Core training has always been part of military PT and fitness testing. From crunches to sit-ups, flutter kicks, leg tucks and plank poses, the U.S. military uses many exercises to test core strength.

Crouch with your hands on the ground. Your heels should be raised, directly below your glutes, and your knees hovering above the floor. Raise your left foot and tense your abs, jumping your right foot ...

Hey, all! Full-body workouts every day are a no-go — you need rest and recovery time. But there is one body part that trainers say it’s safe to work on daily. Take a look.