Effects of High-Intensity Interval Training with Varying Rest Periods on Tryptophan and TMAO Levels in Young Football Players

This study evaluated the biochemical effects of high-intensity interval training (HIIT) protocols with different rest intervals on tryptophan–kynurenine pathway metabolites and trimethylamine N-oxide (TMAO) levels in young football players. Thirty healthy male amateur football athletes were randomly assigned to three groups: 20-s rest HIIT (n = 10), 30-s rest HIIT (n = 10), and a control group (n = 10). The HIIT groups performed the protocol twice weekly for six weeks in addition to routine football training. Serum samples were collected before and after the intervention, and concentrations of tryptophan, kynurenine, kynurenine pathway metabolites, TMAO, and related ratios were analyzed using LC-MS/MS. No significant differences in overall changes were observed between groups. However, within-group analyses revealed protocol-specific responses. In the 20-s rest group, tryptophan and kynurenic acid decreased, while 3-hydroxykynurenic acid increased; the KYN/TRP and KYNA/KYN ratios also changed significantly. In the 30-s rest group, quinolinic acid and the QA/KYN ratio decreased, whereas the 3-HAA/3-HK ratio increased. No significant changes were observed in the control group, and TMAO levels remained unchanged across all groups. These results suggest that rest interval duration can modulate kynurenine pathway metabolism in a protocol-specific manner, highlighting the importance of considering recovery parameters when designing exercise interventions targeting neurometabolic biomarkers.