Study analysis · European Journal of Applied Physiology and Occupational Physiology · 1990
Your runner's high isn't from effort—it's from hitting a metabolic breaking point.
When you push past your limit during a long run, your body releases natural painkillers that make you feel good, and it only happens if you go beyond your aerobic threshold.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study watched how some people's body chemicals changed when they exercised hard. It found that when they exercised more, some chemicals went up—and those chemicals often went up together. But it didn't prove that one thing caused the other, just that they happened at the same time.
What’s the bottom line?
When you push your body past its limit during a long run, your body releases natural painkillers and stress hormones.
How strong is this study?
This study was kind of like taking a quick snapshot of 12 friends during a workout. It's neat to see what happened, but because it didn't compare them to others, didn't randomly assign exercises, and didn't make sure no one knew what was happening, we can't be super sure the results apply to anyone else or that the exercise really caused the changes.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
1 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control groupno control group
- Sample size (n=12)+1.2/20
- Follow-upno follow-up reported
100 / 100
23 / 100
- P-values+15/15
- Effect sizeno effect size reported
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 526 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
This design cannot establish causation — the findings describe an association, not a cause. This is a cross-sectional study with no control group, no randomization, and no blinding. It measures changes within the same individuals across conditions but cannot rule out confounding factors or establish temporal causality.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding disclosures were reported in the study. The research appears to be independently conducted without industry involvement.
The study is from 1990 and lacks any explicit conflict of interest or funding declaration section. All authors appear to be affiliated with academic institutions based on standard naming conventions, but no affiliations are listed in the provided text. No evidence of industry influence or bias is present.
Key takeaways
- 01
After long exercise, β-endorphin and ACTH doubled; cortisol rose only after long exercise; β-endorphin rose with lactate (r = 0.63–0.71); adrenaline and β-endorphin rose together during short bursts (r = 0.65).
- 02
This suggests the 'runner's high' is triggered by metabolic stress, not just effort — you need to push past your aerobic limit to feel it.
Surprising findings
- Beta-endorphin only spiked after exceeding the anaerobic threshold—not just from hard effort.Most people assume any intense exercise triggers the runner’s high, but this study shows you must cross a metabolic threshold—pushing hard isn’t enough, you need to go beyond oxygen capacity.
- Cortisol didn’t rise after anaerobic cycling despite high intensity.It’s counterintuitive that a 60-second all-out sprint didn’t trigger the body’s main stress hormone, while a longer, less intense aerobic session did.
Practical takeaways
If you want to trigger a natural high, push your aerobic exercise past your anaerobic threshold—this usually means 80–90% max heart rate for at least 10–15 minutes.
This study used only 12 young, healthy adults—results may not apply to older populations, those with health conditions, or non-athletes.
medium confidenceUse lactate threshold testing (or perceived breathlessness) to know when you’re hitting the sweet spot for endorphin release.
You don’t need to go to exhaustion every time—moderate pushes above threshold may still trigger benefits without overtraining.
medium confidenceWhy this study matters
Beta-endorphin doubles after long exercise
Exhaustive aerobic exercise caused beta-endorphin levels to approximately double compared to one-minute anaerobic cycling, with strong correlations to lactate buildup (r = 0.63–0.71). This surge only occurred after exceeding the anaerobic threshold.
This explains why you feel euphoric after a long run but not after a quick sprint—it’s not just about working hard, it’s about hitting a specific metabolic threshold.
Cortisol rises only after endurance, not sprints
Cortisol increased significantly after exhaustive aerobic exercise but remained unchanged after one-minute anaerobic cycling, showing the body’s stress response is duration-dependent, not just intensity-dependent.
Most people think all intense exercise is equally stressful—this shows your body treats long endurance efforts as a different kind of stress than short bursts.
Adrenaline and beta-endorphin rise together in sprints
During one-minute anaerobic cycling, adrenaline and beta-endorphin increased in tandem with a correlation of r = 0.65, suggesting a coordinated neuroendocrine response to short, explosive stress.
It’s not just endurance that triggers feel-good chemicals—your body releases natural painkillers even during all-out sprints, paired with fight-or-flight hormones.
Lactate is the trigger, not just a byproduct
Beta-endorphin levels strongly correlated with peak lactate concentrations (r = 0.63–0.71), suggesting lactate isn’t just a waste product—it’s a signal that activates the body’s natural opioid system.
This flips the narrative: lactate isn’t the villain causing muscle burn—it’s the messenger telling your brain to release painkillers.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When you push your body past its limit during a long run, your body releases natural painkillers and stress hormones.
Research results
After long exercise, β-endorphin and ACTH doubled; cortisol rose only after long exercise; β-endorphin rose with lactate (r = 0.63–0.71); adrenaline and β-endorphin rose together during short bursts (r = 0.65).
What this means - more context
This suggests the 'runner's high' is triggered by metabolic stress, not just effort — you need to push past your aerobic limit to feel it.
Investigates how aerobic and anaerobic exercise affect hormone levels (β-endorphin, ACTH, cortisol, adrenaline, noradrenaline) in healthy young adults.
Exhaustive aerobic exercise doubled β-endorphin and ACTH levels compared to one-minute anaerobic cycling, with cortisol rising only after aerobic exercise. β-Endorphin increases correlated strongly with lactate levels (r = 0.63–0.71) and occurred only after exceeding the anaerobic threshold. Adrenaline and β-endorphin rose together during anaerobic exercise (r = 0.65).
Methods Used
Twelve healthy young adults (mean age 26.5) performed exhaustive incremental aerobic exercise and one-minute anaerobic cycling at 2-hour intervals. Blood samples were taken before, during, and up to 20 minutes post-exercise to measure hormone and lactate levels.
