Fatigue in the Endurance Athlete

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Workout associated fatigue is our gauge of a quality workout program. But, excessive or debilitating fatigue adversely affects workout quality, limiting performance gains.

By Michael D. Milligan, MD

Member AMSSM 

Fatigue is both the ally and the bane of the endurance athlete. Application of an adequate training stimulus followed by appropriate recovery is the crux of progressive improvement. Workout associated fatigue is our gauge of a quality workout program. But, excessive or debilitating fatigue adversely affects workout quality, limiting performance gains. Recognizing the difference is essential to progressive performance gains.

Rest and Recovery

The most common cause of fatigue in endurance athletes at every level is inadequate rest and recovery. Athletes rarely lack the will to train and work hard. Combine the time demands of training with life responsibilities (work, family, etc) and the hours available for rest and recovery quickly dwindle. The body makes physiologic gains during rest. Athletes who understand that principle are often able to make the necessary adjustments and produce more rapid performance gains. Adequate nightly sleep of 7-10 hours is best but naps and scheduled recovery may also be implemented. Individuals vary in the amount of rest needed but there is no question that as training demands increase, attention to rest and recovery must also increase.

Don't Limit Your Calories

Inadequate caloric intake is another common cause of fatigue. Endurance athletes frequently limit calories with the goal of weight loss. Others unintentionally ingest inadequate calories for their training load. Finding the balance between adequate caloric intake to maintain performance while obtaining and maintaining appropriate body composition is essential to maximize performance. Combining a consistent structured nutrition program with one or more of the caloric expenditure calculators over an extended period of time is the best way to manage this common cause of fatigue.

Low Iron

Iron deficiency can also cause fatigue. Iron is the key building block of hemoglobin, the oxygen-carrying molecule of red blood cells. Without sufficient iron, the body can not optimally deliver oxygen to working muscles. Iron deficiency may occur with or without anemia. Sources of iron include red meats, spinach, and kidney beans. Iron deficiency can occur due to insufficient intake, failure of the gastrointestinal tract to absorb, or losses through menstrual bleeding, gastrointestinal bleeding, or iron losses in sweat. The diagnosis of iron deficiency and its cause requires evaluation and blood testing by a health care professional. Health risks associated with excess iron intake necessitate that athletes not institute iron supplementation without medical supervision. In addition, there are additional causes of anemia that can be that can be revealed by tests ordered by your health care professional.

Thyroid Dysfunction

Less commonly, hormonal dysfunction can be a source of fatigue. Thyroid dysfunction is the most commonly diagnosed. Evaluation by your physician (which should include appropriate lab testing) can generally differentiate between various causes and guide treatment. Hypothalamic-adrenal dysfunction is most typically seen in the over-trained and/or under-rested athlete. Most frequently seen are lower than normal levels of testosterone, estrogen, growth hormone, cortisol and abnormal values of luteinizing hormone and follicle stimulating hormone.

Colds and the Flu

Viral illnesses such as colds, the flu, and bronchitis often affect the endurance athlete. Athletes sometimes view these illnesses as short-term training setbacks. However, recovery of strength, endurance, and energy can sometimes require many months. Evaluation by a health care professional to exclude other causes should be undertaken prior to making this diagnosis.

Cardiac Disease

Cardiac disease is a cause of fatigue that should never be overlooked when evaluating fatigue in the athlete. Initial symptoms of cardiac disease in the athlete are often non-specific, such as, fatigue, decreased performance, and respiratory symptoms. More typical symptoms of chest pain or feelings of an irregular heart beat are not always present. Any family history of cardiac disease or sudden cardiac death or personal risk factors such as high blood pressure, high cholesterol, or diabetes should increase suspicion for a cardiac cause until excluded.

Fatigue is the training partner of the endurance athlete. Fatigue tells us we are applying an appropriate training stimulus. However, atypical symptoms of fatigue or feelings of fatigue that do not resolve with rest and recovery can be signs of a more serious problem. Such cases warrant further evaluation by an appropriate health care professional.

About the author:
Michael D. Milligan, MD is board certified in Sports Medicine and Family Medicine. He is the Medical Director and Head Team Physician for UNLV athletics, the Program Director for the University of Nevada School of Medicine Sports Medicine Fellowship, and owner of University Sports Medicine, a private practice sports medicine clinic in Las Vegas, Nevada. Additionally, Dr. Milligan is a seasoned endurance athlete having participated in marathons, ultra-marathons, and long distance cycling events.

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date: June 9, 2009