"We naturally lose muscle mass, reaction speed and balance as we age,” says this elite Hollywood coach who's trained everyone from Margot Robbie and Scarlet Johansson to Richard Madden and Pedro Pascal — but recommends doing step-ups to undo the damage of aging in your glutes, quads and calves

There’s a reason why some of the most effective exercises tend to mirror movements in real life. It’s not because personal trainers and coaches lack imagination, but because the body doesn't care how creative your…