High Intensity Energy, also used as the acronym HIE, this is the amount of energy or work capacity an athlete has above Threshold Power (TP). HIE is analogous in many ways to the term W’ used in sports science research, which has also been referred to as Anaerobic Work Capacity (AWC) in the past. HIE is measured in kilojoules (kJ). The most notable difference between HIE and W’ is that HIE can never be completely depleted. During exercise, HIE depletes when work is performed above Threshold and replenishes during rest or when work is performed below TP. At Threshold, HIE remains unchanged.
For example, if your HIE is 20 kJ, after performing 500 seconds at 10 watts above TP, your HIE would be reduced by 500*10 joules or 5kJ, i.e. 15kJ.
It is also important to note that mathematically-speaking, MPA limits how quickly HIE can be depleted. Further, the value of HIE determines an athlete’s MPA in real-time. As HIE is utilized while riding above threshold, MPA simultaneously decreases. As HIE is replenished while recovering below TP, MPA also recovers towards Peak Power.