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Exercise as Disease Detector

E. Randy Eichner, MD; Warren A. Scott, MD


In Brief: Exercise is a well-known stress test for uncovering heart or lung disease, but it can also stress other organs and unmask a range of medical disorders. Practical case examples are given in seven areas: anemia, headache, hematuria, gastrointestinal problems, seizure, anhidrosis, and hypothyroidism. Recognizing the exercise-induced manifestations can lead to timely diagnoses that improve and save lives.

Just as exercise stresses the heart and lungs to uncover pathology, it also stresses other organs and can unmask a host of other disorders. Physicians who care for athletes and active people can benefit from knowing the wide range of exercise-induced manifestations that can be harbingers of underlying medical conditions. This practical information can help physicians make timely diagnoses that can improve or save lives.


Exercise, especially strenuous exercise, helps differentiate common causes of chronic fatigue. Depressed patients, for example, feel fatigued on arising in the morning. During recovery from a viral infection such as infectious mononucleosis or hepatitis, patients feel strong in the morning but tire later and need a nap. Patients who have chronic fatigue syndrome are tired all day long or become exhausted from minimal physical activity. But patients who have mild or moderate anemia generally feel normal at rest and note fatigue only with exertion. Especially with mild anemia, all-out exercise can be the only unmasker.

Take the example of an elite 25-year-old male distance runner. Ordinarily in 5K races on the track, he ran with the lead pack and often won, with times well under 15 minutes. But for 3 months his race performance had been fading to the point where he fell off the pace halfway through the first lap. His legs felt like lead, he sweated profusely, and his breathing was labored. He was eventually staggering across the finish line, dead last, in times well over 18 minutes.

When not racing, he felt normal except for undue breathlessness when climbing stairs. He could not recall any illness and had not changed his training, sleep habits, or diet. He recalled a few days of "indigestion" (with epigastric pain) and black stools 3 months earlier when he had been taking daily aspirin and ibuprofen for knee pain. At that time, he probably had gastrointestinal (GI) bleeding from gastritis.

This runner had moderate iron-deficiency anemia, with a hemoglobin concentration of 8.7 g/dL (normal, 14.0 to 18.0 g/dL). Yet because of his top fitness, he noted symptoms only upon exercise that was strenuous enough to unmask his anemia. With iron therapy his anemia disappeared and his race times improved.

Even mild anemia can impair athletic performance. Consider an 18-year-old female collegiate softball player who had "spells" when exercising hard in the heat. Her spells comprised "heart beating too fast," "breathing too hard," and "dizziness," but never syncope. Because of these spells, along with some premature ventricular contractions on a resting electrocardiogram, she was seen by a cardiologist, who found no cardiac abnormalities on physical exam, treadmill testing, or echocardiogram.

She said she felt normal except when exercising hard. She had been chewing a lot of ice for a few months. She had mild iron-deficiency anemia, with a hemoglobin of 11 g/dL (normal, 12.0 to 16.0 g/dL), presumably from menstrual blood loss. With iron therapy, her anemia disappeared—and so did her spells.

An 18-year-old star college basketball player was experiencing undue breathlessness and fatigue on the court for 2 months when the medical consultant was asked to evaluate him for exercise-induced asthma. The patient was put through a brief, intense workout in which the physician observed him and monitored his peak flow. He had air hunger and early tiring, but no signs of asthma or cardiac problems. His hemoglobin was 11 g/dL (normal, 14.0 to 18.0 g/dL). His anemia was from iron deficiency, probably related to his being a twin (and thus more apt to be iron deficient at birth), having a substantial growth spurt, and suffering from several nosebleeds, including a large one 2 months earlier. With iron therapy his hemoglobin and performance returned to normal.

TAKE-HOME MESSAGE. The milder the anemia, the more likely it is that strenuous exercise will be the only unmasker.


Athletes and active people may suffer from headaches related to their exercise (see "Recognizing Exercise-Related Headache," February 1997, page 33). Probably the most common type of headache during exercise or sports is benign exertional headache. Also common are posttraumatic headache and effort migraine. Other headache syndromes among athletes include cervicogenic headache, goggle headache, diver's headache, and altitude headache. All these headaches are annoying, but most of them are benign (1).

Usually absent in sports medicine articles on headaches is "cardiac cephalgia," another treatable form of exertional headache (2). Consider the 57-year-old man who underwent two negative neurologic workups for a 4-month history of headaches that would begin 5 to 10 minutes into vigorous walking, swimming, or sexual activity. No chest pain was noted, though on a few occasions the exertional headaches were associated with vague chest heaviness.

The third neurologist who saw this patient referred him for a thallium exercise stress test that documented myocardial ischemia in concert with his exertional headache. Coronary angiography found severe three-vessel disease. After coronary artery bypass surgery, he returned to his usual exercise program without exertional headache (2).

Six similar patients have been reported (2); in each, exertional headache was the most prominent symptom of well-documented myocardial ischemia. Two patients had no cardiac symptoms; in such patients, cardiac cephalgia may be a selectively silent form of angina.

