Effect of dietary nitrate ingestion on muscular performance: a systematic review and meta-analysis of randomized controlled trials

Effects of Beetroot-Based Supplements on Muscular Endurance and Strength in Healthy Male Individuals: A Systematic Review and Meta-Analysis

The aim of this study was to systematically review the current literature and analyze the effects of beetroot-based supplements (BRS) on muscular performance. Randomized controlled trials that assessed the acute or short-term effects of BRS administration on muscular endurance and/or strength in healthy male individuals were retrieved from PubMed, EMBASE, CENTRAL, and Web of Science databases from inception to February 20th, 2023. In addition, we also searched preprint papers in medRxiv.org, bibRxiv.org; thesis and dissertations included in oatd.org; and clinical trials published in ClinicalTrials.gov. Data extraction, risk of bias, and study quality were assessed by 2 authors. Meta-analyses and subgroup analyses of standardized mean differences (SMD) were performed using a random-effects model. A total of 1486 records were identified in the databases and 2 were obtained by manual search in the reference list. Of those, 27 studies attended eligibility criteria and composed this systematic review. BRS administration resulted in a positive effect on muscular endurance (SMD: 0.31; 95% confidence interval (CI): 0.10 to 0.51; p < 0.01; n = 16 studies). There was an overall significative effect for muscular strength (SMD: 0.26; 95% CI: 0.03 to 0.48; p < 0.05; n = 18 studies), but a subgroup analysis showed that significant effects were found when strength was measured in a fatigued (SMD: 0.64; 95% CI: 0.25 to 1.03; p < 0.01), but not resting state. BRS administration have a small ergogenic effect on muscular endurance and attenuate the decline in muscular strength in a fatigued state in healthy male individuals.

Physiological Characteristics, Dietary Intake, and Supplement Use in Sport Climbing

PURPOSE OF REVIEW

As sport climbing has become an Olympic sport and keeps gaining in popularity, there is growing interest in the role of diet and the effect of dietary supplements on climbing performance. The aim of this review is to provide an insight into the dietary intake of climbers and discuss ergogenic aids that could improve their performance.

RECENT FINDINGS

Limited information is available regarding the dietary intake and eating habits of climbers, and the studies conducted are few and far between. The diet of climbers is apparently suboptimal, with inadequate energy intakes often owning to insufficient carbohydrate consumption. Likewise, supplement use and ergogenic aids for climbing performance are largely unexplored. Several ergogenic aids have been suggested to improve climbing performance; however, only two have been examined directly on climbing-specific outcomes. The dietary intake, eating behaviors, and supplement use in sport climbers are not well studied, and available information is most likely outdated. Considerably, more work is needed to determine which ergogenic aids can be beneficial for climbing performance.

Advances in nutritional supplementation for sarcopenia management

Sarcopenia is a syndrome characterized by a decline in muscular mass, strength, and function with advancing age. The risk of falls, fragility, hospitalization, and death is considerably increased in the senior population due to sarcopenia. Although there is no conclusive evidence for drug treatment, resistance training has been unanimously recognized as a first-line treatment for managing sarcopenia, and numerous studies have also pointed to the combination of nutritional supplementation and resistance training as a more effective intervention to improve quality of life for people with sarcopenia. People with both malnutrition and sarcopenia have a higher mortality rate, so identifying people at risk of malnutrition and intervening early is extremely important to avoid sarcopenia and its associated problems. This article provides important information for dietary interventions in sarcopenia by summarizing the discoveries and developments of nutritional supplements such as protein, leucine, β-hydroxy-β-methylbutyric acid, vitamin D, vitamin C, vitamin E, omega-3 fatty acids, creatine, inorganic nitrate, probiotics, minerals, collagen peptides, and polyphenols in the management of sarcopenia.

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.

Concurrent dietary intake to nitrate, thiocyanate, and perchlorate is negatively associated with hypertension in adults in the USA

We aimed to comprehensively evaluate the association of urinary nitrate, thiocyanate, and perchlorate metabolites with hypertension among a nationally representative sample of the US adult population. This cross-sectional study investigated data from 15,717 adults aged more than 20 years obtained from the National Health and Nutritional Examination Survey (NHANES) for the years 2005-2016. In the survey, urinary levels of nitrate, thiocyanate, and perchlorate were measured using ion chromatography combined with electrospray tandem mass spectrometry. Blood pressure was calculated as the mean of three measurements. Hypertension was defined as (a) systolic BP ≥130 and/or diastolic BP ≥80 mmHg and/or (b) self-report. Multivariate logistic regression and weighted quantile sum (WQS) regression models were applied to estimate the association between exposure to multiple inorganic anions and hypertension. Restricted cubic spline (RCS) regressions were fitted to discern the potential relationship between the anion exposure and hypertension. These innovation methods used to support our results. Overall, 7533 (49.95%) people with and 7638 (50.35%) without hypertension were included in this study. In the multivariable-adjusted logistic regression models, urinary nitrate (P < 0.001) and perchlorate (P < 0.001) were independently negatively associated with increased occurrence of hypertension, while urinary thiocyanate was insignificantly associated with hypertension (P = 0.664). The WQS regression index showed that, in combination, the three inorganic anions mixture were negatively correlated with hypertension (adjusted OR 0.89; 95% CI 0.83-0.95, P < 0.001). Urinary nitrate was the most heavily weighted component in the hypertension model (weight = 0.784). RCS regression demonstrated that nitrate (nonlinearity P = 0.205) and perchlorate (nonlinearity P = 0.701) were linearly associated with decreased occurrence of hypertension. Concurrent exposure to nitrate, thiocyanate, and perchlorate is associated with a decreased risk of hypertension, with the greatest influence coming from nitrate probably; urinary specific thiocyanate alone had an insignificant association with hypertension.

