Dietary nitrate supplementation (DN) enhances intermittent high-intensity exercise and may therefore improve the adaptations to sprint interval training (SIT). Given that exercise training can augment basal production of nitric oxide, decrease mean arterial blood pressure (MAP) and increase flow-mediated dilation (FMD), combining these interventions may result in a synergistic improvement in these measures.
PURPOSE: To investigate whether DN ingested prior to SIT can increase basal plasma nitrite, reduce MAP and increase FMD beyond SIT alone.
METHODS: 19 healthy males (29 ± 7 yrs) completed an initial baseline assessment of plasma nitrite, and resting MAP and FMD (n=15). Participants were subsequently randomly assigned to a SIT + placebo (PLA) group (n=10) or a SIT + DN (NIT) group (n=9). Participants then underwent 3-weeks of SIT consisting of 4-6 repeated 15 s all out sprints on a cycle ergometer, interspersed with 4 min active recovery. Participants consumed either a DN or PLA dose 2.5 h prior to each training session. The dose consisted of 2 x 60 ml nitrate gels (~8.1 mmol nitrate) or nitrate-depleted PLA. After 48-72 hrs following completion of the SIT protocol all participants returned for re-assessment of baseline measures. Differences between groups, time points and their interaction were established by 2 x 2 repeated measures ANOVA.
RESULTS: There were no differences in plasma nitrite (PLA: 188 ± 78; NIT: 174 ± 51 nM, P=0.662), MAP (PLA: 92 ± 4; NIT: 92 ± 9 mmHg, P=0.871) or FMD (PLA: 8.6 ± 4.2; NIT: 7.8 ± 3.0 %, P=0.657) between groups, prior to training. Following training, plasma nitrite was not different from pre-training in either group (PLA: 213 ± 63; NIT: 168 ± 50 nM, P=0.545). MAP decreased pre - post training (P=0.004). Post-hoc analysis revealed MAP reduced by a similar extent in both PLA (87 ± 6 mmHg, d=0.98, P=0.015) and NIT (87 ± 12 mmHg, d=0.47, P=0.016) groups. FMD increased pre - post training (P=0.004). Post-hoc analysis revealed FMD increased in the NIT group (11.2 ± 1.8 %, d=1.37, P=0.008) but not the PLA group (10.3 ± 4.5 %, d=0.39, P=0.111).
CONCLUSIONS: Results from the current study suggest NIT may enhance some of the cardiovascular adaptations to 3-weeks SIT. This finding is not supported by changes in basal plasma nitrite and the mechanism(s) underpinning this response is currently unknown.