Shaw, A. P. Carmyn, E. C., & Scheuermann, B. W. (2014). The Effect of a pre-exercise nutritional supplement on muscle fatigue during handgrip exercise. Medicine & Science in Sports & Exercise, 46(5), Supplement abstract number 99.

"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."

This study examined the effect of L-arginine on muscle blood flow and muscle deoxygenation during handgrip exercise to fatigue in healthy males (N = 13). Ss completed an 8-day regimen of L-arginine loading (10g/day). Time-to-task failure was determined during handgrip exercise at a constant load corresponding to 45% of S's maximal voluntary contraction prior to and following L-arginine ingestion. Mean blood velocity was measured using ultrasound in the brachial artery at rest, during exercise, and in recovery. Blood pressure and heart rate were measured continuously during exercise and recovery; mean arterial pressure, muscle blood flow, and vascular conductance were calculated from measured variables. Near infrared spectroscopy was used to assess changes in total hemoglobin and muscle deoxyhemoglobin in the microcirculation over the forearm muscles.

Time-to-failure was longer following L-arginine. There was no difference in resting muscle blood flow between the Pre- and Post-L-arginine. Muscle blood flow increased during exercise but no difference was observed during exercise between Pre- and Post-L-arginine trials. Similarly, total hemoglobin increased from resting values during Pre- and Post-L-arginine but there was no difference between conditions. Muscle deoxyhemoglobin increased during exercise from rest but no difference was observed between Pre- and Post-L-arginine.

Implication. The longer time-to-failure following L-arginine is consistent with some previous studies demonstrating improved performance. The similar muscle blood flow and muscle deoxyhemoglobin responses without and with L-arginine suggests that other factor(s) contribute to the improved exercise tolerance.

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