Bruce Rogers

An index of heart rate variability (HRV), detrended fluctuation analysis (DFA a1) has gathered interest as a surrogate marker of exercise intensity boundaries. The aim of this report was to examine heart rate variability threshold (HRVT) behavior across different ramp incremental (RI) slopes. Seventeen participants completed a series of three RI (15, 30, and 45 W · min −1 slopes) with monitoring of gas exchange parameters, heart rate (HR) and HRV. HRVT1 was defined as the V̇O 2 or HR at which DFA a1 reached 0.75 and the HRVT2 at which these values reached 0.5. HRVTs were compared by Pearson's r , Bland–Altman analysis, ICC 3,1 , ANOVA, and paired t ‐testing. An excellent degree of reliability was seen across all three ramps, with an ICC 3,1 of 0.93 and 0.88 for the HRVT1 V̇O 2 and HR, respectively, and 0.90 and 0.92 for the HRVT2 V̇O 2 and HR, respectively. Correlations between HRVT1/2 of the individual ramps were high with r values 0.84–0.95 for both HR and V̇O 2 . Bland–Altman differences ranged between −1.4 and 1.2 mL · kg −1 · min −1 and −2 and +2 bpm. Paired t ‐testing showed no mean differences between any HRVT1/2 ramp comparisons. Cycling ramp slope does not appear to affect either HRVT1 or HRVT2 in terms of HR or V̇O 2 .