Nitrate-rich beetroot juice ingestion reduces skeletal muscle O2 uptake and blood flow during exercise in sedentary men

Evidence-based sports supplements: A redox analysis

Despite the overwhelming number of sports supplements on the market, only seven are currently recognized as effective. Biological functions are largely regulated through redox reactions, yet no comprehensive analysis of the redox properties of these supplements has been compiled. Here, we analyze the redox characteristics of these seven supplements: bicarbonates, beta-alanine, caffeine, creatine, nitrates, carbohydrates, and proteins. Our findings suggest that all sports supplements exhibit some degree of redox activity. However, the precise physiological implications of these redox properties remain unclear. Future research, employing unconventional perspectives and methodologies, will reveal new redox pixels of the exercise physiology and sports nutrition picture.

Acute antioxidant supplementation and performance - Should this be considered

It is well known that a training intervention leads to mitochondrial adaptations with increased skeletal muscle mitochondrial biogenesis and function. Studies have recently indicated that skeletal muscle mitochondrial function is important for athletic performance. During exercise reactive oxygen species are released from skeletal muscle potentially leading to adaptations but maybe also to fatigue. Focus has been on how chronic antioxidant supplementation affects a training adaptation, where some studies are reporting an abolished adaptation. Whether acute antioxidant supplementation could have a positive effect on fatigue and performance is interesting and highly relevant in sports where athletes are competing over several consecutive days or on the same day, with preliminary competitions in the morning and finals in the afternoon, where it is important for the athletes to recover fast. This review provides an overview of the effects of acute antioxidant supplementation and whether it leads to improved performance and/or faster recovery in humans.

Sodium Nitrate Improves Oxidative Energy Contribution and Reduces Phosphocreatine Contribution During High-Intensity Intermittent Exercise

The present study aimed to verify the effect of acute nitrate supplementation on oxidative, phosphocreatine, and glycolytic energy contribution (COXI, CPCr, and CLAC, respectively) during a high-intensity intermittent exercise (HIIE). Fifteen physically active subjects were submitted to incremental running test on a treadmill and two random HIIE (10 × 1 min at maximal aerobic speed with 1 min of passive recovery) in the following conditions: sodium nitrate (SN) or Placebo (PL). Repeated measure ANOVA was used to compare COXI, and CPCr within the 10 efforts. Student t test was used to compare total COXI, CPCr, CLAC, as well oxidative and non-oxidative contribution. Considering the 10 efforts, COXI presented the main effect for condition (F = 16.7; p = .001; SN: 1.9 ± 0.1 L; PL: 1.6 ± 0.1 L), and no interaction effect (F = 0.9; p = .415), while CPCr presented effect for condition (F = 13.4; p = .003; SN: 1.2 ± 0.1; PL: 1.4 ± 0.8 L), and no interaction (F = 1.2; p = .317). Total oxidative contribution were higher (p < .001) after SN (19.1 ± 3.4 L) than Placebo (16.7 ± 3.1 L), while total CPCr were lower (p = .002) after SN (12.4 ± 2.5 L) than PL (14.1 ± 2.6 L). Total energy contribution were not different between trials. Acute dose of SN supplementation improved oxidative contribution during HIIE, and reduced CPCr. Higher COXI is likely related to increased oxygen kinetics, while the lower CPCr might be related to the improved energetic efficiency.

Influence of acute dietary nitrate supplementation on oxygen delivery/consumption and critical impulse during maximal effort forearm exercise in males: a randomized crossover trial

Beetroot juice supplementation (BRJ) should increase nitric oxide bioavailability under conditions of muscle deoxygenation and acidosis that are a normal consequence of the maximal effort exercise test used to identify forearm critical impulse. We hypothesized BRJ would improve oxygen delivery:demand matching and forearm critical impulse performance. Healthy males (20.8 ± 2.4 years) participated in a randomized crossover trial between October 2017 and May 2018 (Queen's University, Kingston, ON). Participants completed 10 min of rhythmic maximal effort forearm handgrip exercise 2.5 h post placebo (PL) vs. BRJ (9 completed PL/BRJ vs. 4 completed BRJ/PL) within a 2 week period. Data are presented as mean ± SD. There was a main effect of drink (PL > BRJ) for oxygen extraction (P = 0.033, ηp2 = 0.351) and oxygen consumption/force (P = 0.017, ηp2 = 0.417). There was a drink × time interaction (PL > BRJ) for oxygen consumption/force (P = 0.035, ηp2 = 0.216) between 75 and 360 s (1.25-6 min) from exercise onset. BRJ did not influence oxygen delivery (P = 0.953, ηp2 = 0.000), oxygen consumption (P = 0.064, ηp2 = 0.278), metabolites ((lactate) (P = 0.196, ηp2 = 0.135), pH (P = 0.759, ηp2 = 0.008)) or power-duration performance parameters (critical impulse (P = 0.379, d = 0.253), W' (P = 0.733, d = 0.097)). BRJ during all-out handgrip exercise does not influence oxygen delivery or exercise performance. Oxygen cost of contraction with BRJ is reduced as contraction impulse is declining during maximal effort exercise resulting in less oxygen extraction.

