Acute Infection: Metabolic Responses, Effects on Performance, Interaction with Exercise, and Myocarditis, Friman et Ilbäck, 1998

[Yann04]

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 symtoms, athletes should be taught the symptoms suggestive of myocarditis. Whenever myocarditis is suspected exercise should be avoided.

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[Yann04]

“These effects [physiological response to acute infection] result in decreased muscle and aerobic performance, the full recovery of which may require several weeks to months following week-long febrile infections.”

 

[forestglip]

Relatively few infectious diseases in humans have been subject to studies of the possible adverse effects of exercise programmes during the acute course.

I also had trouble finding such research, except in tuberculosis, when trying to determine if exercise can cause worsening during acute infections, sort of like PEM.

This paper has some references that might support this though:

One such infection is acute viral hepatitis, where controlled studies have shown no adverse short or long term effects of exercise of various intensities during the early course of the disease (13,60,72). Conversely, in poliomyelitis, exercise may be hazardous and promote the development of palsies (for a review. see ref. [67]). In patients suffering febrile respiratory infections, a mild activity programme of letting the patient out of bed every half hour during waking hours. i.e. "G-training", throughout the entire febrile course resulted in less blood volume reduction and less of an aerobic capacity decrease than conventional bed rest (41).

The effects of strenuous exercise during acute febrile infections have been studied in experimental animals. In one study of a prototype, non-myocarditic, bacterial infection (tularemia) in the rat, it was shown that exhaustive exercise during the febrile phase evoked an anabolic response in striated muscle (myocardium) that limited the infection-associated muscle catabolism (27). Consequently, the exercised rats performed better than the resting controls at the end of the infection. The frequency of serious complications, such as spread of the infection to unusual sites, was however higher among the exercising animals. In another exercise experiment, where the effects in one bacterial (tularemia) and one viral (influenza) in- fection, with similar lethalities at rest, were compared, no beneficial effects of exercise were observed in influenza. In fact, in contrast to the observation in tularemia, exhaustive exercise during influenza evoked no anabolic response in muscle and exercise was associated with increased lethality (49). Likewise, lethality was increased with exercise in rats suffering Streptococcus pneumoniae infection (50).

All animal experiments on non-myocarditic bacterial and viral infections that we are aware of show that strenuous exercise during the febrile phase may be hazardous. For evident ethical reasons, similar experiments in humans are not feasible. Thus, there is no scientific basis for not recommending rest in the acute phase of all such infections.