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Training Zones: Why so many different systems?

Training Zones: Why so many different systems?

As part of the ongoing series on Training Zones, this article looks into why there are so many systems and how to make sense of them all.

As I discussed in prior articles, the purpose of zone systems is to divide the full spectrum of activity output into meaningful ranges. A range is meaningful in that it describes a set of efforts that are metabolically similar, i.e., rely on similar muscle recruitment patterns, activate similar energy systems, impose similar strain on metabolic processes, etc.

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The chaos comes into the picture when different companies or individuals identify and label different ranges of output. Not all endurance sports and disciplines emphasize the same types or ranges of physiological demands, so it makes sense to focus a training zone system on those sport-specific demands. Bottom line, there are many good reasons to come up with unique systems and no system is objectively better than the rest. As the athlete or coach, it is enough to understand the science and method underlying a particular system and then make your own determination about what system makes the most sense to you and your sport.

That said, it can get confusing when you are prescribed a Zone 3 effort and under different systems Zone 3 may mean different things. Make sure you are clear about which system you are using and what a particular zone in that system refers to, e.g., 70-85% of FTP, or 82-90% of MaxHR, etc.

Anchor Points

Most systems rely on anchor point(s) and then calculate ranges based on percentages of these anchor point(s). Here are some common anchor points used in zone systems:

  • Functional Threshold Power (FTP) – this anchor represents the maximum power (watts) you can sustain for 40-60 minutes. Coaches and exercise physiologists can get quite worked up about the specific definition and the best way to establish the actual number (8min Field Test, 20min Field Test, 60min Field Test, etc.). Notwithstanding those disputes, this metric is a good measure of aerobic capacity.
  • Lactate Threshold (LT or LT2) – this anchor is correlated with FTP and will be around the same power value, but is established by lactate testing in the field or lab. Usually, the lab test is looking for the heart rate and/or power that results in a specific concentration of blood lactate (4mmol/l). This metric is a good measure of aerobic capacity. Note that LT1 is an anchor associated with a lower blood lactate value. LT1 occurs when blood lactate levels rise above baseline and indicates that you have exceeded the working muscles' ability to recycle lactate into the energy production process (it often is located near the top of Zone 2 in the 7-Zone system).
  • Ventilatory Threshold (VT or VT2) – this anchor is similar to lactate threshold and is also established with lab testing. A VO2 Test is used to identify this anchor and is describing a similar metabolic status as Lactate Threshold, but from the perspective of gas exchange (O2 and CO2). This metric is also a good measure of aerobic capacity. Like LT1 there is also a VT1 that is associated with a lower output level that indicates a similar metabolic shift in aerobic system.
  • VO2Max – this anchor point is also established with a VO2 Test and identifies the maximum amount of oxygen your system can process as a quantitative value of aerobic capacity and endurance fitness. VO2max is reached at a higher output than FTP/LT2/VT2.
  • Maximum Heart Rate (MaxHR) – this anchor is simply the maximum heart rate you can achieve during your sport activity. Often this is captured during competition events or competitive training scenarios. As this metric represents your maximal cardiac rate, training zones can be defined as percentages of this value.
  • Threshold Heart Rate (tHR) – this anchor is the heart rate you can sustain in a maximal 20-30 minute effort. This is similar approach to the Lactate Threshold, but does not require a lab and blood testing. This metric is a good measure of aerobic capacity.

Phew! That’s a lot of anchor points! The obvious question is: which one is best? The physiology-based answer is complicated and I will address it in a subsequent article. However, the practical answer is relatively straightforward: use the system/anchor point that can be measured with available equipment. Don’t have a power meter? Rule those out. Don’t want to pay for lab testing? Rule those out. If you have power and heart rate, I would personally recommend that you rely on both. (Stay tuned for a future article with tips about how to make the best use of a power meter and heart rate monitor in conjunction.)

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