Critical power: The endurance metric that predicts aging better than VO2 max

VO2 max dominates the conversation around fitness and longevity. But exercise physiologists have quietly known for decades that another metric — critical power — predicts real-world endurance and fatigue resistance far more accurately. And when it comes to aging, the decline in critical power may tell you more about your biological trajectory than your maximum oxygen uptake ever could.

Here’s why that matters: a 2022 study in the Journal of Applied Physiology demonstrated that critical power and its associated parameter W’ (pronounced “W prime”) account for variability in endurance training adaptations that VO2 max simply cannot capture. Two athletes with identical VO2 max values can have dramatically different endurance capacity — and the difference comes down to critical power. Among older adults, this gap widens further, making critical power a potentially superior marker of functional aging.

The implications are profound. Critical power doesn’t just tell you how fit you are — it reveals the boundary between metabolic stability and collapse. And that boundary shifts with every decade of life. This guide breaks down exactly what critical power is, why it matters more than VO2 max for longevity, and how to push it higher regardless of your age.

What you’ll learn:

• Why critical power predicts endurance performance better than VO2 max alone
• How critical power and W’ decline with aging — and the mechanisms driving that decline
• 6 evidence-based strategies to raise your critical power at any age
• How to test critical power without a laboratory
• How “durability” — a concept redefined in 2025 research — extends the critical power framework for real-world endurance

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Quick answer

Critical power (CP) is the highest output you can sustain before fatigue progressively accelerates. VO2 max tells you the ceiling of your aerobic system; CP tells you how much of that ceiling you can use steadily in real life.

For aging, CP is useful because it reflects cardiovascular delivery, mitochondrial function, lactate handling, and neuromuscular efficiency. Those systems decline with age, but they remain trainable through endurance work, threshold intervals, strength training, and recovery.

CP should not replace VO2 max. The best read is the pattern across CP, W’, VO2 max, durability, power-to-weight, symptoms, and your own trend over months.

Key facts

• Critical power -> sustainable intensity: CP marks the boundary between steady effort and time-limited fatigue.
• VO2 max -> aerobic ceiling: it measures peak oxygen uptake, not the power you can hold for a long time.
• W’ -> above-threshold reserve: it represents finite work capacity above CP.
• Durability -> fatigue resistance: it shows how much CP and related metrics fall after prolonged exercise.
• Aging -> lower CP reserve: mitochondrial, cardiovascular, and neuromuscular decline can reduce CP and W’.
• Training -> modifiable signal: Zone 2, threshold work, HIIT, strength training, fueling, and sleep can all influence CP over time.

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What is critical power?

When you exercise, there’s an intensity boundary that separates sustainable effort from inevitable exhaustion. Below this boundary, your body maintains metabolic equilibrium — oxygen consumption stabilizes, blood lactate remains steady, and muscle phosphocreatine stores stay relatively intact. Above it, these systems spiral toward their limits, and fatigue becomes a countdown rather than a possibility.

That boundary is critical power (CP).

Quick definition: Critical power is the highest exercise intensity you can sustain without progressive metabolic fatigue — the dividing line between steady-state and time-limited effort.

In cycling, it’s measured in watts. In running, the equivalent is called critical speed (CS) or critical velocity (CV), measured in miles per hour (km/h). The concept is the same: the maximum output you can hold in a theoretical steady state, though in practice, exercise at CP is sustainable for approximately 20–40 minutes before fatigue emerges from dehydration, glycogen depletion, and thermal stress.

Why critical power matters for your health

Critical power sits at approximately 70-80% of VO2 max in healthy young adults and can reach 80-90% in well-trained individuals. But the significance goes far beyond sport. CP reflects the integrated function of your cardiovascular system, mitochondrial density, lactate clearance capacity, and neuromuscular efficiency — systems that collectively determine how well your body handles physical stress.

A higher critical power relative to your body weight means your muscles are more metabolically efficient, your heart pumps blood more effectively, and your mitochondria convert fuel to energy with less waste. These are precisely the systems that deteriorate with biological aging.

