The Importance of Zone Three

Now that we under that fitness is the ability to do work, let’s just do everything a little bit harder to get faster, right? Well, it's not that simple. Now that we have tools and programs that allow us to quantify the work we are doing, we know you work the same amount if you rode your bike at 22 mph for two hours or if you rode it at 19 mph for 3.5 hours. In other words, done properly, you can ride your bike fewer hours at a higher intensity and do the same amount of work as a longer, easier ride. This training effect is accomplished by upping the intensity—welcome to zone three.
 
Maintaining a heart rate in zone three is the perfect way to rack up lots of work without the negative side effects that more threshold-oriented work can cause. Our athletes spend a lot of time in zone three because this zone allows us to work relatively hard (in terms of aerobic and muscular capacity) without a lot of recovery time. And because you can do lots of it, your Training Stress Score (TSS) per hour trained is much greater than more traditional approaches. Simply put, the athlete who accumulates lots of zone three3 time vs. zone 1 or 21-2  time accumulates more TSS for the same amount of time swimming, biking or running. This is a much more time efficient way to train.
 
If you are a student of endurance training, then you have probably heard of the “perils of zone three.” Zone three is the gray area between endurance (zone two2) and threshold-specific intensity (zones four4 and above). As such, zone three is often demonized as the default zone—or the place where athletes feel they are getting a good workout. Conventional wisdom has suggested that zone three workouts don’t boost your fitness as well as training in zones four 4 and higher—and that you miss out on the endurance/recovery focus of  zones 1 and 2.1-2.

We’ve learned differently: