Sex differences in the effects of inorganic nitrate supplementation on exercise economy and endurance capacity in healthy young adults.

Dietary nitrate (NO3-) is a widely used supplement purported to provide beneficial effects during exercise. Most studies to date include predominantly males. Therefore, the present study aimed to investigate if there is a sex-dependent effect of NO3- supplementation on exercise outcomes. We hypothesized that both sexes would exhibit improvements in exercise economy and exercise capacity following NO3- supplementation, but males would benefit to a greater extent. In a double-blind, randomized, crossover study, twelve females (24 ± 4 yr) and fourteen males (23 ± 4 yr) completed two 4-min moderate-intensity (MOD) exercise bouts followed by a time-to-exhaustion (TTE) task after following 3 days of NO3- supplementation (beetroot juice or BRJ) or NO3--depleted placebo (PL). Females were tested during the early follicular phase of the menstrual cycle. During MOD exercise, BRJ reduced the steady-state V̇o2 by ∼5% in males (M: Δ -87 ± 115 mL·min-1; P < 0.05) but not in females (F: Δ 6 ± 195 mL·min-1). Similarly, BRJ extended TTE by ∼15% in males (P < 0.05) but not in females. Dietary NO3- supplementation improved exercise economy during moderate-intensity exercise and exercise capacity during severe-intensity TTE in males but not in females. These differences could be related to estrogen levels, antioxidant capacity, nitrate-reducing bacteria, or a variety of known physiologic differences such as skeletal muscle calcium handling, and/or fiber type. Overall, our data suggests the ergogenic benefits of oral NO3- supplementation found in studies predominantly on male subjects may not be applicable to females.NEW & NOTEWORTHY While inorganic nitrate (NO3-) supplementation has increased in popularity as an ergogenic aid to improve exercise performance, the role of sex in NO3- supplementation on exercise outcomes is lacking despite known physiological differences during exercise between sex. This study revealed that males, but not females, improved exercise economy during submaximal exercise and exercise capacity during exercise within the severe-intensity domain following NO3- supplementation.

The acute effects of exercise intensity and inorganic nitrate supplementation on vascular health in females after menopause.

Menopause is associated with reduced nitric oxide bioavailability and vascular function. Although exercise is known to improve vascular function, this is blunted in estrogen-deficient females post-menopause (PM). Here, we examined the effects of acute exercise at differing intensities with and without inorganic nitrate (NO3-) supplementation on vascular function in females PM. Participants were tested in a double-blinded, block-randomized design, consuming ∼13 mmol NO3- in the form of beetroot juice (BRJ; n = 12) or placebo (PL; n = 12) for 2 days before experimental visits and 2 h before testing. Visits consisted of vascular health measures before (time point 0) and every 30 min after (time points 60, 90, 120, 150, and 180) calorically matched high-intensity exercise (HIE), moderate-intensity exercise (MIE), and a nonexercise control (CON). Blood was sampled at rest and 5-min postexercise for NO3-, NO2-, and ET-1. BRJ increased N-oxides and decreased ET-1 compared with PL, findings which were unchanged after experimental conditions (P < 0.05). BRJ improved peak Δflow-mediated dilation (FMD) compared with PL (P < 0.05), defined as the largest ΔFMD for each individual participant across all time points. FMD across time revealed an improvement (P = 0.05) in FMD between BRJ + HIE versus BRJ + CON, while BRJ + MIE had medium effects compared with BRJ + CON. In conclusion, NO3- supplementation combined with HIE improved FMD in postmenopausal females. NO3- supplementation combined with MIE may offer an alternative to those unwilling to perform HIE. Future studies should test whether long-term exercise training at high intensities with NO3- supplementation can enhance vascular health in females PM.NEW & NOTEWORTHY This study compared exercise-induced changes in flow-mediated dilation after acute moderate- and high-intensity exercise in females postmenopause supplementing either inorganic nitrate (beetroot juice) or placebo. BRJ improved peak ΔFMD postexercise, and BRJ + HIE increased FMD measured as FMD over time. Neither PL + MIE nor PL + HIE improved FMD. These findings suggest that inorganic nitrate supplementation combined with high-intensity exercise may benefit vascular health in females PM.

Limited Effects of Inorganic Nitrate Supplementation on Exercise Training Responses: A Systematic Review and Meta-analysis.

