Can the Use of an External: Internal Ratio During Standardised Small-Sided Games be a Detector of Fatigue in Professional Adolescent Soccer Players?

 The aim of the investigation was to explore whether the external: internal(E: I) ratio during a standardised small-sided game (SSG) was impacted by fatigue monitoring methods in professional adolescent soccer players. Ten professional male soccer players (Mean ± SD; Age: 19.6 ± 1.4 years) data from seven standardised SSG’s (6v6+GK, 2x4 min, 40 x 35m) were analysed during the study. Total distance (TD):Heart rate exertion (HRe), PlayerLoadTM(PL): HReand Explosive distance (ED): HRewere the E: Iratio’s analysed from the SSG’s. Morning perceived wellness score, using a customised self-report questionnaire (energy levels, sleep and muscle soreness), and Flight time: Contraction time (FT:CT), taken from a counter-movement jump (CMJ) performed prior totraining, were used as markers of fatigue in the study. A Z-score of -1 was considered ‘fatigued’. Mixed-effect linear models revealed a significant effect for perceived wellness Z-score on TD: HRe, PL: HReand ED: HRe, which resulted in a small increase in allE: Iratios. FT: CTZ-score resulted in a non-significant, trivial effect on TD: HRe, PL: HReand ED: HRe. The results suggest E:I ratiosare influenced by subjective fatigue, thus, E: Iratio’s may be a non-invasive tool for fatigue detection. However, caution should be taken when interpreting an increase in E:I ratio, and, therefore, the use of E: Iratio’s as a means for fatigue detection requires further investigation.