When exercise does harm, and why a famous too-much-jogging study rested on two deaths

Key takeaways

• The 2015 Copenhagen study behind “too much jogging” headlines had just 40 people in its strenuous group, and 2 of them died, too few to show a real risk¹.
• Only 47.2% of U.S. adults met the federal aerobic activity guideline in 2024, so for most people the common problem is too little movement³.
• Overtraining syndrome has no single test; doctors diagnose it by ruling out other causes, and a 2013 expert consensus found that only rest and very light training seem to help⁷.
• Eating too little for your training can disrupt periods, hormones and bones in women and men, the International Olympic Committee warned in 2023⁸.
• Muscle pain far worse than expected plus tea- or cola-colored urine after a hard workout can signal rhabdomyolysis, a muscle breakdown that needs care right away¹¹.

In February 2015, the American College of Cardiology announced a startling finding. In a Danish study, strenuous joggers had been about as likely to die over 12 years as healthy people who didn’t exercise at all². The lead author suggested there might be an upper limit to healthy exercise².

Headlines followed. The numbers underneath were thin.

The “strenuous” group in the Copenhagen City Heart Study held just 40 joggers, and 2 of them died¹. The likely range for their risk ran from about half that of sedentary people to about eight times it¹. A range that wide can’t tell harm from benefit. Light joggers in the same study had about a 78% lower risk of death than sedentary people¹.

Meanwhile, the bigger problem in America runs the other way. In 2024, only 47.2% of adults met the federal aerobic activity guideline, and in 2020 just 24.2% met both the aerobic and strength guidelines³.

So can exercise be excessive? Yes, in a handful of specific, named ways, plus some debated heart changes in lifelong athletes. Here is how to recognize each, with a self-check.

Lifelong athletes’ hearts change: what it means is unsettled

Two studies published together in the journal Circulation in 2017 scanned the heart arteries of veteran athletes for calcium, a marker of plaque⁴. We read them through a summary by PACE-CME, a medical education service, not the full papers.

The Dutch MARC study looked at 284 sporty men age 45 and older. Calcium turned up in 68% of those who trained the most, compared with 43% of those who trained the least⁴. Yet among men with plaque, the heaviest trainers more often had the hardened, calcified kind and less often a mixed kind, which the authors called a more benign makeup⁴.

A second team, led by A. Merghani, compared 152 veteran runners and cyclists with 92 people of similar age, sex and heart risk who met ordinary activity guidelines⁴. The athletes had trained for about 31 years and run a median of 13 marathons⁴. Most athletes, 60%, had normal calcium scores, much like the 63% of the comparison group⁴.

The gaps appeared in men alone; women who trained hard looked like women who didn’t⁴. Among men, plaque of any kind turned up in 44.3% of athletes but 22.2% of non-athletes. But the calcified type dominated in 72.7% of the male athletes’ cases, against 30.8% in the other men, and the authors suggested the athletes’ plaque seemed more stable⁴. Two red flags showed up in male athletes and nobody else: 11.3% had very high calcium scores, and 7.5% had an artery at least half blocked⁴.

In 2023, the Dutch team rescanned 289 men after about six years⁵. Total exercise volume wasn’t linked to faster plaque growth⁵. A larger share of very vigorous exercise was linked to more calcium buildup, while a larger share of vigorous exercise was linked to less⁵. The authors said the clinical meaning is unclear, and the study included only men, 99% of them White⁵.

Heart rhythm is the other question. Swedish researchers followed 52,755 finishers of the Vasaloppet, a 90-kilometer ski race, who raced from 1989 to 1998⁶. By 2005, 919 had developed a rhythm problem⁶.

Skiers who finished five or more races in 10 years had a 30% higher risk than one-time finishers, and so did the fastest finishers⁶. The risk was higher for atrial fibrillation (an irregular, often fast heartbeat) and for abnormally slow rhythms⁶.

Yet the researchers found no rise in rhythm problems that caused sudden death⁶. Earlier studies found Vasaloppet skiers were less likely to die than the general population⁶.

Evidence rating: That years of heavy endurance racing raise the risk of atrial fibrillation is promising but early, based on observational studies. That athletes’ plaque changes shorten their lives: not enough evidence. These studies observed people who chose their training, so other factors may explain the links.

