Domínguez et al. reviewed 23 articles concerning the effects of beetroot juice supplementation on endurance athletes (Domínguez et al., 2017). One point worthy of note is, that the effect on the cardiorespiratory endurance (the aerobic metabolism) has been investigated. This is in contrast to many recent studies that focus on the effects of short term and maximum performance or apply animal models.
Briefly, the mechanism of uptake can be explained by the reduction of NO3- from the beetroot juice by bacteria in the saliva and gastrointestinals to NO2- and further reduction to NO. NO as a (second) messenger acts in various ways: it increases blood flow and O2 utilization in the muscle and reduces blood pressure by vasodilation.
The majority of the studies reviewed comprise a test group of trained or competetive athletes. Subjects were tested for their performance of cycling or running excercises (~10-20min / ~4-10km) at submaximal level.
An increased economy (defined as O2-consumption relative to power output) and an increased bloodflow resulting in an increased oxygen supply were identified in most studies. Increased time-to-exhaustion has been reported by some authors.
An acute dosis uptake at 150-180min before workout seems to be favored over a 90-120min pre-excercise uptake. A supplementation of 6 days seems to be crucial for beneficial effects whereas peak NO2- concentration in the blood can be found at 2-3hours post consumption. Furthermore, beetroot juice supplementation seems to improve the performance under hypoxic conditions.
Two main molecular effects are discussed: oxidative phophorylation in the mitochondria may play a role or even the biogenesis of these might be enhanced through beetroot at a cronic supplementation. Others suggest that the mitochondria itself are not affected. It has been supposed that muscle function is improved by facilitated calcium release.
In combination with caffeine supplementation, no significant ergogenic effects could be observed, however more data is needed to support these findings (Domínguez et al., 2017).
Citation:
Domínguez R, Cuenca E, Maté-Muñoz JL, García-Fernández P, Serra-Paya N,
Estevan MC, Herreros PV, Garnacho-Castaño MV. Effects of Beetroot Juice
Supplementation on Cardiorespiratory Endurance in Athletes. A Systematic Review.
Nutrients. 2017 Jan 6;9(1). pii: E43. doi: 10.3390/nu9010043. Review. PubMed
PMID: 28067808; PubMed Central PMCID: PMC5295087.
Scientific endurance 