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Zone 2 Training: Overhyped or Essential for Endurance? Experts Weigh In
“Zone 2 training” has exploded in popularity over the last few years, with endurance athletes and fitness influencers touting it as the key to building aerobic capacity, metabolic efficiency, and longevity.
But what exactly is Zone 2 training, and does it live up to the hype? A panel of 14 sport scientists, endurance coaches, and exercise physiologists collaborated to define zone 2 training and outline its expected physiological adaptations. While there is no universal standard for training zones, the experts largely agreed on the following:
• Zone 2 is the intensity just below the first lactate (LT1) or ventilatory threshold (VT1).
• It is typically performed at ~70-80% of max heart rate (HRmax), with a stable blood lactate level (~1-2 mmol/L).
• It is NOT “junk miles”—it is a deliberate, low-intensity training method designed to build aerobic efficiency.
To establish clearer guidelines, the experts reviewed how zone 2 should be trained, what physiological changes it promotes, and how it compares to other endurance intensities.
• Zone 2 improves mitochondrial function and metabolic efficiency: Training at this intensity increases mitochondrial density and enhances the ability to use fat as fuel.
•Zone 2 training raises the first lactate threshold (LT1): Over time, training in Zone 2 delays the point at which lactate starts accumulating, allowing runners to sustain higher speeds without crossing into lactate accumulation.
• Zone 2 is most effective when accumulated over long durations: The panel emphasized that long, continuous efforts (2+ hours) at zone 2 are more effective than shorter sessions at the same intensity. Elite endurance athletes spend ~70-80% of their total training volume in low-intensity zones, including zone 2.
• Zone 2 training alone won’t maximize performance: While zone 2 is crucial for endurance development, the experts cautioned that it is NOT a substitute for high-intensity work.
• Defining zone 2 can be tricky—HR, power, and lactate should all be considered: Many runners overestimate their zone 2 pace and train too hard, defeating the purpose. The best way to accurately determine zone 2 is through lactate or ventilatory threshold tests. If lab testing isn’t available, monitoring heart rate (~70-80% of max) and perceived exertion (easy effort, nose-breathing pace) can help guide intensity.
What this means for runners
Zone 2 isn’t magic, but it’s foundational. This expert review confirms that low-intensity endurance training is one of the best ways to build long-term aerobic efficiency.
But don’t make the mistake of over-relying on zone 2 and neglecting high-intensity work. The best runners strike a balance: building a strong aerobic engine with zone 2 while layering in faster efforts for race-specific adaptations.
RELATED ARTICLE: Zone 2 Training, Explained: How To Unlock Endurance And Speed Faster
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Can “Too Much” Running Increase Your Risk of Heart Disease?
Most runners assume that logging more miles makes them immune to heart disease. After all, exercise improves cholesterol, lowers blood pressure, and strengthens the heart. But what if—paradoxically—long-term endurance training could increase heart disease risk? A new review explores the complex relationship between running and heart health, revealing that some athletes—especially those training at high volumes for decades—may develop more coronary calcification than expected. But there’s a lot of nuance involved.
Researchers conducted a state-of-the-art review of cardiac imaging studies assessing coronary artery calcification (CAC) and atherosclerotic plaque in endurance athletes. They compared highly trained runners and cyclists to less active populations to determine whether years of intense training increase or decrease the risk of heart disease.
The big question is whether endurance exercise protects against or contributes to coronary artery disease, the leading cause of sudden cardiac death in athletes over 35. Some of the findings challenge conventional wisdom.
For one, endurance athletes have a higher prevalence of coronary plaques than non-athletes. Multiple studies find that high-volume endurance athletes have more CAC and a higher prevalence of plaques than non-athletic control groups.
However, not all plaques are created equal. While athletes have more total plaque burden, the composition of their plaques is less dangerous than what is typically seen in sedentary individuals. Endurance-trained individuals tend to develop densely calcified, stable plaques, which are less likely to rupture and cause heart attacks than the soft, lipid-rich plaques common in sedentary people. For example, in one study, 68% of the plaques found in endurance athletes were calcified, compared to only 47% in non-athletes.
