I wrote about how most people train too hard for their endurance competitions in my post “Hey you! You’re training too hard. Stop it!”  The short-short version is that elite, world/Olympic champion performers in endurance sports like running, cycling, swimming, rowing, cross country skiing, speed skating, and triathlon spend most of their training hours at very low intensity levels.  Most amateurs from ignorance and the “feel” of training, train way too intensely.  They train near, at, or over threshold whereas they should be training way below threshold to build their aerobic capacity.

I was just looking over a publication from the World Conference of Science in Triathlon, and I saw a study called, Training Intensity distribution during an Ironman season: relationship with competition performance.   They studied training distribution in heart rate training zones and eventual performance in Ironman competition.  The zones are broken down as Zone 1/below threshold, Zone 2/Threshold (where most amateurs commonly train), and Zone 3/above threshold.  As you’d expect if you’re familiar with science behind endurance training, the people with a large distribution of training in zone 1/below threshold, performed much better than those training at or above threshold.

It’s counter-intuitive because most racing is done in Zone 2/threshold.  However due to the nature of how the human body fuels those efforts, most training should be done in Zone 1/below threshold.  The findings below:

Discussion
Ironman training was performed mainly in zone 1, although competition is mainly performed in zone 2. While a deeper analysis must be made, the training-competition relationship seems to suggest the importance of easy training versus moderate training (2). These results highlight the importance of training intensity distribution for optimal training (3,4). For triathletes who have more time to train, there seems to be a polarized distribution of training. It should be noted that the 2 subjects who were excluded had trained in zone 2 for 40-50% of the total training time, suggesting an upper limit for Zone 2 training accumulation. These data suggest, apart from specific race pace workouts for swimming and cycling events, there is no need to accumulate additional training in zone 2. However, additional training time seems to result in optimal performance. But to be successful in a triathlon, it appears that any extra training should be performed in zone 1. Since triathletes spend the greatest amount time cycling in both training and competition, it is possible that this is where training can be less intense, limiting time in zone 2. Further research is needed to test this hypothesis.

Conclusion
The Ironman triathlon is performed mainly in zone 2 (swimming and cycling phases), but most of the training should be conducted in zone 1 in all disciplines for maximizing performance.

Study – World Conference of Science in Triathlon