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EFFECTS OF DIETARY NITRATE SUPPLEMENTATION IN RECREATIONAL AND TRAINED CYCLISTS IN NORMOXIC AND HYPOXIC CONDITIONS

Abstract

BACKGROUND: The purpose of this study was to examine the effects of dietary nitrate supplementation on physiological responses and cycling performance in recreationally trained (RT; VO2max = 44 ± 7 ml/kg/min), and highly trained (HT; VO2max = 66 ± 5 ml/kg/min) cyclists in normoxic (NO; 20.9% FiO2) and hypoxic (HY; 15.2% FiO2) conditions. METHODS: 13 cyclists (RT = 8, HT = 5) completed 4 identical exercise trials. For 3 days prior to each trial, subjects consumed 140 mL/d of concentrated beetroot juice (BRJ; 12.8 mmol nitrates) or placebo (PLA). Subjects completed trials for both treatments (PLA or BRJ) in both environmental conditions (NO or HY), in a randomly counterbalanced, double-blinded study design. Exercise trials consisted of 20 min of constant-load cycling (10 min at 45% Wmax, 10 min at 65% Wmax), followed immediately by a 4 km cycling time trial (TT). Physiological responses to exercise (VO2, ventilation, RER, heart rate, RPE, blood glucose/lactate, and O2 saturation) were obtained 5 min into constant-load exercise at each intensity. Performance was assessed as the time to complete the 4 km TT. Treatment effects were assessed using a series of two-way repeated measures ANOVAs, with an alpha-level for statistical significance at p < 0.05. RESULTS: The HT group had significantly faster 4 km TT times than RT (384 ± 16 s versus 446 ± 42 s, respectively), and significant between-group effects were observed for various physiological responses during constant-load exercise (VO2, ventilation, blood lactate, heart rate, and O2 saturation). Similarly, TT times were significantly faster in NO (410 ± 46 s) versus HY (434 ± 45 s), with significantly different physiological values observed between environmental conditions during constant-load exercise (VO2, ventilation, RER, blood lactate, heart rate, O2 saturation, and RPE). However, there was no difference in TT performance between PL (422 ± 44 s) and BRJ treatments (422 ± 46 s), and no significant treatment*altitude or treatment*altitude*group interactions for TT performance or any physiological variables. CONCLUSION: Dietary nitrate supplementation did not alter physiological responses during exercise, or 4 km TT performance in cyclists. Furthermore, the efficacy of dietary nitrate supplementation was not affected by hypoxic conditions or the training status of subjects.

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