Effects of L-Tyrosine Ingestion on Endurance Performance in Mentally Fatigued Cyclists.

L-tyrosine supplementation significantly increased time to exhaustion compared to placebo in mentally fatigued cyclists.

• Time to exhaustion in the TYR-MF condition was 459.9 ± 199.6 s compared to 398.7 ± 222.1 s in the PLA-MF condition.
• The difference was statistically significant (p = 0.008).
• This represents an approximately 16% increase in endurance performance.
• Twelve recreational cyclists completed the crossover study at 80% of maximal endurance power output.
• Mental fatigue was induced via a 60-minute Stroop task prior to both experimental conditions.

The rate of increase in rating of perceived exertion (RPE slope) during cycling to exhaustion was lower with L-tyrosine supplementation than with placebo under mental fatigue.

• RPE slope in TYR-MF was 0.560 ± 0.184 a.u. compared to 0.673 ± 0.251 a.u. in PLA-MF.
• The difference in RPE slope was statistically significant (p = 0.03).
• RPE was measured using the slope technique throughout the cycling test.
• This suggests a psychobiological mechanism whereby L-tyrosine attenuates the perceptual response to exercise under mental fatigue.

No significant differences in oxygen consumption (VO2) or heart rate (HR) were observed between L-tyrosine and placebo conditions.

• Both VO2 and HR data showed no significant differences between TYR-MF and PLA-MF conditions (p > 0.05).
• This indicates that the performance benefit of L-tyrosine was not accompanied by changes in cardiorespiratory physiology.
• The finding suggests the effect of L-tyrosine may operate through a central or perceptual rather than peripheral physiological mechanism.

The study used a double-condition crossover design with mental fatigue induced by a standardized cognitive task prior to each exercise bout.

• Twelve recreational cyclists participated in the study.
• Mental fatigue was induced using a 60-minute Stroop task (ST) before each cycling test.
• L-tyrosine was administered at a dose of 300 mg/kg body weight.
• Cycling tests were constant-workload tests to exhaustion performed at 80% of maximal endurance power output.
• Both conditions (TYR-MF and PLA-MF) involved mental fatigue induction, isolating the effect of L-tyrosine from any mental fatigue manipulation difference.

The authors concluded that L-tyrosine supplementation may offer moderate performance benefits for cyclists under mental fatigue conditions, but noted the preliminary nature of findings.

• The study sample was limited to 12 recreational cyclists.
• Authors explicitly stated that 'confirmatory studies with larger samples are needed.'
• The findings were described as 'preliminary,' indicating caution in generalization.
• The approximately 16% improvement in time to exhaustion was considered a moderate benefit.