Overtraining syndrome is a diagnosis by elimination

Our recovery guide explains the ladder from a normal post-training dip to full overtraining syndrome, which can take months or even years to clear⁷. How common is the deeper end? A 2013 joint consensus from the European College of Sport Science and the American College of Sports Medicine cited surveys suggesting that about 10% of college swimmers and other endurance athletes slide into a deep slump or full overtraining over one training cycle, with a range of 7% to 21%⁷.

There is no blood test for it. The consensus found hormones, heart rate variability, immune markers and other blood tests all fell short on their own⁷. Doctors instead rule out other causes, such as anemia, infections like Epstein-Barr virus, hormone disorders, eating disorders and heart problems⁷.

Training isn’t the only load. The consensus counts sleep loss, harsh environments, job pressure, moving house and strained relationships among the stresses that add up⁷. That is a whole-person view many natural-health readers already hold: stress from every part of life lands on the same body.

Food matters too. In one study the consensus cites, eating 9.4 grams of carbohydrate per kilogram of body weight a day instead of 6.4 reduced the drop in performance during a block of hard training⁷.

Some scientists have even proposed a new name, “unexplained underperformance syndrome,” the consensus notes, though it hasn’t caught on widely⁷. Treatment is simpler than diagnosis: rest and very light training seem to be the only things that bring recovery⁷.

Eating too little for your training has its own name

In 2023, the International Olympic Committee (IOC) updated its consensus on relative energy deficiency in sport, or REDs⁸. The core problem is low energy availability: the food energy left for the rest of your body after exercise takes its share⁸.

The IOC now treats this as a spectrum. Brief, mild shortfalls can be harmless and quickly reversed⁸. Long or severe ones cause trouble⁸. The panel also dropped the idea of one universal cutoff, noting that the long-quoted threshold came from short lab studies of sedentary women⁸.

The effects reach almost every system⁸:

• Hormones: missed periods, low testosterone, low sex drive
• Bones: lower bone density and stress fractures
• Heart and blood: an unusually slow pulse, low blood pressure, low iron
• Gut and immunity: digestive problems, more frequent illness
• Mind: depression, disordered eating, exercise dependence
• Performance: weaker training gains, slower recovery, less strength and endurance

Estimates of how common it is vary widely, from 23% to 79.5% of female athletes and 15% to 70% of male athletes studied, because researchers have measured it in different ways⁸. The IOC also notes that REDs and overtraining syndrome share many symptoms, and it says low energy availability should be ruled out before anyone is diagnosed with overtraining⁸.

Among the IOC’s main warning signs are missing 3 or more periods in a row, low testosterone, and certain bone stress injuries⁸. Treatment centers on restoring enough food energy through changes to eating and training, guided by a team of professionals, with coaches and family engaged, especially when disordered eating is part of the picture⁸. The statement is written for trained and competitive athletes, so its numbers may not fit casual exercisers.

When exercise turns compulsive

Loving exercise isn’t a disorder. The problem is when it feels like an order you can’t refuse.

In 2018, researchers led by Nina Dittmer proposed a definition of compulsive exercise⁹. At its heart is a workout you feel you must do, whether to obey your own strict rules, ward off something you dread or calm upset feelings⁹. Add any of three markers: it eats up more than an hour a day, it disrupts work, home or friendships, or you keep going while hurt, sick or no longer enjoying it⁹.

It’s common in eating disorders, reported in 31% to 81% of people with anorexia and 20% to 66% with bulimia⁹. It predicts relapse, goes with longer hospital stays and has been linked to suicidal behavior⁹.

Volume isn’t the whole story. Another team studied 142 women with bulimia or binge-eating disorder who wore activity monitors¹⁰. Among those with bulimia, 20% scored high on compulsive exercise while getting less than 150 minutes of activity a week¹⁰. The compulsion lived in the rules and the guilt, not the minutes.

Signs to take seriously⁹:

• Guilt, anxiety or irritability when you miss a session
• Exercising to “earn” a meal or burn off what you ate
• Rigid routines that must never change
• Training through injury or illness
• Exercise you no longer enjoy but can’t skip

If this sounds familiar, the National Alliance for Eating Disorders helpline is 1-866-662-1235. If you’re in crisis or thinking about harming yourself, call or text 988.

Rhabdomyolysis can follow a single hard class

Rhabdomyolysis, or rhabdo, happens when overworked muscle breaks down and spills its contents into the blood. The CDC’s job-safety institute, NIOSH, lists its signs¹¹:

• Muscle pain or cramps far worse than you’d expect
• Dark urine that looks like tea or cola
• Weakness, or being unable to finish a workout you normally can

Symptoms can show up hours or days later and can be mistaken for heat cramps or dehydration¹¹. NIOSH advises stopping, drinking fluids, getting care right away and asking for a creatine kinase (CK) blood test, which measures muscle damage¹¹¹⁴.

