🐢 Why Endurance Athletes Need Low-Intensity Training
Elite runners, cyclists, and triathletes—the fastest athletes on the planet—spend an extraordinary amount of time training at what seems like an "easy" pace. Logic (and evidence) would suggest that training closer to race pace or at higher intensities would yield better performance. Yet, athletes across the board continue to pile on miles of slow, low-intensity training. Why is this the case?
A recent perspective article delves into this fascinating paradox, presenting seven intriguing hypotheses that explain why low-intensity training might be the secret behind elite endurance performance.
This one got me to think about—and even question—some of my preconceived notions about why we “run slow” (and why it’s so important).
Understanding the Paradox
At first glance, low-intensity training doesn't seem very stimulating, especially for athletes whose bodies have already adapted to high levels of fitness. Low-intensity training is defined by efforts below the lactate threshold, and generally doesn't significantly challenge the cardiopulmonary system (the heart and lungs) of well-trained athletes. That comes from moderate (think, threshold) and high-intensity training.
Yet, data from marathon runners show that athletes with faster finishing times spend far more time in the low-intensity zone compared to their slower peers. Now, of course, most faster athletes generally spend more time training overall, which somewhat confounds this observation. But why then, don't elite athletes invest their larger allotment of training into moderate- and high-intensity training, those intensities that actually lead to beneficial adaptations?
This suggests there must be hidden benefits at play, and that's precisely what this new article explores.
The Seven Hypotheses
1. Low-intensity training provides fitness maintenance without stress
One of the simplest explanations is that low-intensity training allows athletes to maintain or slightly improve their fitness without accumulating significant stress. High-intensity training sessions, while incredibly effective, require prolonged recovery—up to two days for complete cardiac autonomic recovery. In contrast, low-intensity workouts typically require less than 24 hours, allowing athletes to train frequently without compromising recovery or risking burnout. Most of us (elite or not) can’t do more than a few hard training sessions per week. And we have to fill those other days with something, right?
2. Low-intensity training provides alternative molecular signals
Different training intensities activate different molecular pathways. While high-intensity training primarily triggers metabolic stress pathways (elevating lactate, for example), low-intensity training may stimulate adaptation through fatty acid metabolism and calcium fluxes. By diversifying the adaptation pathways, low-intensity training could enhance overall endurance capacity through complementary mechanisms (there’s a neat little protein called PGC-1 alpha that’s centrally involved here. I’ll spare you the details).
3. Low-intensity training has unique long-term structural adaptations
Consistent, high-volume, low-intensity training over years or decades might facilitate profound structural adaptations. These include increased left ventricular size, greater capillary density, a higher proportion of economical slow-twitch muscle fibers, and expanded mitochondrial mass—all of which enhance endurance performance over a long athletic career. There's even the idea that low-intensity training might preferentially enhance the efficiency of our mitochondria to produce energy, while higher-intensity training preferentially stimulates the production of more or denser mitochondria.
4. Unknown performance factors (we just haven’t measured enough)
As with science, there may be elements of endurance performance enhanced by low-intensity training that we have yet to measure. Factors like durability (a.k.a. "physiological resilience", the ability to maintain performance over prolonged efforts) and rapid recovery might be significantly bolstered by extensive low-intensity training. (More on this later)
5. Low-intensity training benefits psychology and recovery
Let's face it—training hard all the time (while fun) is mentally taxing. Low-intensity training offers a psychological break, reducing mental fatigue and distress. This mental relief might be critical in maintaining an athlete's motivation, consistency, and overall training quality over time.
6. Low-intensity training enhances high-intensity adaptations
Surprisingly, low-intensity training might actually boost the effectiveness of high-intensity workouts. It prepares the body to absorb and recover from intense training by improving baseline fitness and ensuring that the body doesn't resist further adaptations. Essentially, low-intensity training sets the stage for high-intensity efforts to be more effective.
The recovery aspect is something that intrigues me. There's good evidence that combining low-intensity activity (by simply increasing one's daily step count) enhances endurance training adaptations compared to the same training program with fewer steps or more sedentary time outside the context of training. Low-intensity activity might not stimulate beneficial adaptations per se, but rather, augment the benefits of moderate- or high-intensity training sessions.
7. Low-intensity training is potentially replaceable
An intriguing, albeit controversial, hypothesis is that perhaps low-intensity training is replaceable. With optimal programming and meticulous recovery strategies, athletes might sustain high-intensity training without extensive low-intensity work. However, this comes with risks, such as increased injury rates and the potential for overtraining, suggesting that low-intensity training serves as a “safety net” for long-term athlete health and career longevity.
Ultimately, the fact that a majority of elite (and even non-elite) athletes include lots of low-intensity training into their programs indicates—to me at least—it may not in fact be “replaceable.” Decades and perhaps centuries of practice prove otherwise. If there were a better way, we’d likely have figured it out by now.
What This Means for Runners
As a runner, the takeaway from these hypotheses is clear and practical. First, don't underestimate the value of slow, easy miles. They aren't wasted efforts or “junk miles,” they're foundational to your endurance capability and overall athletic longevity.
Second, embrace variety. High-intensity training is critical, but mixing intensities likely enhances overall adaptation and prevents burnout. I’m guilty of writing off low-intensity training as not being “hard enough” to help me improve, but that’s not the point. It most likely permits athletes to do the hard work that does stimulate their body to get faster and fitter.
Third, pay attention to psychological well-being. Training should never feel perpetually exhausting—physically or mentally.
Finally, remember that consistency over months and years—enabled by sustainable training—is where true performance gains are made.
In short, next time you head out for an easy run, think of it as an investment in your endurance, your mental health, and your future performance, even if it’s slightly boring and doesn’t leave you in a puddle of sweat and tears.
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