Intra-Individual and Seasonal Variation of Selected Biomarkers for Internal Load Monitoring in U-19 Soccer Players

• Published in: Frontiers in physiology 2020-08, Vol.11, p.838-838
• Main Authors: Becker, Manuel, Sperlich, Billy, Zinner, Christoph, Achtzehn, Silvia
• Format: Article
• Language: English
• Subjects: biomarker variability; creatine kinase; internal load; monitoring; Physiology; soccer; youth soccer
• ISSN: 1664-042X; 1664-042X
• DOI: 10.3389/fphys.2020.00838

The aim of this study was to investigate inter-day and -week as well as intra- and inter-individual variation of selected biomarkers in high-performance youth soccer players to assist practitioners interpreting player’s internal load to counteract underperformance and unwanted health risks. Eleven male youth soccer players were tested multiple times during two 3-week periods at midpoint (3-wk mid ) and at the end (3-wk end ) of the first half of a German under-19 1. Bundesliga season. The levels of creatine kinase (CK), urea, and C-reactive protein (CRP) were measured during 3-wk mid and 3-wk end each Monday, Wednesday, and Friday. In 3-wk mid the CK median was 14% higher (241 vs. 212 U/L) compared to 3-wk end ( P = 0.26, ES = 0.16). Overall, the medians of CK, urea ( P = 0.59, ES = 0.08), and CRP ( P = 0.56, ES = 0.10) during 3-wk mid did not differ to the values of 3-wk end . Daily coefficient of variations (CVs) ranged from 22 to 71% (CK), 17 to 37% (urea), and 9 to 164% (CRP). Individual medians ranged from 101 to 350 U/L (CK), 23 to 50 mg/dL (urea), and 0.6 to 1.1 mg/L (CRP). High intra-individual variability was demonstrated by large intra-individual CVs (medians: CK 50%, urea 18%, and CRP 45%). Our data show (i) large inter-day and inter-week variability of all biomarkers, depending on the external load and (ii) considerable inter- and intra-individual parameter variations. Creatine kinase concentrations could sensitively reflect soccer-specific loads during the season.