Importance of RR-Interval Variability in Stress Test

The variability of cardiac rhythmogram (CRG) at the early stage of loading and recovery periods has a number of parametersassociated with the functional state of subjects.These parameters can be estimatedby measuring the probability of pairs of RR-intervals with certain length differences (pNNx). At the same time,each of these parameters has its own diagnostic role, such as a binary marker of adaptation reserves (pNN 15), loading tolerance level (pNN5, 10) and a criterion. for the training level (pNN 10, 15). The association of pNNx with the endured load power and the dynamics of heart rate is to a great extent determined by the mixed endurance level. Higher values ofpNNxcorrespond with the predominant load and lower heart rate, regardless of the period. Physiological relevance of pNNxis determinedby their behavior, diagnostic role, the sensitivity of each argument ("x"), and the level of aerobic/anaerobic endurance of a subject.