Blocking Myostatin Increases Muscle Mass (IMAGE) Johns Hopkins Medicine Caption Mice without the gene for myostatin (right) have nearly twice as much muscle mass as normal mice (left). Credit Se-Jin Lee Lab Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.