Exhausted instead of energized after exercise: When training becomes a stressor
Movement is supposed to energize you. When it leaves you drained for days, that is rarely a question of discipline. Often it is a signal from your metabolism, your iron stores, your thyroid or your stress axis.
If exercise regularly makes you feel worse instead of better, what you are missing is usually not willpower. Your body is missing something it needs to answer the load. Exhaustion here is not a failure. It is a message.
You come back from your run and feel empty
You were looking forward to the run. Forty minutes, easy pace, nothing wild. Afterwards, that good feeling should have come. A clear head, warm legs, a little pride.
Instead you sit on the sofa and can't get up again. In the evening you are irritable. At night you sleep restlessly. And the next day the stairs feel like a mountain.
Maybe you have already been told you just need to keep at it. That your body will get used to it. Maybe you have told yourself that. I bet you also know the quiet thought behind it: Is something wrong with me?
A runner in her early thirties, ambitious but not a professional athlete. She had been running for years, several times a week. For a few months, something had been different.
Her blood count had been rated as unremarkable several times. Hemoglobin within the normal range, no anemia. We also looked at her iron stores. Her ferritin was below 30.
The turning point was not a new training plan, but the decision to refill her stores first and to adjust her training during that time. A few weeks later, she reported that recovery after her runs had become noticeably shorter. I cannot claim causality, but I document the timing.
The lesson: A normal blood count does not answer the question of whether your stores are full.
I am not telling this story because iron is always the answer. I am telling it because it illustrates a principle. When exercise drains you instead of energizing you, it is worth asking about the bottleneck. Not about discipline.
Training is a stimulus. The effect only comes from your body's response to it. If your body lacks the energy, oxygen transport or hormonal regulation it needs for that response, all that is left is the stress, without the building up. Then medicine turns into a burden.
And now you know why "just train more" often points in exactly the wrong direction in this situation.
Healthy tiredness or warning sign?
Not every bit of tiredness after exercise is a problem. A hard session is allowed to challenge you. The question is how the tiredness feels and how long it stays.
Healthy training fatigue
- Feels satisfying, not miserable
- Largely gone after a good night's sleep
- Matches the intensity of the session
- Sleep tends to be deeper than usual
- Performance improves over weeks
Exhaustion as a signal
- Even after moderate sessions
- Lasts two days or longer
- Restless sleep despite tiredness
- Irritability, low mood
- Performance stalls or declines
If you recognize yourself more on the right, several causes may be involved. They are not mutually exclusive. Often two or three come together.
Too little energy
You eat for everyday life, but not for everyday life plus training. Your body then cuts back on hormones, the immune system and recovery.
Empty iron stores
A low ferritin may slow down oxygen transport and energy metabolism long before your blood count looks abnormal.
A slowed thyroid
Hypothyroidism or a T3 lowered by energy deficiency can reduce exercise tolerance across many organ systems.
An overloaded stress axis
Training, work and lack of sleep all land on the same axis. When it is under constant demand, recovery may fail to happen.
Low energy: when the tank isn't enough for both
Imagine your body keeps a household budget. The bill for training gets paid first. Whatever is left is distributed to hormones, bones, immune defense, brain and repair. If too little is left, cuts are made. Quietly and without a warning letter.
Sports medicine calls this remainder energy availability. If it is too low over time, it is called Relative Energy Deficiency in Sport, or REDs for short. This does not only affect elite athletes with eating disorders. It often happens unintentionally. For example, when you increase your training and at the same time eat "healthier", which means less.
A syndrome, not just a calorie problem
In 2023, an international expert group led by Mountjoy updated the state of knowledge on REDs on behalf of the International Olympic Committee. More than 170 new original papers had been published since 2018.
The group describes a syndrome that can affect health and performance in women and men. Newly emphasized are the role of low carbohydrate availability and the interaction with mental health.
What this means for you: Exhaustion after exercise can be a sign that your body is saving energy elsewhere. That is not weakness. It is a protective strategy.
Mountjoy M et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). Br J Sports Med. 2023;57(17):1073-1097. DOI: 10.1136/bjsports-2023-106994An older but very clear study showed how directly this saving mode affects hormones. It links energy and the thyroid in a way I recognize again and again in my practice.
