Before and after that procedure, researchers drew blood, biopsied tissues, centrifuged fluids, and microscopically searched for vesicles and other molecular changes in the tissues.
He noted a lot. Before their immediate weight training, the rodents’ leg muscles contained a special piece of genetic material, known as miR-1, that regulates muscle growth. In general, in untrained muscle, miR-1, one of a group of short strands of genetic material known as microRNAs, puts the brakes on muscle building.
After resistance exercise in rodents, which included walking, however, the leg muscles of the animals showed a decrease in miR-1. At the same time, the vesicles in his bloodstream were now filled with the stuff, as were the surrounding adipose tissue. It seems, the scientists concluded, that animal muscle cells somehow packed those bits of microRNA that retard hypertrophy into vesicles and post them to neighboring fat cells, allowing muscle to grow quickly. is permitted.
But what was miR-1 doing after the arrival of fat, the scientist wondered? To find out, they marked vesicles from weight-trained mice with a fluorescent dye, injected them into untrained animals, and tracked the paths of the glowing bubbles. The vesicles were placed on the fat, the scientists observed, then dissolved and deposited their miR-1 cargo there.
Soon after, some of the genes in the fat cells went into overdrive. These genes help direct the breakdown of fat into fatty acids, which other cells can use as fuel, depleting fat stores. In fact, weight training was reducing fat in the mice by forming vesicles in the muscles, which via genetic signals tell the fat that it was time to dissociate itself.
“The process was just remarkable,” said John J. McCarthy, a professor of physiology at the University of Kentucky who co-authored the study with his graduate student Evan J. Vecchetti Jr. and other colleagues.
Rats are not people, though. So, as a final aspect of the study, the scientists collected blood and tissue from healthy men and women who underwent a single, exhausting lower body weight workout and confirmed that, as in mice, the volunteers’ muscles had miR- 1 level dropped after their lifting, while the amount of miR-1-containing vesicles in their bloodstream increased.
Of course, the study mostly involved rats and was not designed to tell us how often or intensely we should lift to maximize vesicle production and fat burning. But, nonetheless, the results serve as a bracing reminder that “muscle mass is important for metabolic health,” Dr. McCarthy said, and we start to build up that mass and talk to our tissues every time we lift a weight.