Effect of diet and training on muscle glycogen storage and utilization in sled dogs

Two groups of eight Alaskan huskies fed either a high-fat (HFD; 60% kcal from fat and 15% kcal from carbohydrate) or a high-carbohydrate diet (HCD; 60% kcal from carbohydrate and 15% kcal from fat) performed standard aerobic (1 h at 4 m/s on a 0% slope) and anaerobic (3 min at 6.7 m/s on a 10% slope) tests before and after training. Before and immediately after each exercise test, venous blood samples were collected and analyzed for lactate and pyruvate, and muscle biopsies were obtained under local anesthesia from the semitendinosus muscle and analyzed for total muscle glycogen (TMG) concentration. Training was associated with a significant increase in preexercise TMG in both diet groups; this effect was most marked in the HCD. There was no effect of diet or training on TMG utilization during the aerobic tests. The rate of TMG utilization during the anaerobic tests was between 20 and 40 times greater than that measured during the aerobic tests. The pre- to postexercise change in TMG was dependent on preexercise TMG in the HCD and HFD for both anaerobic tests (HCD: P < 0.01, r = 0.81; HFD: P < or = 0.03, r = 0.66). It is concluded that the increased glycogen storage associated with the HCD was more than offset by the more rapid rate of glycogen utilization in this group. HFD facilitated carbohydrate sparing during intense exercise and should thus be a better dietary strategy for endurance in sled dogs.