Or dedicated.
There was actually a commercial out in the states about four years ago touching on this, when the drug abuse in baseball was so publicly rampant and getting a lot of press. In the commercial were people asking him if he used performance enhancing drugs and such and when he said no they asked him how he does it. "Simple", he said, "I get on my bike a dawn and ride for 8 hours a day, 7 days a week".
Lance Armstrong has dedication to his sport, which is nice to see these days when so many athletes are there for the wrong reasons, such as fame and money. Lance is dedicated to cycling because he loves to ride his bike. Simple enough.