A debrief with CNN's Ann Kellan

Her talk with a key researcher on IGF-1

Lee Sweeney, an associate professor of physiology and medicine at the University of Pennsylvania Medical School, says he realized early on that the interests of athletic competition might muscle in on his research into IGF-1.

(CNN) -- For her report airing on Next@CNN, CNN Science Correspondent Ann Kellan interviewed physiologist Lee Sweeney at the University of Pennsylvania on his research into the potential applications in humans of IGF-1, or Insulin-like Growth Factor-One.

Kellan later was debriefed on the air about her interview with Sweeney.

Ann Kellan: He showed me the genetically altered mice, obviously more muscular than their siblings. At the time (August), he was planning the next step of the research -- to insert the gene into dogs with muscular dystrophy.

After follow-up discussions with Sweeney this month, he reports that his team is now developing the gene to insert into the dog's muscles. He expects to insert the gene into the first dog by this summer.

CNN: How soon will this genetic therapy be tested in humans?

Kellan: An optimistic estimate would be five years at the earliest.

Gene therapy in humans has not been proven to work. Here's why. To get the gene into a mouse, researchers hollow out a virus and insert the IGF-1 gene into the virus, then inject it into mouse muscles.

In mice, it worked with no side effects. Humans who have had genes delivered via viruses have had mixed results. Some have died from complications involving the viruses. So, even if it worked in mice, how the gene gets into the human muscle may be a challenge for researchers.

CNN: You say in your story that researchers are going to try this gene therapy on dogs. Do these dogs have a disease?

Kellan: Yes, according to the lead scientist, Lee Sweeney, researchers will inject the gene into dogs with muscular dystrophy. Like humans, dogs get MD and their muscles deteriorate.

If it works in dogs like it did in mice, then humans may be next. When mice with MD got the gene therapy, it didn't cure the disease but slowed the progress of muscle deterioration. The muscles were less damaged and stayed strong longer than in normal mice with MD. It didn't cure the disease, but it slowed the muscle damage.

CNN: If one day humans could successfully bulk up with this gene therapy could they inject too much and get too much of a good thing? Could they build up too much muscle, more than their bones and their joints can handle?

Kellan: It's a concern and something researchers are investigating. According to Sweeney, there are mechanisms in our bodies that prevent that problem -- mechanisms that allow only a certain amount of muscle buildup, which the body can handle. But, if scientists shut off that mechanism, theoretically, you could overload the skeleton and joints with muscle, leading to serious injuries -- even death.

CNN: Is this gene therapy something that would benefit already aging and sagging muscles?

Kellan: Yes. Sweeney says if this works in humans as it does in mice, an elderly person with sagging, out-of-shape muscles could benefit from the gene therapy. An injection could restore and tone already aging and sagging muscles, as long as there isn't a lot of damage to the muscles. IGF-1 will not repair scar tissue created when a muscle is damaged or injured.

CNN: Does that mean I wouldn't have to work out to keep muscles toned and in shape?

Kellan: If it works in humans as it does in mice, lifting weights to keep muscles toned could be a thing of the past.

Sweeney says you'd still have to worry about cardiovascular fitness -- keeping the heart pumping. But this gene therapy is still years away for human use; researchers still have a number of hurdles yet to overcome, so don't give up those weights just yet.

Ann Kellan's report on the IGF-1 research airs on this week's Next@CNN -- at 1 p.m. EST on Saturday and 4 p.m. EST on Sunday.