Reproducibility of Heart Rate Variability Threshold in Untrained Individuals.

The aim of this study was to evaluate the reproducibility of the heart rate variability threshold (HRVT) by different HRV indexes and determination criteria. 68 untrained participants, 17 women (24.09±4.91 years old; 21.54±1.97 kg∙m) and 51 men (24.52±3.52 years old; 26.51±6.31 kg∙m), were evaluated on 2 different days (test and retest). The HRVT was determined during an incremental exercise test using 2 indexes (SD1 and RMSSD) and criteria (HRTV first intensity of physical effort with index<3 ms, and HRVT first intensity of physical effort, in which the index presents a difference<1 ms between 2 consecutive intensities). There was no significant difference (<0.05) between the test and retest for any of the variables evaluated. All variables, except for the rate of perceived exertion at HRVT presented moderate to high intraclass correlation coefficient (HRVT: 0.55-0.85 and HRVT:0.58-0.69). All variables at HRVT and the heart rate at HRVT showed coefficient of variation ~ 10%. The HRVT, regardless of criteria and HRV index used, showed satisfactory reproducibility. Thus, these criteria can be used to assess clinically autonomic cardiac modulation and aerobic capacity, and to analyze the effect of different interventions.