Fatigueisoneofthemostcommoncomplaintsbroughttodoctors,friends,andrelatives.You'dthinkinthiseraoflabor-savingdevicesandconvenienttransportationthatfewpeoplewouldhavereasontobesotired.Butprobablymorepeoplecomplainoffatiguetodaythaninthedayswhenhaywasbaledbyhandandlaundryscrubbedonawashboard.
Thecausesofmodern-dayfatiguearediverseandonlyrarelyrelatedtoexcessivephysicalexertion.Therelativelyfewpeoplewhodoheavylaboralldaylongalmostnevercomplainaboutbeingtired,perhapsbecausetheyexpecttobe.Today,physiciansreport,tirednessismorelikelyaconsequenceofunder-exertionthanofwearingyourselfdownwithover-activity.Infact,increasedphysicalactivityisoftenprescribedasacureforloweringenergy.
Physical.Thisisthewell-knownresultofoverworkingyourmusclestothepointwheremetabolic(新成代谢的)wasteproducts—carbondioxideandlacticacid(乳酸)—accumulateinourbloodandreduceyourstrength.Yourmusclescan'tcontinuetoworkefficientlyinabathofthesechemicals.Physicalfatigueisusuallyapleasanttiredness,suchasthatwhichyoumightexperienceafterplayingahardsetoftennis,choppingwood,orclimbingamountain.Thecureissimpleandfast:Yourest,givingyourbodyachancetogetridofaccumulatedwastesandrestoremusclefuel.
Pathological(病理的).Herefatigueisawarningsignorconsequenceofsomeunderlyingphysicaldisorder,perhapsthecommoncoldorfluorsomethingmoreseriouslikediabetesorcancer.Usuallyothersymptomsbesidesfatiguearepresentthatsuggestthetruecause.