Abstract P216: Co-ingestion of Dietary Nitrate and Caffeine Elevates Submaximal Oxygen Consumption and Oxygen-pulse Compared to Nitrate or Caffeine Alone

Abstract

Introduction: Previous studies have examined dietary nitrate's and caffeine’s combined effects on time-trial and peak power output with caffeine improving performance while nitrate exhibits no additive benefit with co-ingestion. However, less is known about their combined effect on submaximal intensity exercise. Dietary nitrate may reduce submaximal oxygen cost while caffeine may increase submaximal cost. Hypothesis: Co-ingestion of dietary nitrate may attenuate the rise in oxygen consumption following caffeine intake. Methods: Ten healthy individuals (4 males; 28 ± 10 years of age) and (6 females; 21 ± 3 years of age) participated in a double-blind, placebo controlled, crossover experiment. The first of five visits consisted of a maximal oxygen consumption (VO 2max ) treadmill test. Prior to visits 2 - 5, participants consumed either a dietary nitrate (~12.4 mmol, NIT) or placebo nitrate supplement (PLN) combined with either a caffeine (3 mg/kg, CAF) or placebo caffeine (PLC) dose for a total of 4 days. The final dose of NIT or PLN and CAF or PLC was consumed 2.5 and 1-hr pre-exercise, respectively. Visits 2 - 5 consisted of a 30-min treadmill run at ~65% VO 2max . During exercise, VO 2 and heart rate (HR) were measured continuously. A linear mixed effects model analysis was performed to determine how each supplementation influenced each dependent variable. Treatments (NIT+CAF, CAF+PLN, NIT+PLC, PLN+PLC) and exercise timepoints (10 and 30 min) served as fixed factors. If p<0.05, p ost-hoc pairwise comparisons were performed. Results: Exercise VO 2 was significantly elevated for NIT+CAF at 10 and 30 minutes (36.2±4.1 and 37.7±5.0 ml/kg/min, respectively) compared to placebo (33.4±3.4 and 35.3±3.8 ml/kg/min, respectively) (p<0.05). However, there was no difference in VO2 at either timepoint (10 or 30 minutes) for conditions CAF+PLN (34.3±3.9, 35.4±3.6, and 36.3±3.2 ml/kg/min, respectively) (p=0.07) and NIT+PLC (34.8±3.9, 36.0±4.2, and 36.6±4.4 ml/kg/min, respectively) (p=0.08) compared to PLN+PLC. No difference was observed for heart rate between conditions at any timepoint. However, oxygen-pulse (VO 2 /HR) at the end of exercise was elevated in NIT+CAF (15.1±2.5 ml/beat) compared to CAF+PLN, NIT+PLC, PLN+PLC (14.5±2.5, 14.2±2.5, 13.8±2.5 ml/beat, respectively). Conclusion: When consumed independently, a low-moderate dose of caffeine or dietary nitrate had no impact on oxygen consumption during 30 minutes of moderate intensity exercise. However, co-ingestion of dietary nitrate and caffeine elevated submaximal oxygen consumption compared to a placebo control; both overall (main effect) and at individual time points of 10 and 30 minutes. Additionally, oxygen-pulse was elevated with co-ingestion compared to all treatments perhaps due to enhanced tissue uptake or altered mitochondrial efficiency. Future work may examine such mechanisms.