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What 2 Hours of Running Really Does to Endurance Physiology
We often treat VO₂max, lactate threshold, and running economy as fixed numbers. We plug them into race calculators and build training zones around them. But if you’re running a marathon, your physiology isn’t staying put for 2+ hours. There’s drift.
A new study delivers one of the most comprehensive looks yet at how the “big three” performance variables—VO₂max, fractional utilization of oxygen, and running economy—change during prolonged running in well-trained male marathoners.
If you’re using static numbers to pace or predict your marathon performance, this paper should make you think twice.
Fourteen sub-2:50 marathoners (average VO₂max of 63.1 ml/kg/min) completed three lab sessions:
1. Baseline testing: VO₂max, lactate thresholds, running economy 2. 90-minute run at ~79% VO₂max (heavy domain intensity), followed by the same baseline tests 3. 120-minute run at the same pace (~79% of VO₂max, then a repeat of baseline tests
They tracked how the performance variables changed with increasing run duration to simulate physiological deterioration during a long run.
VO₂peak declined sharply, dropping by 3.1% after 90 minutes and by 7.1% after 120 minutes. Running economy got worse too, falling by 4.2% at 90 minutes and 5.8% at 120 minutes. Fractional utilization (the oxygen consumption at lactate threshold) increased, rising to 82.8% at 120 min (up from 78.6% in the non-fatigued state). The runners’ speeds at their lactate threshold dropped from 14.0 km/hr when fresh to 13.5 km/hr after 90 minutes to 13.0 km/hr after 120 minutes—a 6.6% decrease after just two hours of running.
This was all accompanied by an increase in perceived intensity, which rose from 79% to 86% to 91% of VO₂peak across the 90-minute and 2-hour runs, respectively. In four athletes, effort drifted into the severe intensity domain (>95% VO₂peak).
What This Means for Runners
The big lesson from this study is that your physiology degrades across a marathon, and those changes aren’t small. By 90 to 120 minutes into a run, VO₂max drops, running economy gets worse, and lactate threshold shifts downward. That means you’re working harder to maintain the same pace, and eventually, that pace may no longer be sustainable.
If you pace your marathon based on “fresh” lab data, you may be setting yourself up for a late-race crash. This also reinforces the importance of training your physiology to hold up under fatigue—or enhancing what’s known as your physiological resilience, the “fourth pillar” of endurance performance.
RELATED ARTICLE: Master Your Marathon Pace: Calculate & Execute the Perfect Race Strategy
🎧 Tempo Run Needs a Redefinition — And We Finally Gave It One
Is “tempo run” the most misused term in running? 🤔🏃♀️
In our latest episode of the Marathon Handbook Podcast 🎙️, Michael Doyle, Katelyn Tocci, and Alex Cyr dig into why “tempo” has become a throwaway label in training plans—and why it might be time to retire the term altogether. 🗑️
They unpack what tempo is supposed to mean 📏, how it differs from lactate threshold, marathon pace, and steady state running 🧠, and share some hilariously awful “tempo” workouts in the debut of their Tempo Run Hall of Shame 😂.
Train Your Lungs Like Your Legs—And Watch Your Pace Drop
I’ll admit it—when I hear anything about lung or inspiratory muscle training, I immediately file it under “probably gimmicky.” For most runners and most people, for that matter, the lungs are perfectly well suited to handle the demands of high-intensity, endurance sports. But a new study has me rethinking that.
Researchers set out to test the idea that strengthening respiratory muscles improves physiological performance in middle-distance runners. This is true not just for VO₂max but also for markers like lactic acid buildup, lactate threshold, and even inspiratory muscle strength.
They recruited 32 high-level Polish middle-distance runners (800–1500m), both male and female, and divided them into subgroups by sex and two different inspiratory muscle training devices, each using a different intensity of inspiratory muscle training.
One group used a device that progressively increased resistance up to 70% of the participants’ maximal inspiratory pressure—a measure of the strength of their breathing muscles, specifically how forcefully they can inhale. Another group trained using a similar device but only ramped up their training to 50% of their maximal inspiratory pressure. A third group (the control group) performed low-load training at just 15% of their maximal inspiratory pressure, not enough to elicit physiological changes. Inspiratory muscle training was performed twice daily for eight weeks while maintaining usual endurance training.
