Here’s a benefit to base training (zone 1/R training) that you typically don’t hear about but I believe is a very important component to the build up process: frequency of workouts (i.e., building durability and recovery ability through high workout frequency). Because the base phase (about 8-12 weeks) of each season is spent primarily in zone 1, the risk for injury is low. We take advantage of that fact by doing very frequent workouts. For most athletes training for IM, this typically means 2-3 workouts per day with about 1 day off per month. What this does is:
1) Build great durability, physical and mental toughness – running and being on tired legs all the time teaches you to keep form together when the going gets tough and prepares you for the demands of IM racing. Since intensity is low and there are no best effort workouts, its okay to have a fried peripheral system most of the time; you don’t need your legs to push on previous bests during key intensity days. Instead, the intent is to just pass the amount of oxygen through your body by workout volume that your season plan calls for.
2) It teaches you to recover faster – due to the frequency of workouts, your body is forces to adapt and learn to recover faster from workouts. This is a great quality to have once into the build phase as the higher intensity work begins to kick in and you need your peripheral system for key workouts day after day.
3) It allows you to build volume safely at a slope much steeper than could safely be done with intensity training or few very long workouts per week. Typically the long workouts are placed at maximum of 35%, 35% and 45% of the week’s swim, run, and bike volume respectively.
4) It prepares you for rigors of the high intensity build phase where key workouts are almost every other day. The volume base that has been laid down through workout frequency, including weight training has prepared the soft tissue for higher intensity work with great resistance to injury.
I hope this has helps open your eyes to some of the benefits of base training that may not be advertised a lot of the time with other proponents of this method.