A rare genetic mutation can double human muscle mass without any exercise

The discovery of myostatin in 1997 revealed a genetic brake that naturally limits muscle growth in humans. While most people produce this protein to keep their physique in check, rare individuals with a specific genetic mutation experience a lifelong reduction in myostatin. This results in the 'Mahler family' phenotype, characterized by 20 percent more lean muscle mass and significantly lower body fat compared to the general population, all achieved without exercise.