Why you should (and shouldn’t) care about training zones

Who is this article for?

• People who want to improve their heart health and longevity
• People who want to advance their training and improve their cardiovascular fitness
• Those interested in training zones and want to know if it is for them

Training zones: Why should we care?

• VO2max
  • VO2max is one of the best predictors of longevity and long term health that we have. If you want to age well and maintain your health into old age then having a high VO2max is essential
  • Heart rate training is an excellent tool to let you know if you are training at the right intensity to improve this
• Endurance
  • Certain heart rate zones can improve aerobic fitness, allowing you to train for longer using the most efficient system our body has
• Preventing aerobic deficiency
  • It’s theorised that doing too much high intensity training whilst training for longer distances could handicap you by teaching your body to work anaerobically and therefore less efficiently

Understanding Training Zones: The Five Zone Model

The ACSM* divide training intensity into five heart-rate zones, which are based on rough percentages of your maximum heart rate. This doesn’t tend to be useful as highly trained athletes can be in Zone 2 at 85% of their maximum heart rate whilst certain heart or metabolic conditions can lead people to be in Zone 4 whilst sat on the sofa. We instead suggest using RPE (rate of perceived exertion out of 10) aka effort to measure which zone you are in.

• 🟢 Zone 1 (RPE 1-2/10): Very light – used for active recovery, warm-up/cool-down, and low-stress aerobic conditioning.
• 🟢 Zone 2 (RPE 3-4/10): Light – used for aerobic base training— Enhances mitochondrial function & endurance capacity. As a guideline for effort, in this zone you should be able to hold a conversation over phone call. It won’t be a comfortable conversation and the person on the other end of the call should know you are exercising but other than taking a breath between phrases the conversation should still be able to flow.
• 🟡 Zone 3 (RPE 5-6/10): Moderate: Tempo running or “grey zone”—elevated lactate production, generally used as race pace training.
• 🔴 Zone 4 (RPE 7-8/10): Vigorous: Anaerobic threshold—improves lactate tolerance, VO₂ threshold output, sustainable high-intensity effort (e.g. tempo intervals). A big feature of “Norwegian Method” style of training
• 🔴 Zone 5 (RPE 9–10/10): Maximal effort—short all-out bursts to raise VO₂max and anaerobic power; only a few minutes per session due to high load.

Why These Zones Matter

Zone 2: Aerobic Base

A study of college triathletes found that those who spent at least 20 % of training time in Zone 2 improved their aerobic efficiency dramatically more than those who stayed predominantly in Zone 1. Between the two groups VO₂ₘₐₓ didn’t differ but this allowed the Zone 2 group to perform at higher intensity with less fatigue.

Zone 3: Race tempo

Largely neglected as a training zone, this is a good option for race specific practice, particularly in distances around 10km. Many consider this zone as “junk volume” where you aren’t focussing on one area to improve.

Zone 4 & 5: Threshold and VO₂ₘₐₓ

Interval-based training in Zones 4–5—such as HIIT or tempo intervals—has been shown to produce greater VO₂ₘₐₓ improvements compared to moderate continuous training, especially in less trained individuals. These zones raise lactate tolerance (muscle burning activities) and power output—critical for race surges and high-demand efforts.

Practical Guidelines

Training Distribution: 80/20, Polarized or Norwegian

• Many experts endorse an 80/20 model: ~80 % of training in Zones 1–2, ~20 % in Zones 4–5, with minimal of Zone
• A polarized model (lots of low plus some very high intensity, little middle) is shown effective across many endurance sports.
• Norwegian – this method is for the data nerds (Paul), it relies on blood lactate testing and being at or near your anaerobic threshold whilst training. The downside is the high amount of time spent at higher intensities can lead to higher risk of injury and overtraining

Discipline specific takeaways

• Runners: Split training between long Zone 2 runs, tempo runs in Zones 3–4, uphill sprints in Zone
• Cyclists: Steady Zone 2 rides; threshold efforts (20–60 min in Zone 4); short power surges in Zone
• Rowers/Swimmers/Team Athletes: Mix extended aerobic drills at Zone 2, repeat high-intensity efforts mimicking game/race conditions in Zones 4–5.

What are the alternatives?

Smart watches & fitness trackers

Using the heart rate ranges on your smartwatch is a common way of tracking exercise intensity but as mentioned above, different people have different zones and there are many factors that can influence this. Additionally, smart watches and fitness trackers use generic algorithms to predict heart rate zones that may not take into account all the individual variation.

 

Blood lactate testing

The most scientific way to assess training intensity is by using blood lactate testing – this gives you an exact indicator of which energy system you are predominantly working in and a number to use for reference. You could use this every time you train or just to help you set heart rate or learn the appropriate amount of effort. Again, lactate can vary day to day depending on how recovered you are but it is the most accurate and scientific way to approach training

 

 

 

*American college of sports and exercise medicine