Effects of dietary nitrate supplementation on peak power output: Influence of supplementation strategy and population

Increasing evidence indicates that dietary nitrate supplementation has the potential to increase muscular power output during skeletal muscle contractions. However, there is still a paucity of data characterizing the impact of different nitrate dosing regimens on nitric oxide bioavailability and its potential ergogenic effects across various population groups. This review discusses the potential influence of different dietary nitrate supplementation strategies on nitric oxide bioavailability and muscular peak power output in healthy adults, athletes, older adults and some clinical populations. Effect sizes were calculated for peak power output and absolute and/or relative nitrate doses were considered where applicable. There was no relationship between the effect sizes of peak power output change following nitrate supplementation and when nitrate dosage when considered in absolute or relative terms. Areas for further research are also recommended including a focus on nitrate dosing regimens that optimize nitric oxide bioavailability for enhancing peak power at times of increased muscular work in a variety of healthy and disease populations.

Effect of Beetroot Juice Supplementation on Muscle Soreness and Performance Recovery after Exercise-Induced Muscle Damage in Female Volleyball Players

BACKGROUND

Beetroot juice (BRJ) contains various bioactive compounds suggested to be effective in improving athlete recovery. However, the number of studies evaluating the effects of BRJ on recovery and muscle soreness (MS) indicators in female athletes is limited. Therefore, the present study aimed to determine the effects of BRJ consumption on the performance recovery indicators and MS after exercise-induced muscle damage (EIMD) in female volleyball players.

METHODS

Twelve young female volleyball players were evaluated in this study. We utilized a randomized, cross-over, and double-blind design during two phases with a 30-day interval (wash-out). During each phase, EIMD was performed first, followed by BRJ or placebo (PLA) supplementation for two days (eight servings of 50 mL). Recovery monitoring of performance indicators and MS was performed after EIMD. The results of wall-sit, V sit and reach (VSFT), vertical jump height (VJH), pressure pain threshold (PPT), and thigh swelling (Sw-T) tests were recorded 48 h after EIMD. Also, the Perceived Muscle Soreness was recorded using the visual analog scale (VAS) 12 (MS-12 h), 24 (MS-24 h), and 48 (MS-48 h) hours after EIMD.

RESULTS

The data were analyzed using two-way repeated measures of ANOVA at p < 0.05. Compared to PLA, BRJ supplementation improves wall-sit performance after EIMD (p < 0.05), while reducing Sw-T and perceived muscle soreness (p < 0.05). However, no significant difference was observed between PLA and BRJ in VJH and VSFT performance after EIMD (p > 0.05).

CONCLUSIONS

Our findings indicate that the consumption of BRJ in female volleyball players can be useful for improving some recovery indicators, such as muscle endurance, perceived muscle soreness, and tissue edema, after EIMD.

Effects of Dietary Nitrate Supplementation on Performance during Single and Repeated Bouts of Short-Duration High-Intensity Exercise: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Inorganic nitrate (NO₃^-) has emerged as a potential ergogenic aid over the last couple of decades. While recent systematic reviews and meta-analyses have suggested some small positive effects of NO₃^- supplementation on performance across a range of exercise tasks, the effect of NO₃^- supplementation on performance during single and repeated bouts of short-duration, high-intensity exercise is unclear. This review was conducted following PRISMA guidelines. MEDLINE and SPORTDiscus were searched from inception to January 2023. A paired analysis model for cross-over trials was incorporated to perform a random effects meta-analysis for each performance outcome and to generate standardized mean differences (SMD) between the NO₃^- and placebo supplementation conditions. The systematic review and meta-analysis included 27 and 23 studies, respectively. Time to reach peak power (SMD: 0.75, p = 0.02), mean power output (SMD: 0.20, p = 0.02), and total distance covered in the Yo-Yo intermittent recovery level 1 test (SMD: 0.17, p < 0.0001) were all improved after NO₃^- supplementation. Dietary NO₃^- supplementation had small positive effects on some performance outcomes during single and repeated bouts of high-intensity exercise. Therefore, athletes competing in sports requiring single or repeated bouts of high-intensity exercise may benefit from NO₃^- supplementation.

