Racial Differences in Blood Pressure and Autonomic Recovery Following Acute Supramaximal Exercise in Women

Despite the growing popularity of high-intensity anaerobic exercise, little is known about the acute effects of this form of exercise on cardiovascular hemodynamics or autonomic modulation, which might provide insight into the individual assessment of responses to training load. The purpose of this study was to compare blood pressure and autonomic recovery following repeated bouts of acute supramaximal exercise in Black and White women. A convenience sample of twelve White and eight Black young, healthy women were recruited for this study and completed two consecutive bouts of supramaximal exercise on the cycle ergometer with 30 min of recovery in between. Brachial and central aortic blood pressures were assessed by tonometry (SphygmoCor Xcel) at rest and 15-min and 30-min following each exercise bout. Central aortic blood pressure was estimated using brachial pressure waveforms and customized software. Autonomic modulation was measured in a subset of ten participants by heart-rate variability and baroreflex sensitivity. Brachial mean arterial pressure and diastolic blood pressure were significantly higher in Blacks compared to Whites across time (race effect, p = 0.043 and p = 0.049, respectively). Very-low-frequency and low-frequency bands of heart rate variability, which are associated with sympathovagal balance and vasomotor tone, were 22.5% and 24.9% lower, respectively, in Blacks compared to Whites (race effect, p = 0.045 and p = 0.006, respectively). In conclusion, the preliminary findings of racial differences in blood pressure and autonomic recovery following supramaximal exercise warrant further investigations of tailored exercise prescriptions for Blacks and Whites.

The effect of exercise hyperpnea on gross efficiency and anaerobic capacity estimates during a 3-min cycle time trial

This study aimed to analyze the effect of exercise-induced hyperpnea on gross efficiency (GE) and anaerobic capacity estimates during a self-paced 3-min supramaximal cycle time trial (TT). Fourteen highly trained male cyclists performed 7 × 4-min submaximal stages, a 6-min passive rest, a 3-min TT, a 5-min passive rest, and a 6-min submaximal stage. Three models were based on the 7 × 4-min linear regression extrapolation method, using 1) the conventional model (7-Y_LIN); 2) the same 7-Y_LIN model but correcting for the additional ventilatory cost (i.e., hyperpnea) (7-Y_LIN-V-cor); and 3) accounting for linearly declining GE during the TT (7-Y_LIN-D). The other three models were based on GE from the last submaximal stage, using the conventional model (GE_LAST) and the same modifications as described for 7+Y_LIN, i.e., 1) GE_LAST, 2) GE_LAST-V-cor, and 3) GE_LAST-D. The GE_LAST model generated 18% higher values of anaerobic capacity than the 7-Y_LIN model (P < 0.05). During the TT, the hyperpnea-corrected model (i.e., 7-Y_LIN-V-cor or GE_LAST-V-cor) generated, compared with the respective conventional model (i.e., 7-Y_LIN or GE_LAST), ∼0.7 percentage points lower GE and ∼11% higher anaerobic capacity (all, P < 0.05). The post-TT GE was 1.9 percentage points lower (P < 0.001) and the 7-Y_LIN-D or GE_LAST-D model generated, compared with the respective conventional model, a lower GE (∼1.0 percentage points) and ∼17% higher anaerobic capacity during the TT (all, P < 0.05). In conclusion, the correction for a declining GE due to hyperpnea during a supramaximal TT resulted in an increased required total metabolic rate and anaerobic energy expenditure compared with the conventional models.NEW & NOTEWORTHY This study demonstrates that GE declines during a 3-min supramaximal cycle TT, which is possibly related to the hyperpneic response during supramaximal exercise. The finding from this study also provides novel insight into how the increased ventilatory energy cost from exercise-induced hyperpnea contributes to decreased GE, increased required total metabolic rate, and increased anaerobic energy expenditure during supramaximal exercise. Therefore, conventional linear models for estimating anaerobic capacity are likely to generate underestimated values.

Anaerobic Capacity in Running: The Effect of Computational Method

Introduction

To date, no study has compared anaerobic capacity (AnC) estimates computed with the maximal accumulated oxygen deficit (MAOD) method and the gross energy cost (GEC) method applied to treadmill running exercise.

Purpose

Four different models for estimating anaerobic energy supply during treadmill running exercise were compared.

Methods

Fifteen endurance-trained recreational athletes performed, after a 10-min warm-up, five 4-min stages at ∼55-80% of peak oxygen uptake, and a 4-min time trial (TT). Two linear speed-metabolic rate (MR) regression models were used to estimate the instantaneous required MR during the TT (MR _{TT_req} ), either including (5+Y _LIN ) or excluding (5-Y _LIN ) a measured Y-intercept. Also, the average GEC (GEC _AVG ) based on all five submaximal stages, or the GEC based on the last submaximal stage (GEC _LAST ), were used as models to estimate the instantaneous MR _{TT_req} . The AnC was computed as the difference between the MR _{TT_req} and the aerobic MR integrated over time.