Below a threshold, the body slows down the thyroid
In 1994, Loucks and Heath had 27 young women exercise under controlled conditions for four days and deliberately set their energy availability at four levels.
Below a threshold, the active thyroid hormone T3 dropped abruptly by 16 percent and free T3 by 9 percent. At the same time, inactive reverse T3 rose by 22 percent.
What this means for you: Just a few days of low energy availability may pull the metabolic brake. Training then feels harder, even though nothing about your training has changed.
Loucks AB, Heath EM. Induction of low-T3 syndrome in exercising women occurs at a threshold of energy availability. Am J Physiol. 1994;266(3 Pt 2):R817-23. DOI: 10.1152/ajpregu.1994.266.3.R817If you crash after exercise, don't first ask yourself "How do I train harder?" Ask "Did I eat enough today to pay for this?" For many people, the most honest answer to their exhaustion is a plate of food, not a training plan.
And now you know why energy availability is the first question I ask exhausted athletes.
Ferritin: the empty store behind a good blood count
Iron is the oxygen carrier in your red blood cells. But it is also found in the myoglobin of your muscles and in the enzymes of your mitochondria, the power plants of your cells. Ferritin shows how full the warehouse is. Hemoglobin shows whether the delivery trucks are still running.
The problem: The delivery trucks often keep running long after the warehouse is almost empty. This is exactly the phase many exhausted female athletes are in.
No anemia, but almost every second female athlete with low ferritin
In 2019, a research group at the University of Tsukuba examined a total of 126 female and male university athletes from several sports.
Not a single person had anemia. Nevertheless, 22 of the 47 female athletes, or 47 percent, had a ferritin of 30 ng/ml or lower. A lower energy intake was associated with low ferritin.
What this means for you: An unremarkable blood count does not rule out empty stores. And energy and iron are more closely linked than you might think.
Nabeyama T et al. Prevalence of iron-deficient but non-anemic university athletes in Japan: an observational cohort study. J Int Soc Sports Nutr. 2023;20(1):2284948. DOI: 10.1080/15502783.2023.2284948There are several reasons why female runners in particular are so often affected: menstruation, mechanical stress from foot strike, and a hormone called hepcidin. Hepcidin is like a bouncer at the gut. When it rises, less iron from food is let in.
Every run opens a short window of elevated hepcidin
Peeling and colleagues from Western Australia had ten endurance runners complete interval and continuous runs and then measured inflammatory and iron markers.
After each session, the inflammatory messenger interleukin 6 and hepcidin activity rose. The breakdown of red blood cells added up when two runs were done within twelve hours.
What this means for you: A lot of running may increase your iron needs and at the same time make absorption around training more difficult. That is not an excuse. It is physiology.
Peeling P et al. Cumulative effects of consecutive running sessions on hemolysis, inflammation and hepcidin activity. Eur J Appl Physiol. 2009;106(1):51-9. DOI: 10.1007/s00421-009-0988-7The obvious question is: Does refilling the stores help if there is no anemia at all? The data here are interesting, because they are not entirely consistent.
Iron in iron-deficient, non-anemic endurance athletes
In 2014, Burden and colleagues pooled seventeen studies on endurance athletes with iron deficiency without anemia.
Iron treatment clearly improved iron levels and improved maximal oxygen uptake to a moderate extent.
What this means for you: With exercise-related exhaustion, full stores may mean more than a nicer lab number.
Burden RJ et al. Is iron treatment beneficial in, iron-deficient but non-anaemic (IDNA) endurance athletes? A systematic review and meta-analysis. Br J Sports Med. 2015;49(21):1389-97. DOI: 10.1136/bjsports-2014-093624Less fatigue, even without anemia
In a randomized trial from France, 198 fatigued, non-anemic women with a ferritin below 50 µg/l received iron or placebo for twelve weeks. The fatigue score fell by 47.7 percent with iron and by 28.8 percent with placebo.
A later systematic review of 18 studies and 1,170 participants confirmed less subjective fatigue, but found no measurable difference in objective performance tests such as maximal oxygen uptake.
