The IGF gene is a multitasker. It makes different proteins, depending on the circumstances. When a muscle is exercised by a long-distance runner, the gene manufactures something called IGF-1. But when a muscle is intensely stretched or contracted, as by a weight lifter, the gene produces Mechano Growth Factor. MGF, which was discovered by University of London professor of anatomy Geoffrey Goldspink, instigates muscle growth by activating the "satellite cells" in the muscle, causing them to divide and fuse, creating the nuclei for new muscle cells.
Both MGF and IGF-1 encourage muscles to grow. (IGF-1 seems to activate protein synthesis necessary for new muscle cells.) Scientists have created mighty mice using both compounds. When Goldspink injected a gene for MGF into mouse muscles, he recorded a 20 percent increase in muscle mass in two weeks and a 25 percent increase in muscle strength—without the mouse hitting the weight room and without apparent side effects. Similar tests have been done on mice using IGF-1. They, too, became supermice, though it took longer.
Goldspink hopes MGF could be a therapy for the sick and frail: Muscular dystrophy and age-related muscle loss are the obvious targets. But he has no doubt "there will be misuse of MGF" by athletes and bodybuilders. (In fact, the International Olympic Committee has already commissioned him to develop a test for MGF, IGF-I, and human-growth hormone abuse.) But it won't just be hard-core muscleheads who experiment with MGF; if it turns out that MGF is safe and effective in 65-year-olds with sarcopenia, 50-year-olds will start asking for it, then all the rest of us. If you could get 25 percent bigger pecs without a visit to the gym, wouldn't you consider it?
No clinical trials of MGF have started yet. The technique for inserting the gene into muscles is not complicated, but gene therapy is never easy. Although Goldspink's experiment resulted in Schwarzenegger mice, that doesn't mean that MGF will successfully pump up normal humans. Goldspink saw no side effects in his mice tests but wonders if prolonged application of the gene would cause damage. (Goldspink expects a single dose of the gene would last about a year.) And as for IGF-1, it may have health risks that MGF does not. For example, it could damage the heart if it is injected directly into the bloodstream.
Goldspink hopes MGF will be used therapeutically within five years. Athletes are already experimenting with IGF-1, which is widely sold on the Internet (mostly by companies that seem less than concerned about its safety). So far, MGF hasn't found its way to the gym black market because Goldspink has tightly limited its distribution and because MGF is tricky to make, but it's just a matter of time before MGF slips out to athletes.