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Exercise puts a demand on skeletal muscle cells to produce energy at a faster rate than at rest. To do this, the body increases the delivery of fats to the muscle mitochondria while increasing the mitochondrial capacity to metabolize fats, a process called beta-oxidation. Researchers of a new study aimed to illuminate the cellular mechanisms of mitochondrial fat metabolism following moderate intensity aerobic exercise.

Mitochondria are cellular structures responsible for the production of energy in the form of adenosine triphosphate (ATP). The inner membrane of mitochondria possess a series of enzymes called the electron transport chain. These enzymes transfer electrons from carbohydrates and fats (as well as proteins and nucleic acids to a lesser extent) to the final enzyme in the chain that produces ATP. Electron transfer flavoprotein is an enzyme in this chain that transfers electrons from fats, specifically. The authors of this report have previously presented data demonstrating an increase in electron transfer flavoprotein activity in mice after aerobic exercise training.

The investigators recruited fifteen healthy sedentary adults (average age, 28 years) with a normal body mass index. Participants completed one hour of cycling at 65 percent of their maximum aerobic capacity on one day and rested the next day. The researchers collected biopsies from the participants' thigh muscle after they had rested and 15 minutes after they exercised. They analyzed the muscle mitochondria for the abundance of electron transfer flavoprotein activity and for the metabolism of fats and nonfat fuel sources.

Following exercise training, mitochondrial metabolism of fats and non-fat sources increased, although this relationship was not statistically significant. Also noted was a six percent increase in hydrogen peroxide, which is a byproduct of fat metabolism that damages cells. Although fat metabolism increased, the authors reported no increase in electron transfer flavoprotein activity abundance.

They authors concluded that just one session of moderate intensity aerobic exercise in sedentary adults increases energy metabolism of both fats and non-fat sources. They suggested future research would include a larger sample of participants.

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