A placebo controlled investigation of the effects of tryptophan or placebo on subjective and objective measures of fatigue.
OBJECTIVE
To examine the effect of L-tryptophan administration on subjective and objective measures of fatigue in healthy volunteers.


METHODS
Six healthy volunteers (4M:2F) were recruited from staff and students at the College.


METHODS
Department of Human Nutrition, St. Bartholomews and the Royal London School of Medicine and Dentistry.


METHODS
Subjects were tested for central and peripheral fatigue using a visual analogue scale, flicker fusion frequency, grip strength, reaction time and wrist ergometry. In addition, plasma free tryptophan concentrations and Trp:LNAA ratio were determined. Measurements were made before, and at 1, 2, 3 and 4 h after drinking one of two test drinks. The drinks were of either caffeine free diet Coca-Cola (placebo) or caffeine free diet Coca-Cola plus L-tryptophan (30 mg/kg: active drink). Each of the six subjects was tested after placebo and active drink with a one week washout period between test days.


RESULTS
Subjective fatigue was significantly increased following tryptophan compared to placebo (P < 0.002), and objective measures of central fatigue were significantly increased by tryptophan compared to placebo (flicker fusion frequency: P < 0.001; reaction time P < 0.001). No significant changes in grip strength were found following tryptophan compared to placebo, but a significant increase in ergometric work output was seen (P < 0.001).


CONCLUSIONS
Tryptophan ingestion in the quantity 30 mg/kg leads to increased subjective and central fatigue. Increases in work output observed following tryptophan may be as a result of a reduced perception of discomfort during ergometry.
Cunliffe
A
A
Department of Human Nutrition, St Bartholomew's and Royal London School of Medicine and Dentistry, Queen Mary and Westfield College.
Obeid
O A
OA
Powell-Tuck
J
J
D000328:Adult; D002253:Carbonated Beverages; D016552:Ergometry; D005221:Fatigue / Q000503:physiopathology; D005260:Female; D005425:Flicker Fusion; D018737:Hand Strength; D006801:Humans; D008297:Male; D010919:Placebos; D011930:Reaction Time; D014364:Tryptophan / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D014953:Wrist
D010919:Placebos; D014364:Tryptophan