You've got your jumping jacks dialed, and you know how to do a plank . . . but have you tried plank jacks? This intermediate bodyweight move has likely cropped up in your workouts at some point - and whether you loved or hated it, it has some impressive benefits. You get all the strength benefits of a plank (think: a strengthened core, shoulders, back, and legs) plus the benefits of cardio. All...

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