Febrile Illness in the Athlete

CONTEXT: Acute febrile illnesses are common in athletes over the course of training and competition seasons. Complete recovery and rapid yet safe return to participation are critical for competitive athletes. Alterations in thermoregulation, metabolism, fluid homeostasis, muscle strength, and endurance, as well as potential complications for the athlete and others, must be considered. EVIDENCE ACQUISITION: The PubMed database was searched (1970-2013) for all English-language articles related to febrile illness in sport, using the keywords fever, febrile, body temperature, thermoregulation, infection, illness, disease, exercise, athlete, sport, performance, return to play, metabolism, hydration, and dehydration. STUDY DESIGN: Clinical review. LEVEL OF EVIDENCE: Level 4. RESULTS: Limited data confirm that febrile illness is correlated with alterations in the body’s thermoregulatory system, with increases in metabolic rate, and with effects in fluid homeostasis. Human and animal studies demonstrate a decrease in muscle strength and endurance secondary to muscle catabolism in febrile illness. However, indirect evidence suggests that regular exercise enhances the immune response. No strong clinical research has been published on return to play during or following acute febrile illness, excluding mononucleosis and myocarditis. CONCLUSION: Fever is correlated with an increase in insensible fluid losses, dehydration, metabolic demands, and dysregulation of body temperature. Fever can have detrimental effects on the musculoskeletal system, including decreasing strength and endurance, generalized muscle catabolism, and increase in perceived fatigue. Participating in strenuous exercise during febrile illness can worsen the illness and has demonstrated increased lethality in animal models. No consensus recommendations support return to activity before resolution of fever, and training should be resumed gradually once fever and dehydration have resolved.