A recently published study by University of New Mexico researchers looks at how intense exercise affects the body. Michael Deyhle, an associate professor in the Department of Health, Exercise and Sports Sciences, oversaw the study led by doctoral students Jonathan Specht, Jeremy Ducharme, and Alyssa Bailly.
The study examined autophagy, a process in which cells break down and recycle damaged or unneeded components so they can be reused. The researchers found that markers associated with autophagy increased after an hour of endurance exercise in participants who were not regularly active. The markers did not change in participants who exercised regularly.
The findings show how the body responds to exercise and may help researchers better understand some of the ways physical activity supports health.
"It's clear that the process of autophagy, when properly regulated, is important for cellular health," said Deyhle. "This might indicate that activating autophagy, which we know is an important cellular process, is one of the many reasons why exercise is beneficial for our health."
Autophagy acts as a recycling system within cells. When cellular components break down, the process allows the body to reuse their building blocks to repair and remodel cells. Although researchers know that fasting and other forms of energy stress can activate autophagy, less is known about how exercise affects the process.
To investigate those effects, the researchers compared people who regularly exercised with those who were inactive. Participants completed an hour of intense endurance exercise on a stationary bicycle. Researchers collected muscle tissue samples and blood samples before and after the exercise session to examine changes in two markers associated with autophagy: LC3-II and p62.
The results showed that the markers changed in the less active participants in a way the researchers interpreted as autophagy activation. The trained participants, however, did not show the same response.
The research team believes the difference may be related to how the body adapts to regular exercise. For someone who is not accustomed to physical activity, an intense workout may place greater stress on the body, triggering cellular responses that help it adapt. For someone who exercises regularly, the same workout may represent less of a challenge.
They observed similar patterns in two other studies using participants from the same experiment, although those studies examined different cellular and physiological responses. In fact, the researchers point out that this phenomenon – that a greater stimulus is required to elicit a physiological response in fitter people – is called the principle of diminishing returns, and it is commonly observed in exercise research.
The findings also suggest that blood samples could help researchers study autophagy responses alongside muscle tissue samples. The researchers observed similar changes in LC3II and P62 in both tissues (blood and muscle). In other words, the changes mirrored each other. This observation is interesting to the researchers because it suggests that a blood sample, which is more easily accessible than a muscle sample, could potentially be used as a surrogate to provide insight into processes occurring in the skeletal muscle. However, future research is needed to confirm this.
However, the study was a pilot project, and the researchers examined only two markers associated with a complex process involving many molecules. They say more research is needed to understand how different stages of autophagy respond to exercise and whether other forms of physical activity produce similar results.
Deyhle said future studies could look at a broader range of molecules involved in autophagy or compare responses to endurance exercises with those triggered by resistance exercise, such as weightlifting.
By examining how the body responds to physical activity at the cellular level, researchers hope to better understand the biological processes behind exercise and its benefits for overall health.
