Training zones are widely used by most athletes to control training intensity. Sometimes we take them in blind faith and follow a training plan based on these zones. Rarely do we stop to ask why or what was the purpose of that long slow zone 2 bike or that interval run that was in zone 5.
Let’s look a little deeper look at these zones. The table below shows a 5-zone model with descriptions of the physiological response to training. It also highlights what the bodies uses to fuel the different training intensities.
Zone 1 is low intensity where most of the energy is supplied by fat oxidation.
Zone 2 is a little more challenging than zone 1. As the effort increases you are still primarily using fat oxidisation to fuel the effort but there is also a little more carbohydrate being used too. In events longer than 6 hours this is where you will spend most of the time at race effort.
Zone 3 is a moderate intensity; fat oxidisation begins to decrease and carbohydrate oxidisation increases. You start to use more of your glycogen stores. You can replace some of these stores through nutrition on the bike. Pro Ironman athletes’ race at this intensity. If you are a recreational athlete and find yourself pushing here, you better be a good runner. It is 70.3 race pace intensity for most.
Zone 4 is threshold or FTP intensity. At this intensity you are going to be using primarily glycogen stores for energy production.
Zone 5 is high intensity work where the energy comes primarily from carbohydrate. For endurance athletes we use these mainly for interval-based work to help increase V02 Max.
We know that the top endurance athletes in the world have high V02 Max numbers and also very high fat oxidisation rates. They have an amazing ability to use high levels of fat at high power output and spare their glycogen for those really hard efforts.
Research conducted by Stephen Seiler took a deep dive into the training journals of some of the top elite endurance athletes. Seiler and his colleagues wanted to understand just how the best of the best allocated their training time. Whether it is cross country skiers, marathon runners, rowers or triathletes the training distribution was the same.
Elite athletes spend 90 to 70% of their total training time in zone 2 and zone 1, around 5% in zone 3 and 20 to 25% of the time in zones 4 and 5.
This Training Intensity Distribution (TID) is known as polarised training. 90 to 70% of training is easy low intensity and 20 to 25% of training is hard intensity. The easy days are easy and hard days are hard promoting supercompensation.
TID will change throughout the year as you get closer to your goal event. This is to factor in race specificity and preparing for your goal race. Let’s take a look at the TID for a potential Ironman athlete 24 weeks out.
In the general phase of training the aim is to increase fitness, improve the bodies ability to oxidate fat all in zone 1 and 2. Intervals are used to work on skills using cadence drills and fast efforts.
In the Specific phase of training the aim is to increase fitness further but more time is allocated to work on improve threshold tolerances and build aerobic capacity.
The competition phase you can see that there is a shift in the TID where more threshold work is. Ironman race intensity occurs at the top of zone 2. We need to prepare the body for the even you need stress the system at long durations above this pace. This is where interval based training should be focused to extend your ability to tolerate efforts slightly quicker than race pace.
But, no matter how you cut and manipulate training one thing should be obvious. You have to spend the majority of training time in zone 1 and zone 2.
Easy days should be easy so that hard days are hard enough to promote super-compensation.