Athletes use nutritional supplementation to enhance the effects of training and achieve improvements in their athletic performance. Beetroot juice increases levels of nitric oxide (NO), which serves multiple functions related to increased blood flow, gas exchange, mitochondrial biogenesis and efficiency, and strengthening of muscle contraction. These biomarker improvements indicate that supplementation with beetroot juice could have ergogenic effects on cardiorespiratory endurance that would benefit athletic performance. The aim of this literature review was to determine the effects of beetroot juice supplementation and the combination of beetroot juice with other supplements on cardiorespiratory endurance in athletes. A keyword search of DialNet, MedLine, PubMed, Scopus and Web of Science databases covered publications from 2010 to 2016. After excluding reviews/meta-analyses, animal studies, inaccessible full-text, and studies that did not supplement with beetroot juice and adequately assess cardiorespiratory endurance, 23 articles were selected for analysis. The available results suggest that supplementation with beetroot juice can improve cardiorespiratory endurance in athletes by increasing efficiency, which improves performance at various distances, increases time to exhaustion at submaximal intensities, and may improve the cardiorespiratory performance at anaerobic threshold intensities and maximum oxygen uptake (VO2max). Although the literature shows contradictory data, the findings of other studies lead us to hypothesize that supplementing with beetroot juice could mitigate the ergolytic effects of hypoxia on cardiorespiratory endurance in athletes. It cannot be stated that the combination of beetroot juice with other supplements has a positive or negative effect on cardiorespiratory endurance, but it is possible that the effects of supplementation with beetroot juice can be undermined by interaction with other supplements such as caffeine.

BackgroundCrossFit is a new strength and conditioning regimen involving short intense daily workouts called workouts of the day (WOD). This study assesses muscular fatigue levels induced by the three modalities of CrossFit WOD; gymnastics (G), metabolic conditioning (M) and weightlifting (W).Material and methods34 healthy subjects undertook three WOD (one per week): a G WOD consisting of completing the highest number of sets of 5 pull-ups, 10 push-ups and 15 air squats in 20 min; an M WOD, in which the maximum number of double skipping rope jumps was executed in 8 sets (20 s), resting (10 s) between sets; and finally, a W WOD in which the maximum number of power cleans was executed in 5 min, lifting a load equivalent to 40% of the individual's 1RM. Before and after each WOD, blood lactate concentrations were measured. Also, before, during, and after each WOD, muscular fatigue was assessed in a countermovement jump test (CMJ).ResultsSignificant reductions were produced in the mechanical variables jump height, average power and maximum velocity in response to G; and in jump height, mean and peak power, maximum velocity and maximum force in response to W (P<0.01). However, in M, significant reductions in mechanical variables were observed between pre- and mid session (after sets 2, 4, 6 and 8), but not between pre- and post session.ConclusionsMuscular fatigue, reflected by reduced CMJ variables, was produced following the G and W sessions, while recovery of this fatigue was observed at the end of M, likely attributable to rest intervals allowing for the recovery of phosphocreatine stores. Our findings also suggest that the high intensity and volume of exercise in G and W WODs could lead to reduced muscular-tendon stiffness causing a loss of jump ability, related here to a longer isometric phase during the CMJ.

Beetroot juice contains high levels of inorganic nitrate (NO3−) and its intake has proved effective at increasing blood nitric oxide (NO) concentrations. Given the effects of NO in promoting vasodilation and blood flow with beneficial impacts on muscle contraction, several studies have detected an ergogenic effect of beetroot juice supplementation on exercise efforts with high oxidative energy metabolism demands. However, only a scarce yet growing number of investigations have sought to assess the effects of this supplement on performance at high-intensity exercise. Here we review the few studies that have addressed this issue. The databases Dialnet, Elsevier, Medline, Pubmed and Web of Science were searched for articles in English, Portuguese and Spanish published from 2010 to March 31 to 2017 using the keywords: beet or beetroot or nitrate or nitrite and supplement or supplementation or nutrition or “sport nutrition” and exercise or sport or “physical activity” or effort or athlete. Nine articles fulfilling the inclusion criteria were identified. Results indicate that beetroot juice given as a single dose or over a few days may improve performance at intermittent, high-intensity efforts with short rest periods. The improvements observed were attributed to faster phosphocreatine resynthesis which could delay its depletion during repetitive exercise efforts. In addition, beetroot juice supplementation could improve muscle power output via a mechanism involving a faster muscle shortening velocity. The findings of some studies also suggested improved indicators of muscular fatigue, though the mechanism involved in this effect remains unclear.

Background: Beetroot juice (BJ) is rich in inorganic nitrates and has proved effective at increasing blood nitric oxide (NO) levels. When used as a supplement BJ has shown an ergogenic effect on cardiorespiratory resistance exercise modalities, yet few studies have examined its impact on high intensity efforts. Objective: To assess the effects of BJ intake on anaerobic performance in a Wingate test. Methods: Fifteen trained men (age 21.46 ± 1.72 years, height 1.78 ± 0.07 cm and weight 76.90 ± 8.67 kg) undertook a 30-s maximum intensity test on an inertial cycle ergometer after drinking 70 mL of BJ (5.6 mmol NO3−) or placebo. Results: Despite no impacts of BJ on the mean power recorded during the test, improvements were produced in peak power (6%) (p = 0.034), average power 0–15 s (6.7%) (p = 0.048) and final blood lactate levels (82.6%) (p < 0.001), and there was a trend towards a shorter time taken to attain peak power (−8.4%) (p = 0.055). Conclusions: Supplementation with BJ has an ergonomic effect on maximum power output and on average power during the first 15 s of a 30-s maximum intensity inertial cycle ergometer test.

