L-citrulline Does Not Change Blood Flow Kinetics At The Onset Of Exercise In Young Women

Abstract

Oral supplementation with L-citrulline (CIT) has been reported to improve muscle oxygenation during moderate-intensity exercise in young men; however, examination of the impact of CIT in young women is scarce. PURPOSE: To examine the influence of CIT on muscle blood flow responses to exercise in young women. METHODS: Women were assessed during the follicular (n=13, 24±2y) and luteal (n=11, 25±2y) phases of the menstrual cycle. Supplementation with CIT (6 g/day) or placebo occurred 7 days prior to the testing day in a crossover design across two menstrual cycles. All women performed rhythmic handgrip exercise at 10% maximal grip strength while forearm blood flow (FBF) was measured in the right brachial artery using Doppler ultrasound. FBFwas calculated per duty cycle (contract:relax, 1:2s) before being fit with a monoexponential model. Amplitude of the FBF response and the number of duty cycles for FBF to reach 63% of the steady-state amplitude (τFBF) were derived from the model. RESULTS: Menstrual cycle groups were similar in age, body mass index, resting brachial artery diameter, and maximal grip strength (all p>0.10). CIT did not change the amplitude of FBF or τFBF as compared to placebo in women tested during the follicular (CIT vs. placebo: 166±50 vs. 158±52 ml/min, p=0.41; 7±5 vs. 6±3 duty cycles, p=0.28) or luteal phases (163±41 vs. 173±49 ml/min, p=0.34; 11±5 vs. 9±4 duty cycles, p=0.26). Interestingly, the amplitude of the FBF response was similar between women tested during the follicular (163±44 ml/min) and luteal (170±41 ml/min, p=0.68) phases, but τFBF was slower for women tested during the luteal as compared to the follicular phase (11±4 vs. 7±3 duty cycles, p=0.01). CONCLUSION: Muscle blood flow response to rhythmic handgrip exercise was not changed by short-term supplementation with CIT in young women irrespective of menstrual cycle phase.