Training Zones and How to Set Them
Training Zones: Setting Them Right
Why arbitrary percentages fail, how to test for individual thresholds, and an 8-zone system built on real physiology.
In earlier posts, we examined the various training adaptations and the time required for each to develop. Now we need a practical system for categorizing training stimuli into "zones" that map onto those adaptations so we can track what we're actually doing and measure whether it's working.
To me, this is the root purpose of training zones: to help us define valid, practically useful inputs that we can later test against an output. In this sense, there is nothing inherently magical about where we draw the boundaries. We could just use arbitrary percentages as many do (Zone 1 = 50-60% max HR, Zone 2 = 60-70%, etc.). But arbitrary percentages have a serious problem.
Why Arbitrary Percentages Fail
An arbitrary limit of "65% of max heart rate" as the ceiling for Zone 2 can mean completely different things for different athletes. One athlete might find this intensity manageable for an entire Ironman. Another might find it close to their second threshold, sustainable for barely an hour. The same percentage produces different physiological responses in different bodies, and even different responses in the same body at different points in the season.
If we want to prescribe the same physiological stimulus for different individuals, we need individual physiological testing.
How to Determine Individual Zones
To accurately map an athlete's physiology, we need a test that spans the full intensity range, from very easy to maximal. A progressive step test accomplishes this: a series of stages at increasing intensity, each held long enough (typically 5 minutes) for physiological markers to stabilize before stepping up.
Equipment options
The most important thing, by far, is individual testing. Moving away from arbitrary percentages and looking instead at actual shifts in physiology. That said, each additional tool adds useful information:
Full Metabolic Test
Metabolic cart + lactate + heart rate. The complete picture: fat/carb oxidation, ventilatory thresholds, lactate curve, and heart rate deflections. Best done at a university lab or here at EO VITA. ~$250-$300 per test. Recommended annually.
Portable Lactate Tester
Shows shifts in net lactate production across the intensity range. Highly informative for tracking peripheral aerobic development and fiber-type shifts. Testable every few months at home. ~$195 for a device.
Heart Rate Monitor
The minimum viable option. Heart rate shows identifiable deflection points during a step test that correspond to key thresholds. Less precise, but far better than arbitrary percentages.
My recommendation: a hybrid model. Full metabolic testing at a lab once a year, supplemented by more frequent lactate testing every few months. Whatever equipment you have, the key is sticking with a consistent protocol so tests are comparable over time.
Protocol essentials
Several factors matter before the test begins. Fatigue level: the athlete should be "training fresh," not coming off a hard session but also not unusually rested. I treat tests as a normal key session within a regular training week. Nutrition: fast for approximately 3 hours before testing. A full overnight fast leaves the athlete too depleted for a solid maximal effort; eating too close to the test artificially elevates carbohydrate oxidation. Warm-up: get lactate below 1.5 mmol/L before starting, which usually takes 30-60 minutes of very easy activity.
The test itself consists of 5-minute stages, starting well below threshold and progressing to volitional failure. The step height and starting point should be scaled to the athlete's fitness to ensure 3-4 stages beyond threshold are possible. Most athletes will manage 2 stages beyond threshold before stopping. Three is rare. Four requires unusual anaerobic capacity.
Interpreting the Curves
The heart rate profile
While heart rate tends to be a noisier metric (influenced by hydration, caffeine, stress, and even what the athlete is thinking), most athletes will show two identifiable deflections during a step test.
The first deflection occurs around the aerobic threshold (~50-60% VO2max). Below this point, the heart accommodates increased oxygen demand partly by filling more completely (stroke volume). At around this intensity, stroke volume maxes out, and further increases must come entirely from heart rate. This creates a visible steepening in the curve. The second deflection occurs when the anaerobic system is increasingly contributing, causing heart rate to level off relative to power increases.
The lactate curve
The lactate curve also shows two critical inflection points. The aerobic threshold (AeT) is where lactate first begins to rise above baseline (I use the point before the first rise of >0.3 mmol/L). Since lactate is a byproduct of glycolysis, this rise signals increasing contribution from glycolytic (Type IIa) fibers over slow-twitch (Type I) fibers. The anaerobic threshold (AnT) marks a second, steeper acceleration in lactate, representing the shift to non-oxidative Type IIx fibers. I use the modified D-max method to identify this point.
The fat oxidation profile
When metabolic cart data is available, the fat oxidation curve adds valuable context. Fat usage typically peaks at or near the aerobic threshold, then falls steadily to zero at the anaerobic threshold. The critical variable is the breadth of this fat-burning plateau, which varies enormously between athletes.