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The science behind critical power

The power-duration relationship

Critical power emerges from a mathematical relationship between power output and time to exhaustion. If you perform several all-out efforts at different intensities — say, efforts lasting 2, 5, 10, and 15 minutes — and plot power against time, you get a characteristic hyperbolic curve.

The asymptote of that curve (the horizontal line it approaches but never quite reaches) is your critical power. The area above CP but below the curve represents W’ (W prime) — your finite anaerobic work capacity, measured in kilojoules (kJ).

Think of it this way:

• CP = your aerobic engine’s ceiling — how much sustained power you can generate
• W’ = your anaerobic battery — how much above-threshold work you can do before you’re forced to stop

Together, CP and W’ define your entire power-duration profile. They explain why you can sprint at 600 watts (W) for 30 seconds but sustain only 220 W for an hour — and they predict exactly how long you can hold any intensity in between.

How critical power differs from VO2 max

VO2 max measures maximum oxygen uptake — the absolute ceiling of your aerobic system. But here’s the critical distinction: you cannot sustain exercise at VO2 max intensity for more than a few minutes. It’s a peak, not a sustainable state.

Critical power, by contrast, measures the highest sustainable intensity — the real-world ceiling for prolonged effort. And this distinction becomes increasingly important with age.

Metric	What it measures	Practical relevance
VO2 max	Maximum oxygen uptake	Absolute aerobic ceiling
Critical power	Highest sustainable intensity	Real-world endurance capacity
Lactate threshold	Onset of lactate accumulation	Moderate-intensity sustainability
W’	Anaerobic work capacity	Sprint/surge reserve

A study from the American Physiological Society found that performance improvements can occur independently of changes in VO2 max — meaning your endurance can get better (via higher CP) even when your VO2 max stays flat. This is especially relevant for older adults whose VO2 max may plateau despite continued training.

Critical power as the true “gold standard” of sustainable intensity

A 2025 study published in Medicine & Science in Sports & Exercise (Lindstrom and colleagues) compared critical power with the estimated maximal metabolic steady state (MMSS) in 24 trained and untrained participants. CP was slightly higher than MMSS by about 8 watts in both groups, but close enough to support CP as a practical proxy when direct MMSS testing is not feasible. The useful takeaway is precision, not hype: CP is closely related to sustainable metabolic steady state, but it is not identical to it.

Critical power and longevity: what the research says

The connection between critical power and aging runs deep. Research published in Circulation demonstrated that low aerobic exercise capacity is a stronger predictor of premature death than smoking, diabetes, or hypertension. While this research often uses VO2 max as the benchmark, the mechanisms that drive critical power — mitochondrial function, cardiovascular efficiency, lactate metabolism — are more directly tied to the hallmarks of biological aging.

A landmark study in the European Journal of Applied Physiology compared physiological responses of young and elderly men during prolonged exercise at critical power intensity. The findings revealed that while both groups could sustain exercise at CP, older adults showed altered metabolic responses — higher relative oxygen consumption and faster glycogen depletion — suggesting that aging doesn’t just lower your CP, it changes the physiological cost of working at your threshold.

Critical speed (the running equivalent of CP) progressively decreases with age due to cumulative decline in:

• Mitochondrial density: fewer and less efficient power plants in muscle cells
• Type II fiber loss: sarcopenia preferentially affects fast-twitch fibers, reducing W’
• Cardiovascular output: lower maximum heart rate and stroke volume reduce oxygen delivery
• Lactate clearance: slower removal of metabolic byproducts at high intensities
• Neuromuscular efficiency: reduced motor unit recruitment and muscle coordination — a key driver of declining running economy with age

These are the same systems that determine biological age. Training your critical power means directly targeting the machinery of aging.

Want broader context? Read our guide on how to improve VO2 max to understand the aerobic ceiling that sits above critical power, or check the VO2 max chart by age and gender to see how your score compares.

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Durability: the 2025 update to the critical power framework

Traditional CP testing measures what you can sustain when rested. But race day — and real life — rarely start that way. In 2025, a series of papers in the Journal of Applied Physiology and Experimental Physiology formalized a concept that reshapes how we think about endurance: durability, defined as the resilience of your physiological systems (and your CP itself) to the accumulating fatigue of prolonged exercise.

