Muscles (including heart) work at a steady, sustained pace get their energy by combining oxygen with glucose (a simple sugar found in certain foods, especially fruits, and a major source of energy in human and animal body fluids and fats to produce and release energy(along with carbon dioxide).
(a simple sugar; found; L:in certain foods, especially fruits, and a major source of energy in human and animal body fluids and fats)
a simple sugar
found
L:in certain foods, especially fruits, and a major source of energy in human and animal body fluids and fats