Indoor cycling classes have been tied to rhabdo in published case reports¹². At a hospital in South Korea, doctors treated 11 healthy women, ages 15 to 46, for rhabdo¹². Every one had taken her first spinning class two to three days earlier¹². All recovered¹².

It can turn deadly. In 1988, 50 police trainees in Massachusetts began academy training with push-ups, squat-thrusts and runs in 75°F to 80°F heat, with water limited to short breaks¹³. All 50 developed rhabdo, 13 were hospitalized, 6 needed dialysis, and one died¹³. The CDC’s recommendations included enough fluids, gradual conditioning before extreme effort, and postponing hard tests during infections¹³.

For a first class, set your own pace, sit out intervals when you need to, drink water, and build new kinds of exercise gradually. Our recovery guide explains why soreness alone isn’t the warning sign.

Heat stroke needs cooling before the ambulance

NIOSH lists heat stroke‘s signs as confusion or slurred speech, passing out, hot dry skin or heavy sweating, seizures, and a very high body temperature¹⁴. Heat exhaustion has its own signs: headache, nausea, dizziness, weakness, heavy sweating and thirst¹⁴.

The National Athletic Trainers’ Association (NATA) defines exertional heat stroke as brain dysfunction plus a core temperature above 105°F¹⁵. Its 2014 position statement calls cold-water immersion the most effective treatment and says to cool the person before transport¹⁵. The goal is to get core temperature below 102.5°F within 30 minutes of collapse¹⁵. With fast recognition and treatment, NATA says, deaths from exertional heat stroke are entirely preventable¹⁵.

If someone collapses or becomes confused while exercising in heat, call 911 and stay with them. Move them to shade, take off extra clothing and start cooling right away: a tub of cold water or ice if you have one, otherwise wet skin and clothes plus cold cloths or ice on the head, neck, armpits and groin¹⁴.

To prevent it, give your body 7 to 14 days to adjust to heat before training hard in it¹⁵. Drinking far too much water carries its own risk, covered in our hydration guide.

A “too much?” self-check

Natural health trusts the body’s signals, and this is where that trust pays off. The warning signs of overdoing it show up in how you feel, eat and live, and the overtraining consensus found no lab test that can stand in for them⁷.

This check is our own design, built from the overtraining, REDs and compulsive-exercise research above⁷⁸⁹. Answer for the past two weeks.

Area	Ask yourself	A warning sign
Body	Is soreness or fatigue lingering past a few days? Am I sick more often?	Yes to either
Mood	Am I more irritable, flat or anxious? Is sleep worse?	Yes to either
Performance	Are usual workouts harder or slower, even after easy days?	Yes, for two weeks or more
Food	Am I eating less than my training needs, or using exercise to burn off food? Have periods stopped?	Yes to any
Life	Do I skip people, work or rest to train? Do I feel guilty when I miss a day?	Yes to either

How to read it:

• No warning signs: carry on, and keep at least one easy or rest day a week.
• One area: ease off for a week, with fewer, shorter or easier sessions, and recheck.
• Two or more areas, or any “Food” sign: talk with a doctor, and ask about overtraining and energy deficiency. A sports dietitian can help with the food side.

How strong is the evidence?

Claim	Evidence level	What the research shows
About half of U.S. adults get too little aerobic activity	Strong evidence	National survey data, 20243
Strenuous jogging is as deadly as not exercising	Not enough evidence	40 strenuous joggers, 2 deaths, very wide uncertainty1
Years of heavy endurance racing raise atrial fibrillation risk	Promising but early	Large observational cohort; association only6
Lifelong athletes’ extra plaque shortens their lives	Not enough evidence	Scans show more, mostly calcified plaque; no outcome data45
Rest and very light training treat overtraining syndrome	Promising but early	Expert consensus; no single test and few treatment studies7
Low energy availability harms hormones, bones and performance	Strong evidence	IOC consensus review8
Compulsive exercise is linked to worse eating-disorder outcomes	Strong evidence	Clinical studies reviewed in a 2018 definition paper9
Jumping into extreme, unaccustomed exercise is safe	Evidence says no, or unsafe	Documented outbreaks and case series of rhabdomyolysis111213
Fast cold-water cooling prevents heat stroke deaths	Strong evidence	Athletic trainers’ position statement15

Questions readers ask

The bottom line

For most people, the real risk is too little exercise, not too much. The study that made headlines about over-jogging rested on two deaths, and most adults still fall short of basic activity guidelines.

