Acute Infection: Metabolic Responses, Effects on Performance, Interaction with Exercise, and Myocarditis

Abstract

Acute infections are associated with multiple host responses that are triggered by cytokines and correlated to fever, malaise and anorexia. The purpose of this systemic acute phase host reaction ("the acute phase response") is to mobilize nutrients for the increased needs of the activated immune system, as well as for energy production and tissue repair. Important effects include wasting of striated muscle, degradation of performance-related metabolic enzymes and, concomitantly, deteriorated central circulatory function. These effects result in decreased muscle and aerobic performance, the full recovery of which may require several weeks to months following week-long febrile infections. Also during early infection and fever, prior to the development of muscle wasting, performance is compromised by other mechanisms. Strenuous exercise may be hazardous during ongoing infection and fever and should always be avoided. In infection, muscle wasting seems to be less pronounced in the conditioned (trained) host than in the unconditioned host. Acute myocarditis most often has a viral etiology but bacteria and their toxins may also be the cause. Furthermore, slow-growing bacteria, previously difficult to diagnose, have emerged as potential "new" causes of subacute to chronic myocarditis. Since myocarditis may or may not be associated with fever, malaise, or catarrhal symptoms, athletes should be taught the symptoms suggestive of myocarditis. Whenever myocarditis is suspected exercise should be avoided.

Reduced physical activity increases intermuscular adipose tissue in healthy young adults

“…This association may be secondary to an effect on muscle function through adipose tissue's role as an endocrine organ (42). For example, TNF-␣, a common cytokine expressed by adipose tissue (16 -18), impairs force production independent of muscle wasting (19,21,(43)(44)(45). This was first believed to be due to decreases in calcium concentrations from the sarcoplasmic reticulum (46) but is now thought to occur downstream of the calcium signal at the myofilament level (19).…”

Interactions between Infections, Nutrients and Xenobiotics

“…Whether in experimental or epidemiological studies, toxic effects of xenobiotics in infections are difficult to evaluate because they influence many mechanisms and responses used by the body to defend itself against the invading microorganism. These several lines of host defence are complex and involve a number of physiological, biochemical, immunological, metabolic, and hormonal mechanisms (Beisel, 1998;Friman and Ilback, 1998;Grimble, 1996;Powanda and Beisel, 2003). Thus, welldesigned experimental studies are needed to pin down effects on each defence mechanism, as well as to clarify the complicated interactions that potentially can occur between microorganisms, nutrients, and chemical substances.…”

“…The host defence mobilisation is normally referred to as the "acute phase reaction" and is initiated during the early incubation period and peaks during fever. Host responses are similar in animals and man in a majority of acute infections (Beisel, 1998) and includes an array of responses, including fever, hormonal changes, immune cell activation, increased synthesis and release of cytokines, antibodies, complement and acute phase proteins, and a simultaneous flow of trace elements between blood and tissues, as well as extensive changes in various metabolic pathways (Beisel, 1998;Friman and Ilback, 1998;Friman et al, 1982;Funseth et al, 2000a;Grimble, 1996;Ilback et al, 1984a;Ilback et al, 2003b).…”

Physical Exercise in Patients with Heart Failure Due to Myocarditis and Dilated Cardiomyopathy

“…Immunosuppression alone increased mortality (40%) when compared with controls (4%). Strong exercise could be hazardous during ongoing infection and should therefore always be avoided [21]. Although the immune system of the conditioned athlete may be more efficient, strong and frequently repeated strenuous exercise could induce some kind of immunosuppression resulting in an increased susceptibility to infection [3,22,23].…”