title: Effect of show jumping training on the development of locomotory muscle in young horses.
abstract: OBJECTIVE
  To investigate whether training for show jumping that is commenced early after birth affects the characteristics of equine locomotory muscle.
  
  
  METHODS
  19 Dutch Warmblood horses.
  
  
  METHODS
  Horses were assigned to a trained or not trained (control) group. After weaning, training (free jumping [2 d/wk] that was alternated with a 20-minute period of exercise in a mechanical rotating walker [3 d/wk]) was started and continued until horses were 3 years old. Fiber type composition (determined from myosin heavy chain [MyHC] content), fiber area, diffusion index (area supplied by 1 capillary), citrate synthase activity, and Na(+),K(+)-ATPase content were assessed in gluteus medius muscle specimens collected at 0.5, 1, 2, and 3 years.
  
  
  RESULTS
  Developmental changes included an increase in MyHC fiber type IIa and a decrease in type IIad; increases in fiber area, diffusion index, and citrate synthase activity; and a decrease in Na(+),K(+)-ATPase content. The MyHC fiber type I and type IId were detected in high and low proportions, respectively. Training increased Na(+),K(+)-ATPase content, but did not affect other variables.
  
  
  CONCLUSIONS
  In horses, show jumping training at an early age resulted in increased Na(+),K(+)-ATPase content of the deep portions of the gluteus medius muscle. The lack of training effects on the other muscle characteristics can partly be explained by the fact that an appropriate (aerobic) fiber type composition was already established at training commencement. These data also suggested that the developmental changes in equine muscle represent sufficient adaptation to meet the demands of this specific training.
authors.affiliation: Department of Pathobiology, Faculty of Veterinary Medicine, Utrecht University, 3508 TD Utrecht, The Netherlands.
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Rietbroek
authors.forename: Elizabeth G
authors.initials: EG
authors.lastname: Dingboom
authors.forename: Brian J L J
authors.initials: BJ
authors.lastname: Joosten
authors.forename: Karin
authors.initials: K
authors.lastname: Eizema
authors.forename: Maria E
authors.initials: ME
authors.lastname: Everts
mesh_terms: D000818:Animals; D001706:Biopsy / Q000379:methods; D002950:Citrate (si)-Synthase / Q000378:metabolism; D006736:Horses / Q000254:growth & development* / Q000378:metabolism; D007150:Immunohistochemistry / Q000662:veterinary; D016014:Linear Models; D024510:Muscle Development / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000201:enzymology / Q000502:physiology; D018482:Muscle, Skeletal / Q000201:enzymology / Q000254:growth & development*; D018995:Myosin Heavy Chains / Q000378:metabolism; D010805:Physical Conditioning, Animal / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D002950:Citrate (si)-Synthase; D018995:Myosin Heavy Chains; D000254:Sodium-Potassium-Exchanging ATPase