Effects of dietary nitrate supplementation on muscular power output: Influence of supplementation strategy and population

Increasing evidence indicates that dietary nitrate supplementation has the potential to increase muscular power output during skeletal muscle contractions. However, there is still a paucity of data characterizing the impact of different nitrate dosing regimens on nitric oxide bioavailability its potential ergogenic effects across various population groups. This narrative review discusses the potential influence of different dietary nitrate supplementation strategies on nitric oxide bioavailability and muscular power output in healthy adults, athletes, older adults and some clinical populations. Areas for further research are also recommended including a focus individualized nitrate dosing regimens to optimize nitric oxide bioavailability and to promote muscular power enhancements in different populations.

Dietary nitrate supplementation enhances heavy load carriage performance in military cadets

PURPOSE

To determine the effects of dietary nitrate (NO₃^-) supplementation on physiological responses, cognitive function, and performance during heavy load carriage in military cadets.

METHODS

Ten healthy males (81.0 ± 6.5 kg; 180.0 ± 4.5 cm; 56.2 ± 3.7 ml·kg·min^-1 VO_2max) consumed 140 mL·d^-1 of beetroot juice (BRJ; 12.8 mmol NO₃^-) or placebo (PL) for six d preceding an exercise trial, which consisted of 45 min of load carriage (55% body mass) at 4.83 km·h^-1 and 1.5% grade, followed by a 1.6-km time-trial (TT) at 4% grade. Gas exchange, heart rate, and perceptual responses were assessed during constant-load exercise and the TT. Cognitive function was assessed immediately prior to, during, and post-exercise via the psychomotor vigilance test (PVT).

RESULTS

Post-TT HR (188 ± 7.1 vs. 185 ± 7.4; d = 0.40; p = 0.03), mean tidal volume (2.15 ± 0.27 vs. 2.04 ± 0.23; p = 0.02; d = 0.47), and performance (770.9 ± 78.2 s vs. 809.8 ± 61.4 s; p = 0.03; d = 0.63) were increased during the TT with BRJ versus PL. There were no effects of BRJ on constant-load gas exchange or perceptual responses, and cognitive function was unchanged at all time points.

CONCLUSION

BRJ supplementation improves heavy load carriage performance in military cadets possibly as a result of attenuated respiratory muscle fatigue, rather than enhanced exercise economy.

Association of urinary nitrate with diabetes complication and disease-specific mortality among adults with hyperglycemia

BACKGROUND

The hyperglycemia condition disrupts the metabolism of nitrate/nitrite and nitric oxide, and dietary nitrate intake can restore nitric oxide homeostasis. This study aims to examine whether urinary nitrate is associated with diabetes complications and long-term survival among people with hyperglycemia.

METHODS

A total of 6208 people with hyperglycemia who participated in the National Health and Nutrition Examination Survey from 2005 to 2014 were enrolled. Diabetes complications included congestive heart failure, coronary heart disease, angina, stroke, myocardial infarction, diabetic retinopathy, and nephropathy. Mortality wasobtained from the National Death Index until 2015. Urinary nitrate was measured by ion chromatography coupled with electrospray tandem mass spectrometry, which was log-transformed and categized into tertiles. Logistic regression models and cox proportional hazards models were respectively performed to assess the association of urinary nitrate with the risk of diabetes complications and disease-specific mortalities.

RESULTS

After adjustment for potential confounders including urinary perchlorate and thiocyanate, compared with the participants in the lowest tertile of nitrate, the participants in the highest tertile had lower risks of congestive heart failure(odd-ratio[OR] = 0.41, 95%CI:0.27-0.60) and diabetic nephropathy(OR = 0.50, 95%CI: 0.41-0.62). Meanwhile, during a total follow-up of 41,463 person-year, the participants in the highest tertile had lower mortality risk of all-cause(hazard-ratio[HR] = 0.78, 95%CI:0.62-0.97), cardiovascular disease(CVD)(HR = 0.56, 95%CI:0.37-0.84) and diabetes(HR = 0.47, 95%CI:0.24-0.90), which showed dose-dependent linear relationships(P for non-linearity > 0.05). Moreover, no association between nitrate and cancer mortality was observed(HR = 1.13, 95%CI:0.71-1.80).

CONCLUSIONS

Higher urinary nitrate is associated with lower risk of congestive heart failure and diabetic nephropathy, and lower risk of all-cause, CVD, and diabetes mortalities. These findings indicated that inorganic nitrate supplementation can be considered as a supplementary treatment for people with hyperglycemia.

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.

