The Heart Rate Maximizer is the aerobic fitness component of the Fit Test for the P90X Home Fitness Workout, involving repeated jumping jacks over two minutes (note: jumping jacks are also called star jumps in many parts of the world).

• purpose: to test the heart rate response to exercise, as a measure of the aerobic energy system.
• equipment required: heart rate monitor (optional)
• procedure: You perform jumping jacks exercises nonstop for 2 minutes - the last 30 seconds as fast as you can to maximize your heart rate. The starting position is standing with both feet together and arms by the side. A jumping jack is performed by jumping up and landing with the legs spread wide and the hands touching overhead, and then jumping again and returning to a position with the feet are together and the arms at the sides. The action is repeated without any rest. When you finish measure your heart rate immediately, then at 1, 2, 3 and 4 minutes afterwards.

• scoring: record your heart rate levels. There is no minimum required for the P90X program, but if you can complete the full 2 minutes including the 30 second sprint, you are able to commit to P90X.
• advantages: this is a simple test to perform with minimal equipment required.
• reliability: as an individual's technique for performing the jumping jack exercise can vary, it is important to perform the exercise the same way each time the test is conducted to.