São Paulo Research Foundation (FAPESP) Oct 8 2025 In addition to strengthening the muscles, lungs, and heart, regular physical exercise also strengthens the immune system. This finding came from a study of older adults with a history of endurance training, which involves prolonged physical activity such as long-distance running, cycling, swimming, rowing, and walking. An international team of researchers analyzed the defense cells of these individuals and found that "natural killer" cells,