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Impact of l-citrulline supplementation on oxygen uptake kinetics during walking.

  • 2018-06
  • Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme 43(6)
    • John Ashley
    • Youngdeok Kim
    • Joaquin U Gonzales

Study Design

Type
Randomized Controlled Trial (RCT)
Sample size
n = 15
Population
26 (15 women, 11 men) adults between the ages of 20-35 years (n = 15) and 64-86 years (n = 11)
Methods
randomized, double-blind study, crossover design, 7-day periods of taking placebo and Cit (6 g/day)
Blinding
Double-blind
Duration
7-day periods
Funding
Unclear
Supplementation with l-citrulline (Cit) has been shown to improve muscle oxygenation and oxygen uptake kinetics during moderate- to high-intensity cycling in young men. The aim of this study was to test the hypothesis that Cit would improve oxygen uptake kinetics during walking in older and young adults. In a randomized, double-blind study, 26 (15 women, 11 men) adults between the ages of 20-35 years (n = 15) and 64-86 years (n = 11) completed 7-day periods of taking placebo and Cit (6 g/day) in a crossover manner. Participants walked on a treadmill at 40% heart rate reserve while pulmonary oxygen uptake 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. Sex-stratified 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 ± 2.1 s, P = 0.01; deficit: -0.15 ± 0.05 vs. 0.01 ± 0.05 L, P = 0.02). All oxygen uptake parameters were unchanged (P > 0.05) following Cit and placebo in women. Cit does not alter the oxygen cost of moderate-intensity walking in young or older adults, but Cit improved the rate of rise in oxygen uptake at exercise onset in men.

Research Insights

  • L-Citrulline→Improved Mean Response Time

    Cit decreased MRT (P = 0.04, Cohen's d = 0.41) ... in men with the change after Cit being greater than the change after placebo (MRT: -4.5 ± 2.1 vs. 3.4 ± 2.1 s, P = 0.01)

    Effect
    Beneficial
    Effect size
    Moderate
    Dose
    6 g/day
  • L-Citrulline→Reduced Net Oxygen Cost

    All oxygen uptake parameters were unchanged (P > 0.05) following Cit and placebo in women

    Effect
    Neutral
    Effect size
    Small
    Dose
    6 g/day
  • L-Citrulline→Reduced Oxygen Deficit

    All oxygen uptake parameters were unchanged (P > 0.05) following Cit and placebo in women

    Effect
    Neutral
    Effect size
    Small
    Dose
    6 g/day
  • L-Citrulline→Reduced Response Time

    All oxygen uptake parameters were unchanged (P > 0.05) following Cit and placebo in women

    Effect
    Neutral
    Effect size
    Small
    Dose
    6 g/day
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