BACKGROUND: Inorganic nitrate (NO3-) supplementation is purported to benefit short-term exercise performance, but it is unclear whether NO3- improves longer-term exercise training responses (such as improvements in VO2peak or time to exhaustion (TTE)) versus exercise training alone. The purpose of this systematic review and meta-analysis was to determine the effects of NO3- supplementation combined with exercise training on VO2peak and TTE, and to identify potential factors that may impact outcomes. METHODS: Electronic databases (PubMed, Medscape, and Web of Science) were searched for articles published through June 2022 with article inclusion determined a priori as: (1) randomized placebo-controlled trials, (2) exercise training lasted at least three weeks, (3) treatment groups received identical exercise training, (4) treatment groups had matched VO2peak at baseline. Study quality was assessed using the Cochrane Risk-of-Bias 2 tool. Standardized mean difference (SMD) with 95% confidence intervals (CI) were calculated using restricted maximum likelihood estimation between pre- and post-training differences in outcomes. Moderator subgroup and meta-regression analyses were completed to determine whether the overall effect was influenced by age, sex, NO3- dosage, baseline VO2peak, health status, NO3- administration route, and training conditions. RESULTS: Nine studies consisting of eleven trials were included: n = 228 (72 females); age = 37.7 ± 21 years; VO2peak: 40 ± 18 ml/kg/min. NO3- supplementation did not enhance exercise training with respect to VO2peak (SMD: 0.18; 95% CI: -0.09, 0.44; p = 0.19) or TTE (SMD: 0.08; 95% CI: - 0.21, 0.37; p = 0.58). No significant moderators were revealed on either outcome. Subset analysis on healthy participants who consumed beetroot juice (BRJ) revealed stronger trends for NO3- improving VO2peak (p = 0.08) compared with TTE (p = 0.19), with no significant moderators. Sunset funnel plot revealed low statistical power in all trials. CONCLUSIONS: NO3- supplementation combined with exercise training may not enhance exercise outcomes such as VO2peak or TTE. A trend for greater improvement in VO2peak in healthy participants supplemented with BRJ may exist (p = 0.08). Overall, future studies in this area need increased sample sizes, more unified methodologies, longer training interventions, and examination of sex as a biological variable to strengthen conclusions.

The effects of inorganic nitrate supplementation on exercise economy and endurance capacity across the menstrual cycle.

Oral inorganic nitrate (NO3-) supplementation has been shown to increase bioavailable NO and provide potential ergogenic benefits in males; however, data in females is scarce. Estrogen is known to increase endogenous NO bioavailability and to fluctuate throughout the menstrual cycle (MC), being lowest in the early follicular (EF) phase and highest during the late follicular (LF) phase. This study examined the effects of oral NO3- supplementation on exercise economy, endurance capacity, and vascular health in young females across the MC. Ten normally menstruating females' MCs were tested in a double-blinded, randomized design during both the EF and LF phases of the MC. Participants consumed ∼13 mmol NO3-, in the form of 140 mL beetroot juice (BRJ) or an identical NO3--depleted placebo (PL) for ∼3 days before lab visits and 2 h before testing on lab visits. Plasma nitrate, nitrite, and estradiol were assessed, as was blood pressure and pulse wave velocity. Moderate-intensity exercise economy and severe intensity time to exhaustion (TTE) were tested on a cycle ergometer. As expected, plasma estradiol was elevated in the LF phase, and plasma nitrite and nitrate were elevated in the BRJ condition. Exercise economy was unaltered by BRJ or the MC, however TTE was significantly worsened by 48 s (∼10%) after BRJ supplementation (P = 0.04), but was not different across the MC with no interaction effects. In conclusion, NO3- supplementation did not affect exercise economy or vascular health and worsened aerobic endurance capacity (TTE), suggesting healthy females should proceed with caution when considering supplementation with BRJ.NEW & NOTEWORTHY Although inorganic nitrate (NO3-) supplementation has increased in popularity as a means of improving exercise performance, data in females at different phases of the menstrual cycle are lacking despite known interactions of estrogen with NO. This study revealed neither NO3- supplementation nor the menstrual cycle influenced exercise economy or vascular health in healthy young naturally menstruating females, while NO3- supplementation significantly worsened endurance capacity (10%) independent of the menstrual cycle phase.

Human skeletal muscle nitrate and nitrite in individuals with peripheral arterial disease: Effect of inorganic nitrate supplementation and exercise.

