Nothing clears up a nasty bacterial infection like a course of antibiotics, but a new study suggests the drugs could also reduce your ability — and willingness — to exercise.

The research

Researchers at the University of California, Riverside (UCR), gave two groups of lab mice a daily dose of antibiotics for 10 days and then checked fecal samples to confirm the loss of gut bacteria. The mice that were bred to be sedentary displayed no change in their behavior, but those bred for running slowed down considerably. The time they spent on the exercise wheel dropped by 21 percent after the antibiotic course and didn’t improve for the next 12 days.

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“We believed an animal’s collection of gut bacteria, its microbiome, would affect digestive processes and muscle function, as well as motivation for various behaviors, including exercise,” explains study leader and UCR evolutionary physiologist Theodore Garland Jr., PhD. “Our study reinforces this belief.”

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The results of the study, published in the journal Behavioural Processes, suggest that the microbiome affects exercise because of its role in transforming carbohydrates into chemicals that trigger muscle performance. “Metabolic end products from bacteria in the gut can be reabsorbed and used as fuel,” Garland notes. “Fewer good bacteria means less available fuel.”

Future research

Further research could identify a specific bacteria that improve athletic performance, he adds. “If we can pinpoint the right microbes, there exists the possibility of using them as a therapeutic to help average people exercise more.”

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Until then, however, don’t be surprised if you find yourself avoiding the gym once you’ve eradicated that pesky bug with a course of antibiotics. It may not be the aftereffects of your illness that are slowing you down; it may be the pills you took to fight it.

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This article originally appeared as “Antibiotic Aftereffects ” in the January/February 2023 issue of Experience Life, written by deputy editor Craig Cox.