The Effect of Dietary Nitrate on the Physiological Responses to 3-Weeks Sprint Interval Training

Dietary nitrate (NIT) supplementation has been shown to increase nitric oxide (NO) metabolites and enhance exercise performance. Sprint interval training (SIT) has been shown to improve aerobic fitness following 2-4 weeks of training. Considering NIT has been shown to enhance intermittent high intensity exercise the addition of NIT prior to SIT may enhance the physiological changes in aerobic fitness.PURPOSE: To investigate whether dietary nitrate ingested prior to SIT can enhance the physiological adaptations to SIT.METHODS: 27 participants completed an initial incremental ramp exercise test to exhaustion (IXT) for determination of VO2max, HRmax and WRmax. Participants were subsequently randomly assigned to a control group (CONT; n=8), SIT + placebo (PLA) group (n=10) or a SIT + NIT group (n=9) and were matched based on VO2max. Participants in each of the SIT groups 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 NIT 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 NIT-depleted PLA. In the control group participants were asked to maintain their normal lifestyle throughout the 3 week training period. Upon completion of the SIT protocol or CONT condition all participants repeated the initial IXT 48 h following the final training session. Differences between groups, time points and their interaction were established by mixed methods repeated measures ANOVA.RESULTS: There were no differences in VO2max prior to training (CONT: 44.8 ± 8.1, SIT + PLA: 40.6 ± 7.3, SIT + NIT: 42.3 ± 6.6 ml•kg•min-1, P=0.494) but VO2max improved pre - post training (P=0.019). Post-hoc analysis revealed changes in VO2max occurred in the SIT + NIT group (45.1 ± 9.3 ml•kg•min-1, 6.7 %, P=0.026) but not the SIT + PLA (42.5 ± 5 ml•kg•min-1, 4.7 %, P=0.097) or CONT groups (45.2 ± 7.8 ml•kg•min-1, 1 %, P=0.738). WRmax improved from pre - post training in both SIT groups (PLA: 274 ± 42 - 287 ± 42 W, P=0.006, NIT: 286 ± 47 - 314 ± 55 W, P<0.001) however no changes were seen in the CONT group (291 ± 60 - 287 ± 63 W, P=0.352).CONCLUSIONS: Results from the current study suggest that NIT may enhance the aerobic adaptations to SIT however the mechanism underpinning this response is currently unknown.