Combining Near-Infrared Spectroscopy and Heart Rate Variability Derived Thresholds to Estimate the Critical Intensity of Exercise.

ABSTRACT: Fleitas-Paniagua, PR, de Almeida Azevedo, R, Trpcic, M, Murias, JM, and Rogers, B. Combining near-infrared spectroscopy and heart rate variability derived thresholds to estimate the critical intensity of exercise. J Strength Cond Res 38(1): e16-e24, 2024-Critical intensity determination often requires costly tools and several testing sessions. Alternative approaches display relatively large individual variation. Therefore, simpler estimations with improved precision are needed. This study evaluated whether averaging the heart rate (HR) and oxygen uptake (V̇O 2 ) responses associated with the muscle deoxyhemoglobin concentration breakpoint ([HHb] BP ) and the heart rate variability (HRV) given by the detrended fluctuation analysis second threshold (HRVT2) during ramp incremental (RI) test improved the accuracy of identifying the HR and V̇O 2 at the respiratory compensation point (RCP). Ten female and 11 male recreationally trained subjects performed a 15 W·minute -1 RI test. Gas exchange, near-infrared spectroscopy (NIRS), and RR interval were recorded to assess the RCP, [HHb] BP , and HRVT2. Heart rate (mean ± SD : 158 ± 14, 156 ± 13, 160 ± 14 and, 158 ± 12 bpm) and V̇O 2 (3.08 ± 0.69, 2.98 ± 0.58, 3.06 ± 0.65, and 3.02 ± 0.60 L·minute -1 ) at the RCP, [HHb] BP , HRVT2, and HRVT2&[HHb] BP average (H&H Av ), respectively, were not significantly different ( p > 0.05). The linear relationship between H&H Av and RCP was higher compared with the relationship between [HHb] BP vs RCP and HRVT2 vs RCP for both HR ( r = 0.85; r = 0.73; r = 0.79, p > 0.05) and V̇O 2 ( r = 0.94; r = 0.93; r = 0.91, p > 0.05). Intraclass correlation between RCP, [HHb] BP , HRVT2, and H&H AV was 0.93 for V̇O 2 and 0.79 for HR. The [HHb] BP and the HRVT2 independently provided V̇O 2 and HR responses that strongly agreed with those at the RCP. Combining [HHb] BP and the HRVT2 resulted in estimations of the V̇O 2 and HR at the RCP that displayed smaller variability compared with each modality alone.

Effect of ramp slope on intensity thresholds based on correlation properties of heart rate variability during cycling.

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 V̇O2 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, ICC3,1 , ANOVA, and paired t-testing. An excellent degree of reliability was seen across all three ramps, with an ICC3,1 of 0.93 and 0.88 for the HRVT1 V̇O2 and HR, respectively, and 0.90 and 0.92 for the HRVT2 V̇O2 and HR, respectively. Correlations between HRVT1/2 of the individual ramps were high with r values 0.84-0.95 for both HR and V̇O2 . 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 V̇O2 .

Different ramp-incremental slopes elicit similar V̇o2max and fatigability profiles in females and males despite differences in peak power output.

The aim of this article is to investigate the effects of different ramp-incremental (RI) slopes on fatigability and its recovery in females and males. Ten females and 11 males performed RI tests with distinct slopes, in separated and randomized sessions, 15 (RI15), 30 (RI30), and 45 (RI45) W·min-1. Performance fatigability was assessed by femoral nerve electrical stimuli evoked during and after isometric maximal voluntary contraction (IMVC) of knee extensors at baseline and after task failure at min 0.5, 1.5, 2.5, 5, and 10. Maximal oxygen uptake (V̇o2max) and peak power output (POpeak) were also measured. There were significant and similar declines from pre- to post-RI test in RI15, RI30, and RI45 for IMVC (-23%; -25%; -25%, respectively; P < 0.05) and potentiated single twitch (-46%; -47%; -49%; P < 0.05), whereas voluntary activation did not change (-1%; -1%; 0%; P > 0.05). There were no RI condition effects, nor time × condition interaction for IMVC, potentiated single twitch and voluntary activation (all P > 0.05). V̇o2max was not different among RI15, RI30, and RI45 conditions (3.30, 3.29, and 3.26 L·min-1, respectively; P = 0.717), but POpeak was (272, 304, and 337 W, respectively; P < 0.001). Overall, performance fatigability profiles were similar between sexes after the RI tests and during recovery. In addition, during recovery, high-frequency doublets and single twitch recovered faster after RI30 and RI45 compared with RI15, regardless of sex (all P > 0.05 for sex differences). In conclusion, RI tests of different slopes that elicited similar V̇o2max but different POpeak did not affect the profile of performance fatigability at task failure in females and males.NEW & NOTEWORTHY It was unknown whether performance fatigability and its recovery are affected by different slopes in a ramp incremental (RI) test. It was also uncertain if females and males would respond differently. Performance fatigability was the same regardless of the RI slope adopted and the sex of the population, which was accompanied by similar maximal oxygen uptake but different power output achieved. The recovery of contractile function was similar between sexes but delayed after slower RI slopes.