If you've ever worked out, you know what it feels like in your body. Your body temperature goes up, your heart rate increases, you start sweating, you feel thirsty, and so on. At the cellular level, you know that you're burning calories and maybe even building muscle. But while health experts have been aware of these processes for years, the actual pathway that the body uses to launch a coordinated response to exercise has been a bit of a mystery. Until now.

A study from researchers from the Garvan Institute of Medical Research in Sydney, Australia has shed new light on what's going on at the cellular level when we exercise. And we now know that it all comes down to vesicles. If it's been a few years since you had high school biology, here's a refresher. Vesicles are the microscopic parts of cells that transport molecules from one place to another within the cell. They're often thought of as the trash collectors, moving discarded bits and pieces within a cell and out of a cell as needed.

But according to the study published in the journal Cell Metabolism, vesicles have a lot more going on than we realized, and they might be responsible for most of the internal communication that goes on within the body, especially during exercise. Researchers learned that vesicles contain not only discarded genetic material, but also thousands of different proteins that we never even knew were there, including hundreds that appear to have a specific function during exercise.

Vesicles Biology 101: Vesicles pick up proteins and other material and transport them into (left image) or out of (right image) the cell. (Photo: Fancy Tapis/Shutterstock)

For the study, the research team drew blood from the femoral arteries of 11 healthy men, before, during, and after they exercised on a stationary bike for one hour. Using new sampling techniques, researchers were able to isolate and quantify the proteins and vesicles in the blood, and what they discovered was surprising.

The men had about 300 more proteins in their vesicles during exercise than they did before they worked out or after four hours of rest. Many of these proteins had already been identified as playing a role in metabolism and energy regulation, but health experts had never realized that they were found in the bloodstream in such large quantities during exercise.

But with the knowledge of the proteins' presence, researchers needed to figure out what their role was during exercise. In animal studies using mice, the team added fluorescent markers to the vesicles of mice, half of which were sedentary and half that exercised. The vesicles in the exercising mice went straight to the animal's liver, an organ that we know is responsible for energy production during exercise. In short, exercise prompts these vesicles to flood with proteins and deliver them straight to the body's energy maker.

"This study reveals a huge amount of complexity in the circulating blood during exercise that we might have previously underestimated," says Martin Whitham, a biologist at the Garvan Institute and a co-author of the study in a press release.

Whitman and his research team acknowledge that this is just a tip of the iceberg when it comes to understanding the internal communication going on within the body during exercise, but with this new knowledge, they hope to unlock more of the body's biochemical mysteries. For instance, the team is planning to conduct future studies that follow exercise-induced vesicles on pathways to other organs in the body, particularly the brain. Maybe then researchers can better understand the mechanics behind the legendary "runner's high" that gives exercisers such a mental boost when they work out.