Endurance races have never been more popular, and chances are many of your clients have committed to a half-marathon, gran fondo (a long-distance cycling ride), triathlon or other long-duration event in the coming year. They are looking to you for guidance on how to train intelligently, and the most useful starting point is still the classic endurance-performance triad: VO₂max, lactate threshold and economy.

That said, the way we talk about endurance physiology has evolved over the past decade. Researchers now more often distinguish between the first and second lactate thresholds (LT1/LT2), compare threshold-based intensity recommendations with generic percentage-based formulas, and discuss emerging concepts such as critical speed/power and durability. The purpose of this article is not to replace the classic framework, but to update it with practical, evidence-based programming strategies that health and exercise professionals can use with endurance-minded clients.

The Physiology of Endurance Performance

Endurance exercise can be defined as the ability to perform a cardiovascular activity, such as running, cycling, swimming, rowing, hiking or cross-country skiing, for an extended period of time. Although endurance performance depends on the integration of multiple systems, from pulmonary ventilation and cardiac output to muscle oxygen extraction, substrate use and neuromuscular coordination, the coaching question is relatively simple: How well can a client sustain repeated muscle contractions over time?

For practical programming purposes, that question is still best answered through three interrelated variables. First, VO₂max reflects the highest rate at which oxygen can be taken up, transported and utilized during intense exercise. Second, lactate threshold reflects the highest intensity a client can sustain before metabolic stress rises sharply and the effort becomes progressively less stable. Third, economy describes how much oxygen or energy is required to maintain a given workload or speed. Individually, each variable matters. Collectively, they do an even better job of explaining why one client can comfortably hold a pace that another client can only touch briefly.

A helpful way to think about the triad is that VO₂max sets the ceiling, lactate threshold determines how much of that ceiling can be used for sustained work, and economy determines the cost of operating at any given pace or power. Because these variables interact, training decisions that improve one often influence the others. A higher VO₂max without a corresponding rise in lactate threshold may not produce a major change in race pace. Likewise, a client with excellent threshold values may still leave performance on the table if the energy cost of movement is too high.

Why Does Improving VO₂max, Threshold and Economy Improve Performance?

The enduring value of the triad is that it explains why athletes with similar fitness profiles can perform quite differently. Imagine two runners with the same VO₂max of 45 mL/kg/min. On paper, they appear evenly matched. But if Runner A reaches LT2 at a much lower percentage of VO₂max than Runner B, Runner B will be able to race at a meaningfully faster sustainable speed. The athlete is not simply more fit in a general sense; that athlete can use more of the available aerobic ceiling before severe fatigue sets in.

The same principle applies to economy. Within more homogeneous groups of runners, economy often helps explain differences that VO₂max alone cannot. A client who needs less oxygen at a given pace can preserve glycogen, accumulate less metabolic strain and delay fatigue. That is one reason performance gains sometimes appear in the field before laboratory markers change dramatically: the client has become more economical, more durable, or better able to express threshold speed late in the session.

More recent evidence also suggests that you should be cautious about reducing performance to a single percentage. A 2025 study of nearly 300 endurance athletes found that lactate threshold expressed as a percentage of VO₂peak did not differ meaningfully across elite, national and regional performers, suggesting that absolute speed or power at threshold may be more informative than threshold percentage alone in already well-trained populations. In other words, the question is not only where threshold occurs relative to VO₂max, but what speed, pace or power that threshold actually supports.

An additional update is the growing importance of durability. Physiological profiling has traditionally been performed in a rested state, but thresholds, economy and other markers can drift during prolonged exercise. For long-course events, that matters. A client whose mechanics, perceived exertion and cardiovascular cost all deteriorate after 90 minutes may need different programming than a client with similar resting lab values who maintains those characteristics much longer.

Strategies for Increasing VO₂max

Traditionally, improving VO₂max meant building training volume through more frequent and longer aerobic sessions. That principle is still correct. Low-intensity aerobic volume promotes central and peripheral adaptations, increases tolerance for training, and provides the base that allows harder sessions to be absorbed productively. For novice and intermediate clients, the biggest mistake is often not too little intensity, but too little sustainable volume.

However, newer research makes equally clear that high-intensity interval training (HIIT) can raise VO₂max efficiently when layered onto that aerobic foundation. Recent meta-analytic work found that HIIT improves VO₂max and related performance measures in trained athletes, and short-to-medium intervention blocks often produce larger VO₂max gains than moderate-intensity continuous work alone. In athletes, HIIT appears especially effective over blocks of one to nine weeks, although the advantage becomes less clear over longer time frames, which is when overall training distribution and accumulated volume matter more.

That is why the current evidence should not be interpreted as "intervals beat base training." A better interpretation is that VO₂max responds well to high-intensity work, but the most effective endurance programs still include a substantial amount of moderate-intensity training. Recent systematic reviews on training-intensity distribution suggest that polarized models—characterized by a large volume of low-intensity work and a smaller but meaningful amount of high-intensity work—are effective for improving VO₂max and related aerobic-capacity measures, as well as work economy, in endurance athletes. Across the studies in one 2024 review, the average distribution was roughly 75 to 80% low-intensity work and 15 to 20% high-intensity work, with very little time spent in the middle.

