Peripheral heart action training is a fitness conditioning system developed Dr. Arthur Steinhaus in the 1940s. It’s said to have garnered popularity in the fitness world by 1960's legendary bodybuilder, Bob Gajda. When doing PHA style training, you perform a circuit of five to six exercises for about four or five rounds. “I would call this circuit training to my clients,” says New York City-based trainer, Melissa Paris, NASM, pre- and post-natal fitness expert. The point in doing these exercises and switching from upper body to lower body exercises sequentially is so that you're not building up lactic acid in either muscle group while still training hard, she adds.