People lose muscle mass as they age, starting around age 40 and even faster from around age 75. Not only do we get weaker overall, our remaining muscles can't bounce back from injury or strain as quickly as younger bodies. It turns out that burned out stem cells are behind this muscle decline – and, researchers have found in an important new study, pepping up those stem cells and injecting them back into the body can make old, injured muscles function as well as young ones.
Muscle stem cells help the body manufacture new muscle cells. By studying mice, scientists found that by old age – the mouse equivalent of 80 years – a huge number of those cells have stopped working right. Two particular proteins in those cells were overactive, making them no longer able to function properly. When the researchers isolated muscle stem cells and treated them with a drug that blocked those two proteins, the stem cells started working again. The team transplanted the old-but-rejuvenated stem cells into elderly mice recovering from injuries–much like elderly humans often have to recover from surgeries, falls, or other muscle damage. In the muscles that got transplanted cells, those mice showed huge improvements compared to normal mice their age.
So far, they've just tested the technique in mice – but even if it works in humans, that doesn't mean it will be turning octogenarians into bodybuilders. "This isn't a magical elixir that will make all of our muscles stronger," says Ben Cosgrove, a stem cell biologist at Stanford who worked on the study. "This therapeutic approach necessitates the transplantation of cells to specific muscles. They can't be injected like a blood transfusion would be."
The treatment could help in situations in improving recovery after hip surgery, for instance, which can be taxing on weak muscles. It could also help strengthen eye, hand, or swallowing muscles, which sometimes atrophy with age. And for now, Cosgrove says, "the most proven therapy is exercise." Regular workouts can help you retain muscle as you age in the first place.