Any couch potato with high self-esteem will say his/her piggy shape is because he/she does not go to the gym. And the big muscles are just the result of hard effort and potentially everybody could display them if trained. Our body shape is the result of the combination of three tissues: muscular, bony and fatty. But while the last two are largely regarded as strictly connected to genetics, the first is not.

But this seems to be wrong and the muscles of a person can be trained but not grown, as found by a new research.

The research team even detected the specific genes responsible for a person's lean body mass and genes, more than any factor telling the percentage of lean muscles in a person's body mass. A lower percentage of lean body mass can result in decreased fitness and a higher risk for frailty, including osteoporosis in women.

"We can now identify the individual genes that underlie lean body mass. This will allow us to understand how the body increases muscle mass, and may lead to new treatments for a variety of metabolic disorders," said lead researcher Dr. Tim Spector of King's College London.

The data investigated in the present research came from the TwinsUK Adult Twin Registry, which recorded more than 3,000 female twins in the United Kingdom.

The research team employed whole dual-energy X-ray absorptiometry (DXA) scans to precisely measure lean body mass, bone mass and fat mass. The results accounted for age, body height, total fat and bone mass. The analysis revealed that genes were about 65 % involved in determining the total lean body mass.

Genetic analysis showed that the genes linked to the body mass are situated on portions of the chromosomes 12 and 14. It clearly appeared that the total lean body mass is highly heritable and not connected with other body traits.