Effect of a single bout of exercise and chronic exercise training on insulin sensitivity in racing sled dogs

Two experiments were designed to investigate the role of exercise on insulin sensitivity (IS) in Alaskan racing sled dogs. In both experiments, IS was quantified with an isoglycemic-hyperinsulinemic clamp (IHC), whereby IS was defined as the glucose infusion rate (GIR) divided by the mean insulin concentration during the clamp. In Experiment 1, IS was quantified in 12 racing sled dogs during three stages of exercise training: unexercised for 4 months over the summer (deconditioned), and after two and four months of exercise conditioning. At each stage IS was assessed in unexercised dogs (n=6) and 60 h following a standard exercise challenge (n=6) consisting of a 35.4 km run completed in 2.5 h. In Experiment 2, IS was assessed in deconditioned dogs (n=6) and in well-conditioned dogs that had either completed a 708 km race 5-days prior (n=3) or were unraced for the previous month (n=3). In Experiment 1, there were no significant differences (P>0.05) in GIR or IS between the three levels of conditioning, nor were there any effects of the exercise bout 60 h prior to the IHC. In Experiment 2 there was no significant difference in IS between well-conditioned dogs and untrained dogs (P>0.05). However, dogs that completed a 708 km race 5-days prior to the IHC had a significantly higher IS than dogs that were deconditioned and those that were conditioned but unraced. These results suggest that the workload of an exercise challenge is a factor in post-exercise changes in IS but that exercise conditioning has little impact on IS in Alaskan sled dogs.