What this means for you: How you feel can change, even if the stopwatch does not show it right away. For endurance athletes, the performance side looks more favorable according to the meta-analysis above.
Vaucher P et al. CMAJ. 2012;184(11):1247-54. DOI: 10.1503/cmaj.110950 · Houston BL et al. BMJ Open. 2018;8(4):e019240. DOI: 10.1136/bmjopen-2017-019240My position on the ferritin target
Many laboratories set the lower limit for ferritin very low. In the past, sometimes only a value below 15 was considered deficient. Values between 30 and 80 are often ticked off as "normal". For exhausted athletes, I see it differently.
I consider a target above 100 µg/l reasonable, provided no inflammation is artificially raising the value and there is no iron overload. That is my clinical position. It is debated among experts and is not set down this way in all guidelines. What is documented: Even below 50, iron supplementation can reduce fatigue.
An iron infusion can be a good option when tablets are not tolerated, do not work well enough, or the stores need to be filled quickly. What matters is that it is done correctly: a clear indication, ruling out iron overload such as hemochromatosis, a modern preparation, and good monitoring during and after the infusion.
The infusion's bad reputation stems largely from the era of old, high-molecular-weight preparations. Modern preparations need to be assessed differently. Whether and how this applies to you belongs in a conversation with a physician.
"Your blood count is fine" and "your iron stores are fine" are two different sentences. If you are wiped out for days after exercise, the second sentence deserves its own check.
And now you know why, with female athletes who have unexplained exhaustion, I almost always ask about ferritin first.
Thyroid: when the engine runs throttled
Do you know the feeling of running with the handbrake on? Your legs want to go, but something is holding you back. The thyroid is something like the throttle control of your metabolism. It helps determine how quickly your cells turn over energy, how your heart responds to exertion, and how well your muscles recover.
Hypothyroidism and exercise tolerance
A research group in Utrecht led by Lankhaar analyzed 38 studies with 1,379 patients with overt or subclinical hypothyroidism.
The reduced exercise tolerance had several causes at once: heart, lungs, muscles, nerves and cellular metabolism. And it did not always fully reverse with hormone therapy.
What this means for you: If your exercise tolerance is poor despite good lab values on treatment, that is a described phenomenon and not your imagination.
Lankhaar JA et al. Impact of overt and subclinical hypothyroidism on exercise tolerance: a systematic review. Res Q Exerc Sport. 2014;85(3):365-89. DOI: 10.1080/02701367.2014.930405This brings us full circle to the energy chapter. The thyroid can be a cause in its own right, for example with Hashimoto's. But it can also react when there is too little energy. And it needs iron as well, because the enzyme for hormone production is iron-dependent. Three causes that can reinforce each other.
A TSH within the normal range is a good start, but not the whole picture. Free T3, free T4 and a look at energy and iron often tell you whether your engine is really running freely or has simply not stalled.
And now you know why the thyroid always belongs on the list when exercise leaves you exhausted.
Stress axis instead of "adrenal fatigue"
Maybe you have already come across the term adrenal fatigue while searching. The idea sounds plausible: too much stress, the adrenal glands are burned out, no more cortisol. I understand why the image appeals. It gives a name to a diffuse feeling.
No evidence for "exhausted" adrenal glands
In 2016, Cadegiani and Kater from São Paulo screened a total of 3,470 papers and included 58 studies that examined cortisol and fatigue together.
The results were almost consistently contradictory. The authors found no substantiation that adrenal fatigue is an actual medical condition.
What this means for you: Your exhaustion is real. Only the explanation "empty adrenal glands" does not hold up scientifically.
Cadegiani FA, Kater CE. Adrenal fatigue does not exist: a systematic review. BMC Endocr Disord. 2016;16(1):48. DOI: 10.1186/s12902-016-0128-4What does exist is a dysregulation of the stress axis. The technical term is the HPA axis: hypothalamus, pituitary, adrenal glands. Think of it as a telephone chain. If calls keep coming in, the rhythm and the volume change. Not because one link is broken, but because the chain is constantly busy.