Supplementation with Nitric Oxide Precursors for Strength Performance: A Review of the Current Literature

Nitric-oxide-stimulating dietary supplements are widely available and marketed to strength athletes and weightlifters seeking to increase muscle performance and augment training adaptations. These supplements contain ingredients classified as nitric oxide (NO) precursors (i.e., "NO boosters"). Endogenous NO is generated via a nitric oxide synthase (NOS)-dependent pathway and a NOS-independent pathway that rely on precursors including L-arginine and nitrates, with L-citrulline serving as an effective precursor of L-arginine. Nitric oxide plays a critical role in endothelial function, promoting relaxation of vascular smooth muscle and subsequent dilation which may favorably impact blood flow and augment mechanisms contributing to skeletal muscle performance, hypertrophy, and strength adaptations. The aim of this review is to describe the NO production pathways and summarize the current literature on the effects of supplementation with NO precursors for strength and power performance. The information will allow for an informed decision when considering the use of L-arginine, L-citrulline, and nitrates to improve muscular function by increasing NO bioavailability.

Principles, Application, and Gaps of High-Intensity Ultrasound and High-Pressure Processing to Improve Meat Texture

In this study, we evaluate the most recently applied emerging non-thermal technologies (NTT) to improve meat tenderization, high-intensity ultrasound (HIUS), and high-pressure processing (HPP), aiming to understand if individual effects are beneficial and how extrinsic and intrinsic factors influence meat toughness. We performed a systematic literature search and meta-analysis in four databases (Web of Science, Scopus, Embase, and PubMed). Among the recovered articles (n = 192), 59 studies were included. We found better sonication time in the range of 2-20 min. Muscle composition significantly influences HIUS effects, being type IIb fiber muscles more difficult to tenderize (p < 0.05). HPP effects are beneficial to tenderization at 200-250 MPa and 15-20 min, being lower and higher conditions considered inconclusive, tending to tenderization. Despite these results, undesirable physicochemical, microstructural, and sensory alterations are still unknown or represent barriers against applying NTT at the industrial level. Optimization studies and more robust analyses are suggested to enable its future implementation. Moreover, combining NTT with plant enzymes demonstrates an interesting alternative to improve the tenderization effect caused by NTT. Therefore, HIUS and HPP are promising technologies for tenderization and should be optimized considering time, intensity, pressure, muscle composition, undesirable changes, and combination with other methods.

Effects of Capsaicin and Capsiate on Endurance Performance: A Meta-Analysis

Several studies have explored the effects of capsaicin and capsiate on endurance performance, with conflicting findings. This systematic review aimed to perform a meta-analysis examining the effects of capsaicin and capsiate vs. placebo on endurance performance in humans. Seven databases were searched to find eligible studies. The effects of capsaicin and capsiate on aerobic endurance (e.g., time-trials or time-to-exhaustion tests), muscular endurance (e.g., repetitions performed to muscular failure), and rating of perceived exertion (RPE) were examined in a random-effects meta-analysis. Fourteen studies (n = 183) were included in the review. Most studies provided capsaicin or capsiate in the dose of 12 mg, 45 min before exercise. In the meta-analysis for aerobic endurance, there was no significant difference between the placebo and capsaicin/capsiate conditions (Cohen’s d: 0.04; 95% confidence interval: −0.16, 0.25; p = 0.69). In subgroup meta-analyses, there were no significant differences between the placebo and capsaicin/capsiate conditions when analyzing only studies that used time-trials (p = 0.20) or time-to-exhaustion tests (p = 0.80). In the meta-analysis for muscular endurance, a significant ergogenic effect of capsaicin/capsiate was found (Cohen’s d: 0.27; 95% confidence interval: 0.10, 0.43; p = 0.002). When analyzing set-specific effects, an ergogenic effect of capsaicin/capsiate was found in set 1, set 2, and set 3 (Cohen’s d: 0.21–29). Capsaicin/capsiate ingestion reduced RPE following muscular endurance (p = 0.03) but not aerobic endurance tests (p = 0.58). In summary, capsaicin/capsiate supplementation acutely enhances muscular endurance, while the effects on aerobic endurance are less clear.