In practical terms, two athletes can share an identical fresh-state critical power, yet after 90 minutes of hard riding or running, one athlete’s CP may have dropped 10% while the other’s barely moves. That difference is durability, and it’s now considered a distinct trainable quality alongside VO2 max, CP, and W’.

Why this matters for aging: durability depends on mitochondrial density, substrate flexibility (your ability to switch between fat and carbohydrate), and neuromuscular resilience — the same systems that erode with age. A 2025 review by Hunter and colleagues (Experimental Physiology) notes that greater intensity and duration of fatiguing exercise produces more marked deterioration of CP, VO2 kinetics, and running economy. The good news: regular prolonged sessions that include high-intensity work at or near race pace, combined with resistance training, appear most effective for building durability and slowing its age-related decline.

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How to test your critical power

You don’t need a laboratory to estimate your critical power. Several validated field tests exist, ranging from a single brutal effort to multi-day protocols.

The 3-minute all-out test

The most practical option. After a thorough warm-up, you perform a maximal 3-minute effort — sprinting from the start and sustaining the highest possible output throughout.

How it works:

• The first 150 seconds depletes your W’ (anaerobic capacity)
• The average power of the last 30 seconds approximates your critical power
• The total work done above CP during the first 150 seconds estimates your W’

Protocol:

1. Warm up for 10-15 minutes at easy intensity
2. Sprint maximally for the full 3 minutes — no pacing
3. Record average power for the last 30 seconds = your estimated CP
4. Calculate total work above CP = your estimated W’

This test requires a power meter for cycling or a GPS watch with pace tracking for running. Reliability research notes that while the 3-minute protocol is valid and reproducible for estimating CP (or critical speed in running), the anaerobic component — W’ or D’ — shows poor test-retest reliability from a single 3-minute effort. If W’ matters to you, use the multi-trial method below.

The multi-trial method

More accurate but requires multiple sessions:

1. Perform 3-4 separate time trials on different days
2. Each trial should last between 2-15 minutes at all-out effort
3. Plot power output versus duration
4. The hyperbolic curve’s asymptote = CP

Example trials for cyclists:

• Trial 1: 3-minute all-out → ~350 W
• Trial 2: 7-minute all-out → ~280 W
• Trial 3: 12-minute all-out → ~250 W

These data points define the power-duration curve, and CP is calculated mathematically.

CP testing by age: what to expect

Age	Typical male CP (cycling)	Typical female CP (cycling)	% of VO2 max
20-30	220-280 W	160-220 W	70-80%
30-40	200-260 W	150-210 W	72-82%
40-50	180-240 W	140-195 W	73-83%
50-60	160-220 W	125-180 W	74-84%
60-70	140-195 W	110-160 W	75-85%
70+	110-170 W	90-140 W	76-86%

Note: trained individuals sit at the higher end. CP as a percentage of VO2 max actually increases with age in trained populations — meaning experienced athletes preserve a higher fraction of their aerobic ceiling even as the ceiling itself drops.

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6 proven strategies to improve critical power

1. Threshold intervals at 95-105% of current CP

Why it works: Training at or slightly above critical power directly stresses the metabolic boundary you’re trying to raise. It maximizes time spent at the intensity where mitochondrial biogenesis, capillary growth, and lactate transporter upregulation are stimulated most effectively.

How to do it:

• Warm up for 15 minutes
• Perform 3-5 intervals of 8-12 minutes at 95-105% of your current CP
• Recovery between intervals: 3-5 minutes at very easy intensity
• Frequency: 2 sessions per week

Expected results: 5-10% improvement in CP within 8-12 weeks. Research shows this approach improves CP more specifically than high-intensity interval training (HIIT) or long slow distance alone.

2. Zone 2 endurance training for mitochondrial density

Why it works: Zone 2 training — sustained effort at 60-75% of your maximum heart rate — selectively builds mitochondrial density and fat oxidation capacity. This expands the aerobic base that underlies critical power. More mitochondria means more power plants producing ATP aerobically, which raises the intensity at which you transition from sustainable to unsustainable metabolism.