Hypothalamus
Assesses the situation: training, deadline pressure, poor sleep, too little food. Everything arrives here as a stress signal.
Pituitary
Passes on the signal ACTH. The more intense the load, the stronger this signal can be.
Adrenal glands
Release cortisol. In the short term, this mobilizes energy and dampens inflammation. That makes sense.
Constant operation
Without breaks, the rhythm may shift. Sleep, mood, the immune system and recovery may react as well.
Intensity determines whether cortisol rises
Hill and colleagues had twelve trained men exercise for 30 minutes each at 40, 60 and 80 percent of their maximal oxygen uptake.
At 40 percent, cortisol did not rise significantly. At 60 percent it rose by almost 40 percent, at 80 percent by about 83 percent.
What this means for you: Easy training puts hardly any load on the stress axis. If that axis is already under demand, switching to calmer sessions may bring noticeable relief.
Hill EE et al. Exercise and circulating cortisol levels: the intensity threshold effect. J Endocrinol Invest. 2008;31(7):587-91. DOI: 10.1007/BF03345606True adrenal insufficiency, meaning Addison's disease or a failure at the level of the pituitary, is rare but serious. Signs can include severe weakness, weight loss, low blood pressure, salt cravings or darker skin. This needs prompt medical evaluation and is something different from the dysregulation described here.
Your adrenal glands are not "empty". They are working in a system that gets too few breaks. That is better news than it sounds. Because a system under constant demand can respond to relief.
And now you know why I prefer to speak of the stress axis rather than adrenal fatigue, without downplaying what you are experiencing.
Overtraining: when the balance tips over weeks
Sometimes the cause is not a single gap, but the sum. Too much training, too little sleep, a demanding job, a skimpy breakfast. Each load on its own would be manageable. Together, the balance tips.
Rule things out first, then talk about overtraining
In 2013, an expert group led by Meeusen set out how overtraining should be classified. It is a diagnosis of exclusion.
The statement explicitly names factors that need to be clarified first: calorie deficit, too little carbohydrate or protein, iron deficiency, magnesium deficiency, infections and other organic causes. According to the consensus, no single marker exists that proves overtraining.
What this means for you: The causes in this article are not alternatives to overtraining. They are the first stop of any thorough evaluation.
Meeusen R et al. Prevention, diagnosis, and treatment of the overtraining syndrome. Med Sci Sports Exerc. 2013;45(1):186-205. DOI: 10.1249/MSS.0b013e318279a10aIf you want to go deeper, you will find the warning signs in detail in the article Recognizing overtraining.
Overtraining rarely arises in training alone. It arises in your whole life. If you only look at the training plan, you often see the smaller half of the equation.
The important boundary: post-exertional malaise
Now comes the part that matters most to me. Because there is a form of exhaustion after exertion in which almost everything I wrote above has to be weighted differently.
Post-exertional malaise, or PEM for short, is the hallmark symptom of ME/CFS, myalgic encephalomyelitis or chronic fatigue syndrome. It also occurs in many people with long COVID. It means a marked worsening of all symptoms after physical or even mental exertion. Often delayed, often disproportionate.
Delayed, wide-ranging, hard to predict
A team from the US National Institutes of Health conducted focus groups with 43 people with ME/CFS, some of them after an exercise test on a bicycle.
17 of 18 respondents reported that symptoms began within 24 hours and peaked within 72 hours. Full bed rest was often needed to recover fully or partially.
What this means for you: If the crash only comes the next day or the day after and throws you far below your baseline, that is a different pattern from normal training fatigue.
Stussman B et al. Characterization of Post-exertional Malaise in Patients With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Front Neurol. 2020;11:1025. DOI: 10.3389/fneur.2020.01025Measurable changes in muscle after PEM
A research group in Amsterdam led by Appelman examined muscle samples from people with long COVID before and after exertion that triggered PEM.
After the exertion, there were increased metabolic disturbances, signs of exercise-induced muscle damage and deposits in the muscle tissue.
What this means for you: PEM is not a problem in your head and not a lack of fitness. There are measurable physical correlates, and exertion beyond your limit may intensify them.
