Give most endurance athletes a training range, and there’s a good chance they’ll gravitate toward the upper end of it. If the prescribed cycling range is 160 to 190 watts, they’ll aim for 190. If their aerobic run pace is somewhere between 8:30 and 9:15 per mile, they’ll settle closer to 8:30. Even when the effort feels comfortable at a lower intensity, there’s often an inclination to push a little harder, as though getting closer to the upper limit means getting more out of the workout.
I understand the thinking. Athletes invest considerable time and energy into training, and naturally they want that investment to produce results. If there’s an opportunity to do a little more without exceeding the prescribed range, why wouldn’t they take it?
The problem is that this assumes the upper end of a training zone provides a greater aerobic benefit than the lower end. It also assumes that because an athlete is capable of sustaining a particular intensity, there’s a reason to train there.
Neither assumption is necessarily correct.
A study published in the October 2026 Journal of Strength and Conditioning Research provides an interesting perspective on this question. The findings reinforce something I’ve observed throughout my coaching career: we generally don’t need as much intensity as we think we do to improve aerobic fitness, and our tendency to make manageable training a little harder may be costing us more than we’re gaining.
What New Research Tells Us About Aerobic Training Intensity
The study, Neuromuscular Adaptations, Performance, and Monitoring of Endurance Training Within Moderate Domain Intensities, compared two groups of trained amateur runners. One group trained near the upper boundary of the moderate-intensity domain, identified using the first lactate-related threshold. The other group trained approximately 10–15% below that boundary.
Both groups completed equivalent training volumes during the six-week comparison period, allowing researchers to examine the effects of different training intensities without deliberately giving one group more training time than the other.
The results were interesting. Both groups improved in measured performance and neuromuscular variables, but there were no statistically significant differences between groups. The researchers also observed that some psychophysiological responses were higher in the group training near the upper boundary, although those responses remained within acceptable limits.
In other words, the athletes who trained harder did not demonstrate a clear performance advantage over those who trained at a lower intensity.
There are limitations to the study. Twenty runners is a small sample, six weeks is a relatively short intervention, and the absence of statistically significant differences doesn’t prove that the two approaches are equivalent over the long term. The study also didn’t directly measure every cellular adaptation that contributes to aerobic development.
Still, the results raise an important question for coaches and athletes: if a lower intensity can produce similar improvements in the outcomes measured, what additional benefit are we getting by pushing harder?
That question becomes particularly relevant when we consider the amount of aerobic training required for long-course triathlon.
The Top of a Training Zone Is a Boundary, Not Necessarily a Target
When I prescribe a training range, I’m not giving an athlete permission to make every session as hard as possible within that range. The range exists because there is more than one appropriate intensity for accomplishing the purpose of a workout.
The lower end isn’t a compromise, nor is it a less productive version of the training. It allows for normal variations in fatigue, readiness, terrain, environmental conditions, and the demands of the surrounding training week. More importantly, it recognizes that the intended physiological stimulus can often be achieved without pushing toward the upper boundary.
Consider an athlete prescribed a two-hour aerobic ride between 160 and 190 watts. They settle comfortably at 170 watts, their breathing is controlled, and the effort feels sustainable. After twenty minutes, they check their computer and decide to increase the power to 185 watts because they believe they’re leaving something on the table.
But what exactly are they leaving on the table?
If the objective is to accumulate aerobic training at an intensity that supports endurance development, they may already be accomplishing that at 170 watts. Increasing the power might create additional metabolic demand without meaningfully improving the intended training response.
Of course, training intensity still needs to be sufficient for the athlete and the purpose of the session. The lower end of an appropriately prescribed range isn’t automatically interchangeable with every intensity below it. But we should stop assuming that moving toward the highest allowable number necessarily makes the workout better.
The distinction I want athletes to understand is that a training zone describes a range of appropriate work, not a competition to see how close they can get to its ceiling.
Why More Training Stress Doesn’t Always Mean More Aerobic Adaptation
One of the more important principles in endurance coaching is understanding the difference between training stress and training adaptation.
Stress is the demand we place on the body. Adaptation is the physiological response to that demand over time, influenced by the athlete’s training history, recovery, nutrition, and the consistency with which training is repeated.
