Abstract: This study applied D-galactose-induced oxidative aging in mice to establish a model of functional and physical decline. The intervention effect of Limosilactobacillus fermentum HYFN13 on liver oxidative stress and the improvement of exercise endurance were observed. In this study, the exhaustive running training of mice was observed. The indicators of serum and liver tissue were detected using the detection kit. The sections of mouse liver tissue were observed by hematoxylin and eosin (H&E) staining method. The mRNA expressions of liver, gastrocnemius muscle and microorganisms in intestinal contents of mice were further detected by quantitative polymerase chain reaction (qPCR), and the protein expressions in the liver of mice were also detected by western blot. The experimental results showed that compared with the model group, HYFN13 could increase the exhaustion running time of mice, reduce the levels of lactic acid (LA), creatine kinase (CK), and lipopolysaccharide (LPS) in the serum, increase the levels of hepatic glycogen (HG) in hepatic tissue and muscle glycogen (MG) in gastrocnemius muscle tissues and reduce tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and reactive oxygen species (ROS) levels. It was found through observing the sections that HYFN13 could alleviate liver tissue lesions caused by oxidative stress. Further experimental results showed that HYFN13 could up-regulate the mRNA expressions of copper-zinc superoxide dismutase (Cu/Zn-SOD), manganese superoxide dismutase (Mn-SOD), catalase (CAT) and glutathione peroxidase 4 (GPx4) in liver tissues and gastrocnemius muscle tissues of mice with exhaustion under oxidative stress. HYFN13 could also up-regulate the mRNA expressions of AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) in liver tissues, as well as the protein expressions of AMPKα1 and mTOR, and increased the ratio of AMPK (AMPKα1)/mTOR. Analysis of intestinal contents showed that HYFN13 could increase the mRNA expression of Firmicutes and Bifidobacterium in the intestine of model mice and reduce the expression of Bacteroidetes. Meanwhile, HYFN13 could significantly increase the expression of Lactobacillus and raise the expression intensity to exceed that of the normal group. The research results indicate that HYFN13 has the effect of regulating oxidative damage and enhancing endurance.