Also used as the acronym See High Intensity Energy...., this is the amount of energy or work capacity an athlete has above Threshold Power (See Threshold Power....). Analogous in many ways to the term W’ used in physiology research, which has also been referred to as Anaerobic Work Capacity (AWC) in the past, See High Intensity Energy.... is measured in kilojoules. The most notable difference between See High Intensity Energy.... and W’ is that See High Intensity Energy.... can never be completely depleted.
During exercise, HIE depletes when work is performed above TP and replenishes during rest or when work is performed below TP. At TP, HIE remains unchanged. For example, if your HIE is 20kJ, after performing 500 seconds at 10 watts above TP, your See High Intensity Energy.... would be reduced by 500*10 joules or 5kJ, i.e. 15kJ.
HIE is used together with TP and Peak Power (which together form your Fitness Signature) in Xert to calculate MPA, second-by-second. Note that mathematically-speaking, MPA stands for Maximum Power Available. It is a measure of the maximum power an athlete can generate at a given moment... More limits how quickly See High Intensity Energy.... can be depleted.