How to do it:

• Maintain a conversational pace (you can speak in complete sentences)
• Duration: 60-120 minutes per session
• Frequency: 3-4 sessions per week
• Target: 75-80% of total training volume at this intensity

Expected results: Measurable improvements in CP after 6-8 weeks of consistent Zone 2 training. This is the foundation that makes threshold intervals more effective — and it’s also the single most potent driver of durability, according to 2025 consensus reviews on resilience in endurance sports.

3. High-intensity interval training (HIIT) for W’ and VO2 max

Why it works: While threshold training directly targets CP, HIIT raises the ceiling above it. Research shows CP increased by 27.5% following HIIT protocols compared to 15.7% with moderate-intensity continuous training. HIIT simultaneously expands W’ — your anaerobic battery — giving you more above-threshold work capacity.

How to do it:

• Warm up thoroughly (15 minutes)
• Perform 4-6 intervals of 3-5 minutes at 90-95% of maximum heart rate
• Recovery: equal duration at very easy intensity
• Frequency: 1-2 sessions per week (not on consecutive days)

Expected results: Significant improvements in both CP and W’ within 6-8 weeks. The combination of HIIT and threshold work is more effective than either approach alone.

4. Strength training for neuromuscular power

Why it works: Critical power isn’t purely cardiovascular — it depends on the force your muscles can generate with each contraction. Strength training, particularly heavy compound movements, improves neuromuscular recruitment and delays the onset of peripheral fatigue. For older adults, this is especially important because sarcopenia (age-related muscle loss) directly reduces CP by lowering the force available per muscle fiber. The 2025 physiological resilience literature explicitly highlights heavy strength and plyometric work as effective for preserving CP under fatigue.

How to do it:

• Focus on compound movements: squats, deadlifts, lunges, step-ups
• 3-5 sets of 4-8 repetitions at 75-85% of one-rep max
• Frequency: 2-3 sessions per week
• Prioritize eccentric control (slow lowering phase)

Expected results: 3-7% improvement in CP when combined with endurance training. Strength training alone won’t raise CP substantially, but it prevents the muscle loss that erodes it with age.

5. Nutrition: fuel the metabolic engine

Why it works: Critical power depends on your body’s ability to sustain aerobic metabolism. Adequate glycogen stores, optimal iron status, and sufficient nitric oxide availability all influence where your CP sits. Nutritional deficiencies can suppress CP even in well-trained athletes.

Key nutritional strategies:

• Carbohydrate periodization: ensure adequate glycogen for key sessions (2.3-4.5 g per pound / 5-10 g per kg body weight on heavy training days)
• Iron monitoring: ferritin below 30 ng/mL can impair oxygen transport — get blood work regularly
• Beetroot juice: 300-500 mg of dietary nitrate (approximately 500 mL / 17 oz of beetroot juice) 2-3 hours before testing has been shown to improve CP by 2-6%
• Creatine: 3-5 g daily may expand W’ by supporting phosphocreatine resynthesis
• Protein timing: 0.18-0.23 g per pound (0.4-0.5 g per kg) of protein within 2 hours post-training supports mitochondrial protein synthesis

Expected results: Nutritional optimization can yield 2-8% improvements in CP, with the most significant gains in those correcting deficiencies.

6. Recovery and sleep: where adaptation happens

Why it works: Training provides the stimulus. Adaptation — the actual improvement in CP — happens during recovery. Sleep deprivation reduces endurance performance by 10-15% through impaired glycogen resynthesis, elevated cortisol, and reduced growth hormone secretion. Chronic sleep debt progressively erodes the training adaptations that raise CP.

How to do it:

• Target 7-9 hours of sleep per night
• Prioritize sleep consistency (same bed and wake time)
• Monitor heart rate variability (HRV) as a readiness indicator
• Schedule easy days after threshold and HIIT sessions
• Consider periodization: 3 weeks of progressive load followed by 1 recovery week

Expected results: Proper recovery doesn’t “add” to CP directly but prevents the 10-15% performance suppression caused by inadequate rest. Over a training block, this difference compounds significantly.

