Acute effects of various doses of nitrate-rich beetroot juice on high-intensity interval exercise responses in women: a randomized, double-blinded, placebo-controlled, crossover trial.

BACKGROUND: This study investigated the acute effects of various doses of nitrate-rich beetroot juice on the responses to high-intensity interval exercise in women. METHODS: A double-blinded, randomized, placebo-controlled, crossover trial was conducted with 13 recreationally active young women (age = 23 ± 2 years). All participants performed interval exercise (8 × 1-min bouts of cycling at 85% of peak power output [PPO] interspersed with 1-min active recovery at 20% of PPO) 2.5 h after consumption of the randomly assigned beetroot juice containing 0 mmol (placebo), 6.45 mmol (single-dose), or 12.9 mmol (double-dose) NO3-. The heart rate (HR), blood pressure, blood lactate, blood glucose, oxygen saturation, rating of perceived exertion (RPE), and emotional arousal were assessed. RESULTS: Nitrate supplementation significantly altered the HR and RPE responses across the three trials. The mean HR was lower in the single- and double-dose groups than in the placebo control group during both work intervals and recovery periods, as well as across the overall protocol (all p < .05). The mean RPE was lower in the single- and double-dose groups than in the control group during recovery periods and across the overall protocol (all p < .001). However, there was no significant difference in either HR or RPE between the single- and double-dose groups at any time point. CONCLUSIONS: Acute nitrate ingestion led to significant decreases in the mean HR and RPE during high-intensity interval exercise, but no additional benefit was observed with higher nitrate content. These findings may assist practitioners in implementing more effective nitrate supplementation strategies during high-intensity interval exercise.

Effect of pre-exercise carbohydrate diets with high vs low glycemic index on exercise performance: a meta-analysis.

Context: Although pre-exercise consumption of a low-glycemic-index (LGI) carbohydrate meal is generally recommended, the findings regarding subsequent exercise performance are inconsistent. Objective: This meta-analytic study was conducted to determine whether a pre-exercise LGI carbohydrate meal leads to greater endurance performance than a pre-exercise high-glycemic-index (HGI) meal. Data sources: The following electronic databases were searched until April 2016: MEDLINE, SPORTDiscus, Web of Science, and Cochrane Central Register of Controlled Trials. The reference lists of selected articles were searched manually. Study selection: Randomized controlled or crossover trials comparing the effects of LGI and HGI pre-exercise carbohydrate meals on subsequent exercise performance of healthy participants were included. Data extraction: The Jadad scale was used to assess the methodological quality of the included studies. A fixed-effects model was used to evaluate overall and subgroup estimates. Results: In total, 15 eligible studies from 727 articles were included in this meta-analysis. All included studies were of low research quality. The synthesized effect size ( d = 0.42, z = 3.40, P = 0.001) indicated that the endurance performance following an LGI meal was superior to that following an HGI meal. Subgroup analyses demonstrated that the treatment effect did not vary across outcome measures (exercise to exhaustion, time trial, and work output) or athletic status (trained or recreational participants). Conclusions: Weak evidence supports the claim that endurance performance following a pre-exercise LGI meal is superior to that following a pre-exercise HGI meal. Further high-quality research in this area is warranted.