TAKE-HOME MESSAGE. Exercise can unmask coronary artery disease by causing headache, not angina, especially in middle-aged men. Not all exertional headaches are benign.


Athletes are vulnerable to hematuria from diverse causes, and proper diagnosis hinges on a careful history, physical examination, and urinalysis, as well as on judicious use of screening tests, imaging studies, and cystoscopy (3). In distance runners, for example, hematuria can be pain free and microscopic (eg, pseudonephritis) or painful and gross from bladder contusion. Bladder contusion in some runners may result from repeated impact of the flaccid posterior wall of the bladder against the bladder base (4).

As for practical management of hematuria in athletes, asymptomatic microhematuria, especially if it occurs only once or twice, is probably best merely followed without invasive workup. Persistent microhematuria, however, can signal disease, and gross hematuria, even in a young adult, can herald bladder cancer.

Take the 27-year-old man who noted gross hematuria twice after 2-mile runs. A filling defect in the posterior bladder wall was seen by intravenous pyelogram, and a 3-cm pedunculated tumor was seen on cystoscopy. The lesion was resected transurethrally and proved to be a low-grade superficial transitional cell bladder carcinoma. The patient returned to jogging and had no recurrence of hematuria or tumor on 2-year follow-up (5).

Four other cases of bladder cancer in patients with exercise-induced hematuria have been reported (6); three were in men ages 22 to 41. In each of the four patients, gross hematuria followed relatively brief bouts of moderately intense exertion—running or aerobic dance. Each patient had a low-grade superficial papillary transitional bladder carcinoma. Another similar case occurred in a young professional football player (Wayne E. Kuhl, MD, written communication, March 1991). In all patients, the cancer was cured.

TAKE-HOME MESSAGE. Not all hematuria in athletes or young active people is benign. Running or aerobic dance can be a "stress test" for the bladder (perhaps by causing the bladder walls to bang together) as well as for the heart. Exercise-induced hematuria can reveal covert bladder cancer while it is still curable.

GI Symptoms

Exercise, especially running, can also be a stress test for the colon. Indeed, GI problems are common among athletes and active people (7,8). Exercise-related problems include upper-GI symptoms such as nausea, bloating, and acid reflux as well as lower-GI symptoms such as cramping, diarrhea, and even rectal bleeding.

GI bleeding, which occurs notably in distance runners or triathletes, stems from the upper or lower GI tract and ranges from occult and trivial to overt and grave (9). Ischemic colitis, often heralded by lower abdominal cramping and bloody diarrhea, is perhaps the most ominous GI complication of endurance racing. This can be considered an "athletic" cause of colitis because it likely results from dehydration and blood diversion from the gut to working muscles. At its worst, ischemic colitis can require subtotal colectomy, as in a female distance runner (10) and in two elite triathletes (one female, one male) in the Ironman Triathlon Championship.

Bloody diarrhea, of course, can also be from nonathletic causes, as in a female swimmer and male baseball pitcher who had bloody diarrhea from ulcerative colitis (8). Vigorous exercise can also be a "colonic stress test" that unveils infectious diarrhea. Examples are an 8-year-old boy who developed diarrhea only when playing basketball and was found to have giardiasis (11), and a 48-year-old man who for 4 months had diarrhea mainly during distance running and eventually was found to have intestinal amebiasis (12).

TAKE-HOME MESSAGE. By stressing the GI tract, exercise—especially distance running—can unmask diverse conditions. Usually, these are just annoying manifestations of disrupted physiology (ie, nausea, bloating, belching). Occasionally, however, cramping and diarrhea can herald serious colitis, be it infectious, inflammatory, or ischemic.


A seizure in an athlete—exercise-related or not—can, of course, be nothing more than epilepsy. Or if a seizure follows syncope, it may signal a life-threatening cardiac arrest. This tragedy was seen in the haunting broadcasts on national television news of the collapse and death of Hank Gathers on the basketball court (13). (Exercise-induced syncope—with or without seizure—is not to be taken lightly. Though some causes of syncope are benign, such as a vasovagal reflex or the use of beta-blockers, others can be ominous, such as mechanical or electrical cardiac disease (14).

Seizures in insulin-taking diabetic athletes can be triggered by hypoglycemia. Such seizures are most likely to occur in the hours after prolonged exercise (15).

But not all seizures in athletes signal epilepsy, syncope, or hypoglycemia. An exercise-induced seizure can be the presenting sign of a curable brain mass. Take the report (16) of three healthy adults who had generalized seizures soon after jogging. Each had a normal neurologic examination after the seizure. In all three patients, computed tomography revealed small frontal-lobe cortical lesions: an arteriovenous malformation, a cyst, and an astrocytoma. The seizures were attributed to hypocarbia and alkalosis; it was assumed that when the patients stopped jogging, hyperventilation continued for a short time while lactic acid production declined.

Hyperventilation was also invoked in a fourth subject in whom exertional seizure or syncope unmasked a frontal-lobe brain tumor (17). This 27-year-old man suffered two brief, unwitnessed syncope episodes (or seizures) in 6 months during recreational running. On electroencephalography, hyperventilation provoked abnormal activity in the right anterior hemisphere. Magnetic resonance imaging revealed a mass in the right frontal lobe that proved to be an astrocytoma.

