Prediction of the Maximal Metabolic Steady State From Heart Rate Variability Using a Submaximal Incremental Ramp Test

Rogers, B, Murias, JM, and Fleitas-Paniagua, PR. Prediction of the maximal metabolic steady state from heart rate variability using a submaximal incremental ramp test. J Strength Cond Res 39(10): e1256-e1264, 2025-Recent studies have demonstrated that the metabolic rate at the heavy-severe exercise intensity boundary can be determined by identifying the respiratory compensation point (RCP) and the second heart rate variability threshold (HRVT2) from incremental ramp testing. This study examined whether the HRVT2 could be extrapolated from submaximal portions of the incremental test. Fifteen subjects (5 men, 10 women, age 23 ± 4 years, V̇ o2 max 42.6 ± 8.0 ml·kg -1 ·min -1 ) underwent incremental cycling ramp testing measuring gas exchange variables along with an open-source application recording detrended fluctuation analysis (DFA a1) and RR intervals. RR data from ramp start to the point at which DFA a1 reached 0.75 were used for HRVT2 extrapolation. Comparisons were made between the V̇ o2 and HR at the RCP and HRVT2. Mean values for RCP vs. HRVT2 V̇ o2 and HR were not statistically different, 39.0 ± 9.7 vs. 38.8 ± 11.1 ml·kg -1 ·min -1 and 168 ± 9 vs. 168 ± 12 bpm, respectively, with equivalence verified. Pearson's r correlation coefficients were 0.92 and 0.60 for RCP vs. HRVT2 V̇ o2 and HR, respectively. Bland-Altman analysis showed negligible bias of 0.2 ml·kg -1 ·min -1 (LOA ±9.0) for V̇ o2 and +1 bpm (LOA ±20 bpm) for HR. DFA a1 at the RR interval testing limit was 0.72 ± 0.04 with an HR of 163 ± 12. In this group of healthy recreationally active subjects, the HRVT2 V̇ o2 and HR extrapolated from submaximal portions of the incremental test maintained similar agreement and equivalence to the V̇ o2 and HR at the RCP as seen in prior studies using testing to exhaustion.