Which of the following is NOT one of the three energy systems?

The correct answer is that "cardiac" is not one of the three main energy systems. The three recognized energy systems for human movement are the aerobic system, the lactic acid system (often referred to as the anaerobic system), and the creatine phosphate system (also known as the phosphagen system).

The aerobic system is utilized during prolonged, lower-intensity activities where oxygen is available for energy production. It primarily uses carbohydrates and fats as fuel sources.

The lactic acid system kicks in during high-intensity, short-duration activities where energy needs exceed oxygen availability. It generates energy quickly but produces lactate, which can lead to muscle fatigue.

The creatine phosphate system provides immediate energy for short bursts of activity, such as sprinting or heavy lifting. It uses stored creatine phosphate in muscles to regenerate ATP, the energy currency of the cell, for quick energy demands.

In contrast, the term "cardiac" relates to the heart and does not describe an energy system. While cardiovascular fitness is essential for overall health, it is not classified among the mechanisms by which energy is produced during exercise.