​How Post-Run Heat Exposure Can Mimic High Altitude Training​

In today's episode, Thomas and Brady discuss altitude training, heat training, cross-adaptation...and how hot baths and saunas AFTER your run can mimic the benefits of altitude training.

Listen and subscribe to the show wherever you get your podcasts:

The Truth About Zone 2 Training: It’s Not One-Size-Fits-All

Ask ten endurance athletes how they define "zone 2," and you’ll probably get 10 different answers. While zone 2 training is hailed as the aerobic engine-builder and fat-burner of champions, a new study suggests that how we define it—and prescribe it—might be way off for many athletes. And if you’re using generic heart rate or lactate targets for your zone 2 runs, there’s a good chance you’re either undertraining or overshooting the metabolic adaptations you’re aiming for.

For the study, fifty trained cyclists (30 men, 20 women) completed both a ramp test and an incremental step test in the lab to determine several commonly used zone 2 thresholds including: percent of maximal heart rate (72% and 82%), blood lactate concentrations (1.5, 2.0, and 2.5 mmol/L), baseline lactate levels + 0.5 mmol/L), the first ventilatory threshold (VT1), power output at maximal fat oxidation, and 65% of VO₂ peak. Each marker was mapped to power output, heart rate, and oxygen uptake. The researchers then compared how well these different demarcations aligned across individuals.

There were massive variations in power output and heart rate at each athlete’s zone 2. The variation ranged from 6% to 29% depending on the marker. For example, power at a blood lactate level of 1.5 mmol/L had a 29% variation, suggesting it captures wildly different intensities across individuals. The two worst proxies for zone 2 were standard targets like 72% of maximal heart rate or 2.0 mmol/L blood lactate, which often missed the mark in capturing the intended training intensity. For many of the athletes, these did not correspond with high-fat oxidation or aerobic thresholds (i.e., the common goals sought by those engaging in zone 2 training). The two markers that most closely agreed were VT1 and baseline blood lactate + 0.5 mmol/L—the difference in these two measures was less than 1 Watt. On average, power output at maximal fat oxidation was around 25% lower than power output at VT1, suggesting that maximal fat oxidation likely captures an entirely different training stimulus; it’s useful for fat oxidation but not necessarily aerobic threshold work.

Finally, males and females differed in how their physiology mapped to zone 2. Women tended to reach their maximal fat oxidation at higher relative heart rates than men. Therefore, prescribing zone 2 intensity based on a percentage of peak power output or maximal heart rate may introduce errors depending on an athlete’s biological sex.

What this means for runners

Generic Zone 2 prescriptions may not be effective for everyone. If you want your low-intensity training to actually target fat oxidation or aerobic adaptation, you need to individualize it.

Here’s how to make that happen:

• If you have access to lactate testing or gas exchange, use VT1 or maximal fat oxidation—not heart rate percentages or generic lactate values—to set zone 2 boundaries.

• Don’t assume 72–82% of maximal heart rate is “safe.” That range captured vastly different metabolic intensities among participants. What’s zone 2 for one athlete might be too hard—or too easy—for another.

• If you’re targeting metabolic flexibility or weight management, maximal fat oxidation may be a better target, even if it's well below your VT1.

• VT1 is likely more relevant for boosting aerobic threshold. Maximal fat oxidation optimizes fat utilization. These are related but not interchangeable zones. Understand the tradeoffs.

And if you don’t have access to a lab? This study suggests that your baseline blood lactate levels + 0.5 mmol/L could be an applicable DIY threshold if you have a handheld lactate meter. It's more individualized than a flat 2.0 mmol/L cutoff.

What this study shows is that “low-intensity training” encompasses a spectrum of physiological states depending on how you define it. The key to unlocking its benefits lies in understanding where your zone 2 really lives.

RELATED ARTICLE: Zone 2 Training, Explained: How To Unlock Endurance And Speed​

Why Runners Should Care About Vitamin D and Magnesium

Two of the most impactful and underappreciated nutrients for athletes are vitamin D and magnesium. A recent review published in Nutrients sheds light on how these two micronutrients support endurance, recovery, immune function, bone health, and even reduce the risk of serious complications, such as stress fractures and sudden cardiac events like a heart attack.

If you’re putting in the hard training but neglecting these essentials, you might be leaving performance gains on the table.

Despite the outdoor lifestyle of many endurance athletes, vitamin D deficiency is shockingly common. Factors such as skin pigmentation, latitude, indoor training, sunscreen use, and season all reduce cutaneous (skin) vitamin D synthesis. Up to 80% of athletes in northern latitudes have suboptimal levels.

Why does vitamin D matter so much? It supports calcium and phosphate absorption and is critical for bone mineralization. Deficiency is linked to a higher risk of stress fractures, which affect up to a third of runners. Vitamin D also activates the vitamin D receptor in muscle tissue, enhancing the growth of type II fibers, increasing strength, and promoting post-exercise recovery. Additionally, it plays a protective role in heart and respiratory health, reducing the risk of upper respiratory tract infections, asthma symptoms, and contributing to cardiovascular adaptations to training.