A 12-Week Randomized Double-Blind Placebo-Controlled Clinical Trial, Evaluating the Effect of Supplementation with a Spinach Extract on Skeletal Muscle Fitness in Adults Older Than 50 Years of Age

The aim of a 12-week randomized double-blind placebo-controlled study was to assess the effect of daily supplementation with a natural extract of Spinacia oleracea L. (4 × 500 mg capsules/day; total 2 g per day) combined with a moderate-intensity training program (1 h session/3 times a week) on skeletal muscle fitness in adults over 50 years of age. Muscle strength assessed by isokinetic and isometric dynamometry improved significantly in the experimental (n = 23) and the placebo (n = 22) groups, but the magnitude of improvement was higher in the experimental group, with between-group differences in almost all variables, including isokinetic at 60° s⁻¹ in knee extension, peak torque (p < 0.007); total work per repetition maximum (p < 0.009); isokinetic at 180°s⁻¹ in knee extension, peak torque (p < 0.002); total work (p < 0.007); total work per repetition maximum (p < 0.005); average power (p < 0.027); isometric in knee extension, peak torque (p < 0.005); and average peak torque (p < 0.002). Similar findings were observed for muscle quality. Changes in quality of life (SF-36) were not found, except for improvements in the role physical (p < 0.023) and role emotional (p < 0.001) domains, likely as a result of the physical training sessions. A nutritional survey did not revealed changes in dietary habits. No adverse events were recorded. In subjects over 50 years of age, moderate-intensity strength training combined with daily supplementation for 12 weeks with a natural extract of Spinacia oleracea L. improved muscle-related variables and muscle quality. Maintaining muscle health is a key component of healthy aging.

The importance of small samples in medical research

Almost all bio-statisticians and medical researchers believe that a large sample is always helpful in providing more reliable results. Whereas this is true for some specific cases, a large sample may not be helpful in more situations than we contemplate because of the higher possibility of errors and reduced validity. Many medical breakthroughs have occurred with self-experimentation and single experiments. Studies, particularly analytical studies, may provide more truthful results with a small sample because intensive efforts can be made to control all the confounders, wherever they operate, and sophisticated equipment can be used to obtain more accurate data. A large sample may be required only for the studies with highly variable outcomes, where an estimate of the effect size with high precision is required, or when the effect size to be detected is small. This communication underscores the importance of small samples in reaching a valid conclusion in certain situations and describes the situations where a large sample is not only unnecessary but may even compromise the validity by not being able to exercise full care in the assessments. What sample size is small depends on the context.

Effect of dietary nitrate on human muscle power: a systematic review and individual participant data meta-analysis

BACKGROUND

Previous narrative reviews have concluded that dietary nitrate (NO3-) improves maximal neuromuscular power in humans. This conclusion, however, was based on a limited number of studies, and no attempt has been made to quantify the exact magnitude of this beneficial effect. Such information would help ensure adequate statistical power in future studies and could help place the effects of dietary NO3- on various aspects of exercise performance (i.e., endurance vs. strength vs. power) in better context. We therefore undertook a systematic review and individual participant data meta-analysis to quantify the effects of NO3- supplementation on human muscle power.

METHODS

The literature was searched using a strategy developed by a health sciences librarian. Data sources included Medline Ovid, Embase, SPORTDiscus, Scopus, Clinicaltrials.gov , and Google Scholar. Studies were included if they used a randomized, double-blind, placebo-controlled, crossover experimental design to measure the effects of dietary NO3- on maximal power during exercise in the non-fatigued state and the within-subject correlation could be determined from data in the published manuscript or obtained from the authors.

RESULTS

Nineteen studies of a total of 268 participants (218 men, 50 women) met the criteria for inclusion. The overall effect size (ES; Hedge's g) calculated using a fixed effects model was 0.42 (95% confidence interval (CI) 0.29, 0.56; p = 6.310 × 10- 11). There was limited heterogeneity between studies (i.e., I2 = 22.79%, H2 = 1.30, p = 0.3460). The ES estimated using a random effects model was therefore similar (i.e., 0.45, 95% CI 0.30, 0.61; p = 1.064 × 10- 9). Sub-group analyses revealed no significant differences due to subject age, sex, or test modality (i.e., small vs. large muscle mass exercise). However, the ES in studies using an acute dose (i.e., 0.54, 95% CI 0.37, 0.71; p = 6.774 × 10- 12) was greater (p = 0.0211) than in studies using a multiple dose regimen (i.e., 0.22, 95% CI 0.01, 0.43; p = 0.003630).

CONCLUSIONS

Acute or chronic dietary NO3- intake significantly increases maximal muscle power in humans. The magnitude of this effect-on average, ~ 5%-is likely to be of considerable practical and clinical importance.