The accuracy of assessment is mainly determined by the accuracy of the devices used to measure power (in the case of cycling) or speed (in case of running, swimming, skating, etc). Both metrics are easy and accurate to measure. Additionally, the data is captured in the conditions to which the user (coach and athlete) wants to relate the results to (on a hill, or a flat TT course).
The sensitivity of the algorithms within INSCYD are robust when it comes to the tolerance of the results in relation to in accuracy of the input data. For example: in the 4min critical power test in Cycling, an error of 10 Watts (either because of a badly calibrated powermeter or because of sloppy data analysis) for a 75 kg athlete, causes a maximum possible error of the estimation of VO2max of 1,07 ml/min/kg. The best metabolic carts, as used in high quality, human performance labs, encounter a typical error of 2% percent. Therefore the accuracy of analysis is on par with INSCYD. (see also: Carter J, Jeukendrup AE, Eur J Appl Physiol. 2002 Mar;86(5):435-41. )