A Half Ironman (or Half Iron-distance) Triathlon consists of a 1.2 mile swim, a 56 mile bike ride, finished off with a 13.1 mile run. Double that for the Full IM. These distances require a great deal of conditioning, time and training.
What conditioning should you have before attempting a triathlon? I like to think of myself as a hockey player and former swimmer and collegiate baseball player trying his best to compete at endurance exercise. Get to know your body and make regeneration and corrective exercise a major part of your training. The key to longer distances is getting to the start line healthy. That said, take your time when starting off. Sign up for sprints and Olympic distance races and do a few before you make the jump to half and full IM distances.
DC Tri Club, the Nation’s 3rd largest Triathlon club offers a great Half Ironman and Full Ironman Distance training program:
They offer some information for base level:
Beginner: An average of 6 workouts per week (2 swim, 3 bike, 2-3 run); participants will have on average one day per week off for rest and recovery. Initially, participants will be required to do an 1:30 hour long ride and a 1 hour long run.
Intermediate: An average of 7 workouts per week (2-3 swim, 3 bike, 2-3 run); participants will typically do one workout per day however they will not have an official day off per week for rest and recovery.
Advanced: An average of 8-10 workouts per week (2-3 swim, 3 bike, 3-4 run); participants are typically seasoned, competitive athletes that want to improve their overall performance.