Aerobic training stimulates changes that improve our ability to sustain exercise, including adaptations involving mitochondrial function, oxygen delivery, and the muscles’ capacity to produce energy aerobically. These processes don’t require every session to be completed near the upper boundary of the moderate-intensity domain.
Increasing intensity generally increases metabolic demand and can strengthen some of the cellular signals associated with adaptation. However, the relationship between the amount of stress we impose and the adaptation we receive isn’t perfectly linear. More stress doesn’t guarantee a proportionally greater response, particularly when the original training intensity already provides an adequate stimulus.
This is where athletes can make a costly mistake. They judge the productivity of a workout by how demanding it was rather than whether it accomplished its intended purpose.
A session completed at the upper end of the range may feel more productive because the athlete generated higher power, ran faster, or finished with a greater sense of exertion. Those things tell us something about the work performed, but they don’t necessarily tell us whether the athlete will experience greater aerobic improvement.
The research doesn’t establish that lower-intensity training always produces identical adaptations, and there are circumstances where additional intensity is exactly what an athlete needs. What it does challenge is the assumption that increasing intensity within the moderate domain automatically provides a greater return.
For Well-Trained Endurance Athletes, the Upper End of Zone 2 Can Be Expensive
This becomes particularly important for experienced endurance athletes whose aerobic thresholds are relatively high.
For a well-trained cyclist, the upper end of their aerobic training range may represent a substantial absolute workload. An athlete with a high first threshold can produce considerable power while remaining within the moderate-intensity domain, but that doesn’t mean the metabolic cost of doing so is insignificant.
As exercise intensity increases, total energy expenditure generally rises, along with the absolute amount of carbohydrate being used. The relative contribution of carbohydrate also often increases as athletes approach higher exercise intensities, although the exact response depends on training status, nutritional availability, and individual physiology.
An athlete may still be working aerobically, yet the difference between riding comfortably below their first threshold and consistently pushing toward it can become meaningful over a long session.
That matters because carbohydrate availability and recovery aren’t unlimited resources.
Consider an experienced Ironman athlete who has a substantial aerobic ceiling and can comfortably ride at power outputs that would represent demanding work for a less-trained athlete. Riding near that ceiling may be entirely appropriate during certain sessions, particularly when we’re targeting race-specific demands or particular physiological adaptations.
But there’s no reason to assume every aerobic ride should be completed there.
If the athlete can achieve the intended aerobic stimulus at a lower power output, consistently riding harder may increase carbohydrate requirements and recovery demands without delivering a proportionate improvement in fitness.
For triathletes, who are already managing the combined demands of swimming, cycling, running, and often strength training, those additional costs deserve consideration.
The question isn’t whether an athlete can tolerate the higher intensity. It’s whether the higher intensity is necessary for the adaptation we’re trying to achieve.
What Happens When You Force an Effort That Should Feel Sustainable?
Another common pattern I see is the athlete who feels unusually tired but continues pushing toward the upper end of the prescribed range because that’s where they believe they should be training.
Perhaps they’ve had a demanding week at work, slept poorly, or accumulated more fatigue than expected. They start their aerobic ride, settle into an effort that feels manageable, and then look at their power meter. The number is lower than usual, so they begin forcing the effort upward.
At that point, I would rather they pay attention to what their body is telling them.
If a session is intended to be comfortable aerobic training, and reaching the upper end of the range requires an unusual amount of effort, there may be little reason to insist on that intensity. Settling into the lower end of the prescribed range may allow the athlete to accomplish the intended work without adding unnecessary stress.
This doesn’t mean every difficult session should be abandoned or that fatigue automatically prevents adaptation. Productive training sometimes requires us to work through discomfort, particularly during deliberately demanding sessions.
But there is a difference between accepting the discomfort associated with a challenging workout and creating additional difficulty during a session that was never intended to be challenging.
Athletes need to learn that distinction.
Part of becoming an experienced endurance athlete is developing the judgment to recognize when more intensity serves the purpose of training and when it simply satisfies the desire to do more.
