A new study published in the Journal of the Federation of American Societies for Experimental Biology shows that resistance exercise causes the muscles to release instructions for the body to begin utilising its fat stores.

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While it is well understood that resistance exercise is the best way to build muscle, it’s less well understood how resistance training effects fat tissue. Now a new study has shown that, as a result of resistance training, muscles release instructions – in the form of little bubbles of genetic material known as vesicles – which tell fat cells to begin processes that lead to fat-burning.

Resistance Training is Better Than You Thought

When talking about the relationship between muscle gain and fat loss, most will say that an increase muscle mass increases the body’s metabolic needs, increasing caloric expenditure which, over time, can lead to fat loss. Of course, they’re right in saying this, but the truth is that new muscle takes a long time to make, and it’s clear that exercise also has more immediate fat-burning effects. A 2018 study, for instance, showed that a single workout can boost the body’s metabolism for days, but the mechanisms by which this happens have remained obscure until now.

Click here to read our article about a study which shows that resistance exercise is the best long-term strategy for staying in shape, especially as you get older.

It has long been accepted that the body’s cells communicate with one another in some manner, for instance via the release of hormones. Such communication is referred to as ‘cellular crosstalk’. One method of communication that particularly interested the researchers behind the new study was the formation of vesicles, microscopic ‘bubbles’ filled with cellular information, including messages in the form of genetic material.

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The researchers carried out their experiments on mice under conditions of muscular growth (hypertrophy). First, they induced hypertrophy in the legs of mice by incapacitating some of the leg muscles, leaving just a single muscle to bear the full demands of movement. This led to rapid muscular growth as an adaptation to the increased load. 

The researchers drew blood and performed other tests before and other the muscular growth and compared the results. In particular, they noticed differences in the levels of miR-1, a section of genetic code that modulates muscular growth. After exercise, miR-1 was evacuated from the muscular tissue in vesicles into the surrounding blood and fat tissue. This happened, the researchers hypothesised, to allow the muscle tissue to grow. 

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The researchers also wanted to know what effect the increased concentration of miR-1 might be having on the fat tissue. To find out, they marked vesicles from weight-trained mice with a fluorescent dye, injected them into untrained animals, and followed them as they travelled directly to the animals’ fat tissues, before depositing the mir-1.

The scientists noted that soon after, certain genes responsible for the breakdown of fat stores were upregulated (i.e. the process of fat breakdown was enhanced). In short, as a result of exercise, the muscles were telling the fat cells to break down.

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“The process was just remarkable,” said John J. McCarthy, a professor of physiology at the University of Kentucky, one of the authors of the study.

To conclude the study and see if there were any direct human implications, the scientists gathered blood and other samples from healthy men and women who performed a single strenuous lower-body weight workout and confirmed that, as in the mice, miR-1 levels in the human volunteers’ muscles dropped after their lifting, while the quantity of miR-1-containing vesicles in their bloodstreams increased significantly.

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The study is yet more evidence that “muscle mass is vitally important for metabolic health”, as Professor McCarthy puts it. We recently reported on another study which showed that weight training is the best long-term strategy – even better than extensive cardio workouts – for staying in shape, especially as you get older. 


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