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

This study investigated whether L-tyrosine supplementation enhances endurance performance in mentally fatigued cyclists. Twelve recreational cyclists completed two constant-workload tests to exhaustion cycling tests under two experimental conditions at 80% of maximal endurance power output: L-tyrosine ingestion (300 mg/kg) under mental fatigue (TYR-MF), and placebo under mental fatigue (PLA-MF). Mental fatigue (MF) was induced by a 60-min Stroop task (ST). Oxygen consumption (VO₂), rating of perceived exertion (RPE), and heart rate (HR) were measured throughout the cycling test. Time to exhaustion in the TYR-MF condition (459.9 ± 199.6 s) was higher when compared to the PLA-MF experimental condition (398.7 ± 222.1 s) (p = 0.008). The increase (i.e., slope technique) of RPE throughout the cycling to exhaustion was lower in the TYR-MF (0.560 ± 0.184 a.u.) than in PLA-MF (0.673 ± 0.251 a.u.) (p = 0.03) experimental condition. No differences were observed between conditions for VO₂ and HR data (p > 0.05). L-tyrosine ingestion increased endurance performance by approximately 16% in mentally fatigued cyclists. This effect was accompanied by a reduction in RPE slope during cycling to exhaustion. Therefore, these preliminary findings suggest that L-tyrosine supplementation may offer moderate benefits in performance for cyclists under mental fatigue conditions, although confirmatory studies with larger samples are needed.