title: Recovery of muscle glycogen concentrations in sled dogs during prolonged exercise.
abstract: OBJECTIVE
  To determine the depletion of muscle glycogen during five consecutive days of endurance exercise in Alaskan sled dogs consuming a high-fat, low-carbohydrate diet.
  
  
  METHODS
  Forty-two fit Alaskan sled dogs were used in the study, of which six dogs served as nonexercising control animals. The remaining 36 dogs ran 160 km x d(-1) for up to 5 d while consuming a diet providing approximately 50% of calories as fat and 15% as carbohydrate. Muscle biopsies were performed on six randomly selected dogs before feeding and within 4 h after each 160-km run was completed. Muscle samples were prepared for analysis of glycogen content and myosin ATPase staining. Serum creatine kinase (CK) activity was measured once before exercise and after each 160-km run.
  
  
  RESULTS
  Thirty-three of 36 dogs completed the runs. Muscle glycogen concentration was highest in sedentary dogs (340 +/- 102 mmol x kg(-1) dry weight), declined to 73 +/- 16 after 160 km and subsequently increased to similar levels between 320 and 800 km (320 km: 177 +/- 34; 800 km: 213 +/- 44). Postexercise serum CK activity was significantly elevated throughout the study.
  
  
  CONCLUSIONS
  Skeletal muscle in Alaskan sled dogs has remarkable glyconeogenic ability as demonstrated by repletion to greater than 50% of resting muscle glycogen concentrations after the second of five consecutive 160-km runs even when fed a low-carbohydrate, high-fat diet. Whether this finding is attributable to rapid repletion of muscle glycogen during brief recovery periods versus progressive utilization of alternative substrates remains to be investigated.
authors.affiliation: Department of Physiological Sciences, Oklahoma State University, Stillwater, OK, USA.
authors.forename: Erica
authors.initials: E
authors.lastname: McKenzie
authors.forename: Todd
authors.initials: T
authors.lastname: Holbrook
authors.forename: Kathy
authors.initials: K
authors.lastname: Williamson
authors.forename: Christopher
authors.initials: C
authors.lastname: Royer
authors.forename: Stephanie
authors.initials: S
authors.lastname: Valberg
authors.forename: Ken
authors.initials: K
authors.lastname: Hinchcliff
authors.forename: Eduard
authors.initials: E
authors.lastname: Jose-Cunilleras
authors.forename: Stuart
authors.initials: S
authors.lastname: Nelson
authors.forename: Michael
authors.initials: M
authors.lastname: Willard
authors.forename: Michael
authors.initials: M
authors.lastname: Davis
mesh_terms: D000818:Animals; D003402:Creatine Kinase / Q000097:blood; D004285:Dogs; D005260:Female; D006003:Glycogen / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010805:Physical Conditioning, Animal
chemical_list: D006003:Glycogen; D003402:Creatine Kinase