Abstract
PurposeDietary nitrate (NO3−) has repeatedly been shown to improve endurance and intermittent, high-intensity events in temperate conditions. However, the ergogenic effects of dietary NO3− on intermittent exercise performance in hot conditions have yet to be investigated.MethodsIn a randomised, counterbalanced, double-blind crossover study, 12 recreationally trained males ingested a nitrate-rich beetroot juice shot (BRJ) (6.2 mmol NO3−) or a nitrate-depleted placebo (PLA) (< 0.004 mmol NO3−) 3 h prior to an intermittent sprint test (IST) in temperate (22 °C, 35% RH) and hot conditions (30 °C, 70% RH). The cycle ergometer IST consisted of twenty maximal 6 s sprints interspersed by 114 s of active recovery. Work done, power output, heart rate and RPE were measured throughout; tympanic temperature was measured prior to and upon completion.ResultsThere were no significant effects of supplement on sprint performance in either temperate or hot, humid conditions (p > 0.05). There was a reduced peak (BRJ: 659 ± 100W vs. PLA: 693 ± 139W; p = 0.056) and mean power (BRJ: 543 ± 29W vs. PLA: 575 ± 38W; p = 0.081) following BRJ compared to PLA in the hot and humid condition, but this was not statistically significant. There was no effect of supplement on total work done irrespective of environmental condition. However, ~ 75% of participants experienced performance decreases following BRJ in the hot and humid environment. No differences were observed between trials for tympanic temperature measured at the conclusion of the exercise trial.ConclusionIn conclusion, an acute dose of inorganic dietary NO3− does not improve repeated-sprint performance in either temperate, or hot and humid conditions.
Highlights
Nitric oxide (NO) is a gaseous signalling compound associated with a plethora of physiological effects including modulating contractile properties of skeletal muscle (Ferguson et al 2013), mitochondrial efficiency (Clerc et al.European Journal of Applied Physiology (2019) 119:723–7332007; Heinonen et al 2011) and peripheral/cutaneous blood flow (Lundberg et al 2008)
Some studies show that inorganic dietary N O3− has been ineffective at improving performance (Cuenca et al 2018; Sandbakk et al 2015; Cermak et al 2012b), which could be attributed to altered oral microbiota important for the initial conversation of NO3− to NO2− (Burleigh et al 2018), chronic vs. acute dosages (Vanhatalo et al 2010; Boorsma et al 2014) and the level of athlete investigated, with those towards elite showing less of an ergogenic aid of nitrate than less-trained individuals (Porcelli et al 2015)
Mean power produced per sprint and total work done was reduced in beetroot juice shot (BRJ) than PLA in the heat, but these were not statistically significant differences
Summary
Nitric oxide (NO) is a gaseous signalling compound associated with a plethora of physiological effects including modulating contractile properties of skeletal muscle (Ferguson et al 2013), mitochondrial efficiency (Clerc et al.European Journal of Applied Physiology (2019) 119:723–7332007; Heinonen et al 2011) and peripheral/cutaneous blood flow (Lundberg et al 2008). Dietary NO3− has been shown to be effective at increasing circulating plasma NO2− and NO3− that coincides with improvement in indices of performance during cycling time trials (TT) (Cermak et al 2012a; Lansley et al 2011; Muggeridge et al 2014), supra-maximal intensity cycling (Aucouturier et al 2015) and explosive running (Sandbakk et al 2015). This has been attributed to a reduced ATP cost during muscular contractions (Bailey et al 2010) and potentially reduced V O2 for mitochondrial ATP resynthesis, the latter has failed to be confirmed more recently (Whitfield et al 2015). Some studies show that inorganic dietary N O3− has been ineffective at improving performance (Cuenca et al 2018; Sandbakk et al 2015; Cermak et al 2012b), which could be attributed to altered oral microbiota important for the initial conversation of NO3− to NO2− (Burleigh et al 2018), chronic vs. acute dosages (Vanhatalo et al 2010; Boorsma et al 2014) and the level of athlete investigated, with those towards elite showing less of an ergogenic aid of nitrate than less-trained individuals (Porcelli et al 2015)
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