Exercise can also unmask other telltale neurologic symptoms. The presenting complaint in a 72-year-old man, an avid softball player, was "slowing down when I sprint to first base." This proved to be the first sign of Parkinson's disease. In another case, a 28-year-old man was brought to the emergency room by family members. While lifting weights, he complained of a severe headache and then became incoherent and clumsy. He had bled into a cerebellar astrocytoma. The brain tumor was resected and he recovered.

TAKE-HOME MESSAGE. Physicians who cover athletic events should keep in mind that exercise can provoke seizures or other neurologic manifestations that can point to diverse disorders, including life-threatening heart disease and curable brain tumors.


Sometimes it's the dog that doesn't bark: The athlete notes the absence of something that should appear with exercise. Take the 33-year-old male recreational runner who for 4 years noticed that when he ran in the heat, he did not sweat on the left side of his face, left upper trunk, or left arm. When he called one of the authors (ERE) about this, he was asked to look in the mirror and, for the first time, noticed that his left eyelid drooped slightly.

This man had Horner's syndrome. He recalled that just before he stopped sweating on his left side, he had chiropractic manipulation of his neck. Horner's syndrome has occurred after chiropractic neck manipulation—probably from traction on or avulsion injury of the white ramus communicans between the first thoracic nerve and the first thoracic or inferior cervical sympathetic ganglion (18).

Other causes are also possible, as in a 56-year-old physical education instructor who for 5 years had a stable pattern of anhidrosis of only his left arm; he did not have full Horner's syndrome. Weight-lifting or stretching may have avulsed the postganglionic ramus that runs from the sympathetic trunk to the first thoracic nerve, just before it enters the lower trunk of the brachial plexus. Variants of Horner's syndrome have also occurred after playing squash, probably from torsion of the thoracic spine, with occlusion of an anterior radicular artery at the third thoracic segment (19).

TAKE-HOME MESSAGE. The bottom line is that Horner's syndrome can be unmasked by exercise. Though the conditions described here are likely traumatic in origin, it is conceivable that exercise-induced Horner's syndrome could unmask an apical lung cancer or Pancoast's tumor.


Fatigue is one of the first symptoms of hypothyroidism, so the diagnosis should be considered whenever a runner experiences chronic fatigue and diminished exercise performance.

A report (20) details six female runners aged 24 to 48 who had chronic fatigue and diminished running performance. All were diagnosed as having primary hypothyroidism and started on levothyroxine sodium. On follow-up, three reported improved running performance.

Though this is unusual, overuse injuries associated with exercise may sometimes be the only presenting symptoms of hypothyroidism. In a report (21) of a 45-year-old male triathlete, tendinitis at three separate sites (knee, shoulder, and elbow) was the first sign of hypothyroidism, which wasn't diagnosed until the patient developed profound fatigue late in the course of his illness. The patient's serum thyroid-stimulating hormone (TSH) was elevated at 20.4 microunits/mL (normal, 2 to 11 microunits/mL), and his serum thyroxine (T4) was low at 2.4 micrograms/dL (4 to 11 micrograms/dL). His hypothyroidism was thought to be idiopathic. The patient returned to competing in triathlons and marathons 3 1/2 months after starting levothyroxine sodium therapy. His musculoskeletal symptoms and fatigue did not recur, and he has since attained personal best race times.

In a somewhat similar case, a 35-year-old man had fatigue that was seasonal and tendinopathies that were puzzling. Over several years, the man became more active every spring, when the weather turned warm. He would begin a jogging program with his wife but would fall behind because of fatigue. He developed tendinopathies (patellar and elsewhere) that seemed too severe for his meager amount of jogging. The patient was found to have hypothyroidism and was cured with thyroid therapy.

TAKE-HOME MESSAGE. Fatigue and overuse injuries aren't always a normal part of training. Active patients often want to train through physical obstacles, which can mask the symptoms of hypothyroidism.

Athletes Aren't Immune

Though exercise carries a host of impressive health benefits, it isn't a shield against all illnesses, and symptoms during activity aren't always benign. Physicians and the active people they care for can benefit from knowing when exercise can uncover an underlying medical condition. The practical clinical vignettes given here show that exercise is a useful "stress test" for many organs of the body. Exercise the unmasker offers opportunities for early diagnosis, reassurance, comfort, and cure.


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Dr Eichner is a professor of medicine in the Department of Medicine at the University of Oklahoma Health Sciences Center in Oklahoma City. Dr Scott is the chief of sports medicine at Kaiser Permanente in Santa Clara, California. Both are fellows of the American College of Sports Medicine, and Dr Eichner is an editorial board member of The Physician and Sportsmedicine. Address correspondence to E. Randy Eichner, MD, Section of Hematology/Oncology, Dept of Medicine, University of Oklahoma Health Sciences Center, Box 26901, Oklahoma City, OK 73190; e-mail to [email protected].



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