title: Effects of L-tyrosine and carbohydrate ingestion on endurance exercise performance.
abstract: To test the effects of tyrosine ingestion with or without carbohydrate supplementation on endurance performance, nine competitive cyclists cycled at 70% peak oxygen uptake for 90 min under four different feeding conditions followed immediately by a time trial. At 30-min intervals, beginning 60 min before exercise, each subject consumed either 5 ml/kg body wt of water sweetened with aspartame [placebo (Pla)], polydextrose (70 g/l) (CHO), L-tyrosine (25 mg/kg body wt) (Tyr), or polydextrose (70 g/l) and L-tyrosine (25 mg/kg body wt) (CHO+Tyr). The experimental trials were given in random order and were carried out by using a counterbalanced double-blind design. No differences were found between treatments for oxygen uptake, heart rate, or rating of perceived exertion at any time during the 90-min ride. Plasma tyrosine rose significantly from 60 min before exercise to test termination (TT) in Tyr (means +/- SE) (480 +/- 26 micromol) and CHO+Tyr (463 +/- 34 micromol) and was significantly higher in these groups from 30 min before exercise to TT vs. CHO (90 +/- 3 micromol) and Pla (111 +/- 7 micromol) (P < 0.05). Plasma free tryptophan was higher after 90 min of exercise, 15 min into the endurance time trial, and at TT in Tyr (10.1 +/- 0.9, 10.4 +/- 0.8, and 12.0 +/- 0.9 micromol, respectively) and Pla (9.7 +/- 0.5, 10.0 +/- 0.3, and 11.7 +/- 0.5 micromol, respectively) vs. CHO (7.8 +/- 0.5, 8.6 +/- 0.5, and 9.3 +/- 0.6 micromol, respectively) and CHO+Tyr (7.8 +/- 0.5, 8.5 +/- 0.5, 9.4 +/- 0.5 micromol, respectively) (P < 0.05). The plasma tyrosine-to-free tryptophan ratio was significantly higher in Tyr and CHO+Tyr vs. CHO and Pla from 30 min before exercise to TT (P < 0.05). CHO (27.1 +/- 0.9 min) and CHO+Tyr (26.1 +/- 1.1 min) treatments resulted in a reduced time to complete the endurance time trial compared with Pla (34.4 +/- 2.9 min) and Tyr (32.6 +/- 3.0 min) (P < 0.05). These findings demonstrate that tyrosine ingestion did not enhance performance during a cycling time trial after 90 min of steady-state exercise.
authors.affiliation: Human Performance Research Center, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Troy D
authors.initials: TD
authors.lastname: Chinevere
authors.forename: Robert D
authors.initials: RD
authors.lastname: Sawyer
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Creer
authors.forename: Robert K
authors.initials: RK
authors.lastname: Conlee
authors.forename: Allen C
authors.initials: AC
authors.lastname: Parcell
mesh_terms: D000328:Adult; D001642:Bicycling; D001786:Blood Glucose / Q000032:analysis; D004040:Dietary Carbohydrates / Q000494:pharmacology*; D015444:Exercise / Q000502:physiology*; D006321:Heart / Q000187:drug effects; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D010807:Physical Endurance / Q000187:drug effects*; D005082:Physical Exertion; D012137:Respiratory System / Q000187:drug effects; D012649:Self Concept; D013997:Time Factors; D014364:Tryptophan / Q000097:blood; D014443:Tyrosine / Q000494:pharmacology*
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D019344:Lactic Acid; D014443:Tyrosine; D014364:Tryptophan