Excess is real, though, and it has recognizable forms: overtraining, under-eating, compulsion, rhabdomyolysis and heat stroke. Years of heavy endurance training may raise the risk of some rhythm problems, though the long-term meaning is unsettled. Listen to the signals your body sends, fuel your training, build up new efforts slowly, and get help early when the warning signs appear.

Related reading

• Fitness gains happen between workouts, so plan the rest
• Sleep, food and easy days beat most recovery gadgets
• How much water you need, since eight glasses a day was never science
• Health tracking has a helpful dose, and past it, checking feeds worry
• Fear of every slip, more than high standards, is usually the problem

Sources

1. Schnohr P, O’Keefe JH, Marott JL, Lange P, Jensen GB. “Dose of Jogging and Long-Term Mortality: The Copenhagen City Heart Study.” Journal of the American College of Cardiology, 2015;65(5):411–419. dcscience.net
2. American College of Cardiology. “Light Jogging May Be Most Optimal for Longevity.” News release, February 2, 2015. acc.org
3. National Center for Health Statistics. “Exercise or Physical Activity.” FastStats, CDC, reviewed April 14, 2026. cdc.gov
4. PACE-CME. “CAC Occurs More Often in Most Active Athletes, but With a More Beneficial Plaque Composition” (on Aengevaeren VL, et al., Circulation, 2017;136:138–148, and Merghani A, et al., Circulation, 2017;136:126–137). July 18, 2017. pace-cme.org
5. Aengevaeren VL, Mosterd A, Bakker EA, et al. “Exercise Volume Versus Intensity and the Progression of Coronary Atherosclerosis in Middle-Aged and Older Athletes: Findings From the MARC-2 Study.” Circulation, 2023;147:993–1003 (St George’s, University of London repository). openaccess.sgul.ac.uk
6. Uppsala University. “Long-Distance Cross-Country Skiers at Increased Risk of Heart Rhythm Disturbances” (on Andersen K, et al., European Heart Journal, 2013). News release, June 12, 2013. uu.se
7. Meeusen R, Duclos M, Foster C, et al. “Prevention, Diagnosis and Treatment of the Overtraining Syndrome: Joint Consensus Statement of the European College of Sport Science and the American College of Sports Medicine.” European Journal of Sport Science, 2013;13(1):1–24. sportgeneeskunde.com
8. Mountjoy M, Ackerman KE, Bailey DM, et al. “2023 International Olympic Committee’s (IOC) Consensus Statement on Relative Energy Deficiency in Sport (REDs).” British Journal of Sports Medicine, 2023;57(17):1073–1097. forening.sls.se
9. Dittmer N, Jacobi C, Voderholzer U. “Compulsive Exercise in Eating Disorders: Proposal for a Definition and a Clinical Assessment.” Journal of Eating Disorders, 2018;6:42. epub.ub.uni-muenchen.de
10. Bratland-Sanda S, Mathisen TF, Sundgot-Borgen J, Rosenvinge JH. “Defining Compulsive Exercise in Eating Disorders: Acknowledging the Exercise Paradox and Exercise Obsessions.” Journal of Eating Disorders, 2019;7:8. jeatdisord.biomedcentral.com
11. National Institute for Occupational Safety and Health. “Signs and Symptoms of Rhabdomyolysis.” CDC, updated January 14, 2025. cdc.gov
12. Kim D, Ko EJ, Cho H, et al. “Spinning-Induced Rhabdomyolysis: Eleven Case Reports and Review of the Literature.” Electrolyte & Blood Pressure, 2015;13(2):58–61. cuk.elsevierpure.com
13. Centers for Disease Control and Prevention. “Exertional Rhabdomyolysis and Acute Renal Impairment — New York City and Massachusetts, 1988.” MMWR, 1990;39(42):751. cdc.gov
14. National Institute for Occupational Safety and Health. “Heat-related Illnesses.” CDC, updated March 3, 2026. cdc.gov
15. National Athletic Trainers’ Association. “Executive Summary of the National Athletic Trainers’ Association Position Statement on Exertional Heat Illnesses.” NATA, 2014.