An athlete with a strong base will have a broad, flat fat-burning plateau extending well above AeT. An athlete with a weak base (or one who has been spending too much time in higher zones) will see fat oxidation drop sharply the moment AeT is exceeded. This information directly informs how wide or narrow certain zones should be set for that individual.
From Thresholds to Training Zones
The simplest approach is a 3-zone model: below AeT, between AeT and AnT, above AnT. This is the framework used in much of the research on elite athlete training distribution. While useful for research, most coaches find it too coarse for practical daily training prescription.
My own zone system, evolved from what I learned from the legendary swim coach Gennadi Touretski during his time coaching Olympic Champion Alex Popov, uses 8 zones referenced to the athlete's individual aerobic and anaerobic thresholds. By anchoring zones to tested physiological markers (and fine-tuning with metabolic data when available), we get zones that are current and tailored to the individual.
The 8 zones explained
Zone 0: Active Recovery
Pure "sharpen the saw" work. The objective is not to add fitness but to improve recoverability. Walks, yoga, easy movement. No floor: literally as easy as you like. The metabolic health benefits (moderating blood glucose, encouraging fat oxidation) are significant.
Zone 1: Easy Aerobic
The vast majority of training time for all athletes lives here, from Olympic sprint swimmers to ultra-endurance athletes. The goal: maximally recruit fat-oxidative Type I fibers and rack up beats with the heart at full stretch to drive cardiac remodeling. Beneficial for everyone.
Zone 2: Steady Endurance
The first tier of specific preparation for fast oxidative fibers. Pushes the first lactate step down and broadens the fat oxidation profile. In novices, this zone is narrow and fibers are quite glycolytic. In well-trained athletes, it becomes broad and metabolically starts to resemble Zone 1. Endurance in this zone can range from under 2 hours (novice) to 12+ hours (elite).
Zone 3: Moderate Aerobic
The training zone I recommend spending the least time in. Glycogen usage is disproportionately high while the intensity isn't sufficient to fully tax the oxidative limits of fast oxidative fibers. Unless the athlete's target event takes place in this zone, minimal time should be spent here. (This aligns with what some methodologies call "Sweet Spot," which, for the reasons above, I completely disagree with.)
Zone 4: Threshold
Taxes and trains the ability of fast oxidative fibers to produce energy aerobically while keeping lactate in balance. A critically important zone for endurance athletes whose events fall in the ~90 second to 90 minute range.
Zone 5: Max VO2
Maximally challenges the ability of all fibers to consume oxygen and generate aerobic energy. Represents a "ceiling" that must be elevated to give the athlete room to grow. That said, for the vast majority of developing athletes, the easy aerobic zone is far weaker than VO2max, so this zone gets less priority during development.
Zone 6: Lactate Tolerance/Production
For events with high anaerobic contribution (under ~60 seconds for pure power, 1-3 minutes for capacity). These qualities are very event-specific, run counter to making fast-twitch fibers more oxidative, and the adaptation is short-term. A little goes a long way.
Zone 7: Speed
The ultimate ceiling: does the athlete have sufficient muscular power and skill to produce competitive speed? Importantly, speed work is alactic, meaning lactate should be kept in check to avoid interfering with technique and creating excessive fatigue. Reps are short. The focus is practicing going fast, not grinding. For best results, it should be "easy speed."
Fine-Tuning Zones with Metabolic Data
The zone boundaries above use approximate offsets from the thresholds (e.g., "~AeT+10bpm" for Zone 2). In practice, these should be fine-tuned according to the athlete's metabolic profile. An athlete with poor metabolic fitness may see fat oxidation plummet as soon as AeT is exceeded, making even a 10bpm Zone 2 window too wide. Conversely, an athlete with excellent metabolic fitness may safely train in a broader Zone 2. This is where annual metabolic testing, while not essential, adds particularly useful context.
Beyond zone-setting, metabolic data also informs how much volume in each zone the athlete can tolerate, something we'll explore in the next post.
We've covered a lot of ground. The core message: determine your individual training zones through physiological testing rather than relying on arbitrary percentages. Whether using full metabolic testing at a lab, lactate testing at home, or even simple heart rate profiling, regularly monitoring the individual and updating zones on a consistent basis ensures that the training intensity you prescribe is the right intensity for that athlete.
In the next post, we'll look at what "good" numbers look like at different levels of the sport, and how to use test results to identify where to direct the training next.