L-Tyrosine Not Effective During Short-Term Exercise

PROVO, Utah--In a study appearing in the November issue of the Journalof Applied Physiology (93:1590-7, 2002) (http://jap.physiology.org),researchers found that L-tyrosine supplementation may not enhance enduranceduring regular bouts of exercise.

Researchers from the Human Performance Research Center at Brigham YoungUniversity (BYU) tested nine competitive cyclists' reactions to ingesting 5ml/kg body weight of water containing: 1) aspartame, 2) 70 g/l of polydextrose,3) 25 mg/kg of L-tyrosine or 4) 70 g/l of polydextrose and 25 mg/kg ofL-tyrosine. The cyclists cycled at 70-percent peak oxygen uptake for 90 minutesunder the four different dietary regimens, consuming the allotted mixture at30-minute intervals. Even though tyrosine plasma levels rose significantly from60 minutes prior to the test to the end of the test, L-tyrosine ingestion didnot enhance performance during cycling.

According to Allen Parcell, a study author, tyrosine's effect on endurancemay kick in after physical activity of five or more hours; the BYU tests lastedno longer than 2.5 hours. "In most cases, a well-balanced diet with anemphasis on carbohydrates has definitely been shown to significantly improveendurance," Parcell noted. "Maybe there's a case to pursue [L-tyrosinesupplementation] with some ultra-endurance, really long-term exercise."

The study was funded in part by the Gatorade Sports Science Institute.