An Unpopular Opinion About Running Frequency and Injury
This same tendency to push toward the upper end of a training range makes me think about another common conversation in coaching: the athlete who describes themselves as too injury-prone to run more frequently.
Many endurance athletes believe their bodies can tolerate only a certain number of runs each week. They may have experienced repeated injuries or noticed that increasing their running frequency has historically led to problems. Their conclusion is that they simply aren’t built to run more often.
Sometimes that’s an appropriate conclusion, particularly when an athlete has a history of significant injuries or underlying issues that require careful management.
But I suspect there are also plenty of athletes who might benefit from reconsidering how hard they’re running before deciding how often they can run.
If every run gravitates toward the faster end of the prescribed range, the athlete may be accumulating more mechanical and physiological stress than necessary. The problem may not be frequency alone, but the intensity, duration, and distribution of the running they’re already doing.
For some athletes, reducing intensity, shortening individual runs, and gradually distributing an appropriate amount of running across more days could provide a more sustainable path toward consistency.
That doesn’t mean simply adding more runs to an existing schedule. Running injuries are multifactorial, and frequency, total volume, prior injury history, tissue capacity, and progression all matter. Any increase in frequency needs to be managed carefully.
Still, I think it’s worth challenging the assumption that the answer to repeated running injuries is always to run less often.
Perhaps the better question is whether we can make the running more manageable so the athlete can tolerate consistent exposure over time.
The goal isn’t to accumulate more runs for the sake of running more frequently. It’s to develop the durability and aerobic fitness that come from training consistently, without repeatedly exceeding what the athlete can absorb.
Why This Matters Even More for Ironman and 70.3 Training
Long-course triathlon requires a substantial amount of aerobic development. Athletes preparing for Ironman and 70.3 events need to sustain work over long periods, manage energy availability, maintain efficient movement under fatigue, and develop the ability to recover from repeated training demands.
These qualities aren’t developed through a handful of particularly demanding sessions. They emerge through the accumulation of appropriate training over months and years.
An athlete training twelve or fifteen hours per week has to consider the entire program, not simply the productivity of each individual workout. A slightly harder aerobic ride may not seem particularly costly on its own, but the additional stress becomes more relevant when followed by a run, another swim, or a demanding weekend of training.
If pushing toward the top of every aerobic range compromises the athlete’s ability to execute subsequent sessions, we’re potentially sacrificing the quality of the larger training program in pursuit of a benefit that may not exist.
This is also why I don’t believe every training session needs to be evaluated according to how much work the athlete managed to complete.
There are sessions where intensity is the objective, and we deliberately ask the athlete to work hard. There are sessions where race-specific power, pace, or fueling demands require a more precise prescription. There are also sessions where the objective is simply to accumulate aerobic work at an intensity the athlete can sustain and recover from.
All of those sessions have value, but they serve different purposes.
The challenge is resisting the urge to turn the easier sessions into something more demanding simply because the athlete is capable of doing so.
How Should Triathletes Use Zone 2 and Aerobic Training Ranges?
One complication in this discussion is that Zone 2 means different things depending on the training model being used.
In a three-zone physiological model, the first zone generally extends below the first lactate or ventilatory threshold. In many five-zone systems, Zone 2 represents a portion of the lower-intensity training spectrum, although its precise boundaries depend on the methodology used.
The first lactate threshold, or LT1, and first ventilatory threshold, or VT1, are related markers of exercise intensity, but they aren’t necessarily identical. The October 2026 study specifically used the first lactate-related boundary to distinguish its two training prescriptions.
These distinctions are important because athletes can become overly focused on training at a precise number without understanding the physiological purpose behind it.
In practice, I want athletes to use their prescribed ranges alongside perceived exertion, breathing, heart rate, and an understanding of the session’s purpose.
If the workout calls for comfortable aerobic training, there should generally be room to settle into an effort that feels controlled and sustainable. If the athlete feels good, that doesn’t automatically mean they need to push higher. If they’re carrying fatigue, they should understand that using the lower end of the range may be entirely appropriate.
Over time, the more useful measures of progress are often the changes we see across comparable conditions: improved pace or power at a similar heart rate, lower perceived exertion at a familiar workload, greater durability over longer sessions, and the ability to sustain consistent training.
