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.