Skeletal muscle may act as a reservoir for N-oxides following inorganic nitrate supplementation. This idea is most intriguing in individuals with peripheral artery disease (PAD) who are unable to endogenously upregulate nitric oxide. This study analyzed plasma and skeletal muscle nitrate and nitrite concentrations along with exercise performance, prior to and following 12-weeks of exercise training combined with oral inorganic nitrate supplementation (EX+BR) or placebo (EX+PL) in participants with PAD. Non-supplemented, at baseline, there were no differences in plasma and muscle nitrate. For nitrite, muscle concentration was higher than plasma (+0.10 nmol.g-1 ). After 12 -weeks, acute oral nitrate increased both plasma and muscle nitrate (455.04 and 121.14 nmol.g-1 , p < 0.01), which were correlated (r = 0.63, p < 0.01), plasma nitrate increase was greater than in muscle (p < 0.01). Nitrite increased in the plasma (1.01 nmol.g-1 , p < 0.05) but not in the muscle (0.22 nmol.g-1 ) (p < 0.05 between compartments). Peak walk time (PWT) increased in both groups (PL + 257.6 s;BR + 315.0 s). Six-minute walk (6 MW) distance increased only in the (EX+BR) group (BR + 75.4 m). We report no substantial gradient of nitrate (or nitrite) from skeletal muscle to plasma, suggesting a lack of reservoir-like function in participants with PAD. Oral nitrate supplementation produced increases in skeletal muscle nitrate, but not skeletal muscle nitrite. The related changes in nitrate concentration between plasma and muscle suggests a potential for inter-compartmental nitrate "communication". Skeletal muscle did not appear to play a role in within compartment nitrate reduction. Muscle nitrate and nitrite concentrations did not appear to contribute to exercise performance in patients with PAD.

Dietary Inorganic Nitrate as an Ergogenic Aid: An Expert Consensus Derived via the Modified Delphi Technique.

INTRODUCTION: Dietary inorganic nitrate is a popular nutritional supplement, which increases nitric oxide bioavailability and may improve exercise performance. Despite over a decade of research into the effects of dietary nitrate supplementation during exercise there is currently no expert consensus on how, when and for whom this compound could be recommended as an ergogenic aid. Moreover, there is no consensus on the safe administration of dietary nitrate as an ergogenic aid. This study aimed to address these research gaps. METHODS: The modified Delphi technique was used to establish the views of 12 expert panel members on the use of dietary nitrate as an ergogenic aid. Over three iterative rounds (two via questionnaire and one via videoconferencing), the expert panel members voted on 222 statements relating to dietary nitrate as an ergogenic aid. Consensus was reached when > 80% of the panel provided the same answer (i.e. yes or no). Statements for which > 80% of the panel cast a vote of insufficient evidence were categorised as such and removed from further voting. These statements were subsequently used to identify directions for future research. RESULTS: The 12 panel members contributed to voting in all three rounds. A total of 39 statements (17.6%) reached consensus across the three rounds (20 yes, 19 no). In round one, 21 statements reached consensus (11 yes, 10 no). In round two, seven further statements reached consensus (4 yes, 3 no). In round three, an additional 11 statements reached consensus (5 yes, 6 no). The panel agreed that there was insufficient evidence for 134 (60.4%) of the statements, and were unable to agree on the outcome of the remaining statements. CONCLUSIONS: This study provides information on the current expert consensus on dietary nitrate, which may be of value to athletes, coaches, practitioners and researchers. The effects of dietary nitrate appear to be diminished in individuals with a higher aerobic fitness (peak oxygen consumption [V̇O2peak] > 60 ml/kg/min), and therefore, aerobic fitness should be taken into account when considering use of dietary nitrate as an ergogenic aid. It is recommended that athletes looking to benefit from dietary nitrate supplementation should consume 8-16 mmol nitrate acutely or 4-16 mmol/day nitrate chronically (with the final dose ingested 2-4 h pre-exercise) to maximise ergogenic effects, taking into consideration that, from a safety perspective, athletes may be best advised to increase their intake of nitrate via vegetables and vegetable juices. Acute nitrate supplementation up to ~ 16 mmol is believed to be safe, although the safety of chronic nitrate supplementation requires further investigation. The expert panel agreed that there was insufficient evidence for most of the appraised statements, highlighting the need for future research in this area.

Impact of a Novel Training Approach on Hemodynamic and Vascular Profiles in Older Adults.

