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.

Sweat drips from every pore and my sorry excuse of a fan isn’t cutting the mustard. I’m 40 minutes into the first zone-two endurance workout of a new training plan and a combination of a few months ...