260. Quote:"If you've done other exercises like yoga or Pilates before, you may be familiar with the plank position already."