How weight training instructs cells to enter fat-burning mode

While jogging, cycling, swimming and other forms of cardio exercise are well-known ways to burn calories, the relationship between weight training and weight loss is more complex. A new study has dug into the molecular underpinnings of this and identified a new mechanism through which muscle cells deliver instructions that send fat cells into fat-burning mode in response to mechanical loading.

For hundreds of years, humans have been using different forms of resistance training to improve muscle strength and size. In the gyms of today, this could involve machines, free weights or resistance bands, all of which damage muscle fibers that the body then repairs by fusing them together to increase their mass.

Resistance training in its many forms has also begun to gain popularity among those looking to shed some extra pounds or protect themselves against obesity. While throwing some iron around is unlikely to burn as many calories as a vigorous session on an exercise bike, it can have indirect benefits for weight management over the longer term.

In addition to strengthening and building muscle, resistance training has an “after-burn” effect in which oxygen uptake remains elevated to help break down fat and carbohydrates to replenish the fatigued muscles, well after the workout has wound up. Increased muscle mass can also increase the body’s resting metabolic rate, which dictates how many calories the body needs to function in a resting state, improving fat-burning over the longer term.

Scientists at the University of Kentucky sought to build on this growing body of evidence around the unique ways resistance training can assist weight management, by digging right into the physiological details. This started with studies on mice, through which the scientists showed that mechanical overload of the muscles, simulating the effects of resistance training, led to the release of what are known as extracellular vesicles, which are particles the cells naturally expel to help rid the body of unwanted proteins, lipids and other materials.

Recent studies have started to show that extracellular vesicles also act as a kind of messenger, relaying communications between different types of cells. And this was the process found to be at play in the muscular mice, with the vesicles released through the resistance training preferentially taken up by white fat cells, and in turn gave them instructions to go into fat-burning mode.

“To our knowledge, this is the first demonstration of how weight training initiates metabolic adaptations in fat tissue, which is crucial for determining whole-body metabolic outcomes,” says John McCarthy, study author. “The ability of resistance exercise-induced extracellular vesicles to improve fat metabolism has significant clinical implications.”

Through follow-up experiments on human tissue, the scientists found similar signaling processes to be at play, leading them to suspect the same effects of resistance training “may be operative in humans.”

In addition to deepening our understanding of how resistance training can help our waistlines, the researchers say the study also sheds further light on how extracellular vesicles can facilitate communication between different body tissues.

The study was published in the FASEB Journal

Source: University of Kentucky

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