Changes in neutrophil functions during a 10-month soccer season and their effects on the physical condition of professional Japanese soccer players.

We examined changes in neutrophil function of soccer players over a 10-month period and determined its effectiveness as an index for athlete physical condition. Subjects included 21 male professional Japanese soccer players. Data on body composition, myogenic enzymes and neutrophil function were obtained before and after 2 h of training at 3 investigation points: one week before opening season, at season mid-point, and one week before the last game of the season. As a result, change ratios of myogenic enzyme levels before and after the 2-hr training session at the third investigation point were significantly higher compared to the two other points. Reactive oxygen species production and phagocytic activity significantly increased after 2-hr training session at point 1, although the extent of the increase became smaller over time and ROS production capability decreased significantly by point 3 assessment. Fatigue, especially muscle fatigue, chronically accumulated along with a gradual decrease in neutrophil immune function over the 10-month season. Therefore, determination of neutrophil function can be used as a useful index to assess and understand an athlete's physical condition.