Exercise training beneficially moderates the effects of vascular aging. This study compared the efficacy of Peripheral Remodeling through Intermittent Muscular Exercise (PRIME), a novel training regimen, versus aerobic training on hemodynamic profiles in participants ≥70 years at risk for losing functional independence. Seventy-five participants (52 females, age: 76 ± 5 years) were assessed for hemodynamic and vascular function at baseline, after 4 weeks of either PRIME or aerobic training (Phase 1) and again after a further 8 weeks of aerobic and resistance training (Phase 2). Data were analyzed using 2 × 2 repeated-measures analysis of variance models on the change in each dependent variable. PRIME demonstrated reductions in brachial and aortic mean arterial pressure and diastolic blood pressure (p < .05) from baseline after Phase 1, which were sustained throughout Phase 2. Earlier and greater reductions in blood pressure following PRIME support the proposal that peripheral muscular training could beneficial for older individuals commencing an exercise program.

The effect of acute exercise on pre-prandial ghrelin levels in healthy adults: A systematic review and meta-analysis.

BACKGROUND: Ghrelin is a gut hormone with numerous physiological effects, including the regulation of energy balance, insulin sensitivity, vascular health, and body composition. Acylated (AG) and des-acylated (DAG) ghrelin constitute approximately 22 % and 78 % of total plasma ghrelin (TG), respectively. Alterations in the TG concentration and the AG/DAG ratio may be implicated in conditions involving energy imbalances and insulin resistant states (e.g., metabolic syndrome or Type 2 diabetes mellitus). Exercise is a therapeutic option that can potentially optimize ghrelin levels. Understanding the precise intensity and dose of exercise to optimize ghrelin levels may lead to targeted interventions to restore metabolic regulation in obesity and other clinical conditions. OBJECTIVE: To perform a systematic review and meta-analysis on the effects of acute exercise on pre-prandial levels of TG, AG, and DAG in healthy adults and to determine if sample demographics or exercise doses moderate such effects. METHODS: Electronic databases (PubMed, Medline, SPORTDiscus, Web of Science, and Google Scholar) were searched with articles published through August 2020. The following criteria was determined a priori for article inclusion: (i) the study was a randomized controlled trial (RCT),(ii) exercise was an acute bout, (iii) the exercise bout for the intervention group(s)/condition was structured, (iv) the control group/condition received no exercise, (v) participants were adults age 18 or older, (vi) ghrelin was sampled through blood, (vii) there was at least one baseline measure and one post-exercise measure of ghrelin, (viii) there were at least 3 timepoints where ghrelin was measured while participants were fasted to allow for pre-prandial total area-under-the-curve (AUCtotal) calculation, (ix) participants were healthy with no overt disease, (x) interventions were carried out without any environmental manipulations. Standardized mean difference (SMD) with 95 % confidence intervals were calculated using the restricted maximum likelihood estimation Moderator analyses to determine whether the overall pooled effect was influenced by: sex, ghrelin form, method of ghrelin analysis, age, body mass index, body fat percentage, fitness, intensity of exercise bout, duration of exercise bout, energy expenditure, and length of AUCtotal data. RESULTS: The analysis included 24 studies that consisted of 52 trials, n = 504 (age 27.0 (8.8) years, BMI 24.7 (2.7) kg/m2) and measured AG (n = 38 trials), DAG (n = 7), and TG (n = 7). The overall model indicated that exercise lowered ghrelin levels compared to control (no exercise); (SMD=-0.44, p < 0.001), and exercise intensity exhibited an inverse relationship with ghrelin levels (regression coefficient (ß)=-0.016, p = 0.04). There was no significant difference by ghrelin form (p = 0.18). DISCUSSION: Acute exercise significantly lowers plasma ghrelin levels, with higher intensity exercise associated with greater ghrelin suppression. The majority of studies applied a moderate intensity exercise bout and measured AG, with limited data on DAG. This exercise dose may be clinically significant in individuals with metabolic dysregulation and energy imbalance as a therapy to optimize AG levels. More work is needed to compare moderate and high intensity exercise and the ghrelin response in clinical populations.

Aerobic Versus Resistance Training Effects on Ventricular-Arterial Coupling and Vascular Function in the STRRIDE-AT/RT Trial.