In practical terms, this means a client does not need to live at race pace to improve aerobic capacity. In fact, many clients improve more when truly easy sessions stay easy and hard sessions are reserved for one or two quality exposures each week. Long intervals of two to five minutes near velocity at VO₂max (vVO₂max), which is the running speed or pace associated with maximal oxygen uptake, as well as uphill repetitions or classic formats such as 4 x 4 minutes can all be effective options. The key is not the exact workout format, but whether the client accumulates enough high-quality time near the target intensity while still recovering well enough to continue progressing.

This is also an area where individualized programming matters. A 2025 meta-analysis found that programming exercise intensity relative to physiological thresholds produced larger average VO₂max improvements than relying on traditional anchors such as fixed percentages of HRmax or VO₂max. In controlled studies, threshold-based programming more than doubled the average VO₂max improvement. For personal trainers, the practical lesson is straightforward: When testing data are available, use them. When they are not, anchor sessions to recent performance, pace, power and carefully observed ratings of perceived exertion (RPE) rather than defaulting to generic formulas.

A useful real-world progression is to earn the right to formal VO2max training. Deconditioned or sedentary clients may first need several weeks of easy aerobic work, short strides, gentle hills and basic resistance training before they are ready for structured intervals. More experienced clients can generally tolerate one VO₂max-oriented session weekly during base-building and up to two during a focused performance block, provided the rest of the week remains predominantly aerobic.

Coaching takeaway: Use HIIT to raise the ceiling, but do not build the whole house out of HIIT.

Strategies for Increasing Lactate Threshold

Of the three classic variables, lactate threshold may be the most directly useful for day-to-day programming because it maps closely onto sustainable race pace and comfortably hard training. It is also where updated terminology has the greatest practical value. LT1 roughly separates easy-to-moderate endurance work from heavier steady-state work, while LT2 marks the high end of sustainable aerobic intensity. Together, they can help you decide when a session is truly easy, when it becomes threshold work and when it tips into high-intensity interval training.

Training can raise threshold through several overlapping adaptations: greater mitochondrial density, improved oxidative enzyme activity, better lactate transport and clearance, improved capillarization and a greater ability to sustain a high fraction of VO2max without excessive disturbance to homeostasis. For recreational clients, the most effective threshold plans usually combine three ingredients: easy volume below LT1, focused steady or interval work above LT1 and below LT2, and work above LT2 to expand tolerance for high metabolic stress.

That broad model still holds up well, but several newer findings sharpen how you can apply it. First, threshold-based intensity programming seems to outperform generic percentage-based methods when the goal is cardiorespiratory improvement. Second, a 2024 meta-analysis in highly trained endurance athletes suggested that HIIT can produce greater anaerobic-threshold adaptation than moderate-intensity continuous training, although the certainty of that evidence was low and the number of studies was small. The message is not that continuous threshold work is obsolete; it is that threshold development appears to respond well to a combination of tempo-like sessions and appropriately dosed interval work.

Classic studies remain useful here. Uphill interval work can be an effective way to improve speed at lactate threshold while also reinforcing posture, force production and specific strength. Likewise, interval sessions that alternate work just above the lactate threshold with short recoveries can improve the sustainable speed associated with that threshold. Those findings align well with what many coaches see in practice: clients often progress fastest when threshold work is broken into repeatable segments that allow more total high-quality time than a single continuous-tempo session would permit.

The most important programming decision is usually dose. Many clients do not need more threshold sessions; they need better threshold sessions. Once weekly is often enough for recreational athletes, particularly when a second quality day already targets VO₂max or hills. Total work at threshold might range from 20 to 40 minutes depending on training age, sport and event demands. More advanced athletes may tolerate larger doses, but piling threshold work into multiple days each week often leads to chronic middle-intensity fatigue—hard enough to compromise recovery, but not hard enough to produce the intended top-end stimulus.

A related practical point is that thresholds are individualized. Recent data in recreational runners showed that fixed heart-rate and RPE anchors can miss LT1 and LT2 by meaningful amounts, and females in that study reached LT1 at a higher relative intensity than males. That does not mean field estimates are useless. It means you should treat them as estimates, then refine the target using conversation, breathing pattern, repeatability of pace and the client's ability to finish the session stronger rather than simply hanging on.

Coaching takeaway: The best lactate threshold session is the one that raises sustainable pace without turning the whole week into moderate misery.

Strategies for Improving Economy

If VO₂max expands aerobic potential and threshold determines how much of that potential can be sustained, economy improves performance by lowering the cost of moving at a given speed or power. For runners, cyclists and triathletes, that makes economy especially attractive because it can improve performance even when laboratory VO₂max barely changes.

