Alicia Keys’ Trainer Shares Singer’s Challenging Workout Routine

Alicia Keys. Karwai Tang/WireImage Alicia Keys’ personal trainer Anna Kaiser says the singer loves a “challenge” when it comes to working out. Kaiser told Us Weekly exclusively that she focuses mainly on “interval based” workouts with Keys, 43, to build endurance for her stage shows. “I created a program with intervals that alternate between power…