Background: The goal was studying the differential effects of aerobic training (AT) vs. resistance training (RT) on cardiac and peripheral arterial capacity on cardiopulmonary (CP) and peripheral vascular (PV) function in sedentary and obese adults. Methods: In a prospective randomized controlled trial, we studied the effects of 6 months of AT vs. RT in 21 subjects. Testing included cardiac and vascular ultrasoundography and serial CP for ventricular-arterial coupling (Ees/Ea), strain-based variables, brachial artery flow-mediated dilation (BAFMD), and peak VO2 (pVO2; mL/kg/min) and peak O2-pulse (O2p; mL/beat). Results: Within the AT group (n = 11), there were significant increases in rVO2 of 4.2 mL/kg/min (SD 0.93) (p = 0.001); O2p of 1.9 mL/beat (SD 1.3) (p = 0.008) and the brachial artery post-hyperemia peak diameter 0.18 mm (SD 0.08) (p = 0.05). Within the RT group (n = 10) there was a significant increase in left ventricular end diastolic volume 7.0 mL (SD 9.8; p = 0.05) and percent flow-mediated dilation (1.8%) (SD 0.47) (p = 0.004). Comparing the AT and RT groups, post exercise, rVO2 2.97, (SD 1.22), (p = 0.03), O2p 0.01 (SD 1.3), (p = 0.01), peak hyperemic blood flow volume (1.77 mL) (SD 140.69) (p = 0.009), were higher in AT, but LVEDP 115 mL (SD 7.0) (p = 0.05) and Ees/Ea 0.68 mmHg/ml (SD 0.60) p = 0.03 were higher in RT. Discussion: The differential effects of AT and RT in this hypothesis generating study have important implications for exercise modality and clinical endpoints.

Effects of inorganic nitrate supplementation on cardiovascular function and exercise tolerance in heart failure.

Heart failure (HF) results in a myriad of central and peripheral abnormalities that impair the ability to sustain skeletal muscle contractions and, therefore, limit tolerance to exercise. Chief among these abnormalities is the lowered maximal oxygen uptake, which is brought about by reduced cardiac output and exacerbated by O2 delivery-utilization mismatch within the active skeletal muscle. Impaired nitric oxide (NO) bioavailability is considered to play a vital role in the vascular dysfunction of both reduced and preserved ejection fraction HF (HFrEF and HFpEF, respectively), leading to the pursuit of therapies aimed at restoring NO levels in these patient populations. Considering the complementary role of the nitrate-nitrite-NO pathway in the regulation of enzymatic NO signaling, this review explores the potential utility of inorganic nitrate interventions to increase NO bioavailability in the HFrEF and HFpEF patient population. Although many preclinical investigations have suggested that enhanced reduction of nitrite to NO in low Po2 and pH environments may make a nitrate-based therapy especially efficacious in patients with HF, inconsistent results have been found thus far in clinical settings. This brief review provides a summary of the effectiveness (or lack thereof) of inorganic nitrate interventions on exercise tolerance in patients with HFrEF and HFpEF. Focus is also given to practical considerations and current gaps in the literature to facilitate the development of effective nitrate-based interventions to improve exercise tolerance in patients with HF.

Skeletal muscle capillary density is related to anaerobic threshold and claudication in peripheral artery disease.

Peripheral artery disease (PAD) is characterized by impaired blood flow to the lower extremities, causing claudication and exercise intolerance. Exercise intolerance may result from reduced skeletal muscle capillary density and impaired muscle oxygen delivery. This cross-sectional study tested the hypothesis that capillary density is related to claudication times and anaerobic threshold (AT) in patients with PAD. A total of 37 patients with PAD and 29 control subjects performed cardiopulmonary exercise testing on a treadmill for AT and gastrocnemius muscle biopsies. Skeletal muscle capillary density was measured using immunofluorescence staining. PAD had decreased capillary density (278 ± 87 vs 331 ± 86 endothelial cells/mm2, p = 0.05), peak VO2 (15.7 ± 3.9 vs 24.3 ± 5.2 mL/kg/min, p ⩽ 0.001), and VO2 at AT (11.5 ± 2.6 vs 16.1 ± 2.8 mL/kg/min, p ⩽ 0.001) compared to control subjects. In patients with PAD, but not control subjects, capillary density was related to VO2 at AT (r = 0.343; p = 0.038), time to AT (r = 0.381; p = 0.020), and time after AT to test termination (r = 0.610; p ⩽ 0.001). Capillary density was also related to time to claudication (r = 0.332; p = 0.038) and time after claudication to test termination (r = 0.584; p ⩽ 0.001). In conclusion, relationships between capillary density, AT, and claudication symptoms indicate that, in PAD, exercise limitations are likely partially dependent on limited skeletal muscle capillary density and oxidative metabolism.

The Effect of Dietary Inorganic Nitrate Supplementation on Cardiac Function during Submaximal Exercise in Men with Heart Failure with Reduced Ejection Fraction (HFrEF): A Pilot Study.

