This article is from the Aerobics Fitness FAQ, by email@example.com (Robles) with numerous contributions by others.
There are several ways to increase intensity. Increase your step
height, use longer lever arms or add propulsion moves (where both
feet are off the step at the same time). If you are going to add
propulsion, or power as it is known today, make sure not to do these
moves for more than one minute at a time as these moves result in
higher vertical impact. All power moves should be done as you go
up onto the platform. Always step down without power. Power moves
are considered advanced, and should not be attempted by beginners.