Results

The GEC remained constant at ∼4.39 ± 0.29 J⋅kg^-1⋅m^-1 across the five submaximal stages and the TT was performed at a speed of 4.7 ± 0.4 m⋅s^-1. Compared with the 5-Y _LIN , GEC _AVG , and GEC _LAST models, the 5+Y _LIN model generated a MR _{TT_req} that was ∼3.9% lower, with corresponding anaerobic capacities from the four models of 0.72 ± 0.20, 0.74 ± 0.16, 0.74 ± 0.15, and 0.54 ± 0.14 kJ⋅kg^-1, respectively (F _1.07,42 = 13.9, P = 0.002). The GEC values associated with the TT were 4.22 ± 0.27 and 4.37 ± 0.30 J⋅kg^-1⋅m^-1 for 5+Y _LIN and 5-Y _LIN , respectively (calculated from the regression equation), and 4.39 ± 0.28 and 4.38 ± 0.27 J⋅kg^-1⋅m^-1 for GEC _AVG and GEC _LAST , respectively (F _1.08,42 = 14.6, P < 0.001). The absolute typical errors in AnC ranged between 0.03 and 0.16 kJ⋅kg^-1 for the six pair-wise comparisons and the overall standard error of measurement (SEM) was 0.16 kJ⋅kg^-1.

Conclusion

These findings demonstrate a generally high disagreement in estimated anaerobic capacities between models and show that the inclusion of a measured Y-intercept in the linear regression (i.e., 5+Y _LIN ) is likely to underestimate the MR _{TT_req} and the GEC associated with the TT, and hence the AnC during maximal 4-min treadmill running.

The Effects of L-Citrulline on Blood-Lactate Removal Kinetics Following Maximal-Effort Exercise

The accumulation of lactate in muscle and blood during high-intensity exercise is negatively correlated with the duration exercise can be sustained. Removal of lactate is a key component of acute recovery between consecutive bouts of such exercise. Low-intensity exercise enhances recovery by accelerating lactate turnover in metabolically active tissues, largely mediated by blood flow to these tissues. Therefore, the purpose of this research was to clarify if L-citrulline, a nutritional supplement purported to promote vasodilation via enhanced nitric oxide availability, would augment the removal of blood lactate during active recovery (AR). L-citrulline ingestion will augment the rate of blood lactate concentration decrease during AR, reduce the oxygen-cost of submaximal exercise, and increase time-to-exhaustion and peak oxygen uptake (V̇O2peak) during a test of maximal aerobic power. Healthy university students (five males & five females) participated in this double-blind, randomized, placebo-controlled study. Participants exercised on a cycle ergometer at submaximal steady-state intensities followed by progressively increasing intensity to exhaustion, 10 min of AR, and then supramaximal intensity exercise to exhaustion. Oxygen uptake was measured throughout the trial and blood lactate was sampled repeatedly during AR. The protocol elicited very high peak blood lactate concentrations after exercise (11.3 + 1.3 mmol/L). L-citrulline supplementation did not significantly alter blood lactate kinetics during AR, the oxygen cost of exercise, V̇O2peak, or time-to-exhaustion. Despite a strong theoretical basis by which L-citrulline could augment lactate removal from the blood, L-citrulline supplementation showed no effect as an exercise-recovery supplement.

Verification Testing to Confirm VO2max Attainment in Inactive Women with Obesity

Incidence of obesity is increasing worldwide which is deleterious to health due to its association with increased risk of cardiovascular disease, diabetes, and some cancers. Completion of regular physical activity in individuals with obesity increases maximal oxygen uptake (VO2max). However, whether individuals with obesity can exhibit 'true' VO2max is unresolved. This study examined efficacy of verification testing (VER) to identify 'true' VO2max in 17 inactive women with obesity (age, body fat, and VO2max = 37 ± 10 yr, 48.7 ± 3.5 %, and 19.4 ± 3.0 mL/kg/min, respectively). They performed ramp exercise (RAMP) to volitional fatigue followed by VER at 105 percent peak power output (%PPO) at baseline and after 3 and 6 wk of high intensity interval training. Results showed no difference in ramp and verification-derived VO2max (1.99 ± 0.37 L/min vs. 1.98 ± 0.32 L/min, 2.00 ± 0.40 L/min vs. 2.04 ± 0.38 L/min, and 2.08 ± 0.34 L/min vs. 2.08 ± 0.32 L/min at 0, 3 and 6 wk of training), although in 40 % of VER tests, VO2max was greater than the RAMP value. Overall, verification testing may be adopted as an additional approach to confirm 'true' VO2max attainment in obese women as ramp exercise frequently underestimates VO2max in this population.