Heart failure with reduced ejection fraction (HFrEF) is a common end point for patients with coronary artery disease and it is characterized by exercise intolerance due, in part, to a reduction in cardiac output. Nitric oxide (NO) plays a vital role in cardiac function and patients with HFrEF have been identified as having reduced vascular NO. This pilot study aimed to investigate if nitrate supplementation could improve cardiac measures during acute, submaximal exercise. Five male participants (61 ± 3 years) with HFrEF (EF 32 ± 2.2%) completed this pilot study. All participants supplemented with inorganic nitrate (beetroot juice) or a nitrate-depleted placebo for ~13 days prior to testing. Participants completed a three-stage submaximal exercise protocol on a recumbent cycle ergometer with simultaneous echocardiography for calculation of cardiac output (Q), stroke volume (SV), and total peripheral resistance (TPR). Heart rate and blood pressure were measured at rest and during each stage. Both plasma nitrate (mean = ~1028%, p = 0.004) and nitrite (mean = ~109%, p = 0.01) increased following supplementation. There were no differences between interventions at rest, but the percent change in SV and Q from rest to stage two and stage three of exercise was higher following nitrate supplementation (all p > 0.05, ES > 0.8). Both interventions showed decreases in TPR during exercise, but the percent reduction TPR in stages two and three was greater following nitrate supplementation (p = 0.09, ES = 0.98 and p = 0.14, ES = 0.82, respectively). There were clinically relevant increases in cardiac function during exercise following supplementation with nitrate. The findings from this pilot study warrant further investigation in larger clinical trials.

Effect of inorganic nitrate on exercise capacity, mitochondria respiration, and vascular function in heart failure with reduced ejection fraction.

Chronic underperfusion of the skeletal muscle tissues is a contributor to a decrease in exercise capacity in patients with heart failure with reduced ejection fraction (HFrEF). This underperfusion is due, at least in part, to impaired nitric oxide (NO) bioavailability. Oral inorganic nitrate supplementation increases NO bioavailability and may be used to improve exercise capacity, vascular function, and mitochondrial respiration. Sixteen patients with HFrEF (fifteen men, 63 ± 4 yr, body mass index: 31.8 ± 2.1 kg/m2) participated in a randomized, double-blind, crossover design study. Following consumption of either nitrate-rich beetroot juice (16 mmol nitrate/day) or a nitrate-depleted placebo for 5 days, participants completed separate visits for assessment of exercise capacity, endothelial function, and muscle mitochondrial respiration. Participants then had a 2-wk washout before completion of the same protocol with the other intervention. Statistical significance was set a priori at P < 0.05, and between-treatment differences were analyzed via paired t test analysis. Following nitrate supplementation, both plasma nitrate and nitrite increased (933%, P < 0.001 and 94%, P < 0.05, respectively). No differences were observed for peak oxygen consumption (nitrate: 18.5 ± 1.4 mL·kg-1·min-1, placebo: 19.3 ± 1.4 mL·kg-1·min-1; P = 0.13) or time to exhaustion (nitrate: 1,165 ± 92 s, placebo: 1,207 ± 96 s; P = 0.16) following supplementation. There were no differences between interventions for measures of vascular function, mitochondrial respiratory function, or protein expression (all P > 0.05). Inorganic nitrate supplementation did not improve exercise capacity and skeletal muscle mitochondrial respiratory function in HFrEF. Future studies should explore alternative interventions to improve peripheral muscle tissue function in HFrEF.NEW & NOTEWORTHY This is the largest study to date to examine the effects of inorganic nitrate supplementation in patients with heart failure with reduced ejection fraction (HFrEF) and the first to include measures of vascular function and mitochondrial respiration. Although daily supplementation increased plasma nitrite, our data indicate that supplementation with inorganic nitrate as a standalone treatment is ineffective at improving exercise capacity, vascular function, or mitochondrial respiration in patients with HFrEF.

Acute Dietary Nitrate Supplementation Improves Flow Mediated Dilatation of the Superficial Femoral Artery in Healthy Older Males.

