Abstract: Objective: To investigate the effects of Lactiplantibacillus plantarum KSFY202408 on exercise capacity in mice and its underlying mechanisms. Methods: Four experimental groups were established: sedentary (Sed), exercise training (Ext), KSFY202408 sedentary (KSFY202408+Sed), and KSFY202408 exercise training (KSFY202408+Ext). Mice in the Ext and KSFY202408+Ext groups underwent 6 weeks of treadmill exercise training, while those in the KSFY202408+Sed and KSFY202408+Ext groups were administered KSFY202408 by gavage. Body weight, exhaustive exercise time, organ indices, and blood lactate levels were measured. Histological changes in the gastrocnemius muscle were observed. Gene expression levels related to mitochondrial activation, energy metabolism, and antioxidant defense in the gastrocnemius muscle were detected, and alterations in gut microbiota were analyzed. Results: Compared with the Sed group, both the KSFY202408+Sed and KSFY202408+Ext groups exhibited significantly prolonged exhaustive running and exhaustive swimming times (P<0.05), accelerated post-exercise blood lactate clearance (P<0.05), improved cardiac function, and alleviated exercise-induced splenomegaly (P<0.05). Gene expression levels of adenosine 5'-monophosphate-activated protein kinase (AMPK), peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), nicotinamide phosphoribosyltransferase (NAMPT), superoxide dismutase 1 (SOD1), SOD2, and catalase were significantly upregulated (P<0.05). Gut microbiota analysis revealed increased microbial diversity in KSFY202408-administered mice, with Lactiplantibacillus identified as the characteristic microbial genus in the KSFY202408+Ext group. Conclusion: Lactiplantibacillus plantarum KSFY202408 may enhance energy capacity in mice by regulating the AMPK/PGC-1α signaling pathway, thereby improving energy metabolism and oxidative stress status in synergy with exercise training. These findings suggest that KSFY202408 has potential as a sports nutritional supplement.