Before and after this process, the researchers took blood, biopsied tissue, centrifuged fluids, and looked under a microscope for vesicles and other molecular changes in the tissue.
They noted a lot. Before their improvised strength training, rodent leg muscles were teeming with a special extract of genetic material known as miR-1, which modulates muscle growth. In normal and untrained muscles, miR-1, one of a group of tiny strands of genetic material known as microRNAs, maintains a brake on muscle building.
After rodent resistance exercise, which consisted of walking around, the animals’ leg muscles appeared to be miR-1 depleted. At the same time, the vesicles in their bloodstream were now filling with the substance, as was neighboring fatty tissue. It seems, the scientists concluded, that the muscle cells of the animals somehow packed these chunks of microRNA that delay the hypertrophy in the vesicles and sent them to neighboring fat cells, which allowed the muscles to grow immediately. .
But what did miR-1 do to the fat once it got there, the scientist wondered? To find out, they labeled the vesicles of weight-trained mice with a fluorescent dye, injected them into untrained animals, and followed the trajectories of the glowing bubbles. The vesicles concentrated on the fat, saw the scientists, then dissolved and deposited their cargo of miR-1 there.
Soon after, some of the genes in fat cells became overdriven. These genes help direct the breakdown of fat into fatty acids, which other cells can then use for fuel, reducing fat stores. This is because weight training reduced fat in mice by creating vesicles in the muscles that, through genetic signals, told the fat it was time to separate.
“The process was just remarkable,” said John J. McCarthy, professor of physiology at the University of Kentucky, who authored the study along with his graduate student Ivan J. Vechetti Jr. and other colleagues. .
Mice aren’t people, however. So, as the latest facet of the study, the scientists collected blood and tissue from healthy men and women who had completed a single tiring lower body workout and confirmed that, like in mice , the levels of miR-1 in the muscles of the volunteers plummeted after they were lifted, while the amount of vesicles containing miR-1 in their bloodstream skyrocketed.
Of course, the study focused on mice and wasn’t designed to tell us how often or how hard we need to stand up to maximize vesicle production and burn fat. But, even so, the results remind us that “muscle mass is vitally important for metabolic health,” said Dr. McCarthy, and that we start to build that mass and get our tissues talking every time we do. let’s lift a weight.