Aging is often associated with reduced leg blood flow, increased arterial stiffness, and endothelial dysfunction, all of which are related to declining nitric oxide (NO) bioavailability. Flow mediated dilatation (FMD) and passive leg movement (PLM) hyperaemia are two techniques used to measure NO-dependent vascular function. We hypothesised that acute dietary nitrate (NO3-) supplementation would improve NO bioavailability, leg FMD, and PLM hyperaemia. Fifteen healthy older men (69 ± 4 years) attended two experiment sessions and consumed either 140 mL of concentrated beetroot juice (800 mg NO3-) or placebo (NO3--depleted beetroot juice) in a randomised, double blind, cross-over design study. Plasma nitrite (NO2-) and NO3-, blood pressure (BP), augmentation index (AIx75), pulse wave velocity (PWV), FMD of the superficial femoral artery, and PLM hyperaemia were measured immediately before and 2.5 h after consuming NO3- and placebo. Placebo had no effect but NO3- led to an 8.6-fold increase in plasma NO2-, which was accompanied by an increase in FMD (NO3-: +1.18 ± 0.94% vs. placebo: 0.23 ± 1.13%, p = 0.002), and a reduction in AIx75 (NO3-: -8.7 ± 11.6% vs. placebo: -4.6 ± 5.5%, p = 0.027). PLM hyperaemia, BP, and PWV were unchanged during both trials. This study showed that a dose of dietary NO3- improved NO bioavailability and enhanced endothelial function as measured by femoral artery FMD. These findings provide insight into the specific central and peripheral vascular responses to dietary NO3- supplementation in older adults.

Beet the Best?

RATIONALE: A primary goal of therapy for patients with peripheral artery disease (PAD) and intermittent claudication is increased ambulatory function. Supervised exercise rehabilitation was recently shown to confer superior walking benefits to pharmacological or surgical interventions. Increases in plasma inorganic nitrite, via oral nitrate, have been shown to increase exercise performance in both human and animal models, especially in hypoxic conditions. OBJECTIVE: To determine whether a 36-session exercise rehabilitation program while consuming oral inorganic nitrate (4.2 mmol concentrated beetroot juice) would produce superior benefits over exercise plus placebo in pain-free walking and markers of increased skeletal muscle perfusion in patients with PAD and intermittent claudication. METHODS AND RESULTS: This was a randomized, double-blind, per-protocol study design. After the 12-week protocol, claudication onset time on a maximal treadmill test increased by 59.2±57.3 s for the exercise plus placebo group (n=13) and by 180.3±46.6 s for the exercise plus beetroot juice group (n=11; P≤0.05). This produced a between treatment medium to large standardized effect size (Cohen d) of 0.62 (95% CI, -0.23 to +1.44). The data for 6-minute walk distance showed a similar pattern with increases of 24.6±12.1 and 53.3±19.6 m ( P≤0.05) in the exercise plus placebo and exercise plus beetroot juice groups, respectively. Measures of gastrocnemius perfusion, including ankle-brachial index, peak reactive hyperemic blood flow, and tissue deoxygenation characteristics, during exercise (assessed my near-infrared spectroscopy) all changed significantly for the exercise plus beetroot juice group with moderate-to-large effect sizes over exercise plus placebo changes. CONCLUSIONS: Although it is premature to speculate on overall clinical utility of a nitrate-based therapy for PAD, this early pilot study evidence is encouraging. Specifically, our data suggests that increasing plasma nitrite before exercise may allow PAD subjects to train with less pain, at higher workloads for longer durations at each training session, thereby maximizing the beneficial peripheral vascular and skeletal muscle adaptations. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov . Unique identifier: NCT01684930 and NCT01785524.

Research Toolbox for Peripheral Arterial Disease　- Minimally Invasive Assessment of the Vasculature and Skeletal Muscle.

In 2010, more than 200 million people were afflicted with peripheral arterial disease (PAD). Because it is atherosclerotic in etiology, it is not surprising that PAD is a leading cause of cardiovascular morbidity. Cardiovascular disease (CVD) risk can be decreased if ambulatory physical function is improved. However, physical function is limited by a mismatch between oxygen supply and demand in the legs, which results in exertional pain, leg weakness, and balance problems. Therefore, a key factor for improving physical function, and decreasing CVD outcomes, is ensuring oxygen supply meets the oxygen demand. The purpose of this review is to highlight and evaluate practical and minimally invasive tools for assessing PAD etiology, with a specific focus on tools suited to studies focusing on improving physical function and CVD outcomes. Specifically, the macrovascular, microvascular, and skeletal muscle pathology of PAD is briefly outlined. Subsequently, the tools for assessing each of these components is discussed, including, where available, the evidence to contextualize these tools to PAD pathology as well as physical function and CVD outcomes. The goal of this review is to guide researchers to the appropriate tools with respect to their methodological design.

Effect of dietary nitrate supplementation on conduit artery blood flow, muscle oxygenation, and metabolic rate during handgrip exercise.

Dietary nitrate supplementation has positive effects on mitochondrial and muscle contractile efficiency during large muscle mass exercise in humans and on skeletal muscle blood flow (Q̇) in rats. However, concurrent measurement of these effects has not been performed in humans. Therefore, we assessed the influence of nitrate supplementation on Q̇ and muscle oxygenation characteristics during moderate- (40 %peak) and severe-intensity(85% peak) handgrip exercise in a randomized, double-blind, crossover design. Nine healthy men (age: 25 ± 2 yr) completed four constant-power exercise tests (2/intensity) randomly assigned to condition [nitrate-rich (nitrate) or nitrate-poor (placebo) beetroot supplementation] and intensity (40 or 85% peak). Resting mean arterial pressure was lower after nitrate compared with placebo (84 ± 4 vs. 89 ± 4 mmHg, P < 0.01). All subjects were able to sustain 10 min of exercise at 40% peak in both conditions. Nitrate had no effect on exercise tolerance during 85% peak (nitrate: 358 ± 29; placebo: 341 ± 34 s; P = 0.3). Brachial artery Q̇ was not different after nitrate at rest or any time during exercise. Deoxygenated [hemoglobin + myoglobin] was not different for 40% peak ( P > 0.05) but was elevated throughout 85% peak ( P < 0.05) after nitrate. The metabolic cost (V̇o2) was not different at the end of exercise; however, the V̇o2 primary amplitude at the onset of exercise was elevated after nitrate for the 85% peak work rate (96 ± 20 vs. 72 ± 12 ml/min, P < 0.05) and had a faster response. These findings suggest that an acute dose of nitrate reduces resting blood pressure and speeds V̇o2 kinetics in young adults but does not augment Q̇ or reduce steady-state V̇o2 during small muscle mass handgrip exercise. NEW & NOTEWORTHY We show that acute dietary nitrate supplementation via beetroot juice increases the amplitude and speed of local muscle V̇o2 on kinetics parameters during severe- but not moderate-intensity handgrip exercise. These changes were found in the absence of an increased blood flow response, suggesting that the increased V̇o2 was attained via improvements in fractional O2 extraction and/or spatial distribution of blood flow within the exercising muscle.

Effects of Dietary Inorganic Nitrate Supplementation on Exercise Performance in Patients With Heart Failure: Protocol for a Randomized, Placebo-Controlled, Cross-Over Trial.

BACKGROUND: Chronic heart failure is characterized by an inability of the heart to pump enough blood to meet the demands of the body, resulting in the hallmark symptom of exercise intolerance. Chronic underperfusion of the peripheral tissues and impaired nitric oxide bioavailability have been implicated as contributors to the decrease in exercise capacity in these patients. nitric oxide bioavailability has been identified as an important mediator of exercise tolerance in healthy individuals, but there are limited studies examining the effects in patients with chronic heart failure. OBJECTIVE: The proposed trial is designed to determine the effects of chronic inorganic nitrate supplementation on exercise tolerance in both patients with heart failure preserved ejection fraction (HFpEF) and heart failure reduced ejection fraction (HFrEF) and to determine whether there are any differential responses between the 2 cohorts. A secondary objective is to provide mechanistic insights into the 2 heart failure groups' exercise responses to the nitrate supplementation. METHODS: Patients with chronic heart failure (15=HFpEF and 15=HFrEF) aged 40 to 85 years will be recruited. Following an initial screen cardiopulmonary exercise test, participants will be randomly allocated in a double-blind fashion to consume either a nitrate-rich beetroot juice (16 mmol nitrate/day) or a nitrate-depleted placebo (for 5 days). Participants will continue daily dosing until the completion of the 4 testing visits (maximal cardiopulmonary exercise test, submaximal exercise test with echocardiography, vascular function assessment, and vastus lateralis muscle biopsy). There will then be a 2-week washout period after which the participants will cross over to the other treatment and complete the same 4 testing visits. RESULTS: This study is funded by National Heart Foundation of Australia and Victoria University. Enrolment has commenced and the data collection is expected to be completed in mid 2018. The initial results are expected to be submitted for publication by the end of 2018. CONCLUSIONS: If inorganic nitrate supplementation can improve exercise tolerance in patients with chronic heart failure, it has the potential to aid in further refining the treatment of patients in this population. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry ACTRN12615000906550; https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=368912 (Archived by WebCite at http://www.webcitation.org/6xymLMiFK).