Intramuscular Triglyceride Utilization by Red,White,and Intermediate Skeletal Muscle and Heart During Exhausting Exercise 1

Summary

A bout of swimming to exhaustion resulted in an approximately 70% depletion of triglyceride stores in the red portion of the quadriceps muscle in rats. In contrast intramuscular triglycerides were unchanged in the white portion of quadriceps, and decreased only 25% in soleus muscle which is made up predominantly of intermediate fibers. Cardiac triglycerides underwent a small (11%) and statistically not significant reduction. Glycogen stores were reduced approximately 70% in all 3 types of skeletal muscle, and 32% in the heart. Liver glycogen was almost completely depleted, resulting in hypoglycemia. Assuming complete oxidation of the glycogen and triglycerides that disappeared from red muscle, triglycerides supplied roughly two-thirds as much energy to the working red fibers as did glycogen.