title: Effect of additional speed endurance training on performance and muscle adaptations.
abstract: OBJECTIVE
  The present study examined the effect of additional speed endurance training (SET) during the season on muscle adaptations and performance of trained soccer players.
  
  
  METHODS
  Eighteen subelite soccer players performed one session with six to nine 30-s intervals at an intensity of 90%-95% of maximal intensity (SET) a week for 5 wk (SET intervention). Before and after the SET intervention, the players carried out the Yo-Yo intermittent recovery level 2 (Yo-Yo IR2) test, a sprint test (10 and 30 m), and an agility test. In addition, seven of the players had a resting muscle biopsy specimen taken and they carried out a running protocol on a motorized treadmill before and after the SET intervention.
  
  
  RESULTS
  After the SET intervention, the Yo-Yo IR2 test (n = 13) performance was 11% better (P < 0.05), whereas sprint (n = 15) and agility (n = 13) performances were unchanged. The expression of the monocarboxylate transporter 1 (n = 6) was 9% higher (P < 0.05). and the expression of the Na(+)/K(+) pump subunit β(1) (n = 6) was 13% lower (P < 0.05) after the SET intervention. The Na(+)/K(+) pump subunits α(1), α(2), as well as the monocarboxylate transporter 4 and the Na(+)/H(+) exchanger 1 (n = 6) were unchanged. After the SET intervention, the relative number of Type IIx fibers and oxygen consumption at 10 km.h(-1) were lower (P < 0.05), whereas VO(2max) was unchanged.
  
  
  CONCLUSIONS
  In conclusion, adding ∼30 min of SET once a week during the season for trained soccer players did lead to an improved ability to perform repeated high-intensity exercise, with a concomitant increase in the expression of monocarboxylate transporter 1 and an improved running economy.
authors.affiliation: Department of Exercise and Sport Sciences, Section of Human Physiology, University of Copenhagen, Denmark.
authors.forename: Thomas Petursson
authors.initials: TP
authors.lastname: Gunnarsson
authors.forename: Peter Møller
authors.initials: PM
authors.lastname: Christensen
authors.forename: Kris
authors.initials: K
authors.lastname: Holse
authors.forename: Danny
authors.initials: D
authors.lastname: Christiansen
authors.forename: Jens
authors.initials: J
authors.lastname: Bangsbo
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D056352:Athletes; D054874:Athletic Performance / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D019344:Lactic Acid / Q000097:blood / Q000378:metabolism; D008297:Male; D027501:Monocarboxylic Acid Transporters / Q000096:biosynthesis; D009124:Muscle Proteins / Q000096:biosynthesis; D018482:Muscle, Skeletal / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D012420:Running / Q000502:physiology*; D012916:Soccer / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis; D027981:Symporters / Q000096:biosynthesis; D055815:Young Adult; D000099233:Monocarboxylate Transport Protein 1
chemical_list: D019344:Lactic Acid; D027501:Monocarboxylic Acid Transporters; D009124:Muscle Proteins; D000254:Sodium-Potassium-Exchanging ATPase; D027981:Symporters; D000099233:Monocarboxylate Transport Protein 1; C406962:SLC16A4 protein, human