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How to track and measure critical power

Key metrics to monitor

Metric	What it tells you	How to measure	Retest frequency
Critical power (W)	Aerobic sustainability ceiling	3-min all-out or multi-trial test	Every 8-12 weeks
W’ (kJ)	Anaerobic work capacity	Multi-trial CP test (more reliable than 3-min)	Every 8-12 weeks
CP as % of VO2 max	Metabolic efficiency	Compare CP to VO2 max estimate	Every 12 weeks
Power-to-weight (W/kg)	Relative endurance capacity	CP divided by body weight	Monthly
Durability (CP drop after 60–120 min)	Resilience under fatigue	Re-test CP after prolonged work	Every 12-16 weeks
CP trend over time	Training effectiveness	Log results across months/years	Ongoing

Interpreting your results

If CP improves but W’ decreases: Your aerobic engine got stronger, but your anaerobic capacity shrank. This is common with heavy Zone 2 training — and it’s generally a good sign for longevity, as aerobic capacity is more protective than anaerobic power.

If W’ improves but CP stays flat: You’ve built sprint capacity without expanding your aerobic base. Add more Zone 2 and threshold work.

If both improve: You’re responding optimally to training. This is the ideal scenario and suggests a well-balanced program.

If both decline: Possible overtraining, illness, or inadequate recovery. Reduce training load and prioritize sleep.

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How SuperAge helps you track your endurance capacity

Manually testing and tracking critical power requires dedicated protocols, a power meter, and consistent retesting schedules. SuperAge simplifies the process of monitoring the fitness metrics that matter most for longevity.

Automatic fitness monitoring

SuperAge integrates with Apple Watch and HealthKit to automatically capture your workout data — including heart rate zones, workout intensity, and estimated VO2 max. These metrics correlate directly with the systems that determine critical power. Your training history also feeds directly into SuperAge’s endurance score, a composite metric that tracks your sustained aerobic capacity alongside VO2 max.

Your biological age, tracked

Critical power reflects the same physiological systems that drive biological aging — mitochondrial function, cardiovascular efficiency, and metabolic flexibility. SuperAge calculates your biological age using validated algorithms and shows you exactly where you stand relative to your chronological age.

Personalized insights

SuperAge analyzes your fitness trends over time and provides actionable recommendations to improve the metrics that matter. Whether your goal is pushing your critical power higher or lowering your biological age, the app connects the dots between daily habits and long-term outcomes.

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Frequently asked questions

What is a good critical power for my age?

Critical power varies widely based on training status, genetics, and sport. For recreational cyclists, a CP of 2.5-3.5 W/kg (watts per kilogram of body weight) is considered good. Well-trained cyclists may reach 3.5-4.5 W/kg. For runners, a critical speed of approximately 7:30-8:30 per mile (4:40-5:15 per km) represents solid fitness for a 40-year-old recreational runner. The most meaningful comparison is your CP relative to your own baseline over time.

Is critical power the same as FTP (functional threshold power)?

Not exactly. FTP is typically defined as the power you can sustain for one hour, and it’s estimated from a 20-minute test with a 5% reduction. Critical power is mathematically derived from the power-duration curve and tends to be slightly higher than FTP (typically 5-10% higher). CP is considered more physiologically rigorous because it’s based on the actual fatigue threshold rather than an arbitrary time duration. For a repeatable 20-minute protocol, calculation caveats, and wattage zones, use our functional threshold power cycling guide.

How does critical power change with aging?

Critical power declines approximately 5-8% per decade after age 30 in sedentary individuals, with the rate accelerating after 60. However, trained individuals can slow this decline substantially. Masters endurance athletes who maintain near-normal training volume show VO2 max (and by extension, CP) decline of only 5-6.5% per decade, roughly half the rate of sedentary peers. The decline is driven by reductions in mitochondrial density, Type II fiber loss, decreased cardiac output, and slower lactate clearance. Anaerobic capacity (W’) declines faster — about 1% per year — because it depends on fast-twitch fibers that are preferentially lost with age.

Can I improve critical power without a power meter?

Yes. While a power meter provides the most accurate CP measurements, you can estimate critical speed (the running equivalent) using GPS pace data from time trials. Many running watches now estimate critical pace from race performances. You can also train the physiological systems that underpin CP — mitochondrial density, lactate clearance, cardiovascular efficiency — without ever measuring CP directly, by following the training principles outlined in this guide.