Training intensity and volume seem to influence plaque development. Studies tracking athletes over time found that vigorous exercise was linked to increased CAC scores, but exercise volume alone did not drive plaque progression.
Despite more plaque, athletes have fewer cardiac events. Even in athletes with higher CAC scores, studies show that higher fitness levels (think VO₂max) are associated with a dramatically lower risk of heart attacks and cardiovascular events.
What this means for runners
Running won’t make you immune to heart disease, but higher fitness levels offer significant protection—even for those with coronary plaques.
Should you get a check-up? The authors did not recommend routine coronary artery scans for symptom-free athletes, as high CAC scores in endurance athletes do not necessarily translate to higher event risk. However, athletes with multiple risk factors (e.g., family history, high blood pressure, abnormal cholesterol) or symptoms should consider screening.
This study doesn’t suggest you should run less, but it does highlight the importance of paying attention to your heart health, especially as you age. The best approach? Keep running, but be aware that miles alone don’t make you invincible.
RELATED ARTICLE: Do Runners Live Longer? Up to 12 Years, According to New Research
Do Super Shoes Really Improve Running Economy? And What About Ketones?
Super shoes—high-tech, carbon-plated racing shoes—have transformed running performance, promising better energy return and improved efficiency. At the same time, ketone supplements have been marketed as a metabolic enhancer that could improve endurance by offering an alternative fuel source. But do either of these actually improve running economy? What about combining them? A new study tested both advanced footwear technology and ketone monoester ingestion to determine their effects on running economy (RE), time-to-exhaustion (TTE), and metabolic efficiency.
Researchers conducted a study with 18 trained middle- and long-distance runners (10 men, eight women, VO₂max: ~60).
Each participant completed four different trials on a treadmill, each consisting of five 8-minute stages of submaximal running (the men ran at a speed progressing from 10–14 km/h and women ran at a speed progressing from 9–13 km/h followed by a ramp test to exhaustion to measure time-to-exhaustion and peak oxygen uptake.
Each trial involved a combination of footwear and supplementation:
1. Standard running shoes (Nike Pegasus Turbo) + Carbohydrate (CHO) drink
2. Standard running shoes + ketone monoester drink
3. Super shoes (Nike ZoomX Vaporfly Next% 3) + CHO drink
4. Super shoes + ketone monoester drink
Participants ingested either a ketone supplement or a 10% carbohydrate solution before and during each session.
Super shoes (not surprisingly) improved running economy—ketones didn’t. Wearing the Vaporfly Next% 3 reduced oxygen consumption by 2.5-4.0% at submaximal speeds compared to the standard running shoes. This means runners used less energy to maintain the same pace, making them more efficient. The improvement was most pronounced at faster running speeds (third, fourth, and fifth stages). Super shoes also improved time-to-exhaustion—runners lasted 7% longer in the Vaporfly+CHO condition (381 sec) compared to Pegasus+CHO (356 sec). With ketones, the Vaporfly group improved time-to-exhaustion by 14% over Pegasus+KME.
Ketones alone did not improve running economy or endurance. There were no significant differences in economy between the carbohydrate and ketone trials despite elevated blood ketone levels. Time-to-exhaustion was actually lower in the ketone condition when runners wore the standard shoes.
What this means for runners
Super shoes genuinely improve running economy and extend time-to-exhaustion, making them one of the few equipment-based performance enhancers that live up to the hype. Ketone supplements, on the other hand, do not deliver on their performance promises and may be more useful for promoting post-exercise recovery or cognitive benefits.
RELATED ARTICLE: Are Super Shoes Worth The Hype, Or Are They Just A Hoax?Performance
SHORT STUFF You Don’t Want To Miss
HERE’S WHAT ELSE YOU WOULD HAVE RECEIVED this week if you were a subscriber to the complete, full-text edition of “Run Long, Run Healthy.”
- What is “zone 2” training? Experts weigh in
- Do supershoes and ketones improve running performance?
- How to break world records at 76 years old
Thanks for reading. As always—Run Long, Run Healthy
~Brady~
