If you have more muscles, you will have more place to store glucose in them (in the form of glycogen), but what seems to be more important is the rate of glucose uptake by muscles, which increases with endurance training (running, swimming...) rather than with resistance training (body building).
The Role of Skeletal Muscle Glycogen Breakdown for Regulation of Insulin Sensitivity by Exercise
The glycogen content is higher in endurance trained subjects compared
to untrained subjects and glycogen content increases in muscles after
The reduction of skeletal muscle glycogen after exercise allows a
healthy storage of carbohydrates after meals and prevents development
of type 2 diabetes.
Exercise increases the glucose uptake by muscles by increasing insulin sensitivity:
Acutely, exercise improves insulin sensitivity in both healthy
subjects and insulin resistant people. The improved insulin
sensitivity after a single bout of exercise is short-lived but
repeated bouts of endurance training improve insulin sensitivity
beyond the acute effect of the last training session.