Ask any experienced triathlon coach to name the most common training mistake and you'll probably get this answer: Doing too much training at moderate intensity and not enough easy training.
Most triathletes have no idea they're making this mistake because they think that moderate intensity is easy. Despite the subtlety of this error, however, it has significant consequences. Triathletes who don't do enough easy training are just a little fatigued for almost every workout, so they don't get as much out of their workouts as they ought to and consequently they don't get as fit or race as well as they should.
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Traditionally, the small minority of triathletes who have managed to avoid "The Mistake" have done so in either of two ways: by training with heart rate monitor or by hiring a coach. Each of these solutions has its advantages and disadvantages. The best solution for you might not be the best solution for someone else.
How Hard Are You Really Working?
Whenever I speak to groups of triathletes about this topic I get funny looks when I tell them that most of them are probably training too hard, too often. This idea doesn't fit with their own perceptions. But misperception of training intensity is at the very heart of the problem.
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This was demonstrated a number of years ago in a study involving runners. Researchers at Arizona State University asked a group of 30 female runners to describe their training. According to these self-reports, the women did three easy runs, one moderate-intensity run, and 1.5 high-intensity runs per week. But data collected from heart rate monitors that the researchers gave to the women to wear through one full week of training told a different story. In reality the women did less than half of their training in the low-intensity range, almost half in the moderate-intensity range, and less than 9 percent in the high-intensity range.
Triathletes generally have the same misperception of their training intensity distribution as these runners.
The 80/10/10 Rule
Research has shown that endurance athletes get the best results from their training when they do 80 percent of it at a truly low intensity (below the lactate threshold), 10 percent at moderate intensity (at or near the lactate threshold), and 10 percent at a high intensity (above the lactate threshold).
For example, in one study runners improved their 10K race times by 2:37 after training for five months according to the "80/10/10 Rule" and by only 2:01 after doing an equal amount of training with a 70/20/10 intensity breakdown.
Like most runners, most triathletes do not follow the 80/10/10 rule in their training and their performance suffers as a result. Recently, researchers monitored the training intensity of 10 age-group triathletes for six months while they trained for an Ironman event.
It was discovered that these athletes spent only 70 percent of their training time below the lactate threshold and the other 30 percent at and above the lactate threshold. Remarkably, testing revealed that, on average, the fitness level of these athletes did not improve during their six months of hard training! Because they did not do enough easy training, they were slightly tired throughout the process and therefore got nothing out of it.