The Effect of Four-Month Training on Biochemical Variables in Amateur Cross-Country Skiers.

: Research on the effects of training on the health of amateur cross-country skiers remains limited, particularly on biochemical parameters. Therefore, this study aimed to assess such changes in response to four months of training for amateur cross-country skiers. : Blood samples were collected after spring training in May (active rest) and in September at the end of the preparatory period. The Wilcoxon signed-rank test was used for comparison of both measurements (initial and final). : Training in a group of amateur cross-country skiers exerts a statistically significant influence on the decrease in leukocyte count (thousand/µL) ( = 0.045) and the decrease in mean corpuscular hemoglobin concentration (MCHC) (g/dL) ( = 0.021). The other parameters did not show statistically significant changes. : The change in MCHC and WBC can be attributed to adaptation to prolonged exercise, with a simultaneous increase in VO max. It should not be identified with pathology. The decrease in MCHC was likely attributable to changes in hydration status and a slight reduction in hemoglobin concentration. Similarly, it is recommended that other biochemical parameters be within the reference ranges.