The purpose of this study was to examine acute metabolic, mechanical, and cardiac responses to half-squat (HS) resistance exercise performed at a workload corresponding to the lactate threshold (LT). Thirteen healthy subjects completed 3 HS exercise tests separated by 48-hour rest periods: a maximal strength or 1 repetition maximum (1RM) test, an incremental load test to establish the % 1RM at which the LT was reached, and a constant load test at the LT intensity. During the last test, metabolic, mechanical, and cardiac responses were monitored respectively through blood lactate concentrations, height (H), average power (AP) and peak power (PP) recorded in a countermovement jump test, and heart rate (HR). During the constant load test, lactate concentrations and HR remained stable whereas significant reductions were detected in H, AP, and PP (p ≤ 0.05). Only low correlation was observed between lactate concentrations and the H (r = 0.028), AP (r = 0.072), and PP (r = 0.359) losses produced. Half-squat exercise at the LT elicits stable HR and blood lactate responses within a predominantly aerobic metabolism, although this exercise modality induces significant mechanical fatigue.

BackgroundBeetroot juice (BJ) is classified as a high-level supplement for improving sports performance. There is some controversy over the benefits of BJ supplementation for endurance exercise performance, especially when referring to well-trained athletes. This study examines the effects of acute BJ supplementation on cardioventilatory responses, exercise economy/efficiency, slow component of oxygen uptake, time trial performance, blood lactate, energy consumption, and carbohydrate and fat oxidation.MethodsTwelve well-trained, male triathletes (aged 21–47 yr) were assigned in a randomized, double-blind, crossover design to receive 70 ml of BJ (6.5 mmol NO3−) or placebo (PL). Three hours after taking the supplement, participants completed an endurance test on a cycle ergometer at a constant work rate (W) corresponding to first ventilatory threshold (VT1) (30 min) and second ventilatory threshold (VT2) time trial (~ 15 min).ResultsMaximal oxygen uptake was 54.78 ± 3.13 mL·min− 1·kg− 1, and gross efficiency was > 22% at each load intensity and experimental condition. No significant interaction effect (supplement*intensity) was observed on any of the cardioventilatory variables, efficiency/economy, VT2 time trial, energy expenditure, carbohydrate oxidation and fat oxidation (p > 0.05).ConclusionOur findings do not support an improvement in the variables examined in response to acute BJ supplementation. Probably, higher doses are needed for improving time trial performance in male triathletes during a cycle ergometer test conducted at a load intensity equivalent to the first and second ventilatory threshold.

Background There is limited information about the impact of coronavirus disease (COVID‐19) on the muscular dysfunction, despite the generalized weakness and fatigue that patients report after overcoming the acute phase of the infection. This study aimed to detect impaired muscle efficiency by evaluating delta efficiency (DE) in patients with COVID‐19 compared with subjects with chronic obstructive pulmonary disease (COPD), ischaemic heart disease (IHD), and control group (CG). Methods A total of 60 participants were assigned to four experimental groups: COVID‐19, COPD, IHD, and CG ( n = 15 each group). Incremental exercise tests in a cycle ergometer were performed to obtain peak oxygen uptake (VO 2 peak). DE was obtained from the end of the first workload to the power output where the respiratory exchange ratio was 1. Results A lower DE was detected in patients with COVID‐19 and COPD compared with those in CG ( P ≤ 0.033). However, no significant differences were observed among the experimental groups with diseases ( P > 0.05). Lower VO 2 peak, peak ventilation, peak power output, and total exercise time were observed in the groups with diseases than in the CG ( P < 0.05). A higher VO 2 , ventilation, and power output were detected in the CG compared with those in the groups with diseases at the first and second ventilatory threshold ( P < 0.05). A higher power output was detected in the IHD group compared with those in the COVID‐19 and COPD groups ( P < 0.05) at the first and second ventilatory thresholds and when the respiratory exchange ratio was 1. A significant correlation ( P < 0.001) was found between the VO 2 peak and DE and between the peak power output and DE ( P < 0.001). Conclusions Patients with COVID‐19 showed marked mechanical inefficiency similar to that observed in COPD and IHD patients. Patients with COVID‐19 and COPD showed a significant decrease in power output compared to IHD during pedalling despite having similar response in VO 2 at each intensity. Resistance training should be considered during the early phase of rehabilitation.

This study compares acute cardiorespiratory, metabolic, mechanical and rating of perceived effort (RPE) responses to 2 different prolonged constant-load exercises, half-squat (HS) and cycle ergometry, performed at a workload corresponding to the lactate threshold (LT). A total of 18 healthy subjects completed 5 exercise tests separated by 48 h rest periods: an incremental cycle ergometer test, a constant-load cycle ergometer test at LT intensity, a one-repetition maximum (1RM) HS test, an incremental HS test and a constant-load HS test at LT intensity. In both constant-load tests, cardiorespiratory, metabolic and RPE data were recorded. Mechanical responses before and after each test were assessed in terms of jump height and mean power measured in a counter movement jump (CMJ) test. In both exercises, cardiorespiratory and metabolic responses stabilized, though cardiorespiratory responses were significantly greater for cycle ergometry (P<0.001), with the exception of respiratory exchange ratio (RER), which was higher for HS (P=0.028). Mechanical fatigue was observed in only HS (P<0.001). In conclusion, different exercise modalities induced different yet stable acute cardiorespiratory and metabolic responses. Although such responses were significantly reduced in HS, greater mechanical fatigue was produced, most likely because of the particular muscle actions involved in this form of exercise.