Effects of l-tyrosine and carbohydrate ingestion on endurance exercise performance

Troy D. Chinevere, Robert D. Sawyer, Andrew R. Creer, Robert K. Conlee, Allen C. Parcell

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 μmol) and CHO+Tyr (463 ± 34 μmol) and was significantly higher in these groups from 30 min before exercise to TT vs. CHO (90 ± 3 μmol) and Pla (111 ± 7 μmol) (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 μmol, respectively) and Pla (9.7 ± 0.5, 10.0 ± 0.3, and 11.7 ± 0.5 μmol, respectively) vs. CHO (7.8 ± 0.5, 8.6 ± 0.5, and 9.3 ± 0.6 μmol, respectively) and CHO+Tyr (7.8 ± 0.5, 8.5 ± 0.5, 9.4 ± 0.5 μmol, 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.

  • central fatigue
  • cycling
  • perceived exertion

Footnotes

  • This work was supported in part by the Gatorade Sports Science Institute and Natures Sunshine.

  • Address for reprint requests and other correspondence: A. C. Parcell, Human Performance Research Center, Brigham Young Univ., 120-E Richards Bldg., Provo, UT 84602 (E-mail:allen_parcell{at}byu.edu).

  • The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

  • July 5, 2002;10.1152/japplphysiol.00625.2001

View Full Text