To investigate the ameliorative effect of Lactobacillus plantarum L15 on excessive exercise-induced skeletal muscle injury in rats.

Forty-eight SD male rats were randomly divided into four groups: quiet control, exercise control, quiet + L15 administration and exercise + L15 administration. Six-week treadmill exercise was used to establish a model of excessive exercise. The daily dose of L. plantarum L15 (3 × 10⁸ CFU) was 0.2 mL. The control groups were given the same volume of normal saline. Following six-week administration, body mass gain, intestinal permeability, and lipopolysaccharide content, antioxidant indexes, cytokine levels and nuclear factor-erythroid 2-related factor 2 (Nrf2) signaling pathway and nuclear factor kappa B (NF-κB) signaling pathway-related gene expression levels in skeletal muscle were measured, and histopathological changes of vastus lateralis muscle were observed.

L. plantarum L15 significantly increased body mass gain (P < 0.05), improved the histopathological changes of vastus lateralis muscle, and decreased D-lactic acid and diamine oxidase levels in the serum as well as lipopolysaccharide (LPS) content in the skeletal muscle of rats with excessive exercise. L. plantarum L15 significantly increased the levels of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and total antioxidant capacity (TAC) (P < 0.05 or P < 0.01), significantly decreased the content of malondialdehyde (MDA) (P < 0.05), and significantly up-regulated the mRNA expression levels of the Nrf2, HO-1 and NQO1 mRNA (P < 0.05 or P < 0.01). L. plantarum L15 significantly reduced the levels of pro-inflammatory cytokines (IL-6, IL-1β and TNF-α) and significantly increased the levels of anti-inflammatory cytokines (IL-10) (P < 0.05 or P < 0.01), as well as significantly down-regulated the mRNA expression levels of the TLR4, MyD88 and NF-κB genes (P < 0.01).

L. plantarum L15 can improve intestinal permeability, reduce LPS levels in the skeletal muscle of rats with excessive exercise, and inhibit oxidative stress by regulating the Nrf2 signaling pathway. In addition, it also can reduce inflammation levels by regulating the NF-κB signaling pathway, thereby alleviating skeletal muscle injury caused by excessive exercise.