Before and after this process, the researchers took blood, biopsied tissue, centrifuged fluids, and microscopically looked for vesicles and other molecular changes in the tissue.
You wrote down a lot. Before their improvised strength training, rodents’ leg muscles were teeming with a specific segment of genetic material known as miR-1, which modulates muscle growth. In normal, untrained muscles, miR-1, one of a group of tiny strands of genetic material known as microRNA, slows muscle growth.
However, after the rodents ‘resistance exercise, which consisted of walking around, the animals’ leg muscles appeared to be exhausted on miR-1. At the same time, the vesicles in her bloodstream were now pushing away from the stuff, as was the fatty tissue nearby. It appears, the scientists concluded, that the animals’ muscle cells somehow packed these parts of the microRNA that delay hypertrophy into vesicles and sent them to neighboring fat cells, which then let the muscles grow immediately.
But what did the miR-1 do to the fat when it arrived, the scientist wondered? To find out, they labeled vesicles from weight-trained mice with a fluorescent dye, injected them into untrained animals, and followed the paths of the glowing bubbles. The vesicles focused on fat, the scientists saw, then disintegrated and deposited their miR-1 cargo there.
Soon after, some of the genes in the fat cells went into high gear. These genes help direct the breakdown of fat into fatty acids that other cells can then use for fuel, thereby reducing fat stores. In fact, strength training caused fat to shrink in mice by creating vesicles in the muscles that, through genetic signals, told the fat it was time to loosen itself.
“The process was just remarkable,” said John J. McCarthy, professor of physiology at the University of Kentucky, who co-authored the study with his then graduate student Ivan J. Vechetti Jr. and other colleagues.
However, mice are not humans. As the final facet of the study, the scientists collected blood and tissue from healthy men and women who had performed a single, tiring, lower-weight exercise and confirmed that, as in mice, miR-1 levels in the subjects’ muscles fell after that Take off as the amount of miR-1 containing vesicles skyrocketed in their bloodstream.
Of course, the study included mostly mice and was not designed to tell us how often or how hard we should exercise in order to maximize vesicle performance and fat burning. Even so, the results serve as a comforting reminder that “muscle mass is critical to metabolic health,” said Dr. McCarthy, and that every time we lift a weight we build that mass and make our tissues talk.