Appelman B et al. Muscle abnormalities worsen after post-exertional malaise in long COVID. Nat Commun. 2024;15(1):17. DOI: 10.1038/s41467-023-44432-3If you notice, after an infection or without a clear trigger, that even small exertions set you back in a delayed and disproportionate way, increasing the load is counterproductive. Pushing through, ramping up and "toughing it out" can make your condition worse.
What makes sense then is pacing: dosing activity so that you stay below your individual exertion limit. And a medical evaluation before you continue training. You can find more on this in the article Exercise with chronic exhaustion.
With overtraining, you ask: How much recovery does my body need to grow again? With PEM, you ask: How do I stay below the limit that sets me back? Two different questions. Both deserve to be taken seriously, and neither has anything to do with a lack of willpower.
And now you know why the question about the timing pattern of your exhaustion is just as important as any lab value.
What this means for you
Energy is not a luxury. Energy is freedom. The freedom to still play with your kids after a run. The freedom to hike up a mountain on the weekend without paying for it for three days afterwards. That is what this is about, not personal bests.
What is documented: Low energy availability, iron deficiency and thyroid disorders can measurably reduce exercise tolerance. What remains open: how these factors interact in your personal case. That can only be clarified individually.
Note the pattern
For two weeks, write down: session, intensity, when the exhaustion comes, how long it stays, how you sleep. If the crash comes delayed and disproportionate, talk to a physician about PEM first.
Check your energy honestly
On three training days, deliberately eat enough, with carbohydrates before and after the session. Watch whether your recovery changes. Your body may give you an answer that no calculator can.
Get targeted lab tests
Have ferritin with transferrin saturation and CRP, blood count, TSH, fT3 and fT4 measured. That way you can see whether a store is empty or an engine is throttled, instead of guessing.
Self-check: Does your exhaustion point to a bottleneck?
- Even after moderate sessions, I am exhausted for two days or longer.
- My sleep is more restless after training instead of deeper.
- I have increased my training but not my food intake.
- My ferritin has never been measured or was below 50.
- I have heavy periods or eat a mostly plant-based diet.
- I get cold more easily, my skin is drier or I gain weight for no reason.
- The exhaustion comes delayed and throws me far below my baseline. (In that case, please get a medical evaluation first.)
If you tick several boxes, that is not a diagnosis. It is a good reason to take a closer look. With curiosity instead of self-reproach.
If you want to explore this topic further
Iron deficiency in athletes and runners
When performance drops and the blood count still looks fine.
LabFerritin above 100 as a target
The debate about a sensible target value.
IronIron deficiency despite normal ferritin
Why a single value is not always enough.
Iron infusionInfusion despite normal hemoglobin
When it may be justified and what matters.
Stress axisAdrenal fatigue: myth and facts
What is behind the term and what is not.
HormonesCortisol and the HPA axis
Dysregulation instead of a simple rule of thumb.
ThyroidFunctional hypothyroidism
When normal values are not enough.
ME/CFSChronic fatigue
When your body pulls the plug.
TrainingRecovery is not doing nothing
Why recovery is your actual training.
Frequently asked questions about exhaustion after exercise
Is it normal to feel exhausted after exercise?
A pleasant tiredness after a hard session is normal. It tends to feel satisfying and is largely gone after a good night's sleep.
It becomes noteworthy when you regularly feel worse after moderate sessions than before, when the exhaustion lasts two to three days, or when your sleep, mood and resting heart rate react as well. Then it is worth looking at energy availability, iron status, the thyroid and the stress axis.
Can iron deficiency without anemia explain exhaustion after exercise?
That is possible. In a Japanese observational study of 126 university athletes, nobody had anemia, yet 47 percent of the female athletes had a ferritin of 30 ng/ml or lower.
A meta-analysis of 17 studies found a moderate improvement in maximal oxygen uptake after iron treatment in iron-deficient, non-anemic endurance athletes. So a blood count alone may miss an empty iron store.
What ferritin level makes sense for athletes?
Laboratory reference ranges often start very low. In studies on fatigue in non-anemic women, the inclusion threshold was a ferritin below 50 µg/l, and iron supplementation was able to measurably reduce fatigue in that group.
