Table 1

Exercise-associated heat illnesses

Heat crampsExercise-associated muscle cramps are a mild form of exertional heat illness familiar to those who watch sports (except perhaps for darts aficionados) characterised by severe muscle pain and spasms/prolonged muscle contraction without other features.
Heat syncopeExercise-associated transient loss of consciousness usually occurs after exercise cessation. The likely cause is a sudden reduction in venous return secondary to reduced skeletal muscle tone, and diversion of blood flow to extremities to lose heat. Recovery is rapid and complete (as in vasovagal syncope) and core body temperature is not elevated.
Heat exhaustionCharacterised by difficulty continuing with exercise with raised core body temperature but no significant or prolonged alteration of mental state.
Heat strokeCombination of elevated core temperatures (above 40°C) and altered mental state. Other end organs may also be damaged, including muscles (raised serum CK), kidneys (acute kidney injury) and liver (elevated liver enzymes).
Heat injuryA description used by military physicians (but not recognised in ICD-10) to describe heat exhaustion and end-organ damage without mental state changes.
  • CK, creatine kinase; ICD-10, International Classification of Diseases, 10th Revision.