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"It's surprising," said principal investigator Todd A. Trappe, an associate professor with the Human Performance Lab at Ball State University in Muncie, Ind. "But the bottom line is that you would have to search pretty long and hard to find anything that would demonstrate the strong and positive effect on muscle growth that we observed. And I certainly don't think you're going to find it in anything that's non-prescription."
His team was to present its research April 6 at the Experimental Biology annual meeting, in San Diego.
The finding stems from an earlier study the team conducted on the short-term impact of ibuprofen and acetaminophen on muscle metabolism among young men and women who lifted weights over a 24-hour period. The impact here was negative, as the two drugs were found to have blocked the workings of an enzyme known as Cox and inhibited the adding of new protein to muscle.
"So we thought we needed to look at this long-term and among older people, who are more likely to be taking these drugs chronically for pain and other reasons, because we're trying to tell them that they need to be more active as they age, yet there may be an interfering effect here," Trappe said.
To explore the question, the researchers tracked 36 men and women between the ages of 60 and 78 for who enrolled in a three-month regimen of knee-extensor weight training at the Human Performance Lab.
Training intensity and duration — 15- to 20-minute sessions three times per week — was set at a level known by the researchers to prompt significant muscle mass and strength growth in a participant's quadriceps muscles, in the absence of any medication.
In conjunction, the participants were randomly divided into an acetaminophen group, an ibuprofen group or a placebo group.
The two drugs were consumed at recommended daily dosage levels, as noted on current over-the-counter packaging.
To the research team's surprise, an analysis of muscle tissue samples taken before and after revealed that while the placebo group experienced a 7 percent growth in muscle mass and strength, those taking either acetaminophen or ibuprofen experienced an even greater gain — 40 percent to 60 percent more.
Trappe theorized that the two drugs could be provoking the body to overcompensate for an initial blocking of the enzyme any muscle needs to grow — prompting muscles to send out fresh and powerful signals demanding even more enzyme than the body would normally produce.
"But as of now, we just don't know," Trappe said. And he cautioned against anyone running out to down over-the-counter drugs of any kind before further research is conducted.
In the meantime, David Bassett Jr., a professor of exercise science at the University of Tennessee in Knoxville, hailed the reputation of the physiology lab that conducted the research and described the finding as "within the realm of believability."
"A 7 percent increase in strength and mass based on resistance training alone doesn't strike me as that great of a gain, relative to other similar studies," he noted. "But I do think it is a new and pretty significant finding that these two drugs would bring about a greater increase than otherwise."
"It's important," Bassett added, "because some even make the case that resistance training among the elderly is almost more important than aerobic training, because weight training can significantly improve functional strength and the ability to carry out the activities of daily independent living."
However, Bassett pointed out that despite the apparent absence of serious side effects, one study is not enough to conclude that ibuprofen and acetaminophen really do confer such muscle gain benefits.
"There's probably no harm taking them, but there also may be no benefit either," he said. "It's still up in the air, and it will be necessary to verify these findings with further research. But if it holds up, it is potentially something that many people would want to try."
SOURCES: Todd A. Trappe, Ph.D., associate professor, Human Performance Lab, Ball State University, Muncie, Ind.; David Bassett Jr., Ph.D., professor, exercise science, University of Tennessee, Knoxville; April 6, 2008, presentation, Experimental Biology annual meeting, San Diego
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