Critical Power Assessment

The Critical Power model is an chance to determine overall performance and to quantitate energy expenditure with the view to prescribing custom interval sessions. Critical power is theoretically defined as the highest, continuously sustainable power output which a cyclist is capable of producing. The critical power calculation complements the Lactate Threshold Profile (the applied aerobic power at the physiological threshold) by measuring the strength of a cyclist’s total anaerobic capacity (energy production without sufficient oxygen). This includes the work done at VO2max, as this occurs above threshold. Maintaining an optimal level of anaerobic capacity is critical for performance success in any type of cycling.

The strength of the anaerobic work capacity can predict the type of rider, with sprinters having a significantly larger anaerobic capacity compared with time-trialists who have a higher critical power or threshold. Using this information is important when assessing:

  • The overall ability of someone new to the sport.
  • Anyone looking to change their type of riding (eg sprinters becoming hill-climbers or time-trialists).
  • Anaerobic capacity while improving threshold power (which have an inverse relationship).

The critical power assessment involves riding at a series of variable maximal and sub-maximal time-trials between 1 – 10 minutes, performed at random. The test is performed under stringently controlled conditions with specific periods of recovery between each effort, and is blinded to reduce the possibility of bias.


The actual amount of energy available to a cyclist is important when riding at intensities above their critical power is termed the Anaerobic Work Capacity (AWC) or more recently known as W’ (W prime). The AWC (or W’) is an important training tool for designing optimal interval sessions unique to any individual cyclist to specifically target and improve the maximal capacity of both aerobic and anaerobic systems. Therefore the critical power calculation provides a full picture of your current physiological condition and is a tremendous basis for formulating personalised training schedules for progression with your training.

The figure above shows an example of a personalised interval session training maximal aerobic capacity (VO2Peak zone). The yellow line indicates the wattage, increasing and decreasing pyramid interval for specified durations. The red line shows the W’, amount of energy left, through the course of the interval session before this is reconstituted during recovery. Failure to initiate and complete any interval session may be due to poor glycogen reserves, inadequate lactate system conditioning, compromised VO2 kinetics, high stress hormone levels or psychological fatigue.

This interval session will strengthen the riders capacity to improve upon the amount of work tolerable at these wattages and lower, after a period of recovery and biogenetic adaptation over a few weeks.

The visit for the CP Assessment should take no more than 2hrs.

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FREE Downloadable Info series PDF: Perfect Intervals