Whether it’s Hyrox or CrossFit, some of this century’s biggest exercise trends have one thing in common: combining cardio with strength training. Here’s how to do it Whether it’s Hyrox or CrossFit, some of this century’s biggest exercise trends have one thing in common: combining cardio with strength training. Here’s how to do it Tough Mudder . CrossFit . Hyrox . Some of this century’s biggest fitness trends have one thing in common: they require feats of both strength and endurance. People