ROOSEVELT PARK, Mich. -- Liam Hoekstra was hanging upside down by his feet when he performed an inverted sit-up, his shirt falling away to expose rippled abdominal muscles.
It was a display of raw power one might expect to see from an Olympic gymnast. Liam is 19 months old.
But this precocious, 22-pound boy with coffee-colored skin, curly hair and washboard abs is far from a typical toddler.
"He could do the iron cross when he was 5 months old," his adoptive mother, Dana Hoekstra of Roosevelt Park, said, referring to a gymnastics move in which a male athlete suspends himself by his arms between two hanging rings, forming the shape of a cross.
"I would hold him up by his hands and he would lift himself into an iron cross. That's when we were like, 'Whoa, this is weird,' " Hoekstra said.
Liam has a rare genetic condition called myostatin-related muscle hypertrophy, or muscle enlargement. The condition promotes above-normal growth of the skeletal muscles; it doesn't affect the heart and has no known negative side effects, according to experts.
Liam has the kind of physical attributes bodybuilders and other athletes dream about: 40 percent more muscle mass than normal, strength, quickness, a speedy metabolism and almost no body fat.
"We call him The Hulk, Hercules, the Terminator," his mother said.
Liam can run like the wind, has the agility of a cat, lifts pieces of furniture that most children his age couldn't push across a slick floor and eats like there is no tomorrow -- without gaining weight.
"He's hungry for a full meal about every hour because of his rapid metabolism," Dana Hoekstra said. Liam's condition is more than a medical rarity: It could help scientists unlock the secrets of muscle growth and muscle deterioration. Research on adults who share Liam's condition could lead to new treatments for debilitating ailments such as muscular dystrophy and osteoporosis.
If researchers can control how the body produces and uses myostatin, the protein could become a powerful weapon in the pharmaceutical arsenal. It also could become a hot commodity among athletes looking to gain an edge, perhaps illegally, on the competition, experts said.
For Liam, the condition has one potential drawback: Infants and toddlers need some body fat to feed brain growth and the development of the central nervous system.
Without adequate body fat, a child's growth can be stunted and the central nervous system can be impaired, said Dr. Erlund Larson, an internist at Hackley Hospital who is familiar with Liam's condition.
That Liam appears to be thriving, physically and mentally, is almost as amazing as his feats of strength. The product of a troubled mother who gave him up for adoption at birth, Liam was born with a suite of medical problems.
The fact that Liam was adopted by a physician assistant's family hundreds of miles from his birthplace -- a stable family with the knowledge and means to give him all the food, nurturing, horseplay and love he needs to thrive -- might be the most miraculous part of his story.
Myostatin-related muscle hypertrophy was first documented in beef cattle and mice in the late 1990s, according to scientific literature.
The first human case was documented in 2000, in a German boy, but wasn't reported in medical literature until 2004. The condition is so rare in humans that scientists don't know how many people have it, said Dr. Kathryn R. Wagner, a genetics expert at Johns Hopkins.
Liam's father, a die-hard University of Michigan fan, already is dreaming big things for him.
"I want him to be a football player. He could be the next Michael Hart," Neil Hoekstra said, referring to U-M's star running back.