Certain parameters above a given intensity of an incremental exercise load are diverging from the linearity of the load and oxygen uptake. This intensity in Watts, speed or percent of the maximal oxygen uptake is called as "anaerobic threshold". The not fully understood events can reflect a relative local oxygen deficiency, levelling off the elimination of lactic acid, consecutive changes in ventilation, levelling off of the stroke volume and/or the macroerg phosphate turnover, uprising of the sympathoadrenal activation, changes in the activation of motor units etc. Empirically the "threshold" has been effectively applied by the performance physiologist and a growing body supports its use in the clinical diagnostics and (cardiac) rehabilitation. Some of the "threshold" parameters (acid-base status, lactic acid level, heart rate deflection) were easily available. Connected to the (spiro)ergometry, "thresholds" offer a valid, objective measure for fitness assessment and for monitoring of the effects of medicaments. It is rational to standardise certain diagnostic parameters to the "threshold" load.