Economy is shaped by both physiology and skill. Repeated exposure to the specific movement pattern matters, which is one reason event-specific practice remains foundational. At the same time, current evidence shows that strength and power training can improve economy in ways that traditional endurance training alone may not. A 2024 systematic review and meta-analysis found that high-load strength training and combined strength methods improved running economy, while plyometric training improved economy particularly at lower running speeds. By contrast, submaximal-load and isometric-only approaches did not consistently improve running economy relative to controls.

That evidence is important for health and exercise professionals because it supports the inclusion of resistance training in endurance programs, not merely for injury prevention, but also for performance. In practice, one to two weekly sessions emphasizing high-load lower-body strength, explosive intent, and progressive overload can be enough to produce meaningful benefit without overwhelming recovery. Exercises such as squats, step-ups, Romanian deadlifts, split squats, calf raises and low-dose plyometrics can all fit, provided the overall training load is managed well.

Session order also matters when endurance and strength are trained on the same day. A 2023 meta-analysis on concurrent training found that performing strength before endurance improved lower-body strength outcomes more than the reverse order, while VO₂max changes were similar regardless of sequence. For endurance-focused clients, that means the order can be chosen based on the primary goal of the day. If preserving strength quality is important, place strength first or separate the sessions.

Biomechanics are another major part of the economy conversation, but updated evidence suggests restraint is warranted. A 2024 systematic review reported that higher step frequency, lower vertical oscillation, and greater lower-limb stiffness were associated with better running economy, yet most single biomechanical variables explained only a modest amount of the variance. That is a useful reminder that there is no universal perfect form cue that reliably fixes economy for every runner. Over-coaching mechanics can sometimes create more tension and inefficiency than it solves. Your clients will usually be better served by targeting one or two meaningful movement cues, then letting strength, practice and exposure do the rest.

Stretching and warm-up practices also deserve an update. Older guidance often warned that static stretching before endurance exercise would impair economy by reducing elastic energy return. A 2025 systematic review with meta-analysis found low-certainty evidence of no significant acute effect of stretching—static, dynamic or proprioceptive neuromuscular facilitation—on running economy. That does not mean warm-ups no longer matter. It means the blanket statement that pre-run stretching hurts economy is no longer well supported. For most clients, the better question is whether the warm-up improves readiness, comfort and stride quality without creating fatigue.

Coaching takeaway: Economy usually improves most when specific practice is paired with smart strength training and minimal over-cueing.

Programming the Triad for Real Clients

When you are working with clients, VO₂max, threshold and economy should not be programmed as isolated silos. Most well-designed endurance plans improve all three at once, but with different emphases over time. Below are some examples of how you can apply these principles to your work with clients.

For a novice endurance client, the first priority is usually consistency. That may mean three to four aerobic sessions each week, most of them below LT1, plus one or two brief doses of faster work such as strides, short hills or controlled intervals. Add one or two resistance-training sessions and the client is already addressing the entire triad: aerobic volume supports VO₂max and LT1, short quality sessions begin to raise top-end capacity and coordination, and strength work supports economy.

For a recreational half-marathoner or cyclist preparing for an event, a classic weekly pattern still works well: one longer low-intensity session; one threshold-focused session; one VO₂max, hill or fartlek session; and mostly easy aerobic work between them. You can adjust the plan according to the client profile. A client with strong raw fitness but poor pacing and an early late-race fade may need more threshold and durability work. A client with good durability but limited top-end aerobic power may benefit from a clearer VO₂max block.

For time-crunched clients, low-volume HIIT can be a valuable tool, but it should be framed honestly. It is an efficient strategy for improving VO₂max and can support threshold development, yet it does not fully replace the technical, metabolic and durability benefits of longer low-intensity sessions. A client training for a 10K may be able to get away with less volume than a client training for a marathon or long-course triathlon. Event demands still matter.

Durability is especially relevant here. Recent reviews have highlighted that physiological characteristics are not static during prolonged exercise, and intervention work suggests both low- and high-intensity endurance training can improve durability. For health and exercise professionals, the practical application is clear: long, easy sessions are not just miles for the sake of miles. They help clients preserve mechanics, pacing, economy and decision-making deeper into the event.

Monitoring should reflect that broader view. Improving endurance is not just about chasing a higher VO₂max score. Watch for a lower heart rate at the same pace, improved pace at the same RPE, faster pace or power at the lactate threshold, and the ability to maintain form and output later in long sessions. Those are highly actionable signs that the program is working.

Conclusion

VO₂max, lactate threshold and economy remain the most useful classic framework for understanding endurance performance. What has changed is not the importance of those variables, but the precision with which health and exercise professionals can now assess and train them.

The evidence published over the past several years supports a clear coaching message: Build a substantial low-intensity foundation, use high-intensity work strategically rather than excessively, program intensity from individualized thresholds whenever possible, include resistance training to improve economy and remember that long-duration performance also depends on durability. Health and exercise professionals who understand the interaction of those qualities will be better equipped to design training that is not only physiologically sound, but also practical, sustainable and specific to the client in front of them.