Abstract:
Purpose: To examine muscle and blood metabolites during soccer match play and relate it to possible changes in sprint performance.

Methods: Thirty-one Danish fourth division players took part in three friendly games. Blood samples were collected frequently during the game, and muscle biopsies were taken before and after the game as well as immediately after an intense period in each half. The players performed five 30-m sprints interspersed by 25-s recovery periods before the game and immediately after each half (N = 11) or after an intense exercise period in each half (N = 20).

Results: Muscle lactate was 15.9 +/- 1.9 and 16.9 +/- 2.3 mmol[middle dot]kg-1 d.w. during the first and second halves, respectively, with blood lactate being 6.0 +/- 0.4 and 5.0 +/- 0.4 mM, respectively. Muscle lactate was not correlated with blood lactate (r2 = 0.06-0.25, P >0.05). Muscle glycogen decreased (P < 0.05) from 449 +/- 23 to 255 +/- 22 mmol[middle dot]kg-1 d.w. during the game, with 47 +/- 7% of the muscle fibers being completely or almost empty of glycogen after the game. Blood glucose remained elevated during the game, whereas plasma FFA increased (P < 0.05) from 0.45 +/- 0.05 to 1.37 +/- 0.23 mM. Mean sprint time was unaltered after the first half, but longer (P < 0.05) after the game (2.8 +/- 0.7%) as well as after intense periods in the first (1.6 +/- 0.6%) and second halves (3.6 +/- 0.5%). The decline in sprint performance during the game was not correlated with muscle lactate, muscle pH, or total glycogen content.

Conclusion: Sprint performance is reduced both temporarily during a game and at the end of a soccer game. The latter finding may be explained by low glycogen levels in individual muscle fibers. Blood lactate is a poor indicator of muscle lactate during soccer match play.