How is critical power related to biological age?

Critical power reflects the integrated function of cardiovascular, mitochondrial, and neuromuscular systems — the same systems that deteriorate with biological aging. A higher CP relative to age-matched norms suggests these systems are functioning at a younger biological level. While CP itself isn’t a direct biological age biomarker, the physiological determinants of CP (VO2 max, mitochondrial density, muscle quality) are core components of biological age algorithms like PhenoAge.

What is durability and how does it relate to critical power?

Durability is the ability of your physiological systems — including your critical power itself — to resist the decline that comes with prolonged exercise. A 2025 consensus in the Journal of Applied Physiology distinguishes durability from fatigability, repeatability, and resilience, and places it at the center of real-world endurance. You can have a high fresh-state CP yet poor durability, meaning your sustainable power collapses over long efforts. Durability is trained primarily through long Zone 2 rides or runs with high-intensity segments in the later stages, alongside heavy strength work.

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Key takeaways

• Critical power is the highest intensity you can sustain without progressive fatigue — it predicts real-world endurance better than VO2 max alone
• CP closely approximates the maximal metabolic steady state in both trained and untrained adults (2025 research), making it a practical gold standard
• CP declines 5-8% per decade after 30 in sedentary individuals, but trained athletes can cut that rate in half through structured training
• Training at 95-105% of CP combined with Zone 2 endurance work is the most effective strategy for raising your threshold
• Durability — your CP’s resistance to prolonged-exercise decline — is the frontier concept added by 2025 physiology and is trained through long sessions with late-stage intensity
• CP and W’ together define your complete power-duration profile — monitor both for a full picture of your fitness
• The physiological systems that determine CP (mitochondria, cardiovascular output, lactate clearance) are the same ones that drive biological aging
• Regular testing every 8-12 weeks using the 3-minute all-out test provides reliable tracking without a lab

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Start pushing your critical power higher today

Your critical power isn’t just a number for athletes — it’s a window into how your body handles the metabolic demands of aging. Every watt you add to your CP represents more efficient mitochondria, better cardiovascular function, and greater metabolic resilience.

Ready to take control? Download SuperAge and start tracking your fitness metrics alongside your biological age — because the best predictor of how you’ll age is what you do about it today.

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References

1. Jones AM et al. — “Critical power: implications for determination of VO2 max and exercise tolerance.” Medicine & Science in Sports & Exercise, 2010
2. Murgatroyd SR et al. — “Critical power and work-prime account for variability in endurance training adaptations not captured by VO2 max.” Journal of Applied Physiology, 2022
3. Mankowski RT et al. — “Intrinsic aerobic capacity sets a divide for aging and longevity.” Circulation Research, 2012
4. Neder JA et al. — “Physiological responses of young and elderly men to prolonged exercise at critical power.” European Journal of Applied Physiology, 1992
5. Vanhatalo A et al. — “The ‘Critical Power’ concept: applications to sports performance.” Sports Medicine, 2017
6. Poole DC et al. — “Critical power: an important fatigue threshold in exercise physiology.” Medicine & Science in Sports & Exercise, 2016
7. Fleg JL et al. — “Accelerated longitudinal decline of aerobic capacity in healthy older adults.” Circulation, 2005
8. Lindstrom BE et al. — “Critical Power Closely Approximates the Power Output at the Estimated Maximal Metabolic Steady State in Trained and Untrained Participants.” Medicine & Science in Sports & Exercise, 2025. DOI: 10.1249/MSS.0000000000003765
9. Meixner B, Joyner MJ, Sperlich B — “Durability, fatigability, repeatability, and resilience in endurance sports: definitions, distinctions, and implications.” Journal of Applied Physiology, 2025
10. Hunter B et al. — “Durability as an index of endurance exercise performance: methodological considerations.” Experimental Physiology, 2025
11. Zanini M, Jones AM, Nybo L — “Defining physiological resilience and durability in the context of endurance performance modeling.” Journal of Applied Physiology, 2025

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Last updated: 2026-06-07. This article is regularly reviewed to ensure accuracy.