J.Lo is known for her fit dancer body, do I was expecting her workouts to be a mix of Zumba and hip hop dance. Turns out, she's a big fan of dumbbells! So pump up Jenny from the Block and grab your weights. Good luck! 1. Quit quick-stepping on the stairclimber! This works fewer muscles and burns fewer calories than long, deep steps. 2. Sit still for no more than three minutes between weight-lifting sets. Waiting longer allows your muscles to cool down, weakening the benefits of the exercise. 3. MUST-DO MOVE: Tricep extension TARGETS: The backs of the arms HOW TO DO IT: Hold one end of a five-to-eight-pound dumbbell in both hands above your head. Slowly lower the weight behind your head so elbows point to the ceiling, then lift. Aim for three sets of eight.