An Intensity-dependent Slow Component of HR Interferes with Accurate Exercise Implementation in Postmenopausal Women

Abstract

Heart rate (HR) targets are commonly used to administer exercise intensity in sport and clinical practice. However, as exercise protracts, a time-dependent dissociation between HR and metabolism can lead to a misprescription of the intensity ingredient of the exercise dose.PurposeWe tested the hypothesis that a slow component of HR (i.e., scHR) occurs in all intensity domains, greater than the slow component of oxygen uptake (scV˙O2), and we developed an equation to predict it across exercise intensities.MethodEighteen healthy, postmenopausal women (54 ± 4 yr) performed on a cycle ergometer: i) a ramp incremental test for thresholds and V˙O2max detection; ii) 30-min constant work exercise at 40%, 50%, 60%, 70%, and 80% V˙O2max for the measurement of scHR, scV˙O2, stroke volume, and body temperature (T°). scHR and scV˙O2 were compared by two-way repeated-measures ANOVA (intensity and variable). Pearson correlation was calculated between the slow component of all variables, relative intensity, and domain. scHR (in beats per minute) was predicted with a linear model based on exercise intensity relative to the respiratory compensation point (RCP).ResultsA positive scHR was present in all domains, twice the size of scV̇O2 (P < 0.001), and significantly correlated with the slow components of V̇O2 (r2 = 0.46), T° (r2 = 0.52), and relative intensity (r2 = 0.66). A linear equation accurately predicts scHR based on %RCP (r2 = 0.66, SEE = 0.15).ConclusionsA mismatch exists between the slow components of HR and metabolic intensity. Whenever exercise is prescribed based on HR, target values should be adjusted over time to grant that the desired metabolic stimulus is maintained throughout the exercise session.

In Cardiac Patients Beta-Blockers Attenuate the Decrease in Work Rate during Exercise at a Constant Submaximal Heart Rate

“…If adequately standardized, the approach described in the present study may be valuable also in diseased populations. The observed phenomena (decreases in work rate and (in no-BB) in V̇O 2 at a fixed HR) represent a sort of a mirror image of the progressive increases in HR and V̇O 2 as a function of time (traditionally termed “slow component”) observed during heavy-intensity (above GET) constant work rate exercise (11–13,29,30). Whereas the V̇O 2 slow component is associated with decreased efficiency of contractions and fatigue (31), the physiological significance of the HR slow component is less clear, and mostly anecdotal observations are present in the literature (17,30,32–36).…”

Effect of individual characteristics and aerobic training on the %HRR‐%V̇O2R relationship

“…approximately the same time period as the HR), one more or one less breath could have been recorded within those 20 sec yielding V̇ O 2 values highly variable and not representative of the stage. Finally, during prolonged exercise several physiological adjustments, namely cardiovascular drift and V̇ O 2 slow component (Zuccarelli et al, 2018), may alter the HR‐ V̇ O 2 relationships, which seem to be affected by the duration (Ferri Marini et al, 2022) and intensity (Teso et al, 2022) of the prolonged aerobic exercises. Indeed, the true nature of the HR‐ V̇ O 2 relationships during prolonged aerobic exercise remains a debated topic (Cunha et al, 2011; Ferri Marini et al, 2022; Teso et al, 2022; Wingo et al, 2012) and using the HR‐ V̇ O 2 relationships derived from incremental exercise to prescribe aerobic exercise training intensity, for a given individual, may not be the final word in exercise intensity prescription.…”

“…Finally, during prolonged exercise several physiological adjustments, namely cardiovascular drift and V̇ O 2 slow component (Zuccarelli et al, 2018), may alter the HR‐ V̇ O 2 relationships, which seem to be affected by the duration (Ferri Marini et al, 2022) and intensity (Teso et al, 2022) of the prolonged aerobic exercises. Indeed, the true nature of the HR‐ V̇ O 2 relationships during prolonged aerobic exercise remains a debated topic (Cunha et al, 2011; Ferri Marini et al, 2022; Teso et al, 2022; Wingo et al, 2012) and using the HR‐ V̇ O 2 relationships derived from incremental exercise to prescribe aerobic exercise training intensity, for a given individual, may not be the final word in exercise intensity prescription.…”

Metabolic and Perceptual Responses to Constant Heart Rate Exercise at Vigorous Intensities in Women

“…Although the desired exercise intensities are identified based on a metabolic (oxygen consumption ( VO 2 )) rate, percentages of HR peak or the corresponding ratings of perceived exertion (RPE) are commonly used to prescribe exercise intensities because they are more practical than measuring VO 2 during an exercise bout (1,2). These exercise recommendations include a range of very light to moderate (30%-59% VO 2 R or HR R , <57%-76% HR peak , <37%-63% VO 2peak , RPE <9-13), vigorous (60%-89% VO 2 R or HR R , 77%-95% HR peak , 64%-90% VO 2peak , RPE [14][15][16][17], and near maximal (≥90% VO 2 R or HR R , ≥91% VO 2peak , ≥96% HR peak ) exercise intensities that are performed most days of the week at an intensity low enough to be sustained for 20 to 60 min, but high enough to elicit metabolic and cardiovascular adaptations (1,2). Although exercise prescriptions using the % VO 2 R or HR R may be more appropriate for deconditioned individuals, the use of relative maximal values (% HR peak ) is more common in training applications (2).…”

“…Above these intensities, the slow rise in VO 2 over time has been termed the VO 2 slow component (13). A slow component of HR has also been demonstrated, but the gradual rise in HR may occur at a lower relative intensity (below VT or GET) than the slow component of VO 2 (12,14). Therefore, during exercise anchored or fixed to HR, power output or running speed is reduced to maintain the designated HR, and VO 2 tracks these reductions in work rate, whereas RPE increases throughout the exercise trials (10,11,15,16).…”