Is a short-stage protocol during an incremental exercise test reliable for heart rate variability threshold analysis?

Abstract

Heart rate variability threshold (HRVT) is a valid method to determine parasympathetic depression during an incremental exercise test (IET). However, HRVT is usually assessed using the last 60s of each 180s stage of an IET, resulting in longer and demotivating tests. This study aimed to evaluate the agreement of HRVT analysis adopting the first and second minute of R-R interval (iRR) segment comparatively to a standard third-minute segment obtained at each 3-min stage on IET. Methods: Seventeen young male subjects (22.2 ± 3.1 years; 23.4 ± 2.3 kg/m 2) underwent IET on a cycle ergometer. HRVT was considered the load corresponding to the point of stabilization of the SD1 index (HRVTV), or the first load with SD1 value < 3ms (HRVT<3), both assessed by the 1 st (HRVT1V, HRVT1<3), 2 nd (HRVT2V, HRVT2<3) and standard 3 rd (HRVT3V, HRVT3<3) 60s iRR segment analyzed at each stage of IET. Agreement and reliability were assessed by the Bland-Altman analysis and the intraclass correlation coefficient (ICC), respectively. Results: High reliability and non-significant bias were observed considering HRVT1V vs HRVT3V (ICC = 0.92; p = 0.18) or HRVT2V vs HRVT3V (ICC = 0.94; p = 0.99). However, lower reliability was observed for HRVT1<3 vs HRVT3<3 (ICC = 0.79; p = 0.75) and for HRVT2<3 vs HRVT3<3 (ICC = 0.91; p = 0.33). Conclusion: HRVT can be similarly assessed by the 1 st , 2 nd or 3 rd 60 seconds iRR segment, mainly when assessed by a visual method.

Intrarater reliability of different methods of heart rate variability threshold analysis and postexercise parasympathetic reactivation in young women

“…It is important to note that lower reliability was observed for HRVT 3ms than HRVT visual in the present study. As didactically demonstrated by Cruz et al (2019) 25 , and shown in Figure 1, a small variation (< 1 ms) in the SD1 is sufficient to change the stage corresponding to HRVT 3ms (i.e., 3.3 to 2.9) despite visible stabilization of this index, which may explain the lower reproducibility of this method identified in our study. In fact, higher reproducibility of HRVT visual compared to mathematical methods was also confirmed in young men exercising on a cycle ergometer 18,25 .…”

“…As didactically demonstrated by Cruz et al (2019) 25 , and shown in Figure 1, a small variation (< 1 ms) in the SD1 is sufficient to change the stage corresponding to HRVT 3ms (i.e., 3.3 to 2.9) despite visible stabilization of this index, which may explain the lower reproducibility of this method identified in our study. In fact, higher reproducibility of HRVT visual compared to mathematical methods was also confirmed in young men exercising on a cycle ergometer 18,25 . Thus, despite the advantage of reducing the possible influence of the evaluator's expectation on the HRVT analysis, these results indicate that the mathematical methods commonly used in HRVT assessment need to be carefully interpreted.…”

“…In this scenario, the visual graphical inspection of SD1 or r-MSSD stabilization during exercise and the first stage of incremental test to present values of SD1 less than 3 ms is the criteria classically adopted to HRVT identification 7,19,24 . Since different criteria of HRVT can identify parasympathetic stabilization at different exercise intensities 25 , it is necessary to know the reproducibility of these different methods of HRVT analysis and the grade of agreement between them, especially in women.…”