For exhausted athletes, I consider a target above 100 µg/l reasonable, provided no inflammation is distorting the value and there is no iron overload. This position is debated among experts and is not set down this way in all guidelines.
What is Relative Energy Deficiency in Sport (REDs)?
According to the 2023 consensus statement of the International Olympic Committee, REDs describes a syndrome in which too little energy is left for the body after the cost of training has been subtracted. This can affect the hormonal system, bones, immune system, metabolism and mental health, in women and men alike.
The role of low carbohydrate availability is newly emphasized. It often happens unintentionally, for example when you increase your training without eating more.
Can my thyroid be to blame if exercise exhausts me?
It can be part of the picture. A systematic review of 38 studies and 1,379 patients describes reduced exercise tolerance across several organ systems in hypothyroidism, which does not always fully disappear even with treatment.
Conversely, low energy availability can itself slow down the thyroid: in a study of 27 exercising women, T3 fell by 16 percent as soon as energy availability dropped below a certain threshold.
Can too much exercise cause adrenal fatigue?
The term adrenal fatigue is not a recognized medical condition. A systematic review of 58 studies found no evidence that the adrenal glands give out under chronic stress in the sense of exhaustion.
What does exist is a dysregulation of the stress axis between the hypothalamus, pituitary and adrenal glands. It can show up as altered cortisol patterns, sleep problems and poor recovery. True adrenal insufficiency, on the other hand, is a rare, serious condition that needs to be evaluated by a physician.
What is the difference between overtraining and post-exertional malaise?
Overtraining arises from an imbalance between load and recovery and can subside with adjusted load, energy and time. Post-exertional malaise is the hallmark symptom of ME/CFS and also occurs in long COVID. Symptoms worsen markedly after physical or mental exertion, often with a delay.
In an NIH study, symptoms began within 24 hours in 17 of 18 respondents and peaked within 72 hours. Here, increasing the load is counterproductive; pacing is the sensible approach.
Should I simply train less if exercise exhausts me?
In the short term, reducing intensity can make sense, because cortisol only rises markedly from moderate to high intensity. In the long term, the more important question is why your body cannot process the load right now.
If iron, energy, sleep or the thyroid is the bottleneck, training less often brings only partial relief. If ME/CFS or long COVID is suspected, the rule is different: get a medical evaluation first, and do not train beyond your limit.
Which blood tests make sense for exhaustion after exercise?
A sensible baseline includes a blood count, ferritin, transferrin saturation and CRP, so that inflammation does not distort the ferritin value. Add TSH and the free thyroid hormones fT3 and fT4, vitamin D, B12 and, depending on the situation, electrolytes and blood sugar. For women, the menstrual cycle matters too.
The ECSS/ACSM consensus statement explicitly names iron deficiency, calorie deficit and too little carbohydrate or protein as factors to rule out before diagnosing overtraining.
Does an iron infusion make sense for athletes?
An iron infusion can make sense when iron deficiency is confirmed, tablets are not tolerated or do not work well enough, and iron overload has been ruled out.
What matters is that it is done correctly: with a clear indication, a check of contraindications, a modern preparation and good monitoring. The infusion's bad reputation stems largely from old, high-molecular-weight preparations that are hardly used today.
Sources
All studies were checked via PubMed for title, year, journal and DOI. Figures are taken from the respective abstracts. The position on a ferritin target above 100 µg/l is a clinical assessment and not a guideline consensus. This article does not replace a medical examination or individual advice.
