Exercise-induced glycogen utilization by the respiratory muscles.

Some controversy exists in the literature as to whether or not diaphragmatic glycogen is utilized during exercise. In this study male Sprague-Dawley rats were used to determine whether prolonged treadmill exercise would result in a significant reduction of glycogen concentration in the respiratory muscles. Untrained rats were run to exhaustion at a speed of 24 m/min, up a 10% grade. Run time averaged 48:30 min. After exercise a significant reduction in glycogen was observed in the diaphragm (43% of control), intercostals (43%), heart (39%), and plantaris (76%). In the diaphragm a significant reduction was shown in both types I and II fibers using the periodic acid-Schiff (PAS) stain for glycogen. These findings show that muscles with vastly different aerobic capacities utilize endogenous glycogen during moderately intense submaximal endurance exercise and that the costal diaphragm muscle is not an exception as has recently been suggested.