Those changes tell us more about aerobic development than whether an athlete managed to reach the upper boundary of their training zone on a particular Tuesday.
The Real Goal Is to Get More From the Training Program, Not Every Workout
One of the recurring themes in conversations with athletes is the desire to get more out of their training.
They want to know whether they should increase their intensity, add another interval, run a little faster, or ride at a higher power output. There’s often an assumption that improvement requires finding another opportunity to do more.
Sometimes it does. Progressive overload remains fundamental to endurance development, and there are times when increasing volume, intensity, or the specificity of training is necessary.
But progression doesn’t mean every session needs to become more demanding, and it certainly doesn’t mean that the highest allowable intensity is always the most effective one.
The October 2026 research is interesting because it gives us another reason to question that assumption. Within the moderate-intensity domain, the athletes training closer to the upper boundary did not demonstrate clearly greater improvements than those training below it.
For me, the larger lesson is about understanding the purpose of training and becoming more comfortable with the idea that a sustainable effort can still be a productive one.
I want athletes to recognize that the lower end of a prescribed range exists for a reason. It’s not a concession to fatigue or a missed opportunity to gain fitness. It’s part of a thoughtful training prescription that accounts for the physiological stimulus we’re trying to create and the demands of the larger program.
There are times to push harder, and those times should be deliberate. On the days when the objective is aerobic development, there’s often more value in settling into the appropriate effort, trusting the work, and leaving enough capacity to do it again.
The top of a training zone is a boundary, not necessarily a target.
The goal isn’t to get the most out of every individual workout. It’s to get the most out of the training program as a whole.
Frequently Asked Questions About Aerobic Training Intensity
Is it better to train at the top of Zone 2?
Not necessarily. The upper boundary of a prescribed aerobic training range isn’t automatically the most effective intensity. The appropriate target depends on the athlete’s fitness, the training-zone model being used, and the purpose of the session. Working comfortably within the range may provide the intended aerobic stimulus without unnecessary additional stress.
Can you improve aerobic fitness by training below VT1 or LT1?
Yes. Training below the first ventilatory or lactate threshold can stimulate meaningful aerobic adaptations. The appropriate training dose depends on intensity, duration, frequency, and the athlete’s training history.
Does higher aerobic training intensity burn more carbohydrates?
Generally, increasing exercise intensity raises total energy expenditure and absolute carbohydrate oxidation. The relative contribution of carbohydrate also tends to increase at higher intensities, although individual responses vary. For endurance athletes completing substantial training volumes, this can influence fueling needs and recovery.
Should triathletes always train at the lower end of their aerobic zones?
No. Both lower and higher intensities within an appropriate aerobic range can serve useful purposes. The objective is to select the intensity that best supports the intended adaptation while considering fatigue, recovery, and the rest of the training program.
Can running easier help injury-prone athletes run more frequently?
For some athletes, reducing intensity and individual session duration may help make a gradual increase in running frequency more manageable. However, injury risk depends on several factors, including total running load, previous injuries, tissue capacity, and progression. More frequent running should be introduced gradually rather than added indiscriminately.
Research and Sources
- Guimarães, M. P., Foresti, Y. F., Papoti, M., & de Azevedo, P. H. S. M. Neuromuscular Adaptations, Performance, and Monitoring of Endurance Training Within Moderate Domain Intensities. Journal of Strength and Conditioning Research, 40(10), e1046–e1055, 2026. (PubMed)
Keep reading
- Stop Chasing Exact Numbers: Why Power and Pace Ranges Work Better in Training
- Relearning Effort: Interoception, RPE, and the Hidden Skill of Internal Awareness
- Data Is a Clue, Not Proof: Learning to Trust Yourself as an Endurance Athlete
About Elizabeth Waterstraat
Elizabeth Waterstraat is the founder and head coach of Multisport Mastery, established in 2007. A USA Triathlon Level III Coach with 20 years of coaching experience and 26 years as an endurance athlete, Elizabeth works with athletes ranging from first-time triathletes to national champions and world championship qualifiers. Her coaching approach emphasizes individualized training, athlete education, consistency, and long-term development.
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