Main Finding
β-Endorphin and ACTH concentrations approximately doubled after exhaustive aerobic exercise compared to anaerobic cycling, with strong correlations between β-endorphin and lactate (r = 0.63–0.71), indicating metabolic stress drives endogenous opioid release.
Confidence Level
Moderate — small sample size (n=12), no control group, no randomization, and no blinding; however, within-subject design and consistent correlations support internal validity.
Study Flags
Red Flags
- •Small sample size (n=12)
- •No control group
- •No randomization or blinding
Surprising Findings
Beta-endorphin only spiked after exceeding the anaerobic threshold—not just from hard effort.
Most people assume any intense exercise triggers the runner’s high, but this study shows you must cross a metabolic threshold—pushing hard isn’t enough, you need to go beyond oxygen capacity.
Practical Takeaways
If you want to trigger a natural high, push your aerobic exercise past your anaerobic threshold—this usually means 80–90% max heart rate for at least 10–15 minutes.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 526 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Human Cross-Sectional
Subject
Lower probability
on the GRADE evidence scale
This study watched how some people's body chemicals changed when they exercised hard. It found that when they exercised more, some chemicals went up—and those chemicals often went up together. But it didn't prove that one thing caused the other, just that they happened at the same time.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Measured multiple biomarkers (hormones, lactate) before and after standardized exercise
- Used repeated measures within subjects to control for individual variability
- Reported statistical significance and correlation coefficients
Weaknesses
- No control group
- No randomization
- Blinding status unknown
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When you push your body past its limit during a long run, your body releases natural painkillers and stress hormones.
Research results
After long exercise, β-endorphin and ACTH doubled; cortisol rose only after long exercise; β-endorphin rose with lactate (r = 0.63–0.71); adrenaline and β-endorphin rose together during short bursts (r = 0.65).
What this means - more context
This suggests the 'runner's high' is triggered by metabolic stress, not just effort — you need to push past your aerobic limit to feel it.
Investigates how aerobic and anaerobic exercise affect hormone levels (β-endorphin, ACTH, cortisol, adrenaline, noradrenaline) in healthy young adults.
Exhaustive aerobic exercise doubled β-endorphin and ACTH levels compared to one-minute anaerobic cycling, with cortisol rising only after aerobic exercise. β-Endorphin increases correlated strongly with lactate levels (r = 0.63–0.71) and occurred only after exceeding the anaerobic threshold. Adrenaline and β-endorphin rose together during anaerobic exercise (r = 0.65).
Methods Used
Twelve healthy young adults (mean age 26.5) performed exhaustive incremental aerobic exercise and one-minute anaerobic cycling at 2-hour intervals. Blood samples were taken before, during, and up to 20 minutes post-exercise to measure hormone and lactate levels.
Main Finding
β-Endorphin and ACTH concentrations approximately doubled after exhaustive aerobic exercise compared to anaerobic cycling, with strong correlations between β-endorphin and lactate (r = 0.63–0.71), indicating metabolic stress drives endogenous opioid release.
Confidence Level
Moderate — small sample size (n=12), no control group, no randomization, and no blinding; however, within-subject design and consistent correlations support internal validity.
Study Flags
Red Flags
- •Small sample size (n=12)
- •No control group
- •No randomization or blinding
Surprising Findings
Beta-endorphin only spiked after exceeding the anaerobic threshold—not just from hard effort.
Most people assume any intense exercise triggers the runner’s high, but this study shows you must cross a metabolic threshold—pushing hard isn’t enough, you need to go beyond oxygen capacity.
Practical Takeaways
If you want to trigger a natural high, push your aerobic exercise past your anaerobic threshold—this usually means 80–90% max heart rate for at least 10–15 minutes.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 526 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Human Cross-Sectional
Subject
Lower probability
on the GRADE evidence scale
This study watched how some people's body chemicals changed when they exercised hard. It found that when they exercised more, some chemicals went up—and those chemicals often went up together. But it didn't prove that one thing caused the other, just that they happened at the same time.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Measured multiple biomarkers (hormones, lactate) before and after standardized exercise
- Used repeated measures within subjects to control for individual variability
- Reported statistical significance and correlation coefficients
Weaknesses
- No control group
- No randomization
- Blinding status unknown
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
This study was kind of like taking a quick snapshot of 12 friends during a workout. It's neat to see what happened, but because it didn't compare them to others, didn't randomly assign exercises, and didn't make sure no one knew what was happening, we can't be super sure the results apply to anyone else or that the exercise really caused the changes.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
1 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control groupno control group
- Sample size (n=12)+1.2/20
- Follow-upno follow-up reported
100 / 100
23 / 100
- P-values+15/15
- Effect sizeno effect size reported
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 526 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
This design cannot establish causation — the findings describe an association, not a cause. This is a cross-sectional study with no control group, no randomization, and no blinding. It measures changes within the same individuals across conditions but cannot rule out confounding factors or establish temporal causality.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding disclosures were reported in the study. The research appears to be independently conducted without industry involvement.
The study is from 1990 and lacks any explicit conflict of interest or funding declaration section. All authors appear to be affiliated with academic institutions based on standard naming conventions, but no affiliations are listed in the provided text. No evidence of industry influence or bias is present.
Standing
Who’s using this study?
The videos and claims on this site that lean on this study, and the researchers who wrote it.
1 video from Max German cite this study, drawing 1 claim from it.
- Contradicted
Evidence contradicts this claim.
Evidence
Authored by
2 researchersIf this is your work, this is how we attribute it on Fit Body Science. Lothar Schwarz is listed as the lead author.