Increasing literature has studied the effects of dietary nitrates and moreover, L-arginine supplementation on tolerance to exercise and O2 consumption during exercise. However, few studies have investigated the effects of L-arginine on performance measures such as a time trial. It was hypothesised that an acute 3-day L-arginine supplementation would elicit a significant improvement in performance and reduce oxygen consumption during a 20 km time trial. 6 healthy male competitive cyclists (23 ± 5 y) participated in a double-blind crossover study, and consumed either one 500 m placebo (PLA) or L-arginine (ARG) beverage, containing 6 g of L-arginine, over a 2 week testing period. Following a 3-day supplementation, participants completed a ramped incremental test to exhaustion, followed by an hours rest and subsequently a 20 km time trial. Time trial completion time was reduced by 34 s (PLA 32:38 ± 1:50 vs ARG 32:04 ± 1:38 min, P<0.05), O2 consumption during the time trial was also reduced (PLA 51.6 ± 8.2 vs ARG 47.5 ± 6.1 mL.kg.min-1, P<0.05). Furthermore, both systolic and diastolic blood pressure were greatly reduced (PLA 132 ± 7 vs ARG 127 ± 7 mm Hg P<0.05 and PLA 79 ± 5 vs ARG 74 ± 5 mm Hg respectively, P<0.05). However, no differences were seen in participants' VO2max during the ramped incremental test to exhaustion (58 ± 8 vs 58 ± 8 ml.kg.min-1, P>0.05) although Wpeak was higher during the same test (PLA 385 ± 38 vs ARG 395 ± 39 W). In conclusion, acute 3-day L-arginine supplementation at a dose of 6 g.day-1 increases 20 km time trial performance and reduces O2 consumption during time trial performance, in addition to reducing systolic and diastolic blood pressure. However, L-arginine appears to have no effect upon VO2max
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