Across the board, runners who trained with a PowerBreathe device (the “high-intensity” training group) saw significant improvements in their VO₂max, several measures of the strength of their breathing muscles,and their lactate threshold. These gains were sustained even six weeks post-training.
While training with the other device (the “lower intensity” training method) slightly improved respiratory muscle strength in men, it didn’t deliver meaningful changes in VO₂max or lactate threshold. In women, some measures of breathing performance decreased after training.
Baseline VO₂max and ventilatory values were lower in women, but both sexes responded similarly to PowerBreathe training. Women had a slight edge in diaphragm fatigue resistance, aligning with previous literature.
What This Means for Runners
If you’re a serious runner—especially one who frequently races middle-distance events like the 800m and 1500m—and not incorporating respiratory muscle training, you might be leaving performance gains on the table. Not all training devices are created equal, though. This study shows that higher-resistance protocols like those used with PowerBreathe device are much more effective than lower-intensity approaches. Treat it like strength training for your lungs: progressive overload, high resistance, and regular sessions. Integrating this during the base or early build phases of training could give runners a physiological edge without adding mileage or musculoskeletal stress.
Maximal oxygen consumption (A is relative and B is absolute) according to gender and training: Blue = PowerBreathe (high-intensity) training; Red = Threshold (lower-intensity) training; Green = Control (no training)
RELATED ARTICLE: How To Increase Lung Capacity For Runners: 3 Breathing Exercises
What Your Overnight Heart Rate Variability Can Tell You About Your Training
Wearables are all the rage these days. Whoop. Garmin. Oura. They all spit out heart rate variability (HRV) and heart rate data, which some runners like to use to monitor their recovery and readiness. But some wearables tell you to track HRV and heart rate right when you wake up. Others say overnight tracking is better. But is one method actually more sensitive or helpful for training decisions?
That’s what researchers tried to answer in a new study.
Twenty-four recreational runners (10 females), training four–six times per week, completed three weeks of baseline training (moderate volume and intensity) followed by two weeks of overload training where they increased training load by 80%, all while monitoring daily heart rate and HRV overnight (four segments from the sleep window: full night, first four hours, start, and the end) and in the morning in the lying down (supine) position and while standing (each for two minutes). They also performed 3000m time trials before and after each block to assess performance adaptations.
The main goal was to compare how morning and nighttime heart rate and HRV aligned with each other; how they responded to the acute 3000m test and chronic (overload) training; and how they related to changes in performance.
Morning and night heart rate and HRV values are generally aligned at baseline. But standing and supine HRV had weak correlations with each other, showing how body position and timing capture different aspects of autonomic control and thus influence HRV. In terms of response to training stress, overnight heart rate and HRV were more responsive. After the 3000m time trial, only nocturnal heart rate and HRV segments showed significant changes (increased heart rate, decreased HRV). Morning HRV, in contrast, didn’t budge—even though the test was hard enough to elevate lactate to 12.8 mmol/L.
Overnight heart rate and HRV were also more sensitive to overload training. After the two-week overload, HRV increased in all overnight and morning segments (except at the very beginning of sleep). Heart rate decreased only in standing measurements, but the largest and most consistent effect sizes came from nocturnal segments.
Importantly, the change in overnight heart rate and HRV correlated with 3000m performance improvement after the overload training block. Overall, sleep (overnight) data offered a better signal-to-noise ratio. This consistency made nocturnal data more reliable for tracking weekly adaptations.
What This Means for Runners
If you’re using HRV to monitor your training, your best bet is to prioritize overnight measurements. The study shows that sleep-derived HRV and heart rate data are more sensitive to both acute and chronic training stress, meaning you’ll catch more of the physiological “signal” without getting lost in daily noise. Nocturnal data was more strongly correlated with performance outcomes (like 3000m time trial improvements) and responded better to both overload and hard efforts. Plus, it’s passive—you don’t have to remember to do a morning test or worry about variations in posture or timing.
RELATED ARTICLE: What Is Heart Rate Variability? + How To Use It In Your Trainingower Up Your Performance By Fueling Right
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.”
- Is cooling your hands the ultimate hack for better interval performance?
- How do men and women respond differently to high-intensity interval training?
- Can mindfulness make you race better?
Thanks for reading. As always—Run Long, Run Healthy
~Brady~
