The gut bacteria of these mice were executed with those antibiotics. After that, the researchers studied muscles of healthy mice with mice having no intact microbiome and found that the mice with no intact microbiome had low muscle growth compared to healthy mice, even after both group of mice were put through same exercise for 9 weeks. https://www.coherentmarketinsights.com/news/healthy-gut-microbiome-may-help-to-tackle-muscle-loss-516