Myostatin is a part of the system of regulation that controls muscle growth. Linked here you'll find recent news of a clinical trial of myostatin inhibition as a treatment for age-related loss of muscle mass, though note that the atrophy of tissue is only one of the reasons for loss of strength. There are also issues within the biochemistry and structure of muscles caused by aging and which must be understood and repaired. Nonetheless, removing the myostatin gene entirely does dramatically increases muscle mass, as demonstrated in natural and engineered mutant lineages in a number of mammalian species. There are even a few rare natural myostatin loss of function human mutants, as muscled as you might expect even at very young ages, and at least one human recipient of gene therapy intended to enhance muscle growth through the same system of regulation. An alternative to one-time, permanent gene therapy is an ongoing treatment with antibodies tailored to block the action of myostatin, as is this case in this clinical trial. The degree of effect is likely to be lower, but from the point of view of the researchers involved the ability to stop the treatment is more important than optimizing performance at this stage:
A proof-of-concept, phase 2 trial by an international research team has found promising results for a myostatin antibody in treating the decline in muscle mass and power associated with aging. "Myostatin is a natural protein produced within the body that inhibits muscle growth. It has been hypothesized for some time that inhibition of myostatin may allow muscle to grow, resulting in improved muscle mass and physical performance. The current study confirms these beliefs."
In the study, injections of a myostatin antibody over a 24-week period resulted in an increase in lean (muscle) mass and improved performance on tasks requiring muscle power in patients older than 75 with low muscle strength, low muscle performance and a history of falling. "This is the first study to show that myostatin antibody treatment improves performance on activities requiring muscle power. 'Muscle power' refers to the ability to generate muscle force quickly. During aging, it is lost more rapidly than muscle strength, contributing to disability, falls, reduced quality of life and, in some instances, death. Myostatin antibody treatment improved muscle power in the elderly, as indicated by improvements in the ability to climb stairs, walk briskly and rise repetitively from a chair. Treatment particularly benefited those who were most frail at baseline, a population who may not be receptive to conventional intervention such as resistance exercise."