- Mountjoy M, Ackerman KE, Bailey DM, Burke LM, Constantini N, Hackney AC, Heikura IA, Melin A, Pensgaard AM, Stellingwerff T, Sundgot-Borgen JK, Torstveit MK, Jacobsen AU, Verhagen E, Budgett R, Engebretsen L, Erdener U. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). Br J Sports Med. 2023;57(17):1073-1097. DOI: 10.1136/bjsports-2023-106994 [Review, IOC consensus statement]
- Loucks AB, Heath EM. Induction of low-T3 syndrome in exercising women occurs at a threshold of energy availability. Am J Physiol. 1994;266(3 Pt 2):R817-23. DOI: 10.1152/ajpregu.1994.266.3.R817 [Pathophysiology, controlled experiment with four energy levels, n=27 women]
- Nabeyama T, Suzuki Y, Saito H, Yamamoto K, Sakane M, Sasaki Y, Shindo H, Takita M, Kami M. Prevalence of iron-deficient but non-anemic university athletes in Japan: an observational cohort study. J Int Soc Sports Nutr. 2023;20(1):2284948. DOI: 10.1080/15502783.2023.2284948 [Real-world, observational study, n=126]
- Peeling P, Dawson B, Goodman C, Landers G, Wiegerinck ET, Swinkels DW, Trinder D. Cumulative effects of consecutive running sessions on hemolysis, inflammation and hepcidin activity. Eur J Appl Physiol. 2009;106(1):51-9. DOI: 10.1007/s00421-009-0988-7 [RCT, crossover, n=10 endurance runners]
- Burden RJ, Morton K, Richards T, Whyte GP, Pedlar CR. Is iron treatment beneficial in, iron-deficient but non-anaemic (IDNA) endurance athletes? A systematic review and meta-analysis. Br J Sports Med. 2015;49(21):1389-97. DOI: 10.1136/bjsports-2014-093624 [Meta-analysis, k=17 studies]
- Vaucher P, Druais PL, Waldvogel S, Favrat B. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ. 2012;184(11):1247-54. DOI: 10.1503/cmaj.110950 [RCT, n=198]
- Houston BL, Hurrie D, Graham J, Perija B, Rimmer E, Rabbani R, Bernstein CN, Turgeon AF, Fergusson DA, Houston DS, Abou-Setta AM, Zarychanski R. Efficacy of iron supplementation on fatigue and physical capacity in non-anaemic iron-deficient adults: a systematic review of randomised controlled trials. BMJ Open. 2018;8(4):e019240. DOI: 10.1136/bmjopen-2017-019240 [Systematic review, meta-analysis, 18 RCTs, n=1,170]
- Lankhaar JA, de Vries WR, Jansen JA, Zelissen PM, Backx FJ. Impact of overt and subclinical hypothyroidism on exercise tolerance: a systematic review. Res Q Exerc Sport. 2014;85(3):365-89. DOI: 10.1080/02701367.2014.930405 [Systematic review, k=38 studies, n=1,379]
- Cadegiani FA, Kater CE. Adrenal fatigue does not exist: a systematic review. BMC Endocr Disord. 2016;16(1):48. DOI: 10.1186/s12902-016-0128-4 [Systematic review, k=58 studies from 3,470 hits]
- Hill EE, Zack E, Battaglini C, Viru M, Viru A, Hackney AC. Exercise and circulating cortisol levels: the intensity threshold effect. J Endocrinol Invest. 2008;31(7):587-91. DOI: 10.1007/BF03345606 [RCT, controlled crossover study, n=12]
- Meeusen R, Duclos M, Foster C, Fry A, Gleeson M, Nieman D, Raglin J, Rietjens G, Steinacker J, Urhausen A. 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. Med Sci Sports Exerc. 2013;45(1):186-205. DOI: 10.1249/MSS.0b013e318279a10a [Review, consensus statement ECSS and ACSM]
- Stussman B, Williams A, Snow J, Gavin A, Scott R, Nath A, Walitt B. Characterization of Post-exertional Malaise in Patients With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Front Neurol. 2020;11:1025. DOI: 10.3389/fneur.2020.01025 [Real-world, qualitative focus group study, n=43]
- Appelman B, Charlton BT, Goulding RP, Kerkhoff TJ, Breedveld EA, Noort W, Offringa C, Bloemers FW, van Weeghel M, Schomakers BV, Coelho P, Posthuma JJ, Aronica E, Wiersinga WJ, van Vugt M, Wüst RCI. Muscle abnormalities worsen after post-exertional malaise in long COVID. Nat Commun. 2024;15(1):17. DOI: 10.1038/s41467-023-44432-3 [Case-control, longitudinal case-control study]