Discrete physiological effects of beetroot juice and potassium nitrate supplementation following 4 weeks sprint interval training

The physiological and exercise performance adaptations to sprint interval training (SIT) may be modified by dietary nitrate (NO3-) supplementation. However, it is possible that different types of NO3- supplementation evoke divergent physiological and performance adaptations to SIT. The purpose of this study was to compare the effects of 4 weeks SIT with and without concurrent dietary NO3- supplementation administered as either NO3--rich beetroot juice (BR) or potassium NO3- (KNO3). Thirty recreationally-active subjects completed a battery of exercise tests before and after a 4 week intervention in which they were allocated to one of three groups: 1) SIT undertaken without dietary NO3- supplementation (SIT); 2) SIT accompanied by concurrent BR supplementation (SIT+BR); or 3) SIT accompanied by concurrent KNO3 supplementation (SIT+KNO3). During severe-intensity exercise, VO2peak and time to task failure were improved to a greater extent with SIT+BR than SIT and SIT+KNO3 (P<0.05). There was also a greater reduction in the accumulation of muscle lactate at 3-min of severe-intensity exercise in SIT+BR compared to SIT+KNO3 (P<0.05). Plasma [NO2-] fell to a greater extent during severe-intensity exercise in SIT+BR compared to SIT and SIT+KNO3 (P<0.05). There were no differences between groups in the reduction in the muscle phosphocreatine recovery time constant from pre- to post-intervention (P>0.05). These findings indicate that 4 weeks SIT with concurrent BR supplementation results in greater exercise capacity adaptations compared to SIT alone and SIT with concurrent KNO3 supplementation. This may be the result of greater NO-mediated signalling in SIT+BR compared to SIT+KNO3.