Article, Applied Physiology Nutrition and Metabolism (PMID: 29394491)

Supplementation with L-citrulline (Cit) has been shown to improve muscle oxygenation and oxygen uptake (VO2) kinetics during moderate-to-high intensity cycling in young men. The aim of this study was to test the hypothesis whether Cit would improve VO2 kinetics during walking

in older and young adults. In a randomized, double-blind study, 26 (15 women, 11 men) adults between the ages of 20-35y (n = 15) and 64-86y (n = 11) completed 7 day periods of taking placebo and L-citrulline (6 g/day) in a crossover manner. Participants walked on a treadmill at

40%HRR while pulmonary VO2 was measured using indirect calorimetry. Net oxygen cost, mean response time (MRT), and the oxygen deficit were calculated before and after each supplement period. There was no significant change (P>0.05) in net oxygen cost, MRT, or the oxygen deficit after Cit in older adults, while young adults showed a decrease (P=0.05) in the oxygen deficit after Cit that tended (P=0.053) to be different than the change after placebo. Sexstratified analysis revealed that Cit decreased MRT (P=0.04, Cohen’s d = 0.41) and the oxygen deficit (P<0.01, Cohen’s d = 0.56) in men with the change after Cit being greater than the change after placebo (MRT: -4.5±2.1 vs. 3.4±2.1s, P=0.01; deficit: -0.15±0.05 vs. 0.01±0.05L, P=0.02). All VO2 parameters were unchanged (P>0.05) following Cit and placebo in women. Citrulline does not alter the oxygen cost of moderate intensity walking in young or older adults, but Cit improved the rate of rise in VO2 at exercise onset in men.