Key points from article :
Cyclists in their 80s had the immune systems of 20-year-olds.
Immune system decline makes older people more susceptible to infections.
Endurance cyclists were producing the same level of T-cells as adults in their 20s.
Did not lose muscle mass or strength, nor see an increase in body fat .
Could prevent conditions like rheumatoid arthritis and, potentially, cancer.
The study was published in the Aging Cell journal.
