After I turned 60, a routine checkup showed that I had lower-than-normal free testosterone levels. I hadn’t noticed anything that would have alerted me. No symptoms. No indication. Everything worked well. But it nagged at me. I knew testosterone did much more for a man’s health than just “build muscle”—which I had no real interest in at this point—so I decided to explore TRT, or testosterone replacement therapy. (This Mark's Daily Apple article was written by Mark Sisson, and is narrated by Tina Leaman)