Neither Beetroot Juice Supplementation nor Increased Carbohydrate Oxidation Enhance Economy of Prolonged Exercise in Elite Race Walkers

Abstract

Given the importance of exercise economy to endurance performance, we implemented two strategies purported to reduce the oxygen cost of exercise within a 4 week training camp in 21 elite male race walkers. Fourteen athletes undertook a crossover investigation with beetroot juice (BRJ) or placebo (PLA) [2 d preload, 2 h pre-exercise + 35 min during exercise] during a 26 km race walking at speeds simulating competitive events. Separately, 19 athletes undertook a parallel group investigation of a multi-pronged strategy (MAX; n = 9) involving chronic (2 w high carbohydrate [CHO] diet + gut training) and acute (CHO loading + 90 g/h CHO during exercise) strategies to promote endogenous and exogenous CHO availability, compared with strategies reflecting lower ranges of current guidelines (CON; n = 10). There were no differences between BRJ and PLA trials for rates of CHO (p = 0.203) or fat (p = 0.818) oxidation or oxygen consumption (p = 0.090). Compared with CON, MAX was associated with higher rates of CHO oxidation during exercise, with increased exogenous CHO use (CON; peak = ~0.45 g/min; MAX: peak = ~1.45 g/min, p < 0.001). High rates of exogenous CHO use were achieved prior to gut training, without further improvement, suggesting that elite athletes already optimise intestinal CHO absorption via habitual practices. No differences in exercise economy were detected despite small differences in substrate use. Future studies should investigate the impact of these strategies on sub-elite athletes’ economy as well as the performance effects in elite groups.

Short-Term Very High Carbohydrate Diet and Gut-Training Have Minor Effects on Gastrointestinal Status and Performance in Highly Trained Endurance Athletes

“…Empirical evidence of the reduction in exercise economy associated with adaptation to ketogenic LCHF diets has led to calculations of theoretical advantages to economy and performance following further increases in the contribution of CHO to exercise substrate use [2]. However, our recent investigation of this hypothesis failed to detect a measurable change in oxygen use when elite athletes implemented dietary strategies to increase CHO availability and oxidation during exercise [9]. Nevertheless, there may be other mechanisms by which strategies to increase availability/utilisation of the finite CHO stores might enhance endurance performance.…”

Defining Training and Performance Caliber: A Participant Classification Framework

“…[8][9][10] Similarly, beetroot juice/nitrate is considered an evidence-based performance enhancing supplement, 11 based largely on studies in lower-caliber athletes, whereas elite athletes do not appear to obtain the same benefits. 12,13 Whether these and other observations are robust and can be explained by innate biometric differences or by the modifying effects of training history and load are of particular interest. However, the results of existing and future studies cannot be effectively harvested unless there is uniformity around the descriptive characteristics and classification of athletic populations.…”

Acute Ingestion of a Ketone Monoester without Co-Ingestion of Carbohydrate Improves Running Economy in Male Endurance Runners

“…The oxygen or energy cost of steady-state running at a given speed, commonly referred to as RE, is recognized as one of the most important physiological factors influencing long-distance running performance (9,23,24). Both short-and long-term training, and nutrition interventions have targeted changes in RE with mixed results reported (11,12,16,25). The development and commercialization of exogenous ketone supplements in the last decade has presented a viable strategy by which RE may be improved.…”