Recovery of muscle glycogen concentrations in sled dogs during prolonged exercise.
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.
McKenzie
Erica
E
Department of Physiological Sciences, Oklahoma State University, Stillwater, OK, USA.
Holbrook
Todd
T
Williamson
Kathy
K
Royer
Christopher
C
Valberg
Stephanie
S
Hinchcliff
Ken
K
Jose-Cunilleras
Eduard
E
Nelson
Stuart
S
Willard
Michael
M
Davis
Michael
M
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
D006003:Glycogen; D003402:Creatine Kinase