Magnesium is involved in over 600 enzymatic reactions in the body and is essential for creating and using ATP (energy). Pretty essential. Why does magnesium matter for runners? Magnesium is required for muscle contraction and relaxation, nerve transmission, and electrolyte balance. It acts as a natural calcium channel blocker, stabilizing cardiac rhythms and preventing cramps. It also plays a pivotal role in mitochondrial function. Roughly one-third of your muscle magnesium is stored in the mitochondria, where it supports oxidative phosphorylation and prevents excess production of reactive oxygen species, also known as ROS. Magnesium deficiency (which is also common) has been linked to muscle weakness, arrhythmias, stress fractures, and even sudden cardiac death, especially concerning in high-performing endurance athletes.

Athletes need more magnesium than most people because sweat and urine losses during long or hot training sessions increase magnesium requirements. Studies show many athletes don’t meet the recommended daily allowance (RDA) for vitamin D, even those of us who think we’re eating a well-balanced diet.

Here’s the kicker: you need magnesium to use vitamin D properly, and vice versa. Magnesium is required for vitamin D binding to its carrier protein, the liver and kidneys activating it to its biologically active form, and its transport and cellular signaling.

A deficiency in one can impair the function of the other, creating a cascade of suboptimal effects. For instance, magnesium-deficient athletes may not benefit from vitamin D supplementation because their bodies can’t activate or transport it effectively. Athletes with both deficiencies are more likely to suffer from stress fractures, immune system suppression, asthma symptoms, and poor recovery and muscle performance.

What this means for runners

Get your 25(OH)D and magnesium levels checked—especially in winter or during high-volume phases. After that, supplement smartly. Consider 3000–5000 IU/day of vitamin D3 and 200–400 mg/day of elemental magnesium (citrate or glycinate forms are preferred).

Let me repeat: Supplementing with vitamin D and/or magnesium won’t shave minutes off of your marathon time overnight, but if you’re depleted, topping off your stores could be the simplest, most impactful upgrade to your training yet.

RELATED ARTICLE: Creatine For Runners: What It Does + 3 Recommended Supplements​

Are Spikes In Heart Damage Markers After Training A Red Flag Or False Alarm?

Elevated cardiac troponin (cTn) is a marker of heart damage. It’s the same kind that shows up during a heart attack. But in endurance athletes, especially after a long race or hard session, it’s not uncommon to see a post-exercise rise in cTn—even when the heart is perfectly healthy.

So what’s the deal? Is it just a training response, or could it be a warning sign of underlying coronary artery disease?

​A new study published in JACC: Cardiovascular Imaging tackled this question head-on, comparing athletes with high vs low cTn levels after exercise to see whether those spikes correlate with actual heart disease.

Researchers analyzed data from 1,011 middle-aged recreational athletes (median age 56; 63% male) who participated in endurance walking, cycling, or running events. Blood samples were taken before and after exercise to measure high-sensitivity cardiac troponin T (hs-cTnT) and troponin I (hs-cTnI)—the most sensitive markers we have for detecting cardiac stress or damage.

Then they zoomed in on two groups: 68 “high responders” with large post-exercise cTn increases and 34 “low responders” with minimal increases. These athletes were matched for age, sex, and sport type, and all underwent scans of their hearts to assess coronary artery calcium (CAC) scores and the presence of atherosclerosis using a special scoring system. They also evaluated the functional impact of any blockages in the runner’s arteries.

There were no significant differences in coronary artery disease between high and low cTn responders. Coronary atherosclerosis was seen in 67.6% of high responders and 50% of low responders, but the difference wasn’t statistically meaningful. Calcium scores—a marker of plaque buildup—were nearly identical (median 9 AU in the high responders and 2 AU in the low responders). Functionally significant narrowing of the arteries occurred in just 11.8% of the high responders compared to just 5.9% of the low responders. Although there were small, statistically significant associations between troponin levels and the severity of coronary artery disease, they explained only about 4–8% of the variation. This means that most of the cTn elevation post-exercise is unrelated to underlying heart disease.

What this means for runners

For recreational endurance athletes, this study provides some reassurance. Spikes in cardiac troponin after exercise are not inherently pathological, and they don’t appear to reflect hidden heart disease in most cases. That said, athletes with other risk factors (e.g., family history, smoking, hypertension, abnormal ECG) should still consider appropriate cardiovascular screening.

RELATED ARTICLE: Is Running Good For You? 14 Health Benefits Of Running​

Here’s what paying subscribers received this week in addition to the studies you just read. If you’d like access to the full RLRH newsletter, consider becoming a paid subscriber!

• Do menstrual cycle symptoms change running biomechanics in female runners?

• How to train a faster cadence with music

• The BEST high-intensity interval training prescription for runners

That’s all for now. Thanks for reading. As always—Run Long, Run Healthy.

~Brady~