You’ve probably seen it all over your feeds: Fitness pros and physical therapists talking about “training the deep core.” But ...

After nearly 20 years teaching grades 4 through 12 in Rhode Island, Willett has became a trusted sounding board for friends and family, navigating their questions and concerns about school life.

In TODAY.com's Expert Tip of the Day, a trainer explains why strength training is so important and reveals the exercises she prefers for beginners.