A-45 Free Communication/Poster - Protein Metabolism

Abstract

The use of pre-workout nutritional supplements continue to increase in athletes and recreationally active individuals. Many supplements contain a known vasodilator stating that an increase in muscle blood flow will improve performance. Since nitric oxide (NO) is an important regulator of muscle blood flow, many pre-exercise supplements contain the NO precursor, L-arginine. PURPOSE:To examine the effect of L-arginine on muscle blood flow and muscle deoxygenation during handgrip exercise to fatigue. METHODS:Thirteen healthy males (23 ± 3 yrs, 88.6 ± 17.5 kg, 183.0 ± 7.3 cm; mean ± SD) completed an 8 day regimen of L-arginine loading (10g/day). Time-to-task failure (TTF) was determined during handgrip exercise at a constant load corresponding to 45% of their maximal voluntary contraction (MVC) prior to and following L-arginine. Mean blood velocity (MBV) was measured using ultrasound in the brachial artery at rest, during exercise and recovery. Blood pressure and heart rate (HR) was measured continuously during exercise and recovery; mean arterial pressure (MAP), muscle blood flow (MBF) and vascular conductance (VC) were calculated from measured variables. Near infrared spectroscopy (NIRS) was used to assess changes in total hemoglobin (t[Hb+Mb]) and deoxyhemoglobin (deoxy[Hb+Mb]) in the microcirculation over the muscles of the forearm. A two-way ANOVA with repeated measures, Bonferroni post hoc and paired T-tests were used to identify significant differences at the p<0.05 level. RESULTS: TTF was longer (p<0.05) following L-arginine (Pre, 6.88 ±1.43 min; Post, 8.68 ±1.84 min). There was no difference in resting MBF between the Pre- and Post-L-arginine; MBF increased during exercise but no difference was observed during exercise between Pre- and Post-L-arginine trials. Similarly, t[Hb+Mb] increased (p<0.05) from resting values during Pre- and Post-L-arginine but there was no difference between conditions. Deoxy[Hb+Mb] increased (p<0.05) during exercise from rest but no difference was observed between Pre- and Post-L-arginine. CONCLUSIONS:The longer TTF following L-arginine is consistent with previous studies demonstrating improved performance. The similar MBF and deoxy[Hb+Mb] responses without and with L-arginine suggests that other factor(s) contribute to the improved exercise tolerance.