The Relationship between Inflammatory Factors, Hemoglobin, and VO2 Max in Male Amateur Long-Distance Cross-Country Skiers in the Preparation Period

<b>Background</b>: Identifying factors affecting heart health in amateur athletes can significantly impact their health and help them achieve high performance. The current knowledge of these predictors is insufficient. The purpose of this study was to identify the biochemical determinants of maximal oxygen uptake (VO2 max) in male amateur long-distance cross-country skiers (37.9 ± 6.58 years, 51.08 ± 4.61 VO2 max ml/kg/min) in the preparation period. <b>Methods</b>: In this cross-sectional study, a time trial test was used to determine VO2 max and venous blood via biochemical markers. Descriptive statistics and Pearson correlation were used to analyze the data. The regression model determined the predictors. <b>Results</b>: VO2 max was significantly correlated with nine moderate or weak variables. Two regression models (<i>R</i>² = 0.94 and <i>R</i>² = 0.9) each identified two determinants of VO2 max, hemoglobin (<i>p</i> < 0.001) and C-reactive protein (<i>p</i> < 0.001), as well as erythrocyte sedimentation (<i>p</i> < 0.001) and platelets (<i>p</i> = 0.03). Only hemoglobin positive affected VO2 max. <b>Conclusions</b>: The results may indicate, in addition to results regarding hemoglobin concentration and its changes, the necessity to monitor the immune system, which may affect the capacity for amateur exercise. Biochemical monitoring is an essential tool for evaluating the individual adaptation to exercise and developing an effective training plan. The application of this knowledge can facilitate the achievement of optimal individual performance capabilities among cross-country skiing amateurs.