Gretchen reynolds
07/22/2021 11:46 AM
Clarín.com
The New York Times International Weekly
Updated 07/22/2021 11:46 AM
We all know that lifting weights can strengthen our muscles.
But by changing the inner workings of cells, weight training can also
reduce fat,
according to an illuminating new study on the molecular fundamentals of resistance exercise.
The study, in which mice and people participated, found that after weight training, muscles create and release
tiny bubbles of genetic material
that can flow into fat cells, triggering processes related to fat burning.
The results add to growing scientific evidence that resistance exercise has
unique benefits
for fat loss.
Dumbbell exercises for shoulders, back, triceps.
Photo Shutterstock.
They also reveal how broad and
interconnected
the internal effects of exercise can be.
Many of us pigeonhole resistance training in the realm of bodybuilding, and for good reason.
Lifting weights - or working against our body weight while doing push-ups, squats, or chair jumps - will dramatically increase the size and strength of our muscles.
Known effects
But there are more and more studies that suggest that weight training also
modifies our metabolism and our waistline.
In recent experiments, weight training increased energy expenditure and fat burning for at least 24 hours afterward in young women, overweight men, and athletes.
Also, in a study I talked about earlier this month, people who lifted weights occasionally were much less prone to obesity than those who never lifted.
But how weight training revolutionizes body fat remains poorly understood.
Part of the effect is because muscle is metabolically active and burns calories, so adding muscle mass by lifting weights should increase energy expenditure and resting metabolic rates.
After six months of lifting weights, for example, your muscles will burn more calories
just because they are bigger.
But that doesn't fully explain the effect, because adding muscle mass takes time and repetition, while some of the metabolic effects of weight training on fat stores appear to occur immediately after exercise.
Perhaps, then, something happens at the molecular level right after resistance training that targets fat cells, a hypothesis that a group of scientists at the University of Kentucky at Lexington, the University of Nebraska-Lincoln, and other institutions decided. research recently.
Researchers had been studying muscle health for years, but they became increasingly interested in other tissues, especially fat.
Perhaps, they speculated, muscle and fat
chatted amicably
after a workout.
In the last decade, the idea that cells and tissues communicate throughout our bodies has been widely accepted, although the
complexity of the interactions remains surprising.
Sophisticated experiments show that muscles, for example, release a cascade of hormones and other proteins after exercise that enter the bloodstream, target various organs, and trigger biochemical reactions there, in a process known as cellular crosstalk.
Our tissues can also pump out tiny bubbles, known as vesicles, during crosstalk.
The vesicles, once thought of as microscopic garbage bags filled with cellular debris, are now known to contain healthy, active genetic material and other substances.
Released into the bloodstream, they transmit this biological matter from tissue to tissue, like tiny messages in bottles.
Interestingly, some experiments indicate that aerobic exercise causes the muscles to release these vesicles, transmitting a series of messages.
But few studies had looked at whether resistance exercise could also lead to vesicle formation and inter-tissue chattering.
Novel study
So for the new study, published in May in
The FASEB Journal
of the Federation of American Societies for Experimental Biology, the researchers decided to examine cells from
bodybuilding mice.
First, they experimentally disabled several of the leg muscles of healthy adult mice, leaving
a single muscle to
support all the physical demands of movement.
That muscle quickly hypertrophied, or bulked up, providing an accelerated version of resistance training.
Before and after that process, the researchers drew blood, biopsied tissues, centrifuged fluids, and looked microscopically for vesicles and other molecular changes in the tissues.
They observed many.
Before their impromptu weight training, the rodents' leg muscles were packed with a specific piece of genetic material, known as miR-1, that modulates muscle growth.
In normal, untrained muscles, miR-1, which is part of a group of small chains of genetic material known as microRNAs,
slows down muscle growth.
However, after the rodents 'endurance exercise, which consisted of walking, the animals' leg muscles appeared void of miR-1.
At the same time, the vesicles in his bloodstream filled with this substance, as did nearby fatty tissue.
The scientists apparently concluded that the animal's muscle cells somehow packaged those hypertrophy-retarding microRNA chunks into vesicles and
sent them to neighboring fat cells
, allowing the muscles to grow immediately.
But what did the miR-1 do in the fat once it arrived, the scientists wondered?
To find out, they labeled the vesicles from weight-trained mice with a fluorescent dye, injected them into untrained animals, and tracked the glowing bubbles.
The scientists observed that the vesicles went to the fat, dissolved and deposited their miR-1 charge there.
Soon after, some of the fat cell genes were activated.
These genes help direct the breakdown of fat into fatty acids, which can be used for fuel by other cells, reducing fat stores.
In effect, weight training was reducing fat in the mice by creating vesicles in the muscles that, through genetic signals, told the fat that it was
time to break down.
"The process was extraordinary," says John J. McCarthy, a professor of physiology at the University of Kentucky, who authored the study along with his graduate student Ivan J. Vechetti Jr. and other colleagues.
But mice are not people.
So as a final facet of the study, the scientists collected blood and tissue from healthy men and women who had undergone a single strenuous lower-body weight training and confirmed that, just like in mice, levels of miR-1 in the volunteers' muscles dropped after they were lifted, while the number of vesicles containing miR-1 in their blood streams skyrocketed.
Of course, the study was done primarily in mice and was not designed to tell us how often or how hard we should lift to maximize vesicle production and fat burning.
But even so, the results serve as an invigorating reminder that "muscle mass is critically important to metabolic health," McCarthy said, and that we begin to build that mass and make our tissues speak every time we lift a weight.
c.2021 The New York Times Company
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