Chronic Exercise Reduces Illness Severity, Decreases Viral Load, and Results in Greater Anti-Inflammatory Effects than Acute Exercise during Influenza Infection

Background. It is assumed that moderate exercise may improve resistance to infection and reduce inflammation, but there are limited data to support this assumption in an infection model. Methods. BALB/cJ mice were assigned to the following groups: no exercise (NON-EX), 1 session of acute exercise (A-EX), or chronic exercise for similar to 3.5 months (C-EX). Mice were infected with influenza (C-EX mice infected at rest; A-EX mice infected 15 min after exercise). Results. C-EX mice demonstrated the lowest severity of infection, assessed by body weight loss and food intake. There was less virus in the lungs at day 5 after infection in C-EX and A-EX mice compared with NON-EX mice (P = .02) and less virus at day 2 after infection only in C-EX mice (P = .07). Soon after infection (day 2), interleukin 6 (IL-6), monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory protein 1 beta, and tumor necrosis factor alpha in the bronchoalveolar lavage (BAL) fluid were lower in C-EX and A-EX than in NON-EX mice. At day 5 after infection, the BAL fluid from C-EX (but not A-EX) mice had less IL-6, interleukin 12p40, granulocyte colony-stimulating factor, keratinococyte-derived chemokine, and MCP-1 than that from NON-EX mice. A trend toward reduced immunopathologic response was found in C-EX mice. Conclusions. Chronic exercise resulted in reduced symptoms, virus load, and levels of inflammatory cytokine and chemokines. Acute exercise also showed some benefit, which was limited to the early phase of infection.