High blood sugar may limit aerobic exercise capacity

Lessard and colleagues increased blood sugar levels in two groups of mice:The mice in both groups exercised equally, running roughly 500 kilometers, or about 311 miles, over the course of the study.Still, compared with a control group that had lower blood sugar levels, both sets of hyperglycemic mice failed to gain significant aerobic capacity.The fact that both groups developed the condition suggests that the effect is related to blood sugar, not obesity or the effects of insulin.According to Prof. Lessard, “to allow more oxygen to be delivered to the muscle, which helps to increase our aerobic fitness levels.”However, the researchers saw no such muscle adaptation in the hyperglycemic mice.They suggest that high levels of sugar are interrupting the remodeling of muscle by altering proteins in the space between muscle cells, where new blood vessels would typically have formed.The study authors add that another possible factor may be a malfunctioning of the c-Jun N-terminal kinase (JNK) pathway.