Beetroot juice does not enhance altitude running performance in well-trained athletes

Abstract

25We hypothesized that acute dietary nitrate (NO3 -) provided as concentrated beetroot juice 26 supplement would improve endurance running performance of well-trained runners in 27 normobaric hypoxia. Ten male runners (mean (SD): sea level V O2max 66 (7) mL . kg -1. min -1 , 10 28 km personal best 36 (2) min) completed incremental exercise to exhaustion at 4000 m and a 10 29 km treadmill time trial at 2500 m simulated altitude on separate days, after supplementation 30 with ~7 mmol NO3 -and a placebo, 2.5 h before exercise. Oxygen cost, arterial oxygen 31 saturation, heart rate and ratings of perceived exertion (RPE) were determined during the 32 incremental exercise test. Differences between treatments were determined using means [95% 33confidence intervals], paired sample t-tests and a probability of individual response analysis.

Dietary nitrate supplementation enhances high-intensity running performance in moderate normobaric hypoxia, independent of aerobic fitness

“…Consistent with previous investigations, plasma nitrate and nitrite, and exhaled NO concentrations were significantly elevated following dietary nitrate supplementation [1,2,5,8,55,22,39,38], signifying an increase in the 'substrates' available for NO generation via the nitrate-nitrite-NO pathway [11]. Peak plasma nitrite concentration was 602 % higher in BRJ versus PLA, similar to Arnold et al [38] (775 %) (~ 7 mmol nitrate), but considerably greater than reported by Muggeridge et al [22] (134 %) (~ 5 mmol nitrate) and Vanhatalo et al [8] (150 %) (~ 9.3 mmol).…”

“…In this study, there was no apparent relationship between average nor post-TT SaO2 values and the percentage improvement in performance (r 2 = 0.05). However, SaO2 reached lower values in the present investigation (post TT PLA: 77.8 ± 6.9 %) than observed by Arnold et al [38], presumably due to the shorter higher-intensity TT, which may be important.…”

“…Peak plasma nitrite concentration was 602 % higher in BRJ versus PLA, similar to Arnold et al [38] (775 %) (~ 7 mmol nitrate), but considerably greater than reported by Muggeridge et al [22] (134 %) (~ 5 mmol nitrate) and Vanhatalo et al [8] (150 %) (~ 9.3 mmol). Importantly, all participants increased plasma nitrite concentration by substantially greater than 30 % -a cut off proposed by Wilkerson [20] for identifying 'non-responders'.…”

“…This is supported by the findings of a recent study, in which nitrate supplementation improved tolerance to severe intensity cycling in hypoxia (FIO2 13.1 %) but not normoxia [36]. However, in other studies, nitrate supplementation has been shown both to improve [8,22,37] and have no effect [38][39][40] on hypoxic exercise performance. These equivocal findings may be attributed to differences in the training status of participants, exercise protocol, supplementation protocol, and hypoxic stimuli applied, and warrant further exploration.…”

“…These findings are supportive of the notion that nitrate supplementation may reduce muscle O2 consumption during exercise in hypoxia, presumably via the aforementioned mitochondrial [35] and/or muscle [7] alterations that also manifest as a reduced V O2. Interestingly, Arnold et al [38] found that runners identified as 'responders' to nitrate supplementation during a 10,000 m TT in moderate hypoxia (FIO2 15.4 %) typically experienced a lower SaO2 during the placebo TT than 'non-responders' (82 vs 84 %). This suggests that the SaO2 response to hypoxia may moderate the performance effects of nitrate supplementation, possibly due to greater nitrite reduction into NO at lower O2 tensions [33].…”