Effect of Ischemic Preconditioning on the Recovery of Cardiac Autonomic Control From Repeated Sprint Exercise

Repeated sprint exercise (RSE) acutely impairs post-exercise heart rate (HR) recovery (HRR) and time-domain heart rate variability (i. e., RMSSD), likely in part, due to lactic acidosis-induced reduction of cardiac vagal reactivation. In contrast, ischemic preconditioning (IPC) mediates cardiac vagal activation and augments energy metabolism efficiency during prolonged ischemia followed by reperfusion. Therefore, we investigated whether IPC could improve recovery of cardiac autonomic control from RSE partially via improved energy metabolism responses to RSE. Fifteen men team-sport practitioners (mean ± SD: 25 ± 5 years) were randomly exposed to IPC in the legs (3 × 5 min at 220 mmHg) or control (CT; 3 × 5 min at 20 mmHg) 48 h, 24 h, and 35 min before performing 3 sets of 6 shuttle running sprints (15 + 15 m with 180° change of direction and 20 s of active recovery). Sets 1 and 2 were followed by 180 s and set 3 by 360 s of inactive recovery. Short-term HRR was analyzed after all sets via linear regression of HR decay within the first 30 s of recovery (T30) and delta from peak HR to 60 s of recovery (HRR60s). Long-term HRR was analyzed throughout recovery from set 3 via first-order exponential regression of HR decay. Moreover, RMSSD was calculated using 30-s data segments throughout recovery from set 3. Energy metabolism responses were inferred via peak pulmonary oxygen uptake (V˙O2peak), peak carbon dioxide output (V˙O2peak), peak respiratory exchange ratio (RERpeak), first-order exponential regression of V˙O2 decay within 360 s of recovery and blood lactate concentration ([Lac-]). IPC did not change T30, but increased HRR60s after all sets (condition main effect: P = 0.03; partial eta square (η²_p) = 0.27, i.e., large effect size). IPC did not change long-term HRR and RMSSD throughout recovery, nor did IPC change any energy metabolism parameter. In conclusion, IPC accelerated to some extent the short-term recovery, but did not change the long-term recovery of cardiac autonomic control from RSE, and such accelerator effect was not accompanied by any IPC effect on surrogates of energy metabolism responses to RSE.

Estimating Hemodynamic Responses to the Wingate Test Using Thoracic Impedance

Techniques including direct Fick and Doppler echocardiography are frequently used to assess hemodynamic responses to exercise. Thoracic impedance has been shown to be a noninvasive alternative to these methods for assessing these responses during graded exercise to exhaustion, yet its feasibility during supramaximal bouts of exercise is relatively unknown. We used thoracic impedance to estimate stroke volume (SV) and cardiac output (CO) during the Wingate test (WAnT) and compared these values to those from graded exercise testing (GXT). Active men (n = 9) and women (n = 7) (mean age = 24.8 ± 5.9 yr) completed two Wingate tests and two graded exercise tests on a cycle ergometer. During exercise, heart rate (HR), SV, and CO were continuously estimated using thoracic impedance. Repeated measures analysis of variance was used to identify potential differences in hemodynamic responses across protocols.

RESULTS

Maximal SV (138.6 ± 37.4 mL vs. 135.6 ± 26.9 mL) and CO (24.5 ± 6.1 L·min(-1) vs. 23.7 ± 5.1 L·min(-1)) were similar (p > 0.05) between repeated Wingate tests. Mean maximal HR was higher (p < 0.01) for GXT (185 ± 7 b·min(-1)) versus WAnT (177 ± 11 b·min(-1)), and mean SV was higher in response to WAnT (137.1 ± 32.1 mL) versus GXT (123.0 ± 32.0 mL), leading to similar maximal cardiac output between WAnT and GXT (23.9 ± 5.6 L·min(-1) vs. 22.5 ± 6.0 L·min(-1)). Our data show no difference in hemodynamic responses in response to repeated administrations of the Wingate test. In addition, the Wingate test elicits similar cardiac output compared to progressive cycling to VO2max. Key pointsMeasurement of cardiac output (CO), the rate of oxygen transport delivered by the heart to skeletal muscle, is not widely-employed in Exercise Physiology due to the level of difficulty and invasiveness characteristic of most techniques used to measure this variable.Nevertheless, thoracic impedance has been shown to provide a noninvasive and simpler approach to continuously measure CO at rest and during exercise.Results show that measurements of CO are not different and highly reliable in response to repeated administrations of the Wingate test.Despite vastly different intensities and durations, maximal CO was similar between the Wingate test and graded exercise to VO2max.