Dietary Nitrate Supplementation and Small Muscle Mass Exercise Hemodynamics in Patients with Essential Hypertension

Exaggerated blood pressure and diminished limb hemodynamics during exercise in patients with hypertension often are not resolved by antihypertensive medications. We hypothesized that, independent of antihypertensive medication status, dietary nitrate supplementation would increase limb blood flow, decrease mean arterial pressure (MAP), and increase limb vascular conductance during exercise in patients with hypertension. Patients with hypertension either abstained from (n=14, Off-Meds) or continued (n=12, On-Meds) antihypertensive medications. Within each group, patients consumed (cross-over design) nitrate-rich or nitrate-depleted (placebo) beetroot juice for 3-days before performing handgrip (HG) and knee-extensor exercise (KE). Blood flow and MAP were measured using Doppler ultrasound and an automated monitor, respectively. Dietary nitrate increased plasma-[nitrite] Off-Meds and On-Meds. There were no significant effects of dietary nitrate on blood flow, MAP, or vascular conductance during HG in Off-Meds or On-Meds. For KE, dietary nitrate decreased MAP (mean±SD across all three exercise intensities, 118±14 vs. 122±14 mmHg, p=0.024) and increased vascular conductance (26.2±6.1 vs. 24.7±7.0 ml/min/mmHg, p=0.024), but did not affect blood flow for Off-Meds, with no effects On-Meds. Dietary nitrate-induced changes in blood flow (r=-0.67, p<0.001), MAP (r=-0.43, p=0.009), and vascular conductance (r=-0.64, p<0.001) during KE, but only vascular conductance (r=-0.35, p=0.039) during HG, were significantly related to the magnitude of placebo values, with no differentiation between groups. Thus, the effects of dietary nitrate on limb hemodynamics and MAP during exercise in patients with hypertension are dependent on the values at baseline, independent of antihypertensive medication status, and dependent on whether exercise was performed by the forearm or quadriceps.

Acute Beetroot Juice Supplementation Enhances Intermittent Running Performance but Does Not Reduce Oxygen Cost of Exercise among Recreational Adults

Nitrate (NO3−) supplementation has been reported to enhance intermittent exercise performance; however, its impact on oxygen (O2) cost during intermittent running exercise is unclear. The aim of this study was to assess if acute NO3− supplementation would elicit performance benefits in recreationally active individuals during the Yo−Yo intermittent recovery level 1 (Yo-Yo IR1) test, with its potential benefit on O2 consumption (VO2), in a double-blind, randomized, crossover study, 12 recreational males consumed NO3−-rich (NIT; ~12.8 mmol), and NO3−-depleted (PLA; 0.04 mmol) concentrated beetroot juice 3 h before completing the Yo-Yo IR1 test. VO2 was measured at 160, 280 and 440 m (sub-maximal) and when the test was terminated (peak). Performance in the Yo−Yo IR1 was greater with NIT (990 ± 442.25 m) compared to PLA (870 ± 357.4 m, p = 0.007). The VO2 was not significantly different at 160 m (1.92 ± 0.99 vs. 2.1 ± 0.88 L·min−1), 280 m (2.62 ± 0.94 vs. 2.83 ± 0.94 L·min−1), 440 m (3.26 ± 1.04 vs. 3.46 ± 0.98 L·min−1) and peak (4.71 ± 1.01 vs. 4.92 ± 1.17 L·min−1) between NIT and PLA trials (all p > 0.05). The present study has indicated that acute supplementation of NO3− enhanced intermittent running performance but had no effect on VO2 during the Yo−Yo IR1 test in recreational young adults.

Effect of beetroot or beetroot plus vitamin C supplementation on cardiovascular function in patients with coronary artery disease: protocol for a double-blind, placebo-controlled, randomised trial

INTRODUCTION

Coronary artery disease (CAD), classified into the atherosclerosis category, is a prevalent cardiovascular disease worldwide that is associated with serious comorbidities and death. The purpose of this study was to evaluate the effect of beetroot/beetroot plus vitamin C on cardiovascular health status and function in patients with CAD.

METHOD AND ANALYSIS

A randomised, placebo-controlled, double-blind clinical trial to recruit 90 patients with CAD at the cardiac outpatient clinic and Imam Reza Hospital, Mashhad, Iran. Participants will be divided into three groups: (1) Those who receive 500 mg three times a day of beetroot capsules, (2) Those who receive 500 mg three times a day of beetroot plus vitamin C capsules, and (3) Those who receive placebo capsules three times a day for 4 weeks. Pulse wave velocity, Augmentation Index, heart rate, volume of oxygen (VO₂) max/VO₂ peak, peak heart rate, blood pressure, interleukin 6 (IL-6), high sensitivity C reactive protein, intercellular adhesion molecule, vascular cell adhesion molecule, lipid profile and anthropometry will be measured at the beginning and end of the intervention.

