Does Fever or Myalgia Indicate Reduced Physical Performance Capacity in Viral Infections?

Abstract

To study prospectively the effects of a brief febrile viral infection on parameters of muscle and circulatory function, seven volunteers were inoculated with sandfly fever virus and two control subjects with sterile saline. During but not after fever, decreased isometric and dynamic strength and endurance were recorded in various muscles. Impairment could not be explained by altered activities of relevant muscle enzymes in serum or muscle tissue or by altered muscle ultrastructure, but correlated with the severity of perceived symptoms, including myalgia, as rated by each subject. Compared to baseline, cardiac stroke volume was lower during and after fever. During fever, an increased heart rate maintained cardiac output at pre‐inoculation values, whereas cardiac output fell in early convalescence. This decrease in cardiac output correlated significantly with the severity of fever. Thus, in brief viral infections a transient impairment of muscle performance capacity is correlated to subjective symptoms such as myalgia, rather than to fever, whereas a decreased cardiac output following such infections seems to be associated with the fever reaction.

Febrile Illness in the Athlete

“…14,15 Muscular impairments noted early in infection may correlate more closely with perceived symptoms than actual alterations in muscle structure caused by fever. 18 On the first day of fever, subjects inoculated with sandfly fever virus demonstrated a decrease in isometric and isotonic muscle strength of up to 30%, though muscle biopsies showed that no significant muscle breakdown or alterations in muscle enzymes had yet occurred. 18 There was a strong correlation between decreased strength and perceived myalgias, as graded by each participant.…”

“…18 On the first day of fever, subjects inoculated with sandfly fever virus demonstrated a decrease in isometric and isotonic muscle strength of up to 30%, though muscle biopsies showed that no significant muscle breakdown or alterations in muscle enzymes had yet occurred. 18 There was a strong correlation between decreased strength and perceived myalgias, as graded by each participant. 18 In addition to seeing decreases in skeletal muscle strength and endurance, we would expect to see changes in the body's circulatory function.…”

“…24 During a brief febrile viral illness, stroke volume is lower during and after fever compared with baseline. 18 An increased heart rate helped to maintain cardiac output at normal values, though cardiac output fell during early convalescence, and this decline was strongly associated with the severity of the fever. 18 Decreases in speed and coordination are observed during and shortly after periods of brief febrile illness.…”

“…18 An increased heart rate helped to maintain cardiac output at normal values, though cardiac output fell during early convalescence, and this decline was strongly associated with the severity of the fever. 18 Decreases in speed and coordination are observed during and shortly after periods of brief febrile illness. 1 These decreases in motor skills are seen as early as 3 or 4 days into acute illness.…”

Exercise and Immunity

“…There are indications that untrained people who start exercising regularly get a progressively stronger immune system and become less susceptible to infections [45]. Intensive endurance training or competition which last for at least one hour stimulates the immune system sharply in the beginning, but a few hours after exercise/competition, a weakened immune system results [46]. This means that the immune system in the hours after hard exercise/competition has a weakened ability to fight against bacteria and viruses and the susceptibility to infection is temporarily increased [47].…”