Effects of short term dietary nitrate supplementation on energy metabolism during isokinetic knee muscle contractions
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The purpose of this study was to investigate whether 3 days of dietary nitrate supplementation has positive effects on exercise performance and energy metabolism at rest and during strenuous knee exercise, and exercise recovery. The experimental protocol was a double blind, placebo-controlled, two-period, and within-subjects design. Fourteen healthy nonsmoking males (22.71 ± 0.72yr, 72.93 ± 2.35kg, and 47.67 ± 1.56 ml/kg/min VO2max) participated in the study. Two supplements (nitrate lozenge; NO-L or placebo; PLA) were orally administrated randomly at 48 and 24 hours before each trial day and again 40 minutes before each exercise trial. Total work, peak torque, and respiratory gases were automatically collected during repeated knee extensions/flexions (isokinetic concentric contractions with dominant leg; 4 sets of 28 repetitions at 180°/sec with 30 sec rest intervals) and recovery (6 contractions of 1 repetition maximum with 120 vii sec between contractions). For these results, peak torque, rate of fatigue, work efficiency, and rate of recovery were calculated. Blood specimens were collected at rest before and after the treatment, post exercise, and end of recovery to track the changes in blood glucose and lactate concentrations. There was a significant inverse correlation for total work during knee extension exercise and oxygen consumption (PLA: r = -.560 and NO-L: r = -.546; p < .01, respectively). During the exercise, RER was significantly higher for PLA compared with NO-L (PLA: 1.42 ± 0.02 vs. NO-L: 1.38 ± 0.02: p = .03). Work within each set and total work performed were higher for NO-L, but these differences were not significant. However, NO-L enhanced exercise efficiency by 3.3% when compared with PLA (PLA: 2497.5 ± 134.56 ft-lb/L/min vs. NO-L: 2578.7 ± 132.24 ftlb/L/min; p = .05). Extensor peak torque recovery rate slope was not significant, but meaningfully faster for NO-L (PLA: 2.39 ± 0.52% vs. NO-L: 3.06 ± 0.54%; p = .09) and significant interaction effect (p = .02) was found during recovery contractions, especially from contractions 2 to 3 (p = .03). It is also worth noting that differences in time to peak torque during knee extension exercise for NO-L and PLA approached significances (PLA: 0.213 ± 0.01 sec vs. NO-L: 0.200 ± 0.01 sec; p = .08). The results suggest that 3 days of dietary nitrate supplementation improves rate of exercise recovery and enhances work efficiency during vigorous resistance exercise.