The core gets a lot of attention when it comes to aesthetics. But your torso muscles—which include your abs, back, glutes, and hip flexors—play a crucial role in running that goes way beyond looks.

Your ab workout could do with a shakeup, and trainer Ben Feiden, ACE-CPT, creator of the new Killer Core in 15 workout program for Men's Health MVP Premium, has just the move. Instead of depending on ...