Everyone who lives in the endurance space is aware of training zones. We know we have them, our friends sound smart talking about them, and we hate to be told to "stay in them". However you view them, they offer us some key opportunities to train (and even race) with specificity.
Here are my Top 5 considerations for respecting the zones!
1. Targeting: Energy Systems
Zones are critical to training specifically for a goal, event, or purpose. We want to target the right energy systems at the right time. Lower levels of effort have a vastly different effect on the body than higher levels of effort and that’s why we have various “thresholds” to mark those physiological changes.
For example: at low intensity we are mobilizing fat and utilizing oxygen to fuel our work in a reliable, efficient manner. Once you begin to dip into higher zones, the body reaches a point (“threshold”) where it begins to rely predominantly on glycolytic systems to produce energy – aka sugar-burning. This brings me to periodization…
Most proper training plans, when they’re focused on an event goal, are periodized to build from bulk endurance work (as discussed in my recent article here) to event-specific intensity work.
Having zones allows us to accumulate the proper amount of work in the right energy system(s) as we go from base to race phases. Zones 1-3 get a lot of love during the base phase. Then you start chipping away at 3-4 in the build phase and finally high intensity (4-5) during the preparation phase.
3. Tracking Progression
Zones allow us to see how our fitness is changing over time. If you are beginning to produce the same power or pace at a lower heart rate (HR) then you can see your fitness has improved. This is because that workload is requiring less energy/effort.
We can track our growth and development by monitoring our capacity to spend time in a specific zone. Additionally, we can re-test for Functional Threshold Power (FTP) or HR and see where our “new numbers” are over time.
For endurance events that are a matter of attrition (think: long gravel race or marathon vs an XC race or 5k) zones can be particularly useful at pacing during it. If you have a grasp of where your FTP or HR threshold is, it allows you to be a bit more mindful about how energy is spent. Too much time spent above your threshold or upper-end zones means you are chipping away at the more “finite” energy system.
However, they should be used to guide us but not direct or limit us in race scenarios.
5. Developing Your RPE
Lastly, establishing zones can help you to develop a natural “feel” of energy output. This is often referred to as the Rate of Perceived Exertion (RPE) in a lab setting but it still stands in the natural setting. I will even advocate for inexperienced athletes to get used to what an effort “feels like” and then reference their power/HR values on the backend so they develop a sense of awareness.
Numbers are not the end-all-be-all of training and racing. At this point in my career, I could go out and ride off of RPE and be within 10watts or 5 BPM of my intention.
The Difference: Power v Heart Rate
Power and HR both have usefulness in training in different ways. Power is often the “golden metric” for cyclists (as pace is to runners) because it is constant, fixed metric. It represents direct workload being produced. Heart rate (HR) is the response to work that your body produces. HR can be affected by a variety of factors though, such as fatigue, temperature, caffeine, etc. I use power when it comes to nailing intervals and pushing limits on intensity. However, during the base phase, I often rely on HR more because I want to accumulate time in and/or below certain zones to stay aerobic.
Now that we’ve dove into “why” we have zones, let’s discuss how to set them. This article is a great reference!
The gold standard for power-based testing is a 20min time trial – simply sustain maximum effort for 20 minutes. Then, take the average power from that effort and subtract 5% to get your Functional Threshold Power (FTP). An alternative testing protocol is to do 2 x 8min efforts; for this you take the average power of both efforts and deduct 10%, since we assume someone can produce a bit more power relatively with the shorter efforts.
Heart Rate (HR) is a bit trickier, as discussed earlier, because of it variability and tendency to be influenced by other factors. However, you can still use it as a great guide. Option one is to ride a mid-length climb (4-8min) 3-4 times at maximal effort; this assumes you’ll reach your HRmax in one of the latter efforts. Then, you can then build your zones out using percentages after identifying that HRmax.
The second option is to complete the same FTP-establishing test that we would with a power meter: 20min TT at max sustainable effort. This will give you an effective “threshold HR” that you can build zones around using a guide or TrainingPeaks “zones” setting.
Get to know your body and work appropriately to chase your goals!