“Discoveries: Mighty Mouse Bred”
U.S. scientists have bred a "Lance Armstrong" mouse. It can't pedal a bike, but it can run on a treadmill for more than six hours before pooping out.
What accounts for the mouse's amazing endurance? For one thing, its muscle cells have 10 times the usual number of mitochondria, according to the scientists, who work at Case Western Reserve University. Mitochondria are the main energy sources in a cell.
The mouse also produces less lactic acid, a byproduct of metabolism that is released in large amounts during physical exercise. If too much lactic acid builds up in the body, the excess can lead to fatigue and a burning sensation in the muscles. The mighty mouse's body is very similar to that of champion cyclist Lance Armstrong, which produces energy without releasing too much lactic acid, keeping Armstrong from tuckering out.
When put through a grueling uphill treadmill test, the mouse ran for 32 minutes, compared with 19 for regular mice. To maintain that pace, the mouse eats 60 percent more food than other mice do yet weighs half as much.
The mighty rodent is called a PEPCK-Cmus mouse after a certain enzyme that is abundant in the mouse's body. An enzyme is a protein that speeds up a chemical reaction in the body. The scientists have bred 500 PEPCK-Cmus mice, with more on the way. Female mice normally stop reproducing at 1 year of age. The PEPCK-Cmus females reproduce until they are 2½, the equivalent of an 80-year-old woman having a baby!
Why might the writer have compared the new breed of mouse to Lance Armstrong? Please cite evidence from the text.
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