There isn’t enough gravity to keep you from floating off the treadmill on the ISS. On the day of the marathon, I strapped in with a ­bungee-​type harness that physically pulled me to the surface. At some points, the strap was so tight that my entire right leg went numb, which was a lot different than the typical muscle aches a runner experiences on Earth. That wasn’t the only quirk of my orbital marathon. By the middle of the race, my clothes were soaked in sweat—but with no wind to dry it, the perspiration just kind of stayed there. Even snack breaks were different: A fellow astronaut cut up oranges (brought up from Earth earlier that week) and tossed the slices at me. I tried to catch them as they floated by, but I ended up missing most of the fruit.