Low impact means you keep one foot on the floor at all times, while with high impact, both feet can leave the floor. A low impact move would be a step-touch side to side, for example, while the higher impact equivalent would be a speed skater. Walking forward and back would be low impact, while jogging forward and back would be high imapct. With the exception of most of Low Max, Cathe's cardio workouts are high impact (there are even a few moves in Low Max, like pendulums, that really aren't low impact).