ETHICS AND DISSEMINATION

This study was approved by the Ethics Committee of Mashhad University of Medical Sciences (IR.MUMS.MEDICAL.REC.1399.717). All participants will be asked to complete the consent form at the beginning of the study. The results will be actively disseminated through peer-reviewed journals and conference presentations.

TRIAL REGISTRATION NUMBER

Iranian Registry of Clinical Trials, IRCT20210217050393N1 (registered 16 May 2021).

Matching of O2 Utilization and O2 Delivery in Contracting Skeletal Muscle in Health, Aging, and Heart Failure

Skeletal muscle is one of the most dynamic metabolic organs as evidenced by increases in metabolic rate of >150-fold from rest to maximal contractile activity. Because of limited intracellular stores of ATP, activation of metabolic pathways is required to maintain the necessary rates of ATP re-synthesis during sustained contractions. During the very early phase, phosphocreatine hydrolysis and anaerobic glycolysis prevails but as activity extends beyond ∼1 min, oxidative phosphorylation becomes the major ATP-generating pathway. Oxidative metabolism of macronutrients is highly dependent on the cardiovascular system to deliver O₂ to the contracting muscle fibres, which is ensured through a tight coupling between skeletal muscle O₂ utilization and O₂ delivery. However, to what extent O₂ delivery is ideal in terms of enabling optimal metabolic and contractile function is context-dependent and determined by a complex interaction of several regulatory systems. The first part of the review focuses on local and systemic mechanisms involved in the regulation of O₂ delivery and how integration of these influences the matching of skeletal muscle O₂ demand and O₂ delivery. In the second part, alterations in cardiovascular function and structure associated with aging and heart failure, and how these impact metabolic and contractile function, will be addressed. Where applicable, the potential of exercise training to offset/reverse age- and disease-related cardiovascular declines will be highlighted in the context of skeletal muscle metabolic function. The review focuses on human data but also covers animal observations.

Effects of dietary nitrate on the O2 cost of submaximal exercise: Accounting for "noise" in pulmonary gas exchange measurements

Dietary nitrate (NO₃^-) supplementation can reduce the oxygen cost of submaximal exercise, but this has not been reported consistently. We hypothesised that the number of step transitions to moderate-intensity exercise, and corresponding effects on the signal-to-noise ratio for pulmonary V˙ O₂, may be important in this regard. Twelve recreationally active participants were assigned in a randomised, double-blind, crossover design to supplement for 4 days in three conditions: 1) control (CON; water); 2); PL (NO₃^--depleted beetroot juice); and 3) BR (NO₃^--rich beetroot juice). On days 3 and 4, participants completed two 6-min step transitions to moderate-intensity cycle exercise. Breath-by-breath V˙ O₂ data were collected and V˙ O₂ kinetic responses were determined for a single transition and when the responses to 2, 3 and 4 transitions were ensemble-averaged. Steady-state V˙ O₂ was not different between PL and BR when the V˙ O₂ response to one-, two- or three-step transition was compared but was significantly lower in BR compared to PL when four-step transitions was considered (PL: 1.33 ± 0.34 vs. BR: 1.31 ± 0.34 L·min^-1, P < 0.05). There were no differences in pulmonary V˙ O₂ responses between CON and PL (P > 0.05). Multiple step transitions may be required to detect the influence of NO₃^- supplementation on steady-state V˙ O₂.

Role of nitric oxide in convective and diffusive skeletal microvascular oxygen kinetics

Progress in understanding physiological mechanisms often consists of discrete discoveries made across different models and species. Accordingly, understanding the mechanistic bases for how altering nitric oxide (NO) bioavailability impacts exercise tolerance (or not) depends on integrating information from cellular energetics and contractile regulation through microvascular/vascular control of O₂ transport and pulmonary gas exchange. This review adopts state-of-the-art concepts including the intramyocyte power grid, the Wagner conflation of perfusive and diffusive O₂ conductances, and the Critical Power/Critical Speed model of exercise tolerance to address how altered NO bioavailability may, or may not, affect physical performance. This question is germane from the elite athlete to the recreational exerciser and particularly the burgeoning heart failure (and other clinical) populations for whom elevating O₂ transport and/or exercise capacity translates directly to improved life quality and reduced morbidity and mortality. The dearth of studies in females is also highlighted, and areas of uncertainty and questions for future research are identified.