title: Muscle glycogen degradation during simulation of a fatiguing soccer match in elite soccer players examined noninvasively by 13C-MRS.
abstract: OBJECTIVE
  The purpose of this research project was to noninvasively determine individual muscle glycogen [Gly] degradation during a test intended to predict individual fatigue in intense soccer matches.
  
  
  METHODS
  The [Gly] of the calf muscles of 17 elite soccer players [age = 17.4 +/- 0.8 (SD)] were measured with 13C-MRS before and after an alternating velocity test to exhaustion. Blood samples were taken before and 3 min after the test for determination of blood metabolites.
  
  
  RESULTS
  Average muscle [Gly] was 135 +/- 53 mmol x (kg wet weight)(-1) before and 87 +/- 27 mmol x (kg wet weight)(-1) (P < 0.001) after exhaustion (42 +/- 25 min). There was a high correlation (r = 0.87, P < 0.0001) between muscle [Gly] at rest and net muscle [Gly] utilized. There was also a more moderate correlation (r = 0.62, P < 0.01) between net muscle [Gly] used and time to exhaustion during the soccer-specific test. There was some evidence of correlation (r = 0.42, P = 0.09) between resting [Gly] and time to exhaustion. Plasma lactate increased (P < 0.001) from 0.8 +/- 0.4 before the test to 2.5 +/- 1.0 mmol x L(-1) at exhaustion, whereas ammonia was raised (P < 0.0001) from 44.1 +/- 10.3 to 89.7 +/- 14.9 micromol x L(-1). Similarly, plasma free fatty acids were elevated (P < 0.0001) from 148 +/- 106 to 797 +/- 401 micromol x L(-1), and glycerol was increased (P < 0.0001) from 48.3 +/- 17.7 to 182.2 +/- 61.8 micromol x L(-1). Insulin levels (11.9 +/- 3.7 vs 11.7 +/- 4.8 microU x mL(-1)) remained the same. Creatine kinase levels increased (P < 0.0001) from 486 +/- 501 to 640 +/- 548 micromol x L(-1) after the test.
  
  
  CONCLUSIONS
  We conclude that exhaustion during soccer-specific performance is related to the capacity to utilize muscle [Gly]. The results underline the importance of dietary counseling (glycogen loading and resynthesis strategies) and proper training to enhance the glycogen levels and glycogenolytic capacity of the players.
authors.affiliation: Department of Biochemistry and Molecular Biology, University Autonoma of Barcelona, Spain. ricosanzj@missouri.edu
authors.forename: J
authors.initials: J
authors.lastname: Rico-Sanz
authors.forename: M
authors.initials: M
authors.lastname: Zehnder
authors.forename: R
authors.initials: R
authors.lastname: Buchli
authors.forename: M
authors.initials: M
authors.lastname: Dambach
authors.forename: U
authors.initials: U
authors.lastname: Boutellier
mesh_terms: D000293:Adolescent; D000641:Ammonia / Q000097:blood; D002247:Carbon Isotopes; D003376:Counseling; D003402:Creatine Kinase / Q000097:blood; D004032:Diet; D017079:Exercise Tolerance / Q000502:physiology; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006003:Glycogen / Q000097:blood / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D007866:Leg; D009682:Magnetic Resonance Spectroscopy; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D012916:Soccer / Q000193:education / Q000502:physiology*; D013997:Time Factors
chemical_list: D002247:Carbon Isotopes; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D019344:Lactic Acid; D000641:Ammonia; D006003:Glycogen; D003402:Creatine Kinase