The researchers next had the men complete a single session of brief, but strenuous, lower-body weight training, using a knee-extension machine. Since none of the men lifted weights, this exercise was expected to stress their muscles in an unfamiliar way. A few hours later, the researchers again drew blood and biopsied the men’s muscles.
Then they checked the tissues for a broad slate of inflammatory cells and gene markers. Bogglingly complex, inflammation involves multiple genes and cells that talk to other genes and cells and dynamically ramp up, or tamp down, the process. Immediately after any bodily injury or strain, which includes strenuous exercise, inflammation helps tissues to heal and strengthen. But if inflammation lingers, it can become harmful and, in muscles, block them from growing larger and stronger after exercise.
The researchers found that inflammatory responses differed in the men. The young athletes displayed the least amount of inflammation in their blood and muscles at the start of the study and continued to do so after the workout. While their muscles flared briefly after exercise with inflammatory cells and related gene activity, the microscopic examination found that countervailing anti-inflammatory signals were also increasing and should soon cool the inflammation.
A similar response occurred inside the muscles of the elderly athletes, although their inflammatory markers were slightly higher and their anti-inflammatory reactions a bit lower.
But in the untrained elderly men, inflammation was much more of a bushfire, spiking higher than among the other men and showing fewer cellular signs of resolving any time soon.
Taken as a whole, these results suggest that long-term exercise may help aging muscles remain healthy in part by readying them to dissipate inflammation, Dr. Trappe says. But on the flip side, sedentary living seems to set up muscles to overreact to strain and remain inflamed, potentially leading to fewer muscular gains when someone does exercise.
This study was small, though, and examined the men’s muscles only once, soon after exercise. It did not look into whether and how their muscles actually changed over time with training.
More important, the findings should not discourage middle-aged or older people who have been inactive from starting to visit the gym, Dr. Trappe says. “Even if inflammation gets in the way a bit at first, your muscles will respond